linux-kernel - Re: [PATCH v6 06/10] kbuild: check static EXPORT

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Date:   Wed, 25 May 2022 19:51:17 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-modules <linux-modules@...r.kernel.org>,
        clang-built-linux <llvm@...ts.linux.dev>,
        Ard Biesheuvel <ardb@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: Re: [PATCH v6 06/10] kbuild: check static EXPORT_SYMBOL* by script
 instead of modpost

On Wed, May 25, 2022 at 5:31 PM Guenter Roeck <linux@...ck-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