diff mbox series

[2/3] arm64: vdso32: lazily invoke COMPAT_CC

Message ID 20211012234606.91717-3-ndesaulniers@google.com (mailing list archive)
State New, archived
Headers show
Series compat vdso cleanups | expand

Commit Message

Nick Desaulniers Oct. 12, 2021, 11:46 p.m. UTC 
When running the following command without arm-linux-gnueabi-gcc in
one's $PATH, the following warning is observed:

$ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make -j72 LLVM=1 mrproper
make[1]: arm-linux-gnueabi-gcc: No such file or directory

This is because KCONFIG is not run for mrproper, so CONFIG_CC_IS_CLANG
is not set, and we end up eagerly evaluating various variables that try
to invoke CC_COMPAT.

This is a similar problem to what was observed in
commit 3ec8a5b33dea ("kbuild: do not export LDFLAGS_vmlinux")

Cc: Masahiro Yamada <masahiroy@kernel.org>
Reported-by: Lucas Henneman <henneman@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 arch/arm64/kernel/vdso32/Makefile | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Comments

Masahiro Yamada Oct. 13, 2021, 3:02 a.m. UTC | #1 
On Wed, Oct 13, 2021 at 8:46 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> When running the following command without arm-linux-gnueabi-gcc in
> one's $PATH, the following warning is observed:
>
> $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make -j72 LLVM=1 mrproper
> make[1]: arm-linux-gnueabi-gcc: No such file or directory
>
> This is because KCONFIG is not run for mrproper, so CONFIG_CC_IS_CLANG
> is not set, and we end up eagerly evaluating various variables that try
> to invoke CC_COMPAT.
>
> This is a similar problem to what was observed in
> commit 3ec8a5b33dea ("kbuild: do not export LDFLAGS_vmlinux")
>
> Cc: Masahiro Yamada <masahiroy@kernel.org>
> Reported-by: Lucas Henneman <henneman@google.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>


There are two ways to fix it:

  [1]: sink the error message to /dev/null
        (as in commit dc960bfeedb01cf832c5632ed1f3daed4416b142)
  [2]: use a recursively-expanded variable as you did.


"Simple variable (:=) vs recursive variable (=)" is a trade-off.

Please be careful about the cost when you try the [2] approach.



Simple variables are immediately expanded while parsing Makefile.
There are 7 call-sites for cc32-option, hence
the compiler is invoked 7 times for building vdso32,
0 times for cleaning.
(Since 57fd251c789647552d32d2fc51bedd4f90d70f9f,
try-run is no-op for 'make clean').




Recursive variables are expanded every time they are used.

IIUC, if_changed expands the command line 3 times.
There are 2 objects (note.o and vgettimeofday.o)
There are 7 call-sites for cc32-option.

So, the compiler is invoked 42 (3 * 2 * 7) times
for building vdso32.







> ---
>  arch/arm64/kernel/vdso32/Makefile | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
> index 89299a26638b..d24b12318f4c 100644
> --- a/arch/arm64/kernel/vdso32/Makefile
> +++ b/arch/arm64/kernel/vdso32/Makefile
> @@ -38,12 +38,12 @@ cc32-disable-warning = $(call try-run,\
>  # As a result we set our own flags here.
>
>  # KBUILD_CPPFLAGS and NOSTDINC_FLAGS from top-level Makefile
> -VDSO_CPPFLAGS := -DBUILD_VDSO -D__KERNEL__ -nostdinc -isystem $(shell $(CC_COMPAT) -print-file-name=include)
> +VDSO_CPPFLAGS = -DBUILD_VDSO -D__KERNEL__ -nostdinc -isystem $(shell $(CC_COMPAT) -print-file-name=include)
>  VDSO_CPPFLAGS += $(LINUXINCLUDE)
>
>  # Common C and assembly flags
>  # From top-level Makefile
> -VDSO_CAFLAGS := $(VDSO_CPPFLAGS)
> +VDSO_CAFLAGS = $(VDSO_CPPFLAGS)
>  ifneq ($(shell $(CC_COMPAT) --version 2>&1 | head -n 1 | grep clang),)
>  VDSO_CAFLAGS += --target=$(notdir $(CROSS_COMPILE_COMPAT:%-=%))
>  endif
> @@ -73,7 +73,7 @@ VDSO_CAFLAGS += -DDISABLE_BRANCH_PROFILING
>  VDSO_CAFLAGS += $(call cc32-option,-march=armv8-a -D__LINUX_ARM_ARCH__=8,\
>                                     -march=armv7-a -D__LINUX_ARM_ARCH__=7)
>
> -VDSO_CFLAGS := $(VDSO_CAFLAGS)
> +VDSO_CFLAGS = $(VDSO_CAFLAGS)
>  VDSO_CFLAGS += -DENABLE_COMPAT_VDSO=1
>  # KBUILD_CFLAGS from top-level Makefile
>  VDSO_CFLAGS += -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
> @@ -108,7 +108,7 @@ else
>  VDSO_CFLAGS += -marm
>  endif
>
> -VDSO_AFLAGS := $(VDSO_CAFLAGS)
> +VDSO_AFLAGS = $(VDSO_CAFLAGS)
>  VDSO_AFLAGS += -D__ASSEMBLY__
>
>  # From arm vDSO Makefile
> --
> 2.33.0.882.g93a45727a2-goog
>


--
Best Regards
Masahiro Yamada
Nick Desaulniers Oct. 14, 2021, 8:59 p.m. UTC | #2 
On Tue, Oct 12, 2021 at 8:03 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Wed, Oct 13, 2021 at 8:46 AM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > When running the following command without arm-linux-gnueabi-gcc in
> > one's $PATH, the following warning is observed:
> >
> > $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make -j72 LLVM=1 mrproper
> > make[1]: arm-linux-gnueabi-gcc: No such file or directory
> >
> > This is because KCONFIG is not run for mrproper, so CONFIG_CC_IS_CLANG
> > is not set, and we end up eagerly evaluating various variables that try
> > to invoke CC_COMPAT.
> >
> > This is a similar problem to what was observed in
> > commit 3ec8a5b33dea ("kbuild: do not export LDFLAGS_vmlinux")
> >
> > Cc: Masahiro Yamada <masahiroy@kernel.org>
> > Reported-by: Lucas Henneman <henneman@google.com>
> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
>
>
> There are two ways to fix it:
>
>   [1]: sink the error message to /dev/null
>         (as in commit dc960bfeedb01cf832c5632ed1f3daed4416b142)
>   [2]: use a recursively-expanded variable as you did.
>
>
> "Simple variable (:=) vs recursive variable (=)" is a trade-off.
>
> Please be careful about the cost when you try the [2] approach.
>
>
>
> Simple variables are immediately expanded while parsing Makefile.
> There are 7 call-sites for cc32-option, hence
> the compiler is invoked 7 times for building vdso32,
> 0 times for cleaning.
> (Since 57fd251c789647552d32d2fc51bedd4f90d70f9f,
> try-run is no-op for 'make clean').
>
>
>
>
> Recursive variables are expanded every time they are used.
>
> IIUC, if_changed expands the command line 3 times.
> There are 2 objects (note.o and vgettimeofday.o)
> There are 7 call-sites for cc32-option.
>
> So, the compiler is invoked 42 (3 * 2 * 7) times
> for building vdso32.

With this patch applied:
$ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
clean defconfig
$ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
arch/arm64/kernel/vdso32/ V=1 | tr -s ' ' | cut -d ' ' -f 2 | grep
clang | wc -l
55
$ find arch/arm64/kernel/vdso32/ -name \*.o | xargs rm
$ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
arch/arm64/kernel/vdso32/ V=1 | tr -s ' ' | cut -d ' ' -f 2 | grep
clang | wc -l
2

Prior to this series:
$ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
clean defconfig
$ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
arch/arm64/kernel/vdso32/ V=1 | tr -s ' ' | cut -d ' ' -f 2 | grep
clang | wc -l
55
$ find arch/arm64/kernel/vdso32/ -name \*.o | xargs rm
$ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
arch/arm64/kernel/vdso32/ V=1 | tr -s ' ' | cut -d ' ' -f 2 | grep
clang | wc -l
2

With patch 3 applied, we can drop CROSS_COMPILE_COMPAT, and we now get:
$ ARCH=arm64 make LLVM=1 -j72 clean defconfig
ARCH=arm64 make LLVM=1 -j72 arch/arm64/kernel/vdso32/ V=1 | tr -s ' '
| cut -d ' ' -f 2 | grep clang | wc -l
44
$ find arch/arm64/kernel/vdso32/ -name \*.o | xargs rm
$ ARCH=arm64 make LLVM=1 -j72 arch/arm64/kernel/vdso32/ V=1 | tr -s '
' | cut -d ' ' -f 2 | grep clang | wc -l
2

Please confirm; perhaps my pipeline missed some invocations? Or was
there a different target you were referring to?

--
Thanks,
~Nick Desaulniers
Masahiro Yamada Oct. 16, 2021, 2:19 p.m. UTC | #3 
On Fri, Oct 15, 2021 at 5:59 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Tue, Oct 12, 2021 at 8:03 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > On Wed, Oct 13, 2021 at 8:46 AM Nick Desaulniers
> > <ndesaulniers@google.com> wrote:
> > >
> > > When running the following command without arm-linux-gnueabi-gcc in
> > > one's $PATH, the following warning is observed:
> > >
> > > $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make -j72 LLVM=1 mrproper
> > > make[1]: arm-linux-gnueabi-gcc: No such file or directory
> > >
> > > This is because KCONFIG is not run for mrproper, so CONFIG_CC_IS_CLANG
> > > is not set, and we end up eagerly evaluating various variables that try
> > > to invoke CC_COMPAT.
> > >
> > > This is a similar problem to what was observed in
> > > commit 3ec8a5b33dea ("kbuild: do not export LDFLAGS_vmlinux")
> > >
> > > Cc: Masahiro Yamada <masahiroy@kernel.org>
> > > Reported-by: Lucas Henneman <henneman@google.com>
> > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> >
> >
> > There are two ways to fix it:
> >
> >   [1]: sink the error message to /dev/null
> >         (as in commit dc960bfeedb01cf832c5632ed1f3daed4416b142)
> >   [2]: use a recursively-expanded variable as you did.
> >
> >
> > "Simple variable (:=) vs recursive variable (=)" is a trade-off.
> >
> > Please be careful about the cost when you try the [2] approach.
> >
> >
> >
> > Simple variables are immediately expanded while parsing Makefile.
> > There are 7 call-sites for cc32-option, hence
> > the compiler is invoked 7 times for building vdso32,
> > 0 times for cleaning.
> > (Since 57fd251c789647552d32d2fc51bedd4f90d70f9f,
> > try-run is no-op for 'make clean').
> >
> >
> >
> >
> > Recursive variables are expanded every time they are used.
> >
> > IIUC, if_changed expands the command line 3 times.
> > There are 2 objects (note.o and vgettimeofday.o)
> > There are 7 call-sites for cc32-option.
> >
> > So, the compiler is invoked 42 (3 * 2 * 7) times
> > for building vdso32.
>
> With this patch applied:
> $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
> clean defconfig
> $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
> arch/arm64/kernel/vdso32/ V=1 | tr -s ' ' | cut -d ' ' -f 2 | grep
> clang | wc -l
> 55
> $ find arch/arm64/kernel/vdso32/ -name \*.o | xargs rm
> $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
> arch/arm64/kernel/vdso32/ V=1 | tr -s ' ' | cut -d ' ' -f 2 | grep
> clang | wc -l
> 2
>
> Prior to this series:
> $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
> clean defconfig
> $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
> arch/arm64/kernel/vdso32/ V=1 | tr -s ' ' | cut -d ' ' -f 2 | grep
> clang | wc -l
> 55
> $ find arch/arm64/kernel/vdso32/ -name \*.o | xargs rm
> $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
> arch/arm64/kernel/vdso32/ V=1 | tr -s ' ' | cut -d ' ' -f 2 | grep
> clang | wc -l
> 2
>
> With patch 3 applied, we can drop CROSS_COMPILE_COMPAT, and we now get:
> $ ARCH=arm64 make LLVM=1 -j72 clean defconfig
> ARCH=arm64 make LLVM=1 -j72 arch/arm64/kernel/vdso32/ V=1 | tr -s ' '
> | cut -d ' ' -f 2 | grep clang | wc -l
> 44
> $ find arch/arm64/kernel/vdso32/ -name \*.o | xargs rm
> $ ARCH=arm64 make LLVM=1 -j72 arch/arm64/kernel/vdso32/ V=1 | tr -s '
> ' | cut -d ' ' -f 2 | grep clang | wc -l
> 2
>
> Please confirm; perhaps my pipeline missed some invocations? Or was
> there a different target you were referring to?






It is pointless to check the build commands.

I am talking about how many times $(call cc32-option, ) is evaluated.


How about adding the following debug code?

(Everytime cc32-option is evaluated, a file "dummy-cc32-option-<PID>"
is created)



diff --git a/arch/arm64/kernel/vdso32/Makefile
b/arch/arm64/kernel/vdso32/Makefile
index 89299a26638b..e40365f5bc38 100644
--- a/arch/arm64/kernel/vdso32/Makefile
+++ b/arch/arm64/kernel/vdso32/Makefile
@@ -26,9 +26,9 @@ LD_COMPAT ?= $(CROSS_COMPILE_COMPAT)ld
 endif

 cc32-option = $(call try-run,\
-        $(CC_COMPAT) $(1) -c -x c /dev/null -o "$$TMP",$(1),$(2))
+        $(CC_COMPAT) $(1) -c -x c /dev/null -o "$$TMP"; touch
dummy-cc32-option-$$$$,$(1),$(2))
 cc32-disable-warning = $(call try-run,\
-       $(CC_COMPAT) -W$(strip $(1)) -c -x c /dev/null -o
"$$TMP",-Wno-$(strip $(1)))
+       $(CC_COMPAT) -W$(strip $(1)) -c -x c /dev/null -o "$$TMP";
touch dummy-cc32-option-$$$$,-Wno-$(strip $(1)))

 # We cannot use the global flags to compile the vDSO files, the main reason
 # being that the 32-bit compiler may be older than the main (64-bit) compiler





Without this patch:

masahiro@grover:~/ref/linux$ rm dummy-cc32-*
masahiro@grover:~/ref/linux$ make -s LLVM=1 ARCH=arm64
CROSS_COMPILE_COMPAT=arm-linux-gnueabi- defconfig clean
arch/arm64/kernel/vdso32/ -j8
masahiro@grover:~/ref/linux$ ls -1 dummy-cc32-*
dummy-cc32-disable-warning-765530
dummy-cc32-option-765495
dummy-cc32-option-765500
dummy-cc32-option-765505
dummy-cc32-option-765510
dummy-cc32-option-765515
dummy-cc32-option-765520
dummy-cc32-option-765525




With this patch:



masahiro@grover:~/ref/linux$ rm dummy-cc32-*
masahiro@grover:~/ref/linux$ make -s LLVM=1 ARCH=arm64
CROSS_COMPILE_COMPAT=arm-linux-gnueabi- defconfig clean
arch/arm64/kernel/vdso32/ -j8
masahiro@grover:~/ref/linux$ ls -1 dummy-cc32-*
dummy-cc32-disable-warning-768908
dummy-cc32-disable-warning-768949
dummy-cc32-disable-warning-768990
dummy-cc32-disable-warning-769035
dummy-cc32-disable-warning-769076
dummy-cc32-disable-warning-769117
dummy-cc32-option-768871
dummy-cc32-option-768878
dummy-cc32-option-768883
dummy-cc32-option-768888
dummy-cc32-option-768893
dummy-cc32-option-768898
dummy-cc32-option-768903
dummy-cc32-option-768914
dummy-cc32-option-768919
dummy-cc32-option-768924
dummy-cc32-option-768929
dummy-cc32-option-768934
dummy-cc32-option-768939
dummy-cc32-option-768944
dummy-cc32-option-768955
dummy-cc32-option-768960
dummy-cc32-option-768965
dummy-cc32-option-768970
dummy-cc32-option-768975
dummy-cc32-option-768980
dummy-cc32-option-768985
dummy-cc32-option-768998
dummy-cc32-option-769005
dummy-cc32-option-769010
dummy-cc32-option-769015
dummy-cc32-option-769020
dummy-cc32-option-769025
dummy-cc32-option-769030
dummy-cc32-option-769041
dummy-cc32-option-769046
dummy-cc32-option-769051
dummy-cc32-option-769056
dummy-cc32-option-769061
dummy-cc32-option-769066
dummy-cc32-option-769071
dummy-cc32-option-769082
dummy-cc32-option-769087
dummy-cc32-option-769092
dummy-cc32-option-769097
dummy-cc32-option-769102
dummy-cc32-option-769107
dummy-cc32-option-769112






The diff of  the number of expansions:

cc32-option                        7    ->   42
cc32-disable-warning         1   ->    6
Nick Desaulniers Oct. 18, 2021, 8:34 p.m. UTC | #4 
On Sat, Oct 16, 2021 at 7:20 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Fri, Oct 15, 2021 at 5:59 AM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > On Tue, Oct 12, 2021 at 8:03 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > >
> > > On Wed, Oct 13, 2021 at 8:46 AM Nick Desaulniers
> > > <ndesaulniers@google.com> wrote:
> > > >
> > > > When running the following command without arm-linux-gnueabi-gcc in
> > > > one's $PATH, the following warning is observed:
> > > >
> > > > $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make -j72 LLVM=1 mrproper
> > > > make[1]: arm-linux-gnueabi-gcc: No such file or directory
> > > >
> > > > This is because KCONFIG is not run for mrproper, so CONFIG_CC_IS_CLANG
> > > > is not set, and we end up eagerly evaluating various variables that try
> > > > to invoke CC_COMPAT.
> > > >
> > > > This is a similar problem to what was observed in
> > > > commit 3ec8a5b33dea ("kbuild: do not export LDFLAGS_vmlinux")
> > > >
> > > > Cc: Masahiro Yamada <masahiroy@kernel.org>
> > > > Reported-by: Lucas Henneman <henneman@google.com>
> > > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> > >
> > >
> > > There are two ways to fix it:
> > >
> > >   [1]: sink the error message to /dev/null
> > >         (as in commit dc960bfeedb01cf832c5632ed1f3daed4416b142)
> > >   [2]: use a recursively-expanded variable as you did.
> > >
> > >
> > > "Simple variable (:=) vs recursive variable (=)" is a trade-off.
> > >
> > > Please be careful about the cost when you try the [2] approach.
> > >
> > >
> > >
> > > Simple variables are immediately expanded while parsing Makefile.
> > > There are 7 call-sites for cc32-option, hence
> > > the compiler is invoked 7 times for building vdso32,
> > > 0 times for cleaning.
> > > (Since 57fd251c789647552d32d2fc51bedd4f90d70f9f,
> > > try-run is no-op for 'make clean').
> > >
> > >
> > >
> > >
> > > Recursive variables are expanded every time they are used.
> > >
> > > IIUC, if_changed expands the command line 3 times.
> > > There are 2 objects (note.o and vgettimeofday.o)
> > > There are 7 call-sites for cc32-option.
> > >
> > > So, the compiler is invoked 42 (3 * 2 * 7) times
> > > for building vdso32.
> >
> > With this patch applied:
> > $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
> > clean defconfig
> > $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
> > arch/arm64/kernel/vdso32/ V=1 | tr -s ' ' | cut -d ' ' -f 2 | grep
> > clang | wc -l
> > 55
> > $ find arch/arm64/kernel/vdso32/ -name \*.o | xargs rm
> > $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
> > arch/arm64/kernel/vdso32/ V=1 | tr -s ' ' | cut -d ' ' -f 2 | grep
> > clang | wc -l
> > 2
> >
> > Prior to this series:
> > $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
> > clean defconfig
> > $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
> > arch/arm64/kernel/vdso32/ V=1 | tr -s ' ' | cut -d ' ' -f 2 | grep
> > clang | wc -l
> > 55
> > $ find arch/arm64/kernel/vdso32/ -name \*.o | xargs rm
> > $ ARCH=arm64 CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72
> > arch/arm64/kernel/vdso32/ V=1 | tr -s ' ' | cut -d ' ' -f 2 | grep
> > clang | wc -l
> > 2
> >
> > With patch 3 applied, we can drop CROSS_COMPILE_COMPAT, and we now get:
> > $ ARCH=arm64 make LLVM=1 -j72 clean defconfig
> > ARCH=arm64 make LLVM=1 -j72 arch/arm64/kernel/vdso32/ V=1 | tr -s ' '
> > | cut -d ' ' -f 2 | grep clang | wc -l
> > 44
> > $ find arch/arm64/kernel/vdso32/ -name \*.o | xargs rm
> > $ ARCH=arm64 make LLVM=1 -j72 arch/arm64/kernel/vdso32/ V=1 | tr -s '
> > ' | cut -d ' ' -f 2 | grep clang | wc -l
> > 2
> >
> > Please confirm; perhaps my pipeline missed some invocations? Or was
> > there a different target you were referring to?
>
>
>
>
>
>
> It is pointless to check the build commands.
>
> I am talking about how many times $(call cc32-option, ) is evaluated.

Of course V=1 doesn't print the cc-option invocations! /s

>
>
> How about adding the following debug code?
>
> (Everytime cc32-option is evaluated, a file "dummy-cc32-option-<PID>"
> is created)
>
>
>
> diff --git a/arch/arm64/kernel/vdso32/Makefile
> b/arch/arm64/kernel/vdso32/Makefile
> index 89299a26638b..e40365f5bc38 100644
> --- a/arch/arm64/kernel/vdso32/Makefile
> +++ b/arch/arm64/kernel/vdso32/Makefile
> @@ -26,9 +26,9 @@ LD_COMPAT ?= $(CROSS_COMPILE_COMPAT)ld
>  endif
>
>  cc32-option = $(call try-run,\
> -        $(CC_COMPAT) $(1) -c -x c /dev/null -o "$$TMP",$(1),$(2))
> +        $(CC_COMPAT) $(1) -c -x c /dev/null -o "$$TMP"; touch
> dummy-cc32-option-$$$$,$(1),$(2))
>  cc32-disable-warning = $(call try-run,\
> -       $(CC_COMPAT) -W$(strip $(1)) -c -x c /dev/null -o
> "$$TMP",-Wno-$(strip $(1)))
> +       $(CC_COMPAT) -W$(strip $(1)) -c -x c /dev/null -o "$$TMP";
> touch dummy-cc32-option-$$$$,-Wno-$(strip $(1)))

heh, I usually add `($info $$VAR is [${VAR}]); \` debugging statements
to these. Touching files is another neat trick.

>
>  # We cannot use the global flags to compile the vDSO files, the main reason
>  # being that the 32-bit compiler may be older than the main (64-bit) compiler
>
>
>
>
>
> Without this patch:
>
> masahiro@grover:~/ref/linux$ rm dummy-cc32-*
> masahiro@grover:~/ref/linux$ make -s LLVM=1 ARCH=arm64
> CROSS_COMPILE_COMPAT=arm-linux-gnueabi- defconfig clean
> arch/arm64/kernel/vdso32/ -j8
> masahiro@grover:~/ref/linux$ ls -1 dummy-cc32-*
> dummy-cc32-disable-warning-765530
> dummy-cc32-option-765495
> dummy-cc32-option-765500
> dummy-cc32-option-765505
> dummy-cc32-option-765510
> dummy-cc32-option-765515
> dummy-cc32-option-765520
> dummy-cc32-option-765525
>
>
>
>
> With this patch:
>
>
>
> masahiro@grover:~/ref/linux$ rm dummy-cc32-*
> masahiro@grover:~/ref/linux$ make -s LLVM=1 ARCH=arm64
> CROSS_COMPILE_COMPAT=arm-linux-gnueabi- defconfig clean
> arch/arm64/kernel/vdso32/ -j8
> masahiro@grover:~/ref/linux$ ls -1 dummy-cc32-*
> dummy-cc32-disable-warning-768908
> dummy-cc32-disable-warning-768949
> dummy-cc32-disable-warning-768990
> dummy-cc32-disable-warning-769035
> dummy-cc32-disable-warning-769076
> dummy-cc32-disable-warning-769117
> dummy-cc32-option-768871
> dummy-cc32-option-768878
> dummy-cc32-option-768883
> dummy-cc32-option-768888
> dummy-cc32-option-768893
> dummy-cc32-option-768898
> dummy-cc32-option-768903
> dummy-cc32-option-768914
> dummy-cc32-option-768919
> dummy-cc32-option-768924
> dummy-cc32-option-768929
> dummy-cc32-option-768934
> dummy-cc32-option-768939
> dummy-cc32-option-768944
> dummy-cc32-option-768955
> dummy-cc32-option-768960
> dummy-cc32-option-768965
> dummy-cc32-option-768970
> dummy-cc32-option-768975
> dummy-cc32-option-768980
> dummy-cc32-option-768985
> dummy-cc32-option-768998
> dummy-cc32-option-769005
> dummy-cc32-option-769010
> dummy-cc32-option-769015
> dummy-cc32-option-769020
> dummy-cc32-option-769025
> dummy-cc32-option-769030
> dummy-cc32-option-769041
> dummy-cc32-option-769046
> dummy-cc32-option-769051
> dummy-cc32-option-769056
> dummy-cc32-option-769061
> dummy-cc32-option-769066
> dummy-cc32-option-769071
> dummy-cc32-option-769082
> dummy-cc32-option-769087
> dummy-cc32-option-769092
> dummy-cc32-option-769097
> dummy-cc32-option-769102
> dummy-cc32-option-769107
> dummy-cc32-option-769112
>
>
>
>
>
>
> The diff of  the number of expansions:
>
> cc32-option                        7    ->   42
> cc32-disable-warning         1   ->    6

Indeed, thanks for confirming.  An unfortunate dichotomy.  Surely
there's another way to avoid cc-option+cc-disable-warning calls for
the `clean` target?  I'll change to just redirecting errors to
/dev/null with your Suggested-by tag, but this seems a bit of an
unfortunate situation.
diff mbox series

Patch

diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
index 89299a26638b..d24b12318f4c 100644
--- a/arch/arm64/kernel/vdso32/Makefile
+++ b/arch/arm64/kernel/vdso32/Makefile
@@ -38,12 +38,12 @@  cc32-disable-warning = $(call try-run,\
 # As a result we set our own flags here.
 
 # KBUILD_CPPFLAGS and NOSTDINC_FLAGS from top-level Makefile
-VDSO_CPPFLAGS := -DBUILD_VDSO -D__KERNEL__ -nostdinc -isystem $(shell $(CC_COMPAT) -print-file-name=include)
+VDSO_CPPFLAGS = -DBUILD_VDSO -D__KERNEL__ -nostdinc -isystem $(shell $(CC_COMPAT) -print-file-name=include)
 VDSO_CPPFLAGS += $(LINUXINCLUDE)
 
 # Common C and assembly flags
 # From top-level Makefile
-VDSO_CAFLAGS := $(VDSO_CPPFLAGS)
+VDSO_CAFLAGS = $(VDSO_CPPFLAGS)
 ifneq ($(shell $(CC_COMPAT) --version 2>&1 | head -n 1 | grep clang),)
 VDSO_CAFLAGS += --target=$(notdir $(CROSS_COMPILE_COMPAT:%-=%))
 endif
@@ -73,7 +73,7 @@  VDSO_CAFLAGS += -DDISABLE_BRANCH_PROFILING
 VDSO_CAFLAGS += $(call cc32-option,-march=armv8-a -D__LINUX_ARM_ARCH__=8,\
                                    -march=armv7-a -D__LINUX_ARM_ARCH__=7)
 
-VDSO_CFLAGS := $(VDSO_CAFLAGS)
+VDSO_CFLAGS = $(VDSO_CAFLAGS)
 VDSO_CFLAGS += -DENABLE_COMPAT_VDSO=1
 # KBUILD_CFLAGS from top-level Makefile
 VDSO_CFLAGS += -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
@@ -108,7 +108,7 @@  else
 VDSO_CFLAGS += -marm
 endif
 
-VDSO_AFLAGS := $(VDSO_CAFLAGS)
+VDSO_AFLAGS = $(VDSO_CAFLAGS)
 VDSO_AFLAGS += -D__ASSEMBLY__
 
 # From arm vDSO Makefile