linux-kernel - Re: [PATCH 2/3] perf: Allow strong and weak functions in LIB

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Date:	Fri, 26 Nov 2010 19:18:36 -0200
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Ian Munsie <imunsie@....ibm.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	tom.leiming@...il.com
Subject: Re: [PATCH 2/3] perf: Allow strong and weak functions in LIB_OBJS

Em Thu, Nov 25, 2010 at 03:12:54PM +1100, Ian Munsie escreveu:
> From: Ian Munsie <imunsie@....ibm.com>
> 
> When we build perf we place all of the .o files from the library files
> (util, arch/x/util, etc) into libperf.a which is then linked into perf.
> The problem is that the linker will by default only consider .o files
> within the .a archive if they are necessary to satisfy an unresolved
> symbol. As weak functions are not unresolved, it will not consider a .o
> file from the archive containing the strong versions of weak functions
> unless it requires it for another reason.
> 
> This patch adds the --whole-archive flags to the linker when passing in
> the libperf.a file to ensure that it will consider every .o file in the
> archive, not just what it believes that it needs. The end result is that
> weak functions can now be overridden by strong variants of them in the
> libperf.a file.

After I applied this patch I got this on a x86_64 Fedora 14 box:

    LINK /home/acme/git/build/perf/perf
/usr/lib64/libpthread_nonshared.a(pthread_atfork.oS): In function `pthread_atfork':
(.text+0x0): multiple definition of `__pthread_atfork'
/usr/lib64/libpthread_nonshared.a(pthread_atfork.oS):(.text+0x0): first defined here
/usr/lib64/libpthread_nonshared.a(pthread_atfork.oS): In function `pthread_atfork':
(.text+0x0): multiple definition of `pthread_atfork'
/usr/lib64/libpthread_nonshared.a(pthread_atfork.oS):(.text+0x0): first defined here
/usr/lib64/libpthread_nonshared.a(pthread_atfork.oS): In function `pthread_atfork':
(.text+0x0): multiple definition of `__pthread_atfork'
/usr/lib64/libpthread_nonshared.a(pthread_atfork.oS):(.text+0x0): first defined here
/usr/lib64/libpthread_nonshared.a(pthread_atfork.oS): In function `pthread_atfork':
(.text+0x0): multiple definition of `pthread_atfork'
/usr/lib64/libpthread_nonshared.a(pthread_atfork.oS):(.text+0x0): first defined here
/usr/lib/gcc/x86_64-redhat-linux/4.5.1/../../../../lib64/libiberty.a(choose-temp.o): In function `choose_temp_base':
(.text+0x57): warning: the use of `mktemp' is dangerous, better use `mkstemp'
/usr/lib/gcc/x86_64-redhat-linux/4.5.1/../../../../lib64/libiberty.a(strerror.o): In function `errno_max':
(.text+0x151): warning: `sys_nerr' is deprecated; use `strerror' or `strerror_r' instead
/usr/lib/gcc/x86_64-redhat-linux/4.5.1/../../../../lib64/libiberty.a(xstrdup.o): In function `xstrdup':
(.text+0x0): multiple definition of `xstrdup'
/home/acme/git/build/perf/libperf.a(wrapper.o):/media/tbs/acme/git/linux/tools/perf/util/wrapper.c:15: first defined here
collect2: ld returned 1 exit status
make: *** [/home/acme/git/build/perf/perf] Error 1
make: Leaving directory `/media/tbs/acme/git/linux/tools/perf'
[acme@...icio linux]$

- Arnaldo
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