linux-kernel - Re: perf build failure on Linus's tree

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Date:	Thu, 3 May 2012 22:14:03 -0400
From:	Arnaud Lacombe <lacombar@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	namhyung.kim@....com, gregkh@...uxfoundation.org,
	a.p.zijlstra@...llo.nl, paulus@...ba.org, mingo@...hat.com,
	acme@...stprotocols.net, jolsa@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: perf build failure on Linus's tree

Hi,

On Thu, May 3, 2012 at 9:50 PM, David Miller <davem@...emloft.net> wrote:
> From: Namhyung Kim <namhyung.kim@....com>
> Date: Fri, 04 May 2012 10:37:24 +0900
>
>> Hi,
>>
>> On Thu, 3 May 2012 14:57:48 -0700, Greg KH wrote:
>>> Linus's tree right now (3.4.rc5.67.gac001.dirty) gives me the following
>>> build error when I try to build perf:
>>>     CC util/parse-events-flex.o
>>> <stdout>: In function ‘yy_get_next_buffer’:
>>> <stdout>:1510:3: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>>> util/parse-events.l: In function ‘parse_events_lex’:
>>> util/parse-events.l:122:1: error: ignoring return value of ‘fwrite’, declared with attribute warn_unused_result [-Werror=unused-result]
>>> cc1: all warnings being treated as errors
>>>
>>> Do you really want to ensure that flex's build warnings fail the build?
>>>
>>> thanks,
>>>
>>> greg k-h
>>
>> Can't reproduce it on my Fedora 17 box:
>
> Because your glibc headers probably don't have the warn_unused_result attribute
> in the extern declaration of fwrite() like Greg's do.
>
`tools/perf/Makefile' adds -D_FORTIFY_SOURCE=2 on the compiler's
command line, which in turn adds `__attribute__
((__warn_unused_result__))' to fwrite(3)'s prototypes, via `__wur'. I
double checked by pre-processing `util/parse-events-flex.c' with the
same arguments used by perf. fwrite(3) ends up being declared as:

extern size_t fwrite (__const void *__restrict __ptr, size_t __size,
        size_t __n, FILE *__restrict __s) __attribute__
((__warn_unused_result__));

So it is definitively enabled, and used, on Fedora.

Above tests were done on Fedora 15/x86_64 and Fedora 16/x86_64, `perf'
build without any issue there too.

my 0.2c,
 - Arnaud
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