netdev - Re: [PATCH bpf] libbpf: fix missing _

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Date:   Fri, 19 Jul 2019 11:26:50 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...com>,
        Kernel Team <kernel-team@...com>, Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...il.com>
Subject: Re: [PATCH bpf] libbpf: fix missing __WORDSIZE definition

On Fri, Jul 19, 2019 at 11:14 AM Arnaldo Carvalho de Melo
<arnaldo.melo@...il.com> wrote:
>
> Em Fri, Jul 19, 2019 at 10:54:44AM -0700, Andrii Nakryiko escreveu:
> > On Thu, Jul 18, 2019 at 6:16 PM Arnaldo Carvalho de Melo
> > <arnaldo.melo@...il.com> wrote:
> > >
> > > Em Thu, Jul 18, 2019 at 02:16:29PM -0700, Andrii Nakryiko escreveu:
> > > > On Thu, Jul 18, 2019 at 12:14 PM Arnaldo Carvalho de Melo
> > > > <arnaldo.melo@...il.com> wrote:
> > > > >
> > > > > Em Thu, Jul 18, 2019 at 03:56:19PM -0300, Arnaldo Carvalho de Melo escreveu:
> > > > > > I'll stop and replace my patch with yours to see if it survives all the
> > > > > > test builds...
> > > > >
> > > > > So, Alpine:3.4, the first image for this distro I did when I started
> > > > > these builds, survives the 6 builds with gcc and clang with your patch:
> > > > >
> > > > >

[...]

> >
> > Ok, did some more googling. This warning (turned error in your setup)
> > is emitted when -Wshadow option is enabled for GCC/clang. It appears
> > to be disabled by default, so it must be enabled somewhere for perf
> > build or something.
>
> Right, I came to the exact same conclusion, doing tests here:
>
> [perfbuilder@...8896a648d tmp]$ gcc -Wshadow shadow_global_decl.c   -o shadow_global_decl
> shadow_global_decl.c: In function 'main':
> shadow_global_decl.c:9: warning: declaration of 'link' shadows a global declaration
> shadow_global_decl.c:4: warning: shadowed declaration is here
> [perfbuilder@...8896a648d tmp]$ gcc --version |& head -1
> gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-23)
> [perfbuilder@...8896a648d tmp]$ gcc shadow_global_decl.c   -o shadow_global_decl
> [perfbuilder@...8896a648d tmp]$
>
> So I'm going to remove this warning from the places where it causes
> problems.
>
> > Would it be possible to disable it at least for libbpf when building
> > from perf either everywhere or for those systems where you see this
> > warning? I don't think this warning is useful, to be honest, just
> > random name conflict between any local and global variables will cause
> > this.
>
> Yeah, I might end up having this applied.

Thanks!

>
> [acme@...co perf]$ git diff
> diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
> index 495066bafbe3..b6e902a2312f 100644
> --- a/tools/scripts/Makefile.include
> +++ b/tools/scripts/Makefile.include
> @@ -32,7 +32,6 @@ EXTRA_WARNINGS += -Wno-system-headers
>  EXTRA_WARNINGS += -Wold-style-definition
>  EXTRA_WARNINGS += -Wpacked
>  EXTRA_WARNINGS += -Wredundant-decls
> -EXTRA_WARNINGS += -Wshadow
>  EXTRA_WARNINGS += -Wstrict-prototypes
>  EXTRA_WARNINGS += -Wswitch-default
>  EXTRA_WARNINGS += -Wswitch-enum
> [acme@...co perf]$
>
>
> Sorry for the noise...

No worries, I learned something new today :)

>
> - Arnaldo