linux-kernel - Re: Linux 4.3-rc1 build error with older elfutils "util/symbol-elf.c:41:5: error: no previous prototype for ‘elf

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Date:	Thu, 17 Sep 2015 11:06:19 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Vinson Lee <vlee@...pensource.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Jiri Olsa <jolsa@...nel.org>,
	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Wang Nan <wangnan0@...wei.com>,
	Victor Kamensky <victor.kamensky@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-perf-users@...r.kernel.org
Subject: Re: Linux 4.3-rc1 build error with older elfutils "util/symbol-elf.c:41:5: error: no previous prototype for ‘elf_getphdrnum’"

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;
> 
> 
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