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Date: Thu, 17 Sep 2015 11:06:19 -0300
From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Vinson Lee <vlee@twopensource.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Ingo Molnar <mingo@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
        Jiri Olsa <jolsa@kernel.org>,
        "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Wang Nan <wangnan0@huawei.com>,
        Victor Kamensky <victor.kamensky@linaro.org>,
        LKML <linux-kernel@vger.kernel.org>, linux-perf-users@vger.kernel.org
Subject: Re: Linux 4.3-rc1 build error =?utf-8?Q?wi?=
 =?utf-8?Q?th_older_elfutils_=22util=2Fsymbol-elf=2Ec=3A41=3A5=3A_error=3A?=
 =?utf-8?Q?_no_previous_prototype_for_=E2=80=98elf=5Fgetphdrnum=E2=80=99?=
 =?utf-8?Q?=22?=
Message-ID: <20150917140619.GK11551@kernel.org>
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Em Thu, Sep 17, 2015 at 09:28:31AM +0300, Adrian Hunter escreveu:
> On 17/09/15 01:10, Vinson Lee wrote:
> > With Linux 4.3-rc1 I get a perf build error using toolchains with
> > older elfutils.
> > 
> > The following build error occurs on both CentOS 5.11 (elfutils 0.137)
> > and Ubuntu 10.04.4 (elfutils 0.143).
> > 
> >   CC       util/symbol-elf.o
> > cc1: warnings being treated as errors
> > util/symbol-elf.c:41: error: no previous prototype for ‘elf_getphdrnum’
> 
> commit f785f2357673d520a0b7b468973cdd197f336494
> removed the 'static' qualifier, presumably because there
> are cases where the prototype is in the header but the function is
> not in the library.
> 
> AFAICT gcc accepts multiple prototypes so long as they are the same
> so just adding the prototype should be ok i.e.

But that looks like a bandaid :-\

The comment I made in f785f2357673d520a0b7b468973cdd197f336494 was not
clear enough, now I'm the one trying to figure out why I did that... Duh
:-\

I.e. if:

"HAVE_ELF_GETPHDRNUM_SUPPORT is false" we shouldn't have any prototype
for that elf_getphdrnum function, i.e. the fact that it is in libelf.h
should mean that it is present, how come the feature test for it failed,
i.e. HAVE_ELF_GETPHDRNUM_SUPPORT wasn't defined?

- Arnaldo
 
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index 53bb5f59ec58..d9abb0307cc5 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -38,6 +38,7 @@ static inline char *bfd_demangle(void __maybe_unused *v,
>  #endif
>  
>  #ifndef HAVE_ELF_GETPHDRNUM_SUPPORT
> +int elf_getphdrnum(Elf *elf, size_t *dst);
>  int elf_getphdrnum(Elf *elf, size_t *dst)
>  {
>  	GElf_Ehdr gehdr;
> 
>