Messages in this thread Patch in this message | | | From | Masahiro Yamada <> | Date | Sat, 16 Oct 2021 23:19:12 +0900 | Subject | Re: [PATCH 2/3] arm64: vdso32: lazily invoke COMPAT_CC |
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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
-- Best Regards Masahiro Yamada
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