linux-kernel - Re: [PATCH v2] perf tools: Work around lack of sched

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Message-ID: <CAHTgTXUQVuxf5u_AZ9g-eLtwdrE4rGfiN5cCHA5ReMe0sObiBA@mail.gmail.com>
Date:	Thu, 19 Mar 2015 14:12:05 -0700
From:	Vinson Lee <vlee@...pensource.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Yann Droneaud <ydroneaud@...eya.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-perf-users@...r.kernel.org, Vinson Lee <vlee@...tter.com>
Subject: Re: [PATCH v2] perf tools: Work around lack of sched_getcpu in glibc
 < 2.6.

On Thu, Mar 19, 2015 at 6:14 AM, Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
> Em Thu, Mar 19, 2015 at 11:13:04AM +0100, Jiri Olsa escreveu:
>> On Wed, Mar 18, 2015 at 04:11:52PM -0700, Vinson Lee wrote:
>> > This patch fixes this build error with glibc < 2.6.
>
>> > +#ifdef __GLIBC_PREREQ
>> > +#if !__GLIBC_PREREQ(2, 6)
>> > +static int sched_getcpu(void)
>> > +{
>> > +   errno = ENOSYS;
>> > +   return -1;
>> > +}
>> > +#endif
>> > +#endif
>
>> you could mark it as __weak and get rid of those ifdef's
>> like we do for strlcpy in utilpath.c
>
> Agreed.
>
> - Arnaldo

I tried this approach but am having trouble getting a patch to compile
with both older glibc and recent glibc.

With older glibc I will get a "no previous prototype" compilation
error. I can fix this error by adding a prototype but this results in
a "redundant redeclaration" error with newer glibc.
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