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Re: dwfl_addrmodule() differences bw F20 and RHEL7
- From: Mark Wielaard <mjw at redhat dot com>
- To: elfutils-devel at lists dot fedorahosted dot org
- Date: Thu, 30 Oct 2014 10:25:45 +0100
- Subject: Re: dwfl_addrmodule() differences bw F20 and RHEL7
On Fri, 2014-10-24 at 18:33 -0700, Sukadev Bhattiprolu wrote:
> We have some code in the perf tool that uses following
> sequence of calls to try and determine if the return address
> for a function is in the link register (LR) or on the stack:
> dwfl = dwfl_begin(&offline_callbacks);
> dwfl_report_offline(dwfl, "" exec_file, -1);
> mod = dwfl_addrmodule(dwfl, pc);
> dwfl_module_eh_cfi(mod, &bias);
> /* etc.. */
> where: exec_file is
> /usr/lib64/power8/libc-2.17.so (on RHEL7)
> /usr/lib64/libc-2.18.so (on Fedora20)
> and 'pc' is an address in libc, say in vfprintf(), rand() etc.
> This sequence of calls works consistently on Fedora20 and fails
> consistently on RHEL7 - where dwfl_addrmodule() returns -1
> (dwfl_errmsg() says "no error").
That should only happen when dwfl == NULL (in which case there should be
an earlier error), or no module contains the given address.
> The versions of elfutils, glibc, gcc are slightly different
> between the two and I have listed them below .
> Is there a difference in the way libc or debug info is
> organized between F20 and RHEL7 ?
I don't believe so. But clearly these are two completely different glibc
> The Fedora20 is a Power7 system and RHEL7 is a Power8.
> With some debug statements, I see that in dwfl_addrsegment():
> lookup() retruns 1,
> dwfl->lookup_module is non-null
> dwfl_addrsegment() returns -1.
> I can collect more debug if necessary.
Could you find out what the module load address is for the Dwfl_Module
you create through dwfl_report_offline? dwfl_module_info will give you
the start and end address range. And what is the pc value you provide to
dwfl_addrmodule in both cases?