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

Masahiro Yamada
2022-05-25T10:53:33Z

On Wed, May 25, 2022 at 5:31 PM Guenter Roeck <linux@roeck-us.net> wrote:
>
> On Fri, May 13, 2022 at 08:39:26PM +0900, 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.
> >
>
> On parisc builds, this patch results in:
>
> Building parisc:allnoconfig ... failed
> --------------
> Error log:
> scripts/check-local-export: sh /opt/buildbot/slave/next-next/build/arch/parisc/nm failed
>
> Guenter

Thanks for the report.

parisc overrides NM:

NM = sh $(srctree)/arch/parisc/nm

I will fix the script to return the correct exit code.

--
Best Regards
Masahiro Yamada