Hello,
I'm trying to improve Linux perf report by adding inliner information to the
callstacks it reports, to make the output more easily interpretable when
looking at complicated C++ applications.
I have a proof of concept locally using bfd_find_inliner_info, but have
noticed the following seemingly broken behavior:
Input file:
~~~~~~~~~test.cpp~~~~~~~
#include <cstdlib>
#include <iostream>
#include <complex>
int main(int argc, char** argv)
{
double a = 0;
double b = 0;
if (argc > 1)
a = atof(argv[1]);
if (argc > 2)
b = atof(argv[2]);
auto c = std::complex<double>(a, b);
std::cout << std::abs(c) << std::endl;
}
~~~~~~~~~~~~~~~~~~~~~~~~
I build it with:
~~~~~~~~~building~~~~~~~
$ g++ -g -O2 -o test test.cpp
~~~~~~~~~~~~~~~~~~~~~~~~
Then I get a "good" backtrace using GDB:
~~~~~~~~~gdb~~~~~~~~~~~~
$ gdb ./test
(gdb) break hypot
Function "hypot" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (hypot) pending.
(gdb) run
Starting program: /tmp/test
Breakpoint 1, 0x00007ffff776e910 in hypot () from /usr/lib/libm.so.6
(gdb) bt
#0 0x00007ffff776e910 in hypot () from /usr/lib/libm.so.6
#1 0x00000000004007f4 in std::__complex_abs (__z=<optimized out>) at /usr/
include/c++/6.2.1/complex:589
#2 std::abs<double> (__z=<synthetic pointer>) at /usr/include/c++/6.2.1/
complex:597
#3 main (argc=<optimized out>, argv=<optimized out>) at test.cpp:14
~~~~~~~~~~~~~~~~~~~~~~~~
Note what inliners it reports for the address 0x00000000004007f4. Let's try
bfd_find_inliner_info via eu-addr2line -i:
~~~~~~~~~eu-addr2line~~~
eu-addr2line -i -a 0x00000000004007f4 -e ./test
0x00000000004007f4
/usr/include/c++/6.2.1/ostream:221
/tmp/test.cpp:14
~~~~~~~~~~~~~~~~~~~~~~~~
This is wrong and seems to be off-by-one:
~~~~~~~~~eu-addr2line~~~
eu-addr2line -i -a 0x00000000004007f3 -e ./test
0x00000000004007f3
/usr/include/c++/6.2.1/complex:589
/usr/include/c++/6.2.1/complex:597
/tmp/test.cpp:14
~~~~~~~~~~~~~~~~~~~~~~~~
Can someone with more knowledge in this area sched some light on what is going
on here please? Is it a bug, or is this fuzzy behavior and GDB happens to be
better at guessing the "right" thing?
Some system info:
linux 4.7.2-1-ARCH
eu-addr2line 0.167
g++ 6.2.1
gdb 7.11.1
Thanks
--
Milian Wolff
mail(a)milianw.de
http://milianw.de