[Bug libc/27576] New: gmon.out not consistently created

["wsnyder at wsnyder dot org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=27576

            Bug ID: 27576
           Summary: gmon.out not consistently created
           Product: glibc
           Version: 2.31
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: wsnyder at wsnyder dot org
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

Created attachment 13307
  --> https://sourceware.org/bugzilla/attachment.cgi?id=13307&action=edit
Testcase

== Description

Type "make" in this tarball's directory.

This will show (extra lines omitted):

  g++  -pg -O0  -c -o Vt_case_huge_prof__main.o Vt_case_huge_prof__main.ii
  @@@@@ Did we get a gmon?
  make: [Makefile:15: x] Error 1 (ignored)

  g++  -pg -Os  -c -o Vt_case_huge_prof__main.o Vt_case_huge_prof__main.ii
  @@@@@ Did we get a gmon?
    4554816     28 -rw-rw-r--   1 user  user     26943 Mar 13 11:33 ./gmon.out

  g++  -pg -O0  -c -o Vt_case_huge_prof__main.o Vt_case_huge_prof__main__ok.ii
  @@@@@ Did we get a gmon?
    4554816    884 -rw-rw-r--   1 user  user    897414 Mar 13 11:33 ./gmon.out


In short gcc -pg with -O0 is not reliably creating a gmon.

The problem goes away using -Os.

The problem goes away if line 60549 of ~/d/case/Vt_case_huge_prof__main.ii

    std::array<CData , 16384> __Vtablechg1;

is changed into

    CData __Vtablechg1[16384];

Others have reported the problem appears timing related and sometimes gmon.out
will get produced but on my system it is completely reliably broken.

Experiments show clang++ (with same glibc on same system) gives same
misbehavior.

While this "feels" like a memory corruption sort of bug, the program is
sanitizer and warning clean. This was originally reported as GCC bug at
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99579 but appears the compiler is
creating reasonable code.

== gcc --version

gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0

== glibc verison

glibc-source/focal-updates 2.31-0ubuntu9.2 all

== cat /etc/*release

DISTRIB_DESCRIPTION="Ubuntu 20.04 LTS"

== cat /proc/cpuinfo

... AMD Ryzen 9 3950X 16-Core

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