[v4,2/2] tools/resolve_btfids: Alter how HOSTCC is forced

Message ID	20230124064324.672022-2-irogers@google.com (mailing list archive)
State	Accepted
Commit	13e07691a16ff31b209fbfce25c01ff296b05e45
Delegated to:	BPF
Headers	show Return-Path: <bpf-owner@vger.kernel.org> Date: Mon, 23 Jan 2023 22:43:24 -0800 In-Reply-To: <20230124064324.672022-1-irogers@google.com> Message-Id: <20230124064324.672022-2-irogers@google.com> Mime-Version: 1.0 References: <20230124064324.672022-1-irogers@google.com> Subject: [PATCH v4 2/2] tools/resolve_btfids: Alter how HOSTCC is forced From: Ian Rogers <irogers@google.com> To: Alexei Starovoitov <ast@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>, Andrii Nakryiko <andrii@kernel.org>, Martin KaFai Lau <martin.lau@linux.dev>, Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>, John Fastabend <john.fastabend@gmail.com>, KP Singh <kpsingh@kernel.org>, Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>, Connor OBrien <connoro@google.com>, Nathan Chancellor <nathan@kernel.org>, Ian Rogers <irogers@google.com>, Kumar Kartikeya Dwivedi <memxor@gmail.com>, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk
Series	[v4,1/2] tools/resolve_btfids: Install subcmd headers \| expand [v4,1/2] tools/resolve_btfids: Install subcmd headers [v4,2/2] tools/resolve_btfids: Alter how HOSTCC is forced

Context	Check	Description
netdev/tree_selection	success	Not a local patch
bpf/vmtest-bpf-next-PR	success	PR summary
bpf/vmtest-bpf-next-VM_Test-11	success	Logs for test_maps on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-1	success	Logs for ShellCheck
bpf/vmtest-bpf-next-VM_Test-2	success	Logs for build for aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-3	success	Logs for build for aarch64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-5	success	Logs for build for x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-6	success	Logs for build for x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-7	success	Logs for llvm-toolchain
bpf/vmtest-bpf-next-VM_Test-8	success	Logs for set-matrix
bpf/vmtest-bpf-next-VM_Test-4	success	Logs for build for s390x with gcc
bpf/vmtest-bpf-next-VM_Test-9	success	Logs for test_maps on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-10	success	Logs for test_maps on aarch64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-12	success	Logs for test_maps on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-13	success	Logs for test_maps on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-14	success	Logs for test_progs on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-18	success	Logs for test_progs on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-19	fail	Logs for test_progs_no_alu32 on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-20	success	Logs for test_progs_no_alu32 on aarch64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-22	success	Logs for test_progs_no_alu32 on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-23	success	Logs for test_progs_no_alu32 on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-24	success	Logs for test_progs_no_alu32_parallel on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-25	success	Logs for test_progs_no_alu32_parallel on aarch64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-27	success	Logs for test_progs_no_alu32_parallel on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-28	success	Logs for test_progs_no_alu32_parallel on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-29	success	Logs for test_progs_parallel on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-30	success	Logs for test_progs_parallel on aarch64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-32	success	Logs for test_progs_parallel on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-33	success	Logs for test_progs_parallel on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-34	success	Logs for test_verifier on aarch64 with gcc
bpf/vmtest-bpf-next-VM_Test-35	success	Logs for test_verifier on aarch64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-37	success	Logs for test_verifier on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-38	success	Logs for test_verifier on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-15	success	Logs for test_progs on aarch64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-17	success	Logs for test_progs on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-26	success	Logs for test_progs_no_alu32_parallel on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-36	success	Logs for test_verifier on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-16	success	Logs for test_progs on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-21	success	Logs for test_progs_no_alu32 on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-31	success	Logs for test_progs_parallel on s390x with gcc

Ian Rogers Jan. 24, 2023, 6:43 a.m. UTC

HOSTCC is always wanted when building. Setting CC to HOSTCC happens
after tools/scripts/Makefile.include is included, meaning flags are
set assuming say CC is gcc, but then it can be later set to HOSTCC
which may be clang. tools/scripts/Makefile.include is needed for host
set up and common macros in objtool's Makefile. Rather than override
CC to HOSTCC, just pass CC as HOSTCC to Makefile.build, the libsubcmd
builds and the linkage step. This means the Makefiles don't see things
like CC changing and tool flag determination, and similar, work
properly.

Also, clear the passed subdir as otherwise an outer build may break by
inadvertently passing an inappropriate value.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/bpf/resolve_btfids/Makefile | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

Jiri Olsa Jan. 24, 2023, 11:08 p.m. UTC | #1

On Mon, Jan 23, 2023 at 10:43:24PM -0800, Ian Rogers wrote:
> HOSTCC is always wanted when building. Setting CC to HOSTCC happens
> after tools/scripts/Makefile.include is included, meaning flags are
> set assuming say CC is gcc, but then it can be later set to HOSTCC
> which may be clang. tools/scripts/Makefile.include is needed for host
> set up and common macros in objtool's Makefile. Rather than override
> CC to HOSTCC, just pass CC as HOSTCC to Makefile.build, the libsubcmd
> builds and the linkage step. This means the Makefiles don't see things
> like CC changing and tool flag determination, and similar, work
> properly.
> 
> Also, clear the passed subdir as otherwise an outer build may break by
> inadvertently passing an inappropriate value.
> 
> Signed-off-by: Ian Rogers <irogers@google.com>

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> ---
>  tools/bpf/resolve_btfids/Makefile | 17 +++++++----------
>  1 file changed, 7 insertions(+), 10 deletions(-)
> 
> diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> index 1fe0082b2ecc..daed388aa5d7 100644
> --- a/tools/bpf/resolve_btfids/Makefile
> +++ b/tools/bpf/resolve_btfids/Makefile
> @@ -18,14 +18,11 @@ else
>  endif
>  
>  # always use the host compiler
> -AR       = $(HOSTAR)
> -CC       = $(HOSTCC)
> -LD       = $(HOSTLD)
> -ARCH     = $(HOSTARCH)
> +HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
> +		  EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> +
>  RM      ?= rm
>  CROSS_COMPILE =
> -CFLAGS  := $(KBUILD_HOSTCFLAGS)
> -LDFLAGS := $(KBUILD_HOSTLDFLAGS)
>  
>  OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
>  
> @@ -56,12 +53,12 @@ $(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT):
>  
>  $(SUBCMDOBJ): fixdep FORCE | $(OUTPUT)/libsubcmd
>  	$(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(SUBCMD_OUT) \
> -		    DESTDIR=$(SUBCMD_DESTDIR) prefix= \
> +		    DESTDIR=$(SUBCMD_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
>  		    $(abspath $@) install_headers
>  
>  $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUT)
>  	$(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) OUTPUT=$(LIBBPF_OUT)    \
> -		    DESTDIR=$(LIBBPF_DESTDIR) prefix= EXTRA_CFLAGS="$(CFLAGS)" \
> +		    DESTDIR=$(LIBBPF_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
>  		    $(abspath $@) install_headers
>  
>  LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> @@ -80,11 +77,11 @@ export srctree OUTPUT CFLAGS Q
>  include $(srctree)/tools/build/Makefile.include
>  
>  $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)
> -	$(Q)$(MAKE) $(build)=resolve_btfids
> +	$(Q)$(MAKE) $(build)=resolve_btfids $(HOST_OVERRIDES)
>  
>  $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
>  	$(call msg,LINK,$@)
> -	$(Q)$(CC) $(BINARY_IN) $(LDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> +	$(Q)$(HOSTCC) $(BINARY_IN) $(KBUILD_HOSTLDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
>  
>  clean_objects := $(wildcard $(OUTPUT)/*.o                \
>                              $(OUTPUT)/.*.o.cmd           \
> -- 
> 2.39.0.246.g2a6d74b583-goog
>

Nathan Chancellor Jan. 31, 2023, 5:20 p.m. UTC | #2

Hi Ian,

On Mon, Jan 23, 2023 at 10:43:24PM -0800, Ian Rogers wrote:
> HOSTCC is always wanted when building. Setting CC to HOSTCC happens
> after tools/scripts/Makefile.include is included, meaning flags are
> set assuming say CC is gcc, but then it can be later set to HOSTCC
> which may be clang. tools/scripts/Makefile.include is needed for host
> set up and common macros in objtool's Makefile. Rather than override
> CC to HOSTCC, just pass CC as HOSTCC to Makefile.build, the libsubcmd
> builds and the linkage step. This means the Makefiles don't see things
> like CC changing and tool flag determination, and similar, work
> properly.
> 
> Also, clear the passed subdir as otherwise an outer build may break by
> inadvertently passing an inappropriate value.
> 
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/bpf/resolve_btfids/Makefile | 17 +++++++----------
>  1 file changed, 7 insertions(+), 10 deletions(-)
> 
> diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> index 1fe0082b2ecc..daed388aa5d7 100644
> --- a/tools/bpf/resolve_btfids/Makefile
> +++ b/tools/bpf/resolve_btfids/Makefile
> @@ -18,14 +18,11 @@ else
>  endif
>  
>  # always use the host compiler
> -AR       = $(HOSTAR)
> -CC       = $(HOSTCC)
> -LD       = $(HOSTLD)
> -ARCH     = $(HOSTARCH)
> +HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
> +		  EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> +
>  RM      ?= rm
>  CROSS_COMPILE =
> -CFLAGS  := $(KBUILD_HOSTCFLAGS)
> -LDFLAGS := $(KBUILD_HOSTLDFLAGS)
>  
>  OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
>  
> @@ -56,12 +53,12 @@ $(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT):
>  
>  $(SUBCMDOBJ): fixdep FORCE | $(OUTPUT)/libsubcmd
>  	$(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(SUBCMD_OUT) \
> -		    DESTDIR=$(SUBCMD_DESTDIR) prefix= \
> +		    DESTDIR=$(SUBCMD_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
>  		    $(abspath $@) install_headers
>  
>  $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUT)
>  	$(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) OUTPUT=$(LIBBPF_OUT)    \
> -		    DESTDIR=$(LIBBPF_DESTDIR) prefix= EXTRA_CFLAGS="$(CFLAGS)" \
> +		    DESTDIR=$(LIBBPF_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
>  		    $(abspath $@) install_headers
>  
>  LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> @@ -80,11 +77,11 @@ export srctree OUTPUT CFLAGS Q
>  include $(srctree)/tools/build/Makefile.include
>  
>  $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)
> -	$(Q)$(MAKE) $(build)=resolve_btfids
> +	$(Q)$(MAKE) $(build)=resolve_btfids $(HOST_OVERRIDES)
>  
>  $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
>  	$(call msg,LINK,$@)
> -	$(Q)$(CC) $(BINARY_IN) $(LDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> +	$(Q)$(HOSTCC) $(BINARY_IN) $(KBUILD_HOSTLDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
>  
>  clean_objects := $(wildcard $(OUTPUT)/*.o                \
>                              $(OUTPUT)/.*.o.cmd           \
> -- 
> 2.39.0.246.g2a6d74b583-goog
> 

I just bisected a linking failure when building resolve_btfids with
clang to this change as commit 13e07691a16f ("tools/resolve_btfids:
Alter how HOSTCC is forced") in the bpf-next tree.

It appears to be related to whether or not CROSS_COMPILE is specified,
which we have to do for certain architectures and configurations still.
arm64 is not one of those but it helps demonstrate the issue.

  # Turn off CONFIG_DEBUG_INFO_REDUCED and turn on CONFIG_DEBUG_INFO_BTF
  $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 defconfig menuconfig

  $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 prepare
  ld.lld: error: $LINUX_SRC/tools/bpf/resolve_btfids//resolve_btfids-in.o is incompatible with elf64-x86-64
  clang-17: error: linker command failed with exit code 1 (use -v to see invocation)
  ...

Before your change, with V=1, I see:

clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11 -Wdeclaration-after-statement -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c

After, I see:

clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o --target=aarch64-linux-gnu -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c

We seem to have taken on a '--target=aarch64-linux-gnu' (changing the
target of resolve_btfids-in.o) and we dropped the warning flags.

I think this comes from the clang block in
tools/scripts/Makefile.include, which is included into the
resolve_btfids Makefile via tools/lib/bpf/Makefile.

I am not super familiar with the tools build system, otherwise I would
try to provide a patch. I tried moving CROSS_COMPILE from a recursive to
simple variable ('=' -> ':=') and moving it to HOST_OVERRIDES but those
did not appear to resolve it for me.

If there is any other information I can provide or patches I can test,
please let me know.

Cheers,
Nathan

Ian Rogers Jan. 31, 2023, 6:08 p.m. UTC | #3

On Tue, Jan 31, 2023 at 9:21 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> Hi Ian,
>
> On Mon, Jan 23, 2023 at 10:43:24PM -0800, Ian Rogers wrote:
> > HOSTCC is always wanted when building. Setting CC to HOSTCC happens
> > after tools/scripts/Makefile.include is included, meaning flags are
> > set assuming say CC is gcc, but then it can be later set to HOSTCC
> > which may be clang. tools/scripts/Makefile.include is needed for host
> > set up and common macros in objtool's Makefile. Rather than override
> > CC to HOSTCC, just pass CC as HOSTCC to Makefile.build, the libsubcmd
> > builds and the linkage step. This means the Makefiles don't see things
> > like CC changing and tool flag determination, and similar, work
> > properly.
> >
> > Also, clear the passed subdir as otherwise an outer build may break by
> > inadvertently passing an inappropriate value.
> >
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> >  tools/bpf/resolve_btfids/Makefile | 17 +++++++----------
> >  1 file changed, 7 insertions(+), 10 deletions(-)
> >
> > diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> > index 1fe0082b2ecc..daed388aa5d7 100644
> > --- a/tools/bpf/resolve_btfids/Makefile
> > +++ b/tools/bpf/resolve_btfids/Makefile
> > @@ -18,14 +18,11 @@ else
> >  endif
> >
> >  # always use the host compiler
> > -AR       = $(HOSTAR)
> > -CC       = $(HOSTCC)
> > -LD       = $(HOSTLD)
> > -ARCH     = $(HOSTARCH)
> > +HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
> > +               EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > +
> >  RM      ?= rm
> >  CROSS_COMPILE =
> > -CFLAGS  := $(KBUILD_HOSTCFLAGS)
> > -LDFLAGS := $(KBUILD_HOSTLDFLAGS)
> >
> >  OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> >
> > @@ -56,12 +53,12 @@ $(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT):
> >
> >  $(SUBCMDOBJ): fixdep FORCE | $(OUTPUT)/libsubcmd
> >       $(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(SUBCMD_OUT) \
> > -                 DESTDIR=$(SUBCMD_DESTDIR) prefix= \
> > +                 DESTDIR=$(SUBCMD_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> >                   $(abspath $@) install_headers
> >
> >  $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUT)
> >       $(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) OUTPUT=$(LIBBPF_OUT)    \
> > -                 DESTDIR=$(LIBBPF_DESTDIR) prefix= EXTRA_CFLAGS="$(CFLAGS)" \
> > +                 DESTDIR=$(LIBBPF_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> >                   $(abspath $@) install_headers
> >
> >  LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> > @@ -80,11 +77,11 @@ export srctree OUTPUT CFLAGS Q
> >  include $(srctree)/tools/build/Makefile.include
> >
> >  $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)
> > -     $(Q)$(MAKE) $(build)=resolve_btfids
> > +     $(Q)$(MAKE) $(build)=resolve_btfids $(HOST_OVERRIDES)
> >
> >  $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
> >       $(call msg,LINK,$@)
> > -     $(Q)$(CC) $(BINARY_IN) $(LDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > +     $(Q)$(HOSTCC) $(BINARY_IN) $(KBUILD_HOSTLDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> >
> >  clean_objects := $(wildcard $(OUTPUT)/*.o                \
> >                              $(OUTPUT)/.*.o.cmd           \
> > --
> > 2.39.0.246.g2a6d74b583-goog
> >
>
> I just bisected a linking failure when building resolve_btfids with
> clang to this change as commit 13e07691a16f ("tools/resolve_btfids:
> Alter how HOSTCC is forced") in the bpf-next tree.
>
> It appears to be related to whether or not CROSS_COMPILE is specified,
> which we have to do for certain architectures and configurations still.
> arm64 is not one of those but it helps demonstrate the issue.
>
>   # Turn off CONFIG_DEBUG_INFO_REDUCED and turn on CONFIG_DEBUG_INFO_BTF
>   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 defconfig menuconfig
>
>   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 prepare
>   ld.lld: error: $LINUX_SRC/tools/bpf/resolve_btfids//resolve_btfids-in.o is incompatible with elf64-x86-64
>   clang-17: error: linker command failed with exit code 1 (use -v to see invocation)
>   ...
>
> Before your change, with V=1, I see:
>
> clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11 -Wdeclaration-after-statement -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
>
> After, I see:
>
> clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o --target=aarch64-linux-gnu -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
>
> We seem to have taken on a '--target=aarch64-linux-gnu' (changing the
> target of resolve_btfids-in.o) and we dropped the warning flags.
>
> I think this comes from the clang block in
> tools/scripts/Makefile.include, which is included into the
> resolve_btfids Makefile via tools/lib/bpf/Makefile.
>
> I am not super familiar with the tools build system, otherwise I would
> try to provide a patch. I tried moving CROSS_COMPILE from a recursive to
> simple variable ('=' -> ':=') and moving it to HOST_OVERRIDES but those
> did not appear to resolve it for me.
>
> If there is any other information I can provide or patches I can test,
> please let me know.
>
> Cheers,
> Nathan

Thanks Nathan, and thanks for all the details in the bug report. I'm
looking into this.

Ian

Ian Rogers Jan. 31, 2023, 7:25 p.m. UTC | #4

On Tue, Jan 31, 2023 at 10:08 AM Ian Rogers <irogers@google.com> wrote:
>
> On Tue, Jan 31, 2023 at 9:21 AM Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > Hi Ian,
> >
> > On Mon, Jan 23, 2023 at 10:43:24PM -0800, Ian Rogers wrote:
> > > HOSTCC is always wanted when building. Setting CC to HOSTCC happens
> > > after tools/scripts/Makefile.include is included, meaning flags are
> > > set assuming say CC is gcc, but then it can be later set to HOSTCC
> > > which may be clang. tools/scripts/Makefile.include is needed for host
> > > set up and common macros in objtool's Makefile. Rather than override
> > > CC to HOSTCC, just pass CC as HOSTCC to Makefile.build, the libsubcmd
> > > builds and the linkage step. This means the Makefiles don't see things
> > > like CC changing and tool flag determination, and similar, work
> > > properly.
> > >
> > > Also, clear the passed subdir as otherwise an outer build may break by
> > > inadvertently passing an inappropriate value.
> > >
> > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > ---
> > >  tools/bpf/resolve_btfids/Makefile | 17 +++++++----------
> > >  1 file changed, 7 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> > > index 1fe0082b2ecc..daed388aa5d7 100644
> > > --- a/tools/bpf/resolve_btfids/Makefile
> > > +++ b/tools/bpf/resolve_btfids/Makefile
> > > @@ -18,14 +18,11 @@ else
> > >  endif
> > >
> > >  # always use the host compiler
> > > -AR       = $(HOSTAR)
> > > -CC       = $(HOSTCC)
> > > -LD       = $(HOSTLD)
> > > -ARCH     = $(HOSTARCH)
> > > +HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
> > > +               EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > +
> > >  RM      ?= rm
> > >  CROSS_COMPILE =
> > > -CFLAGS  := $(KBUILD_HOSTCFLAGS)
> > > -LDFLAGS := $(KBUILD_HOSTLDFLAGS)
> > >
> > >  OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> > >
> > > @@ -56,12 +53,12 @@ $(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT):
> > >
> > >  $(SUBCMDOBJ): fixdep FORCE | $(OUTPUT)/libsubcmd
> > >       $(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(SUBCMD_OUT) \
> > > -                 DESTDIR=$(SUBCMD_DESTDIR) prefix= \
> > > +                 DESTDIR=$(SUBCMD_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > >                   $(abspath $@) install_headers
> > >
> > >  $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUT)
> > >       $(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) OUTPUT=$(LIBBPF_OUT)    \
> > > -                 DESTDIR=$(LIBBPF_DESTDIR) prefix= EXTRA_CFLAGS="$(CFLAGS)" \
> > > +                 DESTDIR=$(LIBBPF_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > >                   $(abspath $@) install_headers
> > >
> > >  LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> > > @@ -80,11 +77,11 @@ export srctree OUTPUT CFLAGS Q
> > >  include $(srctree)/tools/build/Makefile.include
> > >
> > >  $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)
> > > -     $(Q)$(MAKE) $(build)=resolve_btfids
> > > +     $(Q)$(MAKE) $(build)=resolve_btfids $(HOST_OVERRIDES)
> > >
> > >  $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
> > >       $(call msg,LINK,$@)
> > > -     $(Q)$(CC) $(BINARY_IN) $(LDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > > +     $(Q)$(HOSTCC) $(BINARY_IN) $(KBUILD_HOSTLDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > >
> > >  clean_objects := $(wildcard $(OUTPUT)/*.o                \
> > >                              $(OUTPUT)/.*.o.cmd           \
> > > --
> > > 2.39.0.246.g2a6d74b583-goog
> > >
> >
> > I just bisected a linking failure when building resolve_btfids with
> > clang to this change as commit 13e07691a16f ("tools/resolve_btfids:
> > Alter how HOSTCC is forced") in the bpf-next tree.
> >
> > It appears to be related to whether or not CROSS_COMPILE is specified,
> > which we have to do for certain architectures and configurations still.
> > arm64 is not one of those but it helps demonstrate the issue.
> >
> >   # Turn off CONFIG_DEBUG_INFO_REDUCED and turn on CONFIG_DEBUG_INFO_BTF
> >   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 defconfig menuconfig
> >
> >   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 prepare
> >   ld.lld: error: $LINUX_SRC/tools/bpf/resolve_btfids//resolve_btfids-in.o is incompatible with elf64-x86-64
> >   clang-17: error: linker command failed with exit code 1 (use -v to see invocation)
> >   ...
> >
> > Before your change, with V=1, I see:
> >
> > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11 -Wdeclaration-after-statement -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> >
> > After, I see:
> >
> > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o --target=aarch64-linux-gnu -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> >
> > We seem to have taken on a '--target=aarch64-linux-gnu' (changing the
> > target of resolve_btfids-in.o) and we dropped the warning flags.
> >
> > I think this comes from the clang block in
> > tools/scripts/Makefile.include, which is included into the
> > resolve_btfids Makefile via tools/lib/bpf/Makefile.
> >
> > I am not super familiar with the tools build system, otherwise I would
> > try to provide a patch. I tried moving CROSS_COMPILE from a recursive to
> > simple variable ('=' -> ':=') and moving it to HOST_OVERRIDES but those
> > did not appear to resolve it for me.
> >
> > If there is any other information I can provide or patches I can test,
> > please let me know.
> >
> > Cheers,
> > Nathan
>
> Thanks Nathan, and thanks for all the details in the bug report. I'm
> looking into this.
>
> Ian

Given the somewhat complicated cross compile I wasn't able to get a
reproduction. Could you see if the following addresses the problem:

```
diff --git a/tools/bpf/resolve_btfids/Makefile
b/tools/bpf/resolve_btfids/Makefile
index daed388aa5d7..a06966841df4 100644
--- a/tools/bpf/resolve_btfids/Makefile
+++ b/tools/bpf/resolve_btfids/Makefile
@@ -19,10 +19,9 @@ endif

# always use the host compiler
HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)"
ARCH="$(HOSTARCH)" \
-                 EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
+                 EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
CROSS_COMPILE=""

RM      ?= rm
-CROSS_COMPILE =

OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
```

Thanks,
Ian

Nathan Chancellor Jan. 31, 2023, 7:33 p.m. UTC | #5

On Tue, Jan 31, 2023 at 11:25:38AM -0800, Ian Rogers wrote:
> On Tue, Jan 31, 2023 at 10:08 AM Ian Rogers <irogers@google.com> wrote:
> >
> > On Tue, Jan 31, 2023 at 9:21 AM Nathan Chancellor <nathan@kernel.org> wrote:
> > >
> > > Hi Ian,
> > >
> > > On Mon, Jan 23, 2023 at 10:43:24PM -0800, Ian Rogers wrote:
> > > > HOSTCC is always wanted when building. Setting CC to HOSTCC happens
> > > > after tools/scripts/Makefile.include is included, meaning flags are
> > > > set assuming say CC is gcc, but then it can be later set to HOSTCC
> > > > which may be clang. tools/scripts/Makefile.include is needed for host
> > > > set up and common macros in objtool's Makefile. Rather than override
> > > > CC to HOSTCC, just pass CC as HOSTCC to Makefile.build, the libsubcmd
> > > > builds and the linkage step. This means the Makefiles don't see things
> > > > like CC changing and tool flag determination, and similar, work
> > > > properly.
> > > >
> > > > Also, clear the passed subdir as otherwise an outer build may break by
> > > > inadvertently passing an inappropriate value.
> > > >
> > > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > > ---
> > > >  tools/bpf/resolve_btfids/Makefile | 17 +++++++----------
> > > >  1 file changed, 7 insertions(+), 10 deletions(-)
> > > >
> > > > diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> > > > index 1fe0082b2ecc..daed388aa5d7 100644
> > > > --- a/tools/bpf/resolve_btfids/Makefile
> > > > +++ b/tools/bpf/resolve_btfids/Makefile
> > > > @@ -18,14 +18,11 @@ else
> > > >  endif
> > > >
> > > >  # always use the host compiler
> > > > -AR       = $(HOSTAR)
> > > > -CC       = $(HOSTCC)
> > > > -LD       = $(HOSTLD)
> > > > -ARCH     = $(HOSTARCH)
> > > > +HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
> > > > +               EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > > +
> > > >  RM      ?= rm
> > > >  CROSS_COMPILE =
> > > > -CFLAGS  := $(KBUILD_HOSTCFLAGS)
> > > > -LDFLAGS := $(KBUILD_HOSTLDFLAGS)
> > > >
> > > >  OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> > > >
> > > > @@ -56,12 +53,12 @@ $(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT):
> > > >
> > > >  $(SUBCMDOBJ): fixdep FORCE | $(OUTPUT)/libsubcmd
> > > >       $(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(SUBCMD_OUT) \
> > > > -                 DESTDIR=$(SUBCMD_DESTDIR) prefix= \
> > > > +                 DESTDIR=$(SUBCMD_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > > >                   $(abspath $@) install_headers
> > > >
> > > >  $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUT)
> > > >       $(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) OUTPUT=$(LIBBPF_OUT)    \
> > > > -                 DESTDIR=$(LIBBPF_DESTDIR) prefix= EXTRA_CFLAGS="$(CFLAGS)" \
> > > > +                 DESTDIR=$(LIBBPF_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > > >                   $(abspath $@) install_headers
> > > >
> > > >  LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> > > > @@ -80,11 +77,11 @@ export srctree OUTPUT CFLAGS Q
> > > >  include $(srctree)/tools/build/Makefile.include
> > > >
> > > >  $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)
> > > > -     $(Q)$(MAKE) $(build)=resolve_btfids
> > > > +     $(Q)$(MAKE) $(build)=resolve_btfids $(HOST_OVERRIDES)
> > > >
> > > >  $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
> > > >       $(call msg,LINK,$@)
> > > > -     $(Q)$(CC) $(BINARY_IN) $(LDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > > > +     $(Q)$(HOSTCC) $(BINARY_IN) $(KBUILD_HOSTLDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > > >
> > > >  clean_objects := $(wildcard $(OUTPUT)/*.o                \
> > > >                              $(OUTPUT)/.*.o.cmd           \
> > > > --
> > > > 2.39.0.246.g2a6d74b583-goog
> > > >
> > >
> > > I just bisected a linking failure when building resolve_btfids with
> > > clang to this change as commit 13e07691a16f ("tools/resolve_btfids:
> > > Alter how HOSTCC is forced") in the bpf-next tree.
> > >
> > > It appears to be related to whether or not CROSS_COMPILE is specified,
> > > which we have to do for certain architectures and configurations still.
> > > arm64 is not one of those but it helps demonstrate the issue.
> > >
> > >   # Turn off CONFIG_DEBUG_INFO_REDUCED and turn on CONFIG_DEBUG_INFO_BTF
> > >   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 defconfig menuconfig
> > >
> > >   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 prepare
> > >   ld.lld: error: $LINUX_SRC/tools/bpf/resolve_btfids//resolve_btfids-in.o is incompatible with elf64-x86-64
> > >   clang-17: error: linker command failed with exit code 1 (use -v to see invocation)
> > >   ...
> > >
> > > Before your change, with V=1, I see:
> > >
> > > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11 -Wdeclaration-after-statement -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> > >
> > > After, I see:
> > >
> > > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o --target=aarch64-linux-gnu -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> > >
> > > We seem to have taken on a '--target=aarch64-linux-gnu' (changing the
> > > target of resolve_btfids-in.o) and we dropped the warning flags.
> > >
> > > I think this comes from the clang block in
> > > tools/scripts/Makefile.include, which is included into the
> > > resolve_btfids Makefile via tools/lib/bpf/Makefile.
> > >
> > > I am not super familiar with the tools build system, otherwise I would
> > > try to provide a patch. I tried moving CROSS_COMPILE from a recursive to
> > > simple variable ('=' -> ':=') and moving it to HOST_OVERRIDES but those
> > > did not appear to resolve it for me.
> > >
> > > If there is any other information I can provide or patches I can test,
> > > please let me know.
> > >
> > > Cheers,
> > > Nathan
> >
> > Thanks Nathan, and thanks for all the details in the bug report. I'm
> > looking into this.
> >
> > Ian
> 
> Given the somewhat complicated cross compile I wasn't able to get a
> reproduction. Could you see if the following addresses the problem:

As long as you have an LLVM toolchain that targets AArch64 and your
host, you should be able to reproduce this issue with those commands
verbatim, as that command should not use any GNU binutils. I am pretty
sure I tried it in a fresh container before reporting it but it is
possible that I did not.

> ```
> diff --git a/tools/bpf/resolve_btfids/Makefile
> b/tools/bpf/resolve_btfids/Makefile
> index daed388aa5d7..a06966841df4 100644
> --- a/tools/bpf/resolve_btfids/Makefile
> +++ b/tools/bpf/resolve_btfids/Makefile
> @@ -19,10 +19,9 @@ endif
> 
> # always use the host compiler
> HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)"
> ARCH="$(HOSTARCH)" \
> -                 EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> +                 EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> CROSS_COMPILE=""
> 
> RM      ?= rm
> -CROSS_COMPILE =
> 
> OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> ```
> 

Unfortunately, it does not. I still see '--target=' end up in the
CFLAGS of those files.

Cheers,
Nathan

Ian Rogers Jan. 31, 2023, 8:59 p.m. UTC | #6

On Tue, Jan 31, 2023 at 11:33 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> On Tue, Jan 31, 2023 at 11:25:38AM -0800, Ian Rogers wrote:
> > On Tue, Jan 31, 2023 at 10:08 AM Ian Rogers <irogers@google.com> wrote:
> > >
> > > On Tue, Jan 31, 2023 at 9:21 AM Nathan Chancellor <nathan@kernel.org> wrote:
> > > >
> > > > Hi Ian,
> > > >
> > > > On Mon, Jan 23, 2023 at 10:43:24PM -0800, Ian Rogers wrote:
> > > > > HOSTCC is always wanted when building. Setting CC to HOSTCC happens
> > > > > after tools/scripts/Makefile.include is included, meaning flags are
> > > > > set assuming say CC is gcc, but then it can be later set to HOSTCC
> > > > > which may be clang. tools/scripts/Makefile.include is needed for host
> > > > > set up and common macros in objtool's Makefile. Rather than override
> > > > > CC to HOSTCC, just pass CC as HOSTCC to Makefile.build, the libsubcmd
> > > > > builds and the linkage step. This means the Makefiles don't see things
> > > > > like CC changing and tool flag determination, and similar, work
> > > > > properly.
> > > > >
> > > > > Also, clear the passed subdir as otherwise an outer build may break by
> > > > > inadvertently passing an inappropriate value.
> > > > >
> > > > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > > > ---
> > > > >  tools/bpf/resolve_btfids/Makefile | 17 +++++++----------
> > > > >  1 file changed, 7 insertions(+), 10 deletions(-)
> > > > >
> > > > > diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> > > > > index 1fe0082b2ecc..daed388aa5d7 100644
> > > > > --- a/tools/bpf/resolve_btfids/Makefile
> > > > > +++ b/tools/bpf/resolve_btfids/Makefile
> > > > > @@ -18,14 +18,11 @@ else
> > > > >  endif
> > > > >
> > > > >  # always use the host compiler
> > > > > -AR       = $(HOSTAR)
> > > > > -CC       = $(HOSTCC)
> > > > > -LD       = $(HOSTLD)
> > > > > -ARCH     = $(HOSTARCH)
> > > > > +HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
> > > > > +               EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > > > +
> > > > >  RM      ?= rm
> > > > >  CROSS_COMPILE =
> > > > > -CFLAGS  := $(KBUILD_HOSTCFLAGS)
> > > > > -LDFLAGS := $(KBUILD_HOSTLDFLAGS)
> > > > >
> > > > >  OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> > > > >
> > > > > @@ -56,12 +53,12 @@ $(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT):
> > > > >
> > > > >  $(SUBCMDOBJ): fixdep FORCE | $(OUTPUT)/libsubcmd
> > > > >       $(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(SUBCMD_OUT) \
> > > > > -                 DESTDIR=$(SUBCMD_DESTDIR) prefix= \
> > > > > +                 DESTDIR=$(SUBCMD_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > > > >                   $(abspath $@) install_headers
> > > > >
> > > > >  $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUT)
> > > > >       $(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) OUTPUT=$(LIBBPF_OUT)    \
> > > > > -                 DESTDIR=$(LIBBPF_DESTDIR) prefix= EXTRA_CFLAGS="$(CFLAGS)" \
> > > > > +                 DESTDIR=$(LIBBPF_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > > > >                   $(abspath $@) install_headers
> > > > >
> > > > >  LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> > > > > @@ -80,11 +77,11 @@ export srctree OUTPUT CFLAGS Q
> > > > >  include $(srctree)/tools/build/Makefile.include
> > > > >
> > > > >  $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)
> > > > > -     $(Q)$(MAKE) $(build)=resolve_btfids
> > > > > +     $(Q)$(MAKE) $(build)=resolve_btfids $(HOST_OVERRIDES)
> > > > >
> > > > >  $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
> > > > >       $(call msg,LINK,$@)
> > > > > -     $(Q)$(CC) $(BINARY_IN) $(LDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > > > > +     $(Q)$(HOSTCC) $(BINARY_IN) $(KBUILD_HOSTLDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > > > >
> > > > >  clean_objects := $(wildcard $(OUTPUT)/*.o                \
> > > > >                              $(OUTPUT)/.*.o.cmd           \
> > > > > --
> > > > > 2.39.0.246.g2a6d74b583-goog
> > > > >
> > > >
> > > > I just bisected a linking failure when building resolve_btfids with
> > > > clang to this change as commit 13e07691a16f ("tools/resolve_btfids:
> > > > Alter how HOSTCC is forced") in the bpf-next tree.
> > > >
> > > > It appears to be related to whether or not CROSS_COMPILE is specified,
> > > > which we have to do for certain architectures and configurations still.
> > > > arm64 is not one of those but it helps demonstrate the issue.
> > > >
> > > >   # Turn off CONFIG_DEBUG_INFO_REDUCED and turn on CONFIG_DEBUG_INFO_BTF
> > > >   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 defconfig menuconfig
> > > >
> > > >   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 prepare
> > > >   ld.lld: error: $LINUX_SRC/tools/bpf/resolve_btfids//resolve_btfids-in.o is incompatible with elf64-x86-64
> > > >   clang-17: error: linker command failed with exit code 1 (use -v to see invocation)
> > > >   ...
> > > >
> > > > Before your change, with V=1, I see:
> > > >
> > > > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11 -Wdeclaration-after-statement -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> > > >
> > > > After, I see:
> > > >
> > > > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o --target=aarch64-linux-gnu -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> > > >
> > > > We seem to have taken on a '--target=aarch64-linux-gnu' (changing the
> > > > target of resolve_btfids-in.o) and we dropped the warning flags.
> > > >
> > > > I think this comes from the clang block in
> > > > tools/scripts/Makefile.include, which is included into the
> > > > resolve_btfids Makefile via tools/lib/bpf/Makefile.
> > > >
> > > > I am not super familiar with the tools build system, otherwise I would
> > > > try to provide a patch. I tried moving CROSS_COMPILE from a recursive to
> > > > simple variable ('=' -> ':=') and moving it to HOST_OVERRIDES but those
> > > > did not appear to resolve it for me.
> > > >
> > > > If there is any other information I can provide or patches I can test,
> > > > please let me know.
> > > >
> > > > Cheers,
> > > > Nathan
> > >
> > > Thanks Nathan, and thanks for all the details in the bug report. I'm
> > > looking into this.
> > >
> > > Ian
> >
> > Given the somewhat complicated cross compile I wasn't able to get a
> > reproduction. Could you see if the following addresses the problem:
>
> As long as you have an LLVM toolchain that targets AArch64 and your
> host, you should be able to reproduce this issue with those commands
> verbatim, as that command should not use any GNU binutils. I am pretty
> sure I tried it in a fresh container before reporting it but it is
> possible that I did not.

Thanks, do you have instructions on setting up the container?

> > ```
> > diff --git a/tools/bpf/resolve_btfids/Makefile
> > b/tools/bpf/resolve_btfids/Makefile
> > index daed388aa5d7..a06966841df4 100644
> > --- a/tools/bpf/resolv

Ian
e_btfids/Makefile
> > +++ b/tools/bpf/resolve_btfids/Makefile
> > @@ -19,10 +19,9 @@ endif
> >
> > # always use the host compiler
> > HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)"
> > ARCH="$(HOSTARCH)" \
> > -                 EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > +                 EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > CROSS_COMPILE=""
> >
> > RM      ?= rm
> > -CROSS_COMPILE =
> >
> > OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> > ```
> >
>
> Unfortunately, it does not. I still see '--target=' end up in the
> CFLAGS of those files.
>
> Cheers,
> Nathan

Hmm.. I can see the issue. We avoid this in places like libsubcmd
because the Makefile there includes tools/scripts/Makefile.include,
but here the Makefile.build inclusion is direct and we have CC set up
for cross compilation. This is messy and it will take some playing
around to come up with a simple fix.

Thanks,
Ian

Nathan Chancellor Jan. 31, 2023, 9:17 p.m. UTC | #7

On Tue, Jan 31, 2023 at 12:59:04PM -0800, Ian Rogers wrote:
> On Tue, Jan 31, 2023 at 11:33 AM Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > On Tue, Jan 31, 2023 at 11:25:38AM -0800, Ian Rogers wrote:
> > > On Tue, Jan 31, 2023 at 10:08 AM Ian Rogers <irogers@google.com> wrote:
> > > >
> > > > On Tue, Jan 31, 2023 at 9:21 AM Nathan Chancellor <nathan@kernel.org> wrote:
> > > > >
> > > > > Hi Ian,
> > > > >
> > > > > On Mon, Jan 23, 2023 at 10:43:24PM -0800, Ian Rogers wrote:
> > > > > > HOSTCC is always wanted when building. Setting CC to HOSTCC happens
> > > > > > after tools/scripts/Makefile.include is included, meaning flags are
> > > > > > set assuming say CC is gcc, but then it can be later set to HOSTCC
> > > > > > which may be clang. tools/scripts/Makefile.include is needed for host
> > > > > > set up and common macros in objtool's Makefile. Rather than override
> > > > > > CC to HOSTCC, just pass CC as HOSTCC to Makefile.build, the libsubcmd
> > > > > > builds and the linkage step. This means the Makefiles don't see things
> > > > > > like CC changing and tool flag determination, and similar, work
> > > > > > properly.
> > > > > >
> > > > > > Also, clear the passed subdir as otherwise an outer build may break by
> > > > > > inadvertently passing an inappropriate value.
> > > > > >
> > > > > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > > > > ---
> > > > > >  tools/bpf/resolve_btfids/Makefile | 17 +++++++----------
> > > > > >  1 file changed, 7 insertions(+), 10 deletions(-)
> > > > > >
> > > > > > diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> > > > > > index 1fe0082b2ecc..daed388aa5d7 100644
> > > > > > --- a/tools/bpf/resolve_btfids/Makefile
> > > > > > +++ b/tools/bpf/resolve_btfids/Makefile
> > > > > > @@ -18,14 +18,11 @@ else
> > > > > >  endif
> > > > > >
> > > > > >  # always use the host compiler
> > > > > > -AR       = $(HOSTAR)
> > > > > > -CC       = $(HOSTCC)
> > > > > > -LD       = $(HOSTLD)
> > > > > > -ARCH     = $(HOSTARCH)
> > > > > > +HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
> > > > > > +               EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > > > > +
> > > > > >  RM      ?= rm
> > > > > >  CROSS_COMPILE =
> > > > > > -CFLAGS  := $(KBUILD_HOSTCFLAGS)
> > > > > > -LDFLAGS := $(KBUILD_HOSTLDFLAGS)
> > > > > >
> > > > > >  OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> > > > > >
> > > > > > @@ -56,12 +53,12 @@ $(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT):
> > > > > >
> > > > > >  $(SUBCMDOBJ): fixdep FORCE | $(OUTPUT)/libsubcmd
> > > > > >       $(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(SUBCMD_OUT) \
> > > > > > -                 DESTDIR=$(SUBCMD_DESTDIR) prefix= \
> > > > > > +                 DESTDIR=$(SUBCMD_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > > > > >                   $(abspath $@) install_headers
> > > > > >
> > > > > >  $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUT)
> > > > > >       $(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) OUTPUT=$(LIBBPF_OUT)    \
> > > > > > -                 DESTDIR=$(LIBBPF_DESTDIR) prefix= EXTRA_CFLAGS="$(CFLAGS)" \
> > > > > > +                 DESTDIR=$(LIBBPF_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > > > > >                   $(abspath $@) install_headers
> > > > > >
> > > > > >  LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> > > > > > @@ -80,11 +77,11 @@ export srctree OUTPUT CFLAGS Q
> > > > > >  include $(srctree)/tools/build/Makefile.include
> > > > > >
> > > > > >  $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)
> > > > > > -     $(Q)$(MAKE) $(build)=resolve_btfids
> > > > > > +     $(Q)$(MAKE) $(build)=resolve_btfids $(HOST_OVERRIDES)
> > > > > >
> > > > > >  $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
> > > > > >       $(call msg,LINK,$@)
> > > > > > -     $(Q)$(CC) $(BINARY_IN) $(LDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > > > > > +     $(Q)$(HOSTCC) $(BINARY_IN) $(KBUILD_HOSTLDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > > > > >
> > > > > >  clean_objects := $(wildcard $(OUTPUT)/*.o                \
> > > > > >                              $(OUTPUT)/.*.o.cmd           \
> > > > > > --
> > > > > > 2.39.0.246.g2a6d74b583-goog
> > > > > >
> > > > >
> > > > > I just bisected a linking failure when building resolve_btfids with
> > > > > clang to this change as commit 13e07691a16f ("tools/resolve_btfids:
> > > > > Alter how HOSTCC is forced") in the bpf-next tree.
> > > > >
> > > > > It appears to be related to whether or not CROSS_COMPILE is specified,
> > > > > which we have to do for certain architectures and configurations still.
> > > > > arm64 is not one of those but it helps demonstrate the issue.
> > > > >
> > > > >   # Turn off CONFIG_DEBUG_INFO_REDUCED and turn on CONFIG_DEBUG_INFO_BTF
> > > > >   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 defconfig menuconfig
> > > > >
> > > > >   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 prepare
> > > > >   ld.lld: error: $LINUX_SRC/tools/bpf/resolve_btfids//resolve_btfids-in.o is incompatible with elf64-x86-64
> > > > >   clang-17: error: linker command failed with exit code 1 (use -v to see invocation)
> > > > >   ...
> > > > >
> > > > > Before your change, with V=1, I see:
> > > > >
> > > > > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11 -Wdeclaration-after-statement -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> > > > >
> > > > > After, I see:
> > > > >
> > > > > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o --target=aarch64-linux-gnu -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> > > > >
> > > > > We seem to have taken on a '--target=aarch64-linux-gnu' (changing the
> > > > > target of resolve_btfids-in.o) and we dropped the warning flags.
> > > > >
> > > > > I think this comes from the clang block in
> > > > > tools/scripts/Makefile.include, which is included into the
> > > > > resolve_btfids Makefile via tools/lib/bpf/Makefile.
> > > > >
> > > > > I am not super familiar with the tools build system, otherwise I would
> > > > > try to provide a patch. I tried moving CROSS_COMPILE from a recursive to
> > > > > simple variable ('=' -> ':=') and moving it to HOST_OVERRIDES but those
> > > > > did not appear to resolve it for me.
> > > > >
> > > > > If there is any other information I can provide or patches I can test,
> > > > > please let me know.
> > > > >
> > > > > Cheers,
> > > > > Nathan
> > > >
> > > > Thanks Nathan, and thanks for all the details in the bug report. I'm
> > > > looking into this.
> > > >
> > > > Ian
> > >
> > > Given the somewhat complicated cross compile I wasn't able to get a
> > > reproduction. Could you see if the following addresses the problem:
> >
> > As long as you have an LLVM toolchain that targets AArch64 and your
> > host, you should be able to reproduce this issue with those commands
> > verbatim, as that command should not use any GNU binutils. I am pretty
> > sure I tried it in a fresh container before reporting it but it is
> > possible that I did not.
> 
> Thanks, do you have instructions on setting up the container?

Sure thing, this worked for me in the Linux source you would like to
build (I marked it readonly to make sure any modifications were done in
my host environment, remove the ':ro' if you would like to make edits to
the source within the container). Docker should work as well but I did
not test it.

$ podman run --rm -ti -v $PWD:/linux:ro docker.io/archlinux:base-devel
# pacman -Syyu --noconfirm bc clang lib32-glibc lld llvm python
...

# To turn on CONFIG_DEBUG_INFO_BTF
# make -C /linux -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 O=/build defconfig menuconfig

# make -C /linux -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 O=/build prepare
ld.lld: error: /build/tools/bpf/resolve_btfids//resolve_btfids-in.o is incompatible with elf64-x86-64
clang-15: error: linker command failed with exit code 1 (use -v to see invocation)

> > > ```
> > > diff --git a/tools/bpf/resolve_btfids/Makefile
> > > b/tools/bpf/resolve_btfids/Makefile
> > > index daed388aa5d7..a06966841df4 100644
> > > --- a/tools/bpf/resolv
> 
> Ian
> e_btfids/Makefile
> > > +++ b/tools/bpf/resolve_btfids/Makefile
> > > @@ -19,10 +19,9 @@ endif
> > >
> > > # always use the host compiler
> > > HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)"
> > > ARCH="$(HOSTARCH)" \
> > > -                 EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > +                 EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > CROSS_COMPILE=""
> > >
> > > RM      ?= rm
> > > -CROSS_COMPILE =
> > >
> > > OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> > > ```
> > >
> >
> > Unfortunately, it does not. I still see '--target=' end up in the
> > CFLAGS of those files.
> >
> > Cheers,
> > Nathan
> 
> Hmm.. I can see the issue. We avoid this in places like libsubcmd
> because the Makefile there includes tools/scripts/Makefile.include,
> but here the Makefile.build inclusion is direct and we have CC set up
> for cross compilation. This is messy and it will take some playing
> around to come up with a simple fix.

Ack, if you have any issues with reproducing it, please let me know.

Cheers,
Nathan

Jiri Olsa Jan. 31, 2023, 10:40 p.m. UTC | #8

On Tue, Jan 31, 2023 at 02:17:08PM -0700, Nathan Chancellor wrote:
> On Tue, Jan 31, 2023 at 12:59:04PM -0800, Ian Rogers wrote:
> > On Tue, Jan 31, 2023 at 11:33 AM Nathan Chancellor <nathan@kernel.org> wrote:
> > >
> > > On Tue, Jan 31, 2023 at 11:25:38AM -0800, Ian Rogers wrote:
> > > > On Tue, Jan 31, 2023 at 10:08 AM Ian Rogers <irogers@google.com> wrote:
> > > > >
> > > > > On Tue, Jan 31, 2023 at 9:21 AM Nathan Chancellor <nathan@kernel.org> wrote:
> > > > > >
> > > > > > Hi Ian,
> > > > > >
> > > > > > On Mon, Jan 23, 2023 at 10:43:24PM -0800, Ian Rogers wrote:
> > > > > > > HOSTCC is always wanted when building. Setting CC to HOSTCC happens
> > > > > > > after tools/scripts/Makefile.include is included, meaning flags are
> > > > > > > set assuming say CC is gcc, but then it can be later set to HOSTCC
> > > > > > > which may be clang. tools/scripts/Makefile.include is needed for host
> > > > > > > set up and common macros in objtool's Makefile. Rather than override
> > > > > > > CC to HOSTCC, just pass CC as HOSTCC to Makefile.build, the libsubcmd
> > > > > > > builds and the linkage step. This means the Makefiles don't see things
> > > > > > > like CC changing and tool flag determination, and similar, work
> > > > > > > properly.
> > > > > > >
> > > > > > > Also, clear the passed subdir as otherwise an outer build may break by
> > > > > > > inadvertently passing an inappropriate value.
> > > > > > >
> > > > > > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > > > > > ---
> > > > > > >  tools/bpf/resolve_btfids/Makefile | 17 +++++++----------
> > > > > > >  1 file changed, 7 insertions(+), 10 deletions(-)
> > > > > > >
> > > > > > > diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> > > > > > > index 1fe0082b2ecc..daed388aa5d7 100644
> > > > > > > --- a/tools/bpf/resolve_btfids/Makefile
> > > > > > > +++ b/tools/bpf/resolve_btfids/Makefile
> > > > > > > @@ -18,14 +18,11 @@ else
> > > > > > >  endif
> > > > > > >
> > > > > > >  # always use the host compiler
> > > > > > > -AR       = $(HOSTAR)
> > > > > > > -CC       = $(HOSTCC)
> > > > > > > -LD       = $(HOSTLD)
> > > > > > > -ARCH     = $(HOSTARCH)
> > > > > > > +HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
> > > > > > > +               EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > > > > > +
> > > > > > >  RM      ?= rm
> > > > > > >  CROSS_COMPILE =
> > > > > > > -CFLAGS  := $(KBUILD_HOSTCFLAGS)
> > > > > > > -LDFLAGS := $(KBUILD_HOSTLDFLAGS)
> > > > > > >
> > > > > > >  OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> > > > > > >
> > > > > > > @@ -56,12 +53,12 @@ $(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT):
> > > > > > >
> > > > > > >  $(SUBCMDOBJ): fixdep FORCE | $(OUTPUT)/libsubcmd
> > > > > > >       $(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(SUBCMD_OUT) \
> > > > > > > -                 DESTDIR=$(SUBCMD_DESTDIR) prefix= \
> > > > > > > +                 DESTDIR=$(SUBCMD_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > > > > > >                   $(abspath $@) install_headers
> > > > > > >
> > > > > > >  $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUT)
> > > > > > >       $(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) OUTPUT=$(LIBBPF_OUT)    \
> > > > > > > -                 DESTDIR=$(LIBBPF_DESTDIR) prefix= EXTRA_CFLAGS="$(CFLAGS)" \
> > > > > > > +                 DESTDIR=$(LIBBPF_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > > > > > >                   $(abspath $@) install_headers
> > > > > > >
> > > > > > >  LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> > > > > > > @@ -80,11 +77,11 @@ export srctree OUTPUT CFLAGS Q
> > > > > > >  include $(srctree)/tools/build/Makefile.include
> > > > > > >
> > > > > > >  $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)
> > > > > > > -     $(Q)$(MAKE) $(build)=resolve_btfids
> > > > > > > +     $(Q)$(MAKE) $(build)=resolve_btfids $(HOST_OVERRIDES)
> > > > > > >
> > > > > > >  $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
> > > > > > >       $(call msg,LINK,$@)
> > > > > > > -     $(Q)$(CC) $(BINARY_IN) $(LDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > > > > > > +     $(Q)$(HOSTCC) $(BINARY_IN) $(KBUILD_HOSTLDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > > > > > >
> > > > > > >  clean_objects := $(wildcard $(OUTPUT)/*.o                \
> > > > > > >                              $(OUTPUT)/.*.o.cmd           \
> > > > > > > --
> > > > > > > 2.39.0.246.g2a6d74b583-goog
> > > > > > >
> > > > > >
> > > > > > I just bisected a linking failure when building resolve_btfids with
> > > > > > clang to this change as commit 13e07691a16f ("tools/resolve_btfids:
> > > > > > Alter how HOSTCC is forced") in the bpf-next tree.
> > > > > >
> > > > > > It appears to be related to whether or not CROSS_COMPILE is specified,
> > > > > > which we have to do for certain architectures and configurations still.
> > > > > > arm64 is not one of those but it helps demonstrate the issue.
> > > > > >
> > > > > >   # Turn off CONFIG_DEBUG_INFO_REDUCED and turn on CONFIG_DEBUG_INFO_BTF
> > > > > >   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 defconfig menuconfig
> > > > > >
> > > > > >   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 prepare
> > > > > >   ld.lld: error: $LINUX_SRC/tools/bpf/resolve_btfids//resolve_btfids-in.o is incompatible with elf64-x86-64
> > > > > >   clang-17: error: linker command failed with exit code 1 (use -v to see invocation)
> > > > > >   ...
> > > > > >
> > > > > > Before your change, with V=1, I see:
> > > > > >
> > > > > > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11 -Wdeclaration-after-statement -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> > > > > >
> > > > > > After, I see:
> > > > > >
> > > > > > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o --target=aarch64-linux-gnu -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> > > > > >
> > > > > > We seem to have taken on a '--target=aarch64-linux-gnu' (changing the
> > > > > > target of resolve_btfids-in.o) and we dropped the warning flags.
> > > > > >
> > > > > > I think this comes from the clang block in
> > > > > > tools/scripts/Makefile.include, which is included into the
> > > > > > resolve_btfids Makefile via tools/lib/bpf/Makefile.
> > > > > >
> > > > > > I am not super familiar with the tools build system, otherwise I would
> > > > > > try to provide a patch. I tried moving CROSS_COMPILE from a recursive to
> > > > > > simple variable ('=' -> ':=') and moving it to HOST_OVERRIDES but those
> > > > > > did not appear to resolve it for me.
> > > > > >
> > > > > > If there is any other information I can provide or patches I can test,
> > > > > > please let me know.
> > > > > >
> > > > > > Cheers,
> > > > > > Nathan
> > > > >
> > > > > Thanks Nathan, and thanks for all the details in the bug report. I'm
> > > > > looking into this.
> > > > >
> > > > > Ian
> > > >
> > > > Given the somewhat complicated cross compile I wasn't able to get a
> > > > reproduction. Could you see if the following addresses the problem:
> > >
> > > As long as you have an LLVM toolchain that targets AArch64 and your
> > > host, you should be able to reproduce this issue with those commands
> > > verbatim, as that command should not use any GNU binutils. I am pretty
> > > sure I tried it in a fresh container before reporting it but it is
> > > possible that I did not.
> > 
> > Thanks, do you have instructions on setting up the container?
> 
> Sure thing, this worked for me in the Linux source you would like to
> build (I marked it readonly to make sure any modifications were done in
> my host environment, remove the ':ro' if you would like to make edits to
> the source within the container). Docker should work as well but I did
> not test it.
> 
> $ podman run --rm -ti -v $PWD:/linux:ro docker.io/archlinux:base-devel
> # pacman -Syyu --noconfirm bc clang lib32-glibc lld llvm python
> ...
> 
> # To turn on CONFIG_DEBUG_INFO_BTF
> # make -C /linux -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 O=/build defconfig menuconfig
> 
> # make -C /linux -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 O=/build prepare
> ld.lld: error: /build/tools/bpf/resolve_btfids//resolve_btfids-in.o is incompatible with elf64-x86-64
> clang-15: error: linker command failed with exit code 1 (use -v to see invocation)
> 
> > > > ```
> > > > diff --git a/tools/bpf/resolve_btfids/Makefile
> > > > b/tools/bpf/resolve_btfids/Makefile
> > > > index daed388aa5d7..a06966841df4 100644
> > > > --- a/tools/bpf/resolv
> > 
> > Ian
> > e_btfids/Makefile
> > > > +++ b/tools/bpf/resolve_btfids/Makefile
> > > > @@ -19,10 +19,9 @@ endif
> > > >
> > > > # always use the host compiler
> > > > HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)"
> > > > ARCH="$(HOSTARCH)" \
> > > > -                 EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > > +                 EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > > CROSS_COMPILE=""
> > > >
> > > > RM      ?= rm
> > > > -CROSS_COMPILE =
> > > >
> > > > OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> > > > ```
> > > >
> > >
> > > Unfortunately, it does not. I still see '--target=' end up in the
> > > CFLAGS of those files.

hi,
I can reproduce that and I think the reason is that the patch removes
CFLAGS setup

  CFLAGS  := $(KBUILD_HOSTCFLAGS)

so now the 'include ../../scripts/Makefile.include' will set CFLAGS
with the  --target=... and we fail

I can compile with the change below.. we could also set CROSS_COMPILE
before including tools/scripts/Makefile.include ... not sure which
on is better

also I need to check if we should keep LDFLAGS setup as well

jirka


---
diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
index daed388aa5d7..875e3fcce7cd 100644
--- a/tools/bpf/resolve_btfids/Makefile
+++ b/tools/bpf/resolve_btfids/Makefile
@@ -64,6 +64,7 @@ $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OU
 LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
 LIBELF_LIBS  := $(shell $(HOSTPKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf)
 
+CFLAGS := $(KBUILD_HOSTCFLAGS)
 CFLAGS += -g \
           -I$(srctree)/tools/include \
           -I$(srctree)/tools/include/uapi \

Ian Rogers Jan. 31, 2023, 10:50 p.m. UTC | #9

On Tue, Jan 31, 2023 at 2:40 PM Jiri Olsa <olsajiri@gmail.com> wrote:
>
> On Tue, Jan 31, 2023 at 02:17:08PM -0700, Nathan Chancellor wrote:
> > On Tue, Jan 31, 2023 at 12:59:04PM -0800, Ian Rogers wrote:
> > > On Tue, Jan 31, 2023 at 11:33 AM Nathan Chancellor <nathan@kernel.org> wrote:
> > > >
> > > > On Tue, Jan 31, 2023 at 11:25:38AM -0800, Ian Rogers wrote:
> > > > > On Tue, Jan 31, 2023 at 10:08 AM Ian Rogers <irogers@google.com> wrote:
> > > > > >
> > > > > > On Tue, Jan 31, 2023 at 9:21 AM Nathan Chancellor <nathan@kernel.org> wrote:
> > > > > > >
> > > > > > > Hi Ian,
> > > > > > >
> > > > > > > On Mon, Jan 23, 2023 at 10:43:24PM -0800, Ian Rogers wrote:
> > > > > > > > HOSTCC is always wanted when building. Setting CC to HOSTCC happens
> > > > > > > > after tools/scripts/Makefile.include is included, meaning flags are
> > > > > > > > set assuming say CC is gcc, but then it can be later set to HOSTCC
> > > > > > > > which may be clang. tools/scripts/Makefile.include is needed for host
> > > > > > > > set up and common macros in objtool's Makefile. Rather than override
> > > > > > > > CC to HOSTCC, just pass CC as HOSTCC to Makefile.build, the libsubcmd
> > > > > > > > builds and the linkage step. This means the Makefiles don't see things
> > > > > > > > like CC changing and tool flag determination, and similar, work
> > > > > > > > properly.
> > > > > > > >
> > > > > > > > Also, clear the passed subdir as otherwise an outer build may break by
> > > > > > > > inadvertently passing an inappropriate value.
> > > > > > > >
> > > > > > > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > > > > > > ---
> > > > > > > >  tools/bpf/resolve_btfids/Makefile | 17 +++++++----------
> > > > > > > >  1 file changed, 7 insertions(+), 10 deletions(-)
> > > > > > > >
> > > > > > > > diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> > > > > > > > index 1fe0082b2ecc..daed388aa5d7 100644
> > > > > > > > --- a/tools/bpf/resolve_btfids/Makefile
> > > > > > > > +++ b/tools/bpf/resolve_btfids/Makefile
> > > > > > > > @@ -18,14 +18,11 @@ else
> > > > > > > >  endif
> > > > > > > >
> > > > > > > >  # always use the host compiler
> > > > > > > > -AR       = $(HOSTAR)
> > > > > > > > -CC       = $(HOSTCC)
> > > > > > > > -LD       = $(HOSTLD)
> > > > > > > > -ARCH     = $(HOSTARCH)
> > > > > > > > +HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
> > > > > > > > +               EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > > > > > > +
> > > > > > > >  RM      ?= rm
> > > > > > > >  CROSS_COMPILE =
> > > > > > > > -CFLAGS  := $(KBUILD_HOSTCFLAGS)
> > > > > > > > -LDFLAGS := $(KBUILD_HOSTLDFLAGS)
> > > > > > > >
> > > > > > > >  OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> > > > > > > >
> > > > > > > > @@ -56,12 +53,12 @@ $(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT):
> > > > > > > >
> > > > > > > >  $(SUBCMDOBJ): fixdep FORCE | $(OUTPUT)/libsubcmd
> > > > > > > >       $(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(SUBCMD_OUT) \
> > > > > > > > -                 DESTDIR=$(SUBCMD_DESTDIR) prefix= \
> > > > > > > > +                 DESTDIR=$(SUBCMD_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > > > > > > >                   $(abspath $@) install_headers
> > > > > > > >
> > > > > > > >  $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUT)
> > > > > > > >       $(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) OUTPUT=$(LIBBPF_OUT)    \
> > > > > > > > -                 DESTDIR=$(LIBBPF_DESTDIR) prefix= EXTRA_CFLAGS="$(CFLAGS)" \
> > > > > > > > +                 DESTDIR=$(LIBBPF_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > > > > > > >                   $(abspath $@) install_headers
> > > > > > > >
> > > > > > > >  LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> > > > > > > > @@ -80,11 +77,11 @@ export srctree OUTPUT CFLAGS Q
> > > > > > > >  include $(srctree)/tools/build/Makefile.include
> > > > > > > >
> > > > > > > >  $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)
> > > > > > > > -     $(Q)$(MAKE) $(build)=resolve_btfids
> > > > > > > > +     $(Q)$(MAKE) $(build)=resolve_btfids $(HOST_OVERRIDES)
> > > > > > > >
> > > > > > > >  $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
> > > > > > > >       $(call msg,LINK,$@)
> > > > > > > > -     $(Q)$(CC) $(BINARY_IN) $(LDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > > > > > > > +     $(Q)$(HOSTCC) $(BINARY_IN) $(KBUILD_HOSTLDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > > > > > > >
> > > > > > > >  clean_objects := $(wildcard $(OUTPUT)/*.o                \
> > > > > > > >                              $(OUTPUT)/.*.o.cmd           \
> > > > > > > > --
> > > > > > > > 2.39.0.246.g2a6d74b583-goog
> > > > > > > >
> > > > > > >
> > > > > > > I just bisected a linking failure when building resolve_btfids with
> > > > > > > clang to this change as commit 13e07691a16f ("tools/resolve_btfids:
> > > > > > > Alter how HOSTCC is forced") in the bpf-next tree.
> > > > > > >
> > > > > > > It appears to be related to whether or not CROSS_COMPILE is specified,
> > > > > > > which we have to do for certain architectures and configurations still.
> > > > > > > arm64 is not one of those but it helps demonstrate the issue.
> > > > > > >
> > > > > > >   # Turn off CONFIG_DEBUG_INFO_REDUCED and turn on CONFIG_DEBUG_INFO_BTF
> > > > > > >   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 defconfig menuconfig
> > > > > > >
> > > > > > >   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 prepare
> > > > > > >   ld.lld: error: $LINUX_SRC/tools/bpf/resolve_btfids//resolve_btfids-in.o is incompatible with elf64-x86-64
> > > > > > >   clang-17: error: linker command failed with exit code 1 (use -v to see invocation)
> > > > > > >   ...
> > > > > > >
> > > > > > > Before your change, with V=1, I see:
> > > > > > >
> > > > > > > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11 -Wdeclaration-after-statement -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> > > > > > >
> > > > > > > After, I see:
> > > > > > >
> > > > > > > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o --target=aarch64-linux-gnu -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> > > > > > >
> > > > > > > We seem to have taken on a '--target=aarch64-linux-gnu' (changing the
> > > > > > > target of resolve_btfids-in.o) and we dropped the warning flags.
> > > > > > >
> > > > > > > I think this comes from the clang block in
> > > > > > > tools/scripts/Makefile.include, which is included into the
> > > > > > > resolve_btfids Makefile via tools/lib/bpf/Makefile.
> > > > > > >
> > > > > > > I am not super familiar with the tools build system, otherwise I would
> > > > > > > try to provide a patch. I tried moving CROSS_COMPILE from a recursive to
> > > > > > > simple variable ('=' -> ':=') and moving it to HOST_OVERRIDES but those
> > > > > > > did not appear to resolve it for me.
> > > > > > >
> > > > > > > If there is any other information I can provide or patches I can test,
> > > > > > > please let me know.
> > > > > > >
> > > > > > > Cheers,
> > > > > > > Nathan
> > > > > >
> > > > > > Thanks Nathan, and thanks for all the details in the bug report. I'm
> > > > > > looking into this.
> > > > > >
> > > > > > Ian
> > > > >
> > > > > Given the somewhat complicated cross compile I wasn't able to get a
> > > > > reproduction. Could you see if the following addresses the problem:
> > > >
> > > > As long as you have an LLVM toolchain that targets AArch64 and your
> > > > host, you should be able to reproduce this issue with those commands
> > > > verbatim, as that command should not use any GNU binutils. I am pretty
> > > > sure I tried it in a fresh container before reporting it but it is
> > > > possible that I did not.
> > >
> > > Thanks, do you have instructions on setting up the container?
> >
> > Sure thing, this worked for me in the Linux source you would like to
> > build (I marked it readonly to make sure any modifications were done in
> > my host environment, remove the ':ro' if you would like to make edits to
> > the source within the container). Docker should work as well but I did
> > not test it.
> >
> > $ podman run --rm -ti -v $PWD:/linux:ro docker.io/archlinux:base-devel
> > # pacman -Syyu --noconfirm bc clang lib32-glibc lld llvm python
> > ...
> >
> > # To turn on CONFIG_DEBUG_INFO_BTF
> > # make -C /linux -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 O=/build defconfig menuconfig
> >
> > # make -C /linux -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 O=/build prepare
> > ld.lld: error: /build/tools/bpf/resolve_btfids//resolve_btfids-in.o is incompatible with elf64-x86-64
> > clang-15: error: linker command failed with exit code 1 (use -v to see invocation)
> >
> > > > > ```
> > > > > diff --git a/tools/bpf/resolve_btfids/Makefile
> > > > > b/tools/bpf/resolve_btfids/Makefile
> > > > > index daed388aa5d7..a06966841df4 100644
> > > > > --- a/tools/bpf/resolv
> > >
> > > Ian
> > > e_btfids/Makefile
> > > > > +++ b/tools/bpf/resolve_btfids/Makefile
> > > > > @@ -19,10 +19,9 @@ endif
> > > > >
> > > > > # always use the host compiler
> > > > > HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)"
> > > > > ARCH="$(HOSTARCH)" \
> > > > > -                 EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > > > +                 EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > > > CROSS_COMPILE=""
> > > > >
> > > > > RM      ?= rm
> > > > > -CROSS_COMPILE =
> > > > >
> > > > > OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> > > > > ```
> > > > >
> > > >
> > > > Unfortunately, it does not. I still see '--target=' end up in the
> > > > CFLAGS of those files.
>
> hi,
> I can reproduce that and I think the reason is that the patch removes
> CFLAGS setup
>
>   CFLAGS  := $(KBUILD_HOSTCFLAGS)
>
> so now the 'include ../../scripts/Makefile.include' will set CFLAGS
> with the  --target=... and we fail
>
> I can compile with the change below.. we could also set CROSS_COMPILE
> before including tools/scripts/Makefile.include ... not sure which
> on is better
>
> also I need to check if we should keep LDFLAGS setup as well
>
> jirka

Right, but the code shouldn't be doing that - it was the purpose of
the patch to remove it. If you include tools/scripts/Makefile.include,
which is done on line 2, then a bunch of warnings, cflags, etc. are
set based on CC. To then overwrite those values with various HOST
values is at best confusing - CC no longer being CC but HOSTCC, but
other values may or may not have changed. As we build using submakes,
the goal here was to push the problem into the submake which will only
ever see CC and other values being passed in.

So perhaps:
HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)"
ARCH="$(HOSTARCH)" \
  EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)" CROSS_COMPILE=""

should be:
HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)"
ARCH="$(HOSTARCH)" \
  CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)" CROSS_COMPILE=""

I'm still trying to get a reproduction.

Thanks,
Ian

>
> ---
> diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> index daed388aa5d7..875e3fcce7cd 100644
> --- a/tools/bpf/resolve_btfids/Makefile
> +++ b/tools/bpf/resolve_btfids/Makefile
> @@ -64,6 +64,7 @@ $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OU
>  LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
>  LIBELF_LIBS  := $(shell $(HOSTPKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf)
>
> +CFLAGS := $(KBUILD_HOSTCFLAGS)
>  CFLAGS += -g \
>            -I$(srctree)/tools/include \
>            -I$(srctree)/tools/include/uapi \
>

Ian Rogers Feb. 1, 2023, 2 a.m. UTC | #10

On Tue, Jan 31, 2023 at 2:50 PM Ian Rogers <irogers@google.com> wrote:
>
> On Tue, Jan 31, 2023 at 2:40 PM Jiri Olsa <olsajiri@gmail.com> wrote:
> >
> > On Tue, Jan 31, 2023 at 02:17:08PM -0700, Nathan Chancellor wrote:
> > > On Tue, Jan 31, 2023 at 12:59:04PM -0800, Ian Rogers wrote:
> > > > On Tue, Jan 31, 2023 at 11:33 AM Nathan Chancellor <nathan@kernel.org> wrote:
> > > > >
> > > > > On Tue, Jan 31, 2023 at 11:25:38AM -0800, Ian Rogers wrote:
> > > > > > On Tue, Jan 31, 2023 at 10:08 AM Ian Rogers <irogers@google.com> wrote:
> > > > > > >
> > > > > > > On Tue, Jan 31, 2023 at 9:21 AM Nathan Chancellor <nathan@kernel.org> wrote:
> > > > > > > >
> > > > > > > > Hi Ian,
> > > > > > > >
> > > > > > > > On Mon, Jan 23, 2023 at 10:43:24PM -0800, Ian Rogers wrote:
> > > > > > > > > HOSTCC is always wanted when building. Setting CC to HOSTCC happens
> > > > > > > > > after tools/scripts/Makefile.include is included, meaning flags are
> > > > > > > > > set assuming say CC is gcc, but then it can be later set to HOSTCC
> > > > > > > > > which may be clang. tools/scripts/Makefile.include is needed for host
> > > > > > > > > set up and common macros in objtool's Makefile. Rather than override
> > > > > > > > > CC to HOSTCC, just pass CC as HOSTCC to Makefile.build, the libsubcmd
> > > > > > > > > builds and the linkage step. This means the Makefiles don't see things
> > > > > > > > > like CC changing and tool flag determination, and similar, work
> > > > > > > > > properly.
> > > > > > > > >
> > > > > > > > > Also, clear the passed subdir as otherwise an outer build may break by
> > > > > > > > > inadvertently passing an inappropriate value.
> > > > > > > > >
> > > > > > > > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > > > > > > > ---
> > > > > > > > >  tools/bpf/resolve_btfids/Makefile | 17 +++++++----------
> > > > > > > > >  1 file changed, 7 insertions(+), 10 deletions(-)
> > > > > > > > >
> > > > > > > > > diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> > > > > > > > > index 1fe0082b2ecc..daed388aa5d7 100644
> > > > > > > > > --- a/tools/bpf/resolve_btfids/Makefile
> > > > > > > > > +++ b/tools/bpf/resolve_btfids/Makefile
> > > > > > > > > @@ -18,14 +18,11 @@ else
> > > > > > > > >  endif
> > > > > > > > >
> > > > > > > > >  # always use the host compiler
> > > > > > > > > -AR       = $(HOSTAR)
> > > > > > > > > -CC       = $(HOSTCC)
> > > > > > > > > -LD       = $(HOSTLD)
> > > > > > > > > -ARCH     = $(HOSTARCH)
> > > > > > > > > +HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
> > > > > > > > > +               EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > > > > > > > +
> > > > > > > > >  RM      ?= rm
> > > > > > > > >  CROSS_COMPILE =
> > > > > > > > > -CFLAGS  := $(KBUILD_HOSTCFLAGS)
> > > > > > > > > -LDFLAGS := $(KBUILD_HOSTLDFLAGS)
> > > > > > > > >
> > > > > > > > >  OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> > > > > > > > >
> > > > > > > > > @@ -56,12 +53,12 @@ $(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT):
> > > > > > > > >
> > > > > > > > >  $(SUBCMDOBJ): fixdep FORCE | $(OUTPUT)/libsubcmd
> > > > > > > > >       $(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(SUBCMD_OUT) \
> > > > > > > > > -                 DESTDIR=$(SUBCMD_DESTDIR) prefix= \
> > > > > > > > > +                 DESTDIR=$(SUBCMD_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > > > > > > > >                   $(abspath $@) install_headers
> > > > > > > > >
> > > > > > > > >  $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUT)
> > > > > > > > >       $(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) OUTPUT=$(LIBBPF_OUT)    \
> > > > > > > > > -                 DESTDIR=$(LIBBPF_DESTDIR) prefix= EXTRA_CFLAGS="$(CFLAGS)" \
> > > > > > > > > +                 DESTDIR=$(LIBBPF_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> > > > > > > > >                   $(abspath $@) install_headers
> > > > > > > > >
> > > > > > > > >  LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> > > > > > > > > @@ -80,11 +77,11 @@ export srctree OUTPUT CFLAGS Q
> > > > > > > > >  include $(srctree)/tools/build/Makefile.include
> > > > > > > > >
> > > > > > > > >  $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)
> > > > > > > > > -     $(Q)$(MAKE) $(build)=resolve_btfids
> > > > > > > > > +     $(Q)$(MAKE) $(build)=resolve_btfids $(HOST_OVERRIDES)
> > > > > > > > >
> > > > > > > > >  $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
> > > > > > > > >       $(call msg,LINK,$@)
> > > > > > > > > -     $(Q)$(CC) $(BINARY_IN) $(LDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > > > > > > > > +     $(Q)$(HOSTCC) $(BINARY_IN) $(KBUILD_HOSTLDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> > > > > > > > >
> > > > > > > > >  clean_objects := $(wildcard $(OUTPUT)/*.o                \
> > > > > > > > >                              $(OUTPUT)/.*.o.cmd           \
> > > > > > > > > --
> > > > > > > > > 2.39.0.246.g2a6d74b583-goog
> > > > > > > > >
> > > > > > > >
> > > > > > > > I just bisected a linking failure when building resolve_btfids with
> > > > > > > > clang to this change as commit 13e07691a16f ("tools/resolve_btfids:
> > > > > > > > Alter how HOSTCC is forced") in the bpf-next tree.
> > > > > > > >
> > > > > > > > It appears to be related to whether or not CROSS_COMPILE is specified,
> > > > > > > > which we have to do for certain architectures and configurations still.
> > > > > > > > arm64 is not one of those but it helps demonstrate the issue.
> > > > > > > >
> > > > > > > >   # Turn off CONFIG_DEBUG_INFO_REDUCED and turn on CONFIG_DEBUG_INFO_BTF
> > > > > > > >   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 defconfig menuconfig
> > > > > > > >
> > > > > > > >   $ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 prepare
> > > > > > > >   ld.lld: error: $LINUX_SRC/tools/bpf/resolve_btfids//resolve_btfids-in.o is incompatible with elf64-x86-64
> > > > > > > >   clang-17: error: linker command failed with exit code 1 (use -v to see invocation)
> > > > > > > >   ...
> > > > > > > >
> > > > > > > > Before your change, with V=1, I see:
> > > > > > > >
> > > > > > > > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11 -Wdeclaration-after-statement -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> > > > > > > >
> > > > > > > > After, I see:
> > > > > > > >
> > > > > > > > clang -Wp,-MD,$LINUX_SRC/tools/bpf/resolve_btfids/.main.o.d -Wp,-MT,$LINUX_SRC/tools/bpf/resolve_btfids/main.o --target=aarch64-linux-gnu -g -I$LINUX_SRC/tools/include -I$LINUX_SRC/tools/include/uapi -I$LINUX_SRC/tools/bpf/resolve_btfids/libbpf/include -I$LINUX_SRC/tools/bpf/resolve_btfids/libsubcmd/include -D"BUILD_STR(s)=#s" -c -o $LINUX_SRC/tools/bpf/resolve_btfids/main.o main.c
> > > > > > > >
> > > > > > > > We seem to have taken on a '--target=aarch64-linux-gnu' (changing the
> > > > > > > > target of resolve_btfids-in.o) and we dropped the warning flags.
> > > > > > > >
> > > > > > > > I think this comes from the clang block in
> > > > > > > > tools/scripts/Makefile.include, which is included into the
> > > > > > > > resolve_btfids Makefile via tools/lib/bpf/Makefile.
> > > > > > > >
> > > > > > > > I am not super familiar with the tools build system, otherwise I would
> > > > > > > > try to provide a patch. I tried moving CROSS_COMPILE from a recursive to
> > > > > > > > simple variable ('=' -> ':=') and moving it to HOST_OVERRIDES but those
> > > > > > > > did not appear to resolve it for me.
> > > > > > > >
> > > > > > > > If there is any other information I can provide or patches I can test,
> > > > > > > > please let me know.
> > > > > > > >
> > > > > > > > Cheers,
> > > > > > > > Nathan
> > > > > > >
> > > > > > > Thanks Nathan, and thanks for all the details in the bug report. I'm
> > > > > > > looking into this.
> > > > > > >
> > > > > > > Ian
> > > > > >
> > > > > > Given the somewhat complicated cross compile I wasn't able to get a
> > > > > > reproduction. Could you see if the following addresses the problem:
> > > > >
> > > > > As long as you have an LLVM toolchain that targets AArch64 and your
> > > > > host, you should be able to reproduce this issue with those commands
> > > > > verbatim, as that command should not use any GNU binutils. I am pretty
> > > > > sure I tried it in a fresh container before reporting it but it is
> > > > > possible that I did not.
> > > >
> > > > Thanks, do you have instructions on setting up the container?
> > >
> > > Sure thing, this worked for me in the Linux source you would like to
> > > build (I marked it readonly to make sure any modifications were done in
> > > my host environment, remove the ':ro' if you would like to make edits to
> > > the source within the container). Docker should work as well but I did
> > > not test it.
> > >
> > > $ podman run --rm -ti -v $PWD:/linux:ro docker.io/archlinux:base-devel
> > > # pacman -Syyu --noconfirm bc clang lib32-glibc lld llvm python
> > > ...
> > >
> > > # To turn on CONFIG_DEBUG_INFO_BTF
> > > # make -C /linux -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 O=/build defconfig menuconfig
> > >
> > > # make -C /linux -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTLDFLAGS=-fuse-ld=lld LLVM=1 O=/build prepare
> > > ld.lld: error: /build/tools/bpf/resolve_btfids//resolve_btfids-in.o is incompatible with elf64-x86-64
> > > clang-15: error: linker command failed with exit code 1 (use -v to see invocation)
> > >
> > > > > > ```
> > > > > > diff --git a/tools/bpf/resolve_btfids/Makefile
> > > > > > b/tools/bpf/resolve_btfids/Makefile
> > > > > > index daed388aa5d7..a06966841df4 100644
> > > > > > --- a/tools/bpf/resolv
> > > >
> > > > Ian
> > > > e_btfids/Makefile
> > > > > > +++ b/tools/bpf/resolve_btfids/Makefile
> > > > > > @@ -19,10 +19,9 @@ endif
> > > > > >
> > > > > > # always use the host compiler
> > > > > > HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)"
> > > > > > ARCH="$(HOSTARCH)" \
> > > > > > -                 EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > > > > +                 EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > > > > CROSS_COMPILE=""
> > > > > >
> > > > > > RM      ?= rm
> > > > > > -CROSS_COMPILE =
> > > > > >
> > > > > > OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> > > > > > ```
> > > > > >
> > > > >
> > > > > Unfortunately, it does not. I still see '--target=' end up in the
> > > > > CFLAGS of those files.
> >
> > hi,
> > I can reproduce that and I think the reason is that the patch removes
> > CFLAGS setup
> >
> >   CFLAGS  := $(KBUILD_HOSTCFLAGS)
> >
> > so now the 'include ../../scripts/Makefile.include' will set CFLAGS
> > with the  --target=... and we fail
> >
> > I can compile with the change below.. we could also set CROSS_COMPILE
> > before including tools/scripts/Makefile.include ... not sure which
> > on is better
> >
> > also I need to check if we should keep LDFLAGS setup as well
> >
> > jirka
>
> Right, but the code shouldn't be doing that - it was the purpose of
> the patch to remove it. If you include tools/scripts/Makefile.include,
> which is done on line 2, then a bunch of warnings, cflags, etc. are
> set based on CC. To then overwrite those values with various HOST
> values is at best confusing - CC no longer being CC but HOSTCC, but
> other values may or may not have changed. As we build using submakes,
> the goal here was to push the problem into the submake which will only
> ever see CC and other values being passed in.
>
> So perhaps:
> HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)"
> ARCH="$(HOSTARCH)" \
>   EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)" CROSS_COMPILE=""
>
> should be:
> HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)"
> ARCH="$(HOSTARCH)" \
>   CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)" CROSS_COMPILE=""
>
> I'm still trying to get a reproduction.
>
> Thanks,
> Ian

So I got a reproduction from Nathan's steps and I believe:
https://lore.kernel.org/lkml/20230201015015.359535-1-irogers@google.com/
Fixes the issue and tidies the Makefile a little. I was a little
unclear on the target being built, and tested some with -C, etc. I'm
always quite capable of making more errors though, so please help me
to check.

Apologies again for the problem and hopefully this fixes it. Thanks,
Ian

> >
> > ---
> > diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> > index daed388aa5d7..875e3fcce7cd 100644
> > --- a/tools/bpf/resolve_btfids/Makefile
> > +++ b/tools/bpf/resolve_btfids/Makefile
> > @@ -64,6 +64,7 @@ $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OU
> >  LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> >  LIBELF_LIBS  := $(shell $(HOSTPKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf)
> >
> > +CFLAGS := $(KBUILD_HOSTCFLAGS)
> >  CFLAGS += -g \
> >            -I$(srctree)/tools/include \
> >            -I$(srctree)/tools/include/uapi \
> >

[v4,2/2] tools/resolve_btfids: Alter how HOSTCC is forced

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