[Bug gprof/21189] New: gprof doesn't work with code built with PIE

[doko at debian dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=21189

            Bug ID: 21189
           Summary: gprof doesn't work with code built with PIE
           Product: binutils
           Version: 2.28
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gprof
          Assignee: unassigned at sourceware dot org
          Reporter: doko at debian dot org
  Target Milestone: ---

[forwarded from https://bugs.debian.org/854704]

"""
Since --enabled-default-pie was enabled in Debian for GCC 6, gprof no longer
works. I run a simple program compiled with default flags and gprof's output is
empty.

$ cat infloop.c
int main() {
    for(long i = 0; i < 1000000000; i ++) {}
    return 0;
}
$ gcc infloop.c -o infloop -pg
$ time ./infloop

real    0m2.067s
user    0m2.064s
sys     0m0.004s
$ gprof ./infloop | grep main
$

However, when I compile the same program with any earlier version of gcc, such
as gcc 5.4.1, or with the option -no-pie to disable PIE, it works.

$ gcc-5 infloop.c -o infloop -pg
$ rm gmon.out
$ time ./infloop

real    0m2.041s
user    0m2.036s
sys     0m0.000s
$ gprof ./infloop | grep main
101.41      2.06     2.06                             main
$ gcc -no-pie infloop.c -o infloop -pg
$ rm gmon.out
$ time ./infloop

real    0m2.019s
user    0m2.016s
sys     0m0.000s
$ gprof ./infloop | grep main
101.41      2.03     2.03                             main
$

This is the case for more complex programs too: gprof simply outputs nothing
other than the help-text. It looks like gcc is correctly generating the
gmon.out file, since it gets quite large and contains non-zero values.

Since GCC 6 moved to --enable-default-pie, all executables are of type DYN (not
EXEC), like shared libraries, and may be loaded at any base address. I suspect
this is breaking gprof's symbol lookup functionality. For instance, 0 is now a
valid address within the DYN ELF file. A good workaround for now is -no-pie,
but it would be great to get this fixed since Debian GCC now defaults to PIE.
"""

-- 
You are receiving this mail because:
You are on the CC list for the bug.