Re: [PATCH v6 06/10] kbuild: check static EXPORT_SYMBOL* by script instead of modpost

Jon Hunter
2022-06-07T14:22:36Z

On 13/05/2022 12:39, Masahiro Yamada wrote:
> The 'static' specifier and EXPORT_SYMBOL() are an odd combination.
>
> Commit 15bfc2348d54 ("modpost: check for static EXPORT_SYMBOL*
> functions") tried to detect it, but this check has false negatives.
>
> Here is the sample code.
>
> Makefile:
>
> obj-y += foo1.o foo2.o
>
> foo1.c:
>
> #include <linux/export.h>
> static void foo(void) {}
> EXPORT_SYMBOL(foo);
>
> foo2.c:
>
> void foo(void) {}
>
> foo1.c exports the static symbol 'foo', but modpost cannot catch it
> because it is fooled by foo2.c, which has a global symbol with the
> same name.
>
> s->is_static is cleared if a global symbol with the same name is found
> somewhere, but EXPORT_SYMBOL() and the global symbol do not necessarily
> belong to the same compilation unit.
>
> This check should be done per compilation unit, but I do not know how
> to do it in modpost. modpost runs against vmlinux.o or modules, which
> merges multiple objects, then forgets their origin.
>
> It is true modpost gets access to the lists of all the member objects
> (.vmlinux.objs and *.mod), but modpost cannot parse individual objects
> because they may not be ELF but LLVM IR when CONFIG_LTO_CLANG=y.
>
> Add a simple bash script to parse the output from ${NM}. This works for
> CONFIG_LTO_CLANG=y because llvm-nm can dump symbols of LLVM IR files.
>
> Revert 15bfc2348d54.
>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Tested-by: Nathan Chancellor <nathan@kernel.org>

One some older build machines this is causing some builds (ARM/ARM64)
to fail ...

/dvs/git/dirty/git-master_l4t-upstream/kernel/scripts/check-local-export: line 54: wait: pid 48433 is not a child of this shell
/dvs/git/dirty/git-master_l4t-upstream/kernel/scripts/Makefile.build:250: recipe for target 'scripts/mod/empty.o' failed
make[2]: *** [scripts/mod/empty.o] Error 127
make[2]: *** Deleting file 'scripts/mod/empty.o'
make[2]: *** Waiting for unfinished jobs....
/dvs/git/dirty/git-master_l4t-upstream/kernel/Makefile:1285: recipe for target 'prepare0' failed
make[1]: *** [prepare0] Error 2
make[1]: Leaving directory '/dvs/git/dirty/git-master_l4t-upstream/artifacts/linux/arm64-defconfig-jetson'
Makefile:228: recipe for target '__sub-make' failed
make: *** [__sub-make] Error 2

Any ideas?

Thanks
Jon

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