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

Guenter Roeck
2022-05-25T08:32:05Z

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