linux-kernel - Re: [PATCH] tools lib: Disable redundant-delcs error for strlcpy

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Message-ID: <20191217200420.GD7095@redhat.com>
Date:   Tue, 17 Dec 2019 17:04:20 -0300
From:   Arnaldo Carvalho de Melo <acme@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        "Dmitry V . Levin" <ldv@...linux.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Vineet Gupta <Vineet.Gupta1@...opsys.com>,
        stable@...r.kernel.org, acme@...nel.org
Subject: Re: [PATCH] tools lib: Disable redundant-delcs error for strlcpy

Em Tue, Dec 17, 2019 at 03:23:32PM +0300, Vitaly Chikunov escreveu:
> Arnaldo,
> 
> Ping. Can you accept or comment on this patch? There is further
> explanations of it:

Will this work when building with clang

- Arnaldo
 
> 1. It seems that people putting strlcpy() into the tools was already aware of
> the problems it causes and tried to solve them. Probably, that's why they put
> `__weak` attribute on it (so it would be linkable in the presence of another
> strlcpy). Then `#ifndef __UCLIBC__`ed and later `#if defined(__GLIBC__) &&
> !defined(__UCLIBC__)` its declaration. But, solution was incomplete and could
> be improved to make kernel buildable on more systems (where libc contains
> strlcpy).
> 
> There is not need to make `redundant redeclaration` warning an error in
> this case.
> 
> 2. `#pragma GCC diagnostic ignored` trick is already used multiple times
> in the kernel:
> 
>   $ git grep  '#pragma GCC diagnostic ignored'
>   arch/arm/lib/xor-neon.c:#pragma GCC diagnostic ignored "-Wunused-variable"
>   tools/build/feature/test-gtk2-infobar.c:#pragma GCC diagnostic ignored "-Wstrict-prototypes"
>   tools/build/feature/test-gtk2.c:#pragma GCC diagnostic ignored "-Wstrict-prototypes"
>   tools/include/linux/string.h:#pragma GCC diagnostic ignored "-Wredundant-decls"
>   tools/lib/bpf/libbpf.c:#pragma GCC diagnostic ignored "-Wformat-nonliteral"
>   tools/perf/ui/gtk/gtk.h:#pragma GCC diagnostic ignored "-Wstrict-prototypes"
>   tools/testing/selftests/kvm/lib/assert.c:#pragma GCC diagnostic ignored "-Wunused-result"
>   tools/usb/ffs-test.c:#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
> 
> So the solution does not seem alien in the kernel and should be acceptable.
> 
> (I also send this to another of your emails in case I used wrong one before.)
> 
> Thanks,
> 
> 
> On Mon, Dec 09, 2019 at 12:46:07AM +0300, Vitaly Chikunov wrote:
> > Disable `redundant-decls' error for strlcpy declaration and solve build
> > error allowing users to compile vanilla kernels.
> > 
> > When glibc have strlcpy (such as in ALT linux since 2004) objtool and
> > perf build fails with something like:
> > 
> >   In file included from exec-cmd.c:3:
> >   tools/include/linux/string.h:20:15: error: redundant redeclaration of ‘strlcpy’ [-Werror=redundant-decls]
> >      20 | extern size_t strlcpy(char *dest, const char *src, size_t size);
> > 	|               ^~~~~~~
> > 
> > It's very hard to produce a perfect fix for that since it is a header
> > file indirectly pulled from many sources from different Makefile builds.
> > 
> > Fixes: ce99091 ("perf tools: Move strlcpy() from perf to tools/lib/string.c")
> > Fixes: 0215d59 ("tools lib: Reinstate strlcpy() header guard with __UCLIBC__")
> > Signed-off-by: Vitaly Chikunov <vt@...linux.org>
> > Cc: Dmitry V. Levin <ldv@...linux.org>
> > Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> > Cc: Vineet Gupta <Vineet.Gupta1@...opsys.com>
> > Cc: stable@...r.kernel.org
> > ---
> >  tools/include/linux/string.h | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/tools/include/linux/string.h b/tools/include/linux/string.h
> > index 980cb9266718..99ede7f5dfb8 100644
> > --- a/tools/include/linux/string.h
> > +++ b/tools/include/linux/string.h
> > @@ -17,7 +17,10 @@ int strtobool(const char *s, bool *res);
> >   * However uClibc headers also define __GLIBC__ hence the hack below
> >   */
> >  #if defined(__GLIBC__) && !defined(__UCLIBC__)
> > +#pragma GCC diagnostic push
> > +#pragma GCC diagnostic ignored "-Wredundant-decls"
> >  extern size_t strlcpy(char *dest, const char *src, size_t size);
> > +#pragma GCC diagnostic pop
> >  #endif
> >  
> >  char *str_error_r(int errnum, char *buf, size_t buflen);