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Date: Thu, 3 May 2012 22:14:03 -0400
Message-ID: <CACqU3MVqpz=azeUOUfmtoLEPvqngfJHSHFe7ujemeRT1-B=osA@mail.gmail.com>
Subject: Re: perf build failure on Linus's tree
From: Arnaud Lacombe <lacombar@gmail.com>
To: David Miller <davem@davemloft.net>
Cc: namhyung.kim@lge.com, gregkh@linuxfoundation.org, a.p.zijlstra@chello.nl,
        paulus@samba.org, mingo@redhat.com, acme@ghostprotocols.net,
        jolsa@redhat.com, linux-kernel@vger.kernel.org
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Hi,

On Thu, May 3, 2012 at 9:50 PM, David Miller <davem@davemloft.net> wrote:
> From: Namhyung Kim <namhyung.kim@lge.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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