We have some code in the perf tool[1] 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").
The versions of elfutils, glibc, gcc are slightly different
between the two and I have listed them below [2][3][4].
Is there a difference in the way libc or debug info is
organized between F20 and RHEL7 ?
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.
Appreciate any help in understanding what is going on.
Sukadev
[1]
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/tools/perf/arch/powerpc/util/skip-callchain-idx.c
[2] elfutils RPMS that I have on my systems:
Fedora20:
elfutils-libelf-devel-0.158-1.fc20.ppc64
elfutils-0.158-1.fc20.ppc64
elfutils-libs-0.158-1.fc20.ppc64
elfutils-libelf-0.158-1.fc20.ppc64
elfutils-devel-0.158-1.fc20.ppc64
RHEL7:
elfutils-0.158-3.el7.ppc64
elfutils-libelf-0.158-3.el7.ppc64
elfutils-libs-0.158-3.el7.ppc64
elfutils-libelf-devel-0.158-3.el7.ppc64
elfutils-devel-0.158-3.el7.ppc64
[3] glibc RPMS on my systems:
Fedora20:
glibc-common-2.18-11.fc20.ppc64p7
glibc-2.18-11.fc20.ppc64p7
glibc-headers-2.18-11.fc20.ppc64p7
glibc-debuginfo-common-2.18-11.fc20.ppc64p7
glibc-devel-2.18-11.fc20.ppc64p7
glibc-debuginfo-2.18-11.fc20.ppc64p7
RHEL7:
glibc-common-2.17-55.el7.ppc64
glibc-headers-2.17-55.el7.ppc64
glibc-debuginfo-2.17-55.el7.ppc64
glibc-2.17-55.el7.ppc64
glibc-devel-2.17-55.el7.ppc64
glibc-debuginfo-common-2.17-55.el7.ppc64
[4] gcc RPMS
Fedora20:
libgcc-4.8.2-7.fc20.ppc64
gcc-4.8.2-7.fc20.ppc64
gcc-c++-4.8.2-7.fc20.ppc64
RHEL7:
gcc-4.8.2-16.el7.ppc64
gcc-c++-4.8.2-16.el7.ppc64
libgcc-4.8.2-16.el7.ppc64
gcc-gfortran-4.8.2-16.el7.ppc64
