diff mbox series

[bpf-next,3/3] selftests/bpf: Allow ignoring some flags for Clang builds

Message ID 08becac5b0b536d918adeb90efd63bdd7dcc856c.1728975031.git.vmalik@redhat.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series selftests/bpf: Improve building with extra | expand

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netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for bpf-next, async
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 6 this patch: 6
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netdev/check_selftest success No net selftest shell script
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Commit Message

Viktor Malik Oct. 15, 2024, 6:54 a.m. UTC 
There exist compiler flags supported by GCC but not supported by Clang
(e.g. -specs=...). Currently, these cannot be passed to BPF selftests
builds, even when building with GCC, as some binaries (urandom_read and
liburandom_read.so) are always built with Clang and the unsupported
flags make the compilation fail (as -Werror is turned on).

Add new Makefile variable CLANG_FILTEROUT_FLAGS which can be used by
users to specify which flags (from the user-provided CFLAGS or LDFLAGS)
should be filtered out for Clang invocations.

This allows to do things like:

    $ CFLAGS="-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1" \
      CLANG_FILTEROUT_FLAGS="-specs=%" \
      make -C tools/testing/selftests/bpf

Without this patch, the compilation would fail with:

    [...]
    clang: error: argument unused during compilation: '-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1' [-Werror,-Wunused-command-line-argument]
    make: *** [Makefile:273: /bpf-next/tools/testing/selftests/bpf/liburandom_read.so] Error 1
    [...]

Signed-off-by: Viktor Malik <vmalik@redhat.com>
---
 tools/testing/selftests/bpf/Makefile | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

Comments

Andrii Nakryiko Oct. 16, 2024, 8:37 p.m. UTC | #1 
On Mon, Oct 14, 2024 at 11:55 PM Viktor Malik <vmalik@redhat.com> wrote:
>
> There exist compiler flags supported by GCC but not supported by Clang
> (e.g. -specs=...). Currently, these cannot be passed to BPF selftests
> builds, even when building with GCC, as some binaries (urandom_read and
> liburandom_read.so) are always built with Clang and the unsupported
> flags make the compilation fail (as -Werror is turned on).
>
> Add new Makefile variable CLANG_FILTEROUT_FLAGS which can be used by
> users to specify which flags (from the user-provided CFLAGS or LDFLAGS)
> should be filtered out for Clang invocations.
>
> This allows to do things like:
>
>     $ CFLAGS="-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1" \
>       CLANG_FILTEROUT_FLAGS="-specs=%" \
>       make -C tools/testing/selftests/bpf
>
> Without this patch, the compilation would fail with:
>
>     [...]
>     clang: error: argument unused during compilation: '-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1' [-Werror,-Wunused-command-line-argument]

maybe we should just not error out (i.e., enable
-Wno-unused-command-line-argument)?

>     make: *** [Makefile:273: /bpf-next/tools/testing/selftests/bpf/liburandom_read.so] Error 1
>     [...]
>
> Signed-off-by: Viktor Malik <vmalik@redhat.com>
> ---
>  tools/testing/selftests/bpf/Makefile | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index d81583b2aef9..89662fe0470a 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -31,6 +31,11 @@ SAN_LDFLAGS  ?= $(SAN_CFLAGS)
>  RELEASE                ?=
>  OPT_FLAGS      ?= $(if $(RELEASE),-O2,-O0)
>
> +# Some flags supported by GCC are not supported by Clang.
> +# This variable allows users to specify such flags so that they can use custom
> +# CFLAGS and binaries built with Clang do not fail to build.
> +CLANG_FILTEROUT_FLAGS ?=
> +
>  LIBELF_CFLAGS  := $(shell $(PKG_CONFIG) libelf --cflags 2>/dev/null)
>  LIBELF_LIBS    := $(shell $(PKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf)
>
> @@ -271,7 +276,7 @@ endif
>  $(OUTPUT)/liburandom_read.so: urandom_read_lib1.c urandom_read_lib2.c liburandom_read.map
>         $(call msg,LIB,,$@)
>         $(Q)$(CLANG) $(CLANG_TARGET_ARCH) \
> -                    $(filter-out -static,$(CFLAGS) $(LDFLAGS)) \
> +                    $(filter-out -static $(CLANG_FILTEROUT_FLAGS),$(CFLAGS) $(LDFLAGS)) \
>                      $(filter %.c,$^) $(filter-out -static,$(LDLIBS)) \
>                      -fuse-ld=$(LLD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
>                      -Wl,--version-script=liburandom_read.map \
> @@ -280,7 +285,7 @@ $(OUTPUT)/liburandom_read.so: urandom_read_lib1.c urandom_read_lib2.c liburandom
>  $(OUTPUT)/urandom_read: urandom_read.c urandom_read_aux.c $(OUTPUT)/liburandom_read.so
>         $(call msg,BINARY,,$@)
>         $(Q)$(CLANG) $(CLANG_TARGET_ARCH) \
> -                    $(filter-out -static,$(CFLAGS) $(LDFLAGS)) $(filter %.c,$^) \
> +                    $(filter-out -static $(CLANG_FILTEROUT_FLAGS),$(CFLAGS) $(LDFLAGS)) $(filter %.c,$^) \
>                      -lurandom_read $(filter-out -static,$(LDLIBS)) -L$(OUTPUT) \
>                      -fuse-ld=$(LLD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
>                      -Wl,-rpath=. -o $@
> --
> 2.47.0
>
Eduard Zingerman Oct. 16, 2024, 10:18 p.m. UTC | #2 
On Wed, 2024-10-16 at 13:37 -0700, Andrii Nakryiko wrote:
> On Mon, Oct 14, 2024 at 11:55 PM Viktor Malik <vmalik@redhat.com> wrote:
> > 
> > There exist compiler flags supported by GCC but not supported by Clang
> > (e.g. -specs=...). Currently, these cannot be passed to BPF selftests
> > builds, even when building with GCC, as some binaries (urandom_read and
> > liburandom_read.so) are always built with Clang and the unsupported
> > flags make the compilation fail (as -Werror is turned on).
> > 
> > Add new Makefile variable CLANG_FILTEROUT_FLAGS which can be used by
> > users to specify which flags (from the user-provided CFLAGS or LDFLAGS)
> > should be filtered out for Clang invocations.
> > 
> > This allows to do things like:
> > 
> >     $ CFLAGS="-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1" \
> >       CLANG_FILTEROUT_FLAGS="-specs=%" \
> >       make -C tools/testing/selftests/bpf
> > 
> > Without this patch, the compilation would fail with:
> > 
> >     [...]
> >     clang: error: argument unused during compilation: '-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1' [-Werror,-Wunused-command-line-argument]
> 
> maybe we should just not error out (i.e., enable
> -Wno-unused-command-line-argument)?

I agree with Andrii, grepping for FILTEROUT in kernel source code does
not show anything similar to this. Are such filter-out variables some
kind of convention?

Another option might be to remove `-Werror` and add it on CI via EXTRA_CFLAGS.

[...]
Viktor Malik Oct. 17, 2024, 8:34 a.m. UTC | #3 
On 10/17/24 00:18, Eduard Zingerman wrote:
> On Wed, 2024-10-16 at 13:37 -0700, Andrii Nakryiko wrote:
>> On Mon, Oct 14, 2024 at 11:55 PM Viktor Malik <vmalik@redhat.com> wrote:
>>>
>>> There exist compiler flags supported by GCC but not supported by Clang
>>> (e.g. -specs=...). Currently, these cannot be passed to BPF selftests
>>> builds, even when building with GCC, as some binaries (urandom_read and
>>> liburandom_read.so) are always built with Clang and the unsupported
>>> flags make the compilation fail (as -Werror is turned on).
>>>
>>> Add new Makefile variable CLANG_FILTEROUT_FLAGS which can be used by
>>> users to specify which flags (from the user-provided CFLAGS or LDFLAGS)
>>> should be filtered out for Clang invocations.
>>>
>>> This allows to do things like:
>>>
>>>     $ CFLAGS="-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1" \
>>>       CLANG_FILTEROUT_FLAGS="-specs=%" \
>>>       make -C tools/testing/selftests/bpf
>>>
>>> Without this patch, the compilation would fail with:
>>>
>>>     [...]
>>>     clang: error: argument unused during compilation: '-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1' [-Werror,-Wunused-command-line-argument]
>>
>> maybe we should just not error out (i.e., enable
>> -Wno-unused-command-line-argument)?
> 
> I agree with Andrii, grepping for FILTEROUT in kernel source code does
> not show anything similar to this. Are such filter-out variables some
> kind of convention?
> 
> Another option might be to remove `-Werror` and add it on CI via EXTRA_CFLAGS.

Enabling -Wno-unused-command-line-argument is the simplest way here,
let's do that.

Thank you both for suggestions!

> 
> [...]
>
diff mbox series

Patch

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index d81583b2aef9..89662fe0470a 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -31,6 +31,11 @@  SAN_LDFLAGS	?= $(SAN_CFLAGS)
 RELEASE		?=
 OPT_FLAGS	?= $(if $(RELEASE),-O2,-O0)
 
+# Some flags supported by GCC are not supported by Clang.
+# This variable allows users to specify such flags so that they can use custom
+# CFLAGS and binaries built with Clang do not fail to build.
+CLANG_FILTEROUT_FLAGS ?=
+
 LIBELF_CFLAGS	:= $(shell $(PKG_CONFIG) libelf --cflags 2>/dev/null)
 LIBELF_LIBS	:= $(shell $(PKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf)
 
@@ -271,7 +276,7 @@  endif
 $(OUTPUT)/liburandom_read.so: urandom_read_lib1.c urandom_read_lib2.c liburandom_read.map
 	$(call msg,LIB,,$@)
 	$(Q)$(CLANG) $(CLANG_TARGET_ARCH) \
-		     $(filter-out -static,$(CFLAGS) $(LDFLAGS)) \
+		     $(filter-out -static $(CLANG_FILTEROUT_FLAGS),$(CFLAGS) $(LDFLAGS)) \
 		     $(filter %.c,$^) $(filter-out -static,$(LDLIBS)) \
 		     -fuse-ld=$(LLD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
 		     -Wl,--version-script=liburandom_read.map \
@@ -280,7 +285,7 @@  $(OUTPUT)/liburandom_read.so: urandom_read_lib1.c urandom_read_lib2.c liburandom
 $(OUTPUT)/urandom_read: urandom_read.c urandom_read_aux.c $(OUTPUT)/liburandom_read.so
 	$(call msg,BINARY,,$@)
 	$(Q)$(CLANG) $(CLANG_TARGET_ARCH) \
-		     $(filter-out -static,$(CFLAGS) $(LDFLAGS)) $(filter %.c,$^) \
+		     $(filter-out -static $(CLANG_FILTEROUT_FLAGS),$(CFLAGS) $(LDFLAGS)) $(filter %.c,$^) \
 		     -lurandom_read $(filter-out -static,$(LDLIBS)) -L$(OUTPUT) \
 		     -fuse-ld=$(LLD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
 		     -Wl,-rpath=. -o $@