Re: [PATCH v2] module: Ignore _GLOBAL_OFFSET_TABLE_ when warning for undefined symbols

[Jessica Yu]

+++ Nick Desaulniers [14/01/21 14:01 -0800]:
> On Thu, Jan 14, 2021 at 1:54 PM 'Fangrui Song' via Clang Built Linux
> <clang-built-linux@xxxxxxxxxxxxxxxx> wrote:
> > clang-12 -fno-pic (since
> > https://github.com/llvm/llvm-project/commit/a084c0388e2a59b9556f2de0083333232da3f1d6)
> > can emit `call __stack_chk_fail@PLT` instead of `call __stack_chk_fail`
> > on x86.  The two forms should have identical behaviors on x86-64 but the
> > former causes GNU as<2.37 to produce an unreferenced undefined symbol
> > _GLOBAL_OFFSET_TABLE_.
> >
> > (On x86-32, there is an R_386_PC32 vs R_386_PLT32 difference but the
> > linker behavior is identical as far as Linux kernel is concerned.)
> >
> > Simply ignore _GLOBAL_OFFSET_TABLE_ for now, like what
> > scripts/mod/modpost.c:ignore_undef_symbol does. This also fixes the
> > problem for gcc/clang -fpie and -fpic, which may emit `call foo@PLT` for
> > external function calls on x86.
> >
> > Note: ld -z defs and dynamic loaders do not error for unreferenced
> > undefined symbols so the module loader is reading too much.  If we ever
> > need to ignore more symbols, the code should be refactored to ignore
> > unreferenced symbols.
> >
> > Reported-by: Marco Elver <elver@xxxxxxxxxx>
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1250
> > Signed-off-by: Fangrui Song <maskray@xxxxxxxxxx>
>
> Thanks for the patch.
>
> Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
>
> Jessica, would you mind adding when applying:
>
> Cc: <stable@xxxxxxxxxxxxxxx>
>
> as I suspect we might want this fixed in stable tree's branches, too.
> It might of interest to add:
>
> Link: https://sourceware.org/bugzilla/show_bug.cgi?id=27178
>
> too.

Sure, will do!

Thanks,

Jessica