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

[Jon Hunter]

On 07/06/2022 15:25, Nathan Chancellor wrote:
> On Tue, Jun 07, 2022 at 03:22:21PM +0100, Jon Hunter wrote:
> > 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@xxxxxxxxxx>
> > > Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> > > Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> >
> >
> > 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?
>
> https://lore.kernel.org/20220607084317.211785-1-masahiroy@xxxxxxxxxx/
> should resolve it if you wanted to give it a test.

Thanks! Works for me.

Tested-by: Jon Hunter <jonathanh@xxxxxxxxxx>

Cheers
Jon

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