Bug 703919

Description of problem:
The libvirt testsuite had a program that altered its own environment via assignment to environ.  When running this program under gcov, the program dumped core, even though the program had successfully reached exit().  Why?  Because gcov called getenv("GCOV_PREFIX") after the program's array for environ had gone out of scope.

For gcov to be useful, it should not let itself be affected by the operations of the program that it is tracing.  I think that gcov should cache all environment variables that it intends on reading up front, before starting main(), rather than re-reading them on every use case, so as to be immune to anything the traced program might do to its own environment.

Version-Release number of selected component (if applicable):
gcc-4.5.1-4.fc14.x86_64

How reproducible:
it was happening all the time for me with libvirt on the program tests/commandtest, until commit ba13a37 fixed the test to give environ a better scope.  I couldn't reproduce a crash on a simpler test case, but even then, gdb can show the problem

Steps to Reproduce:
Method 1: how I found the problem
1. git clone git://libvirt.org/libvirt.git
2. cd libvirt
3. git checkout ba13a37^
4. ./autobuild.sh

Method 2:
1. $ cat > bar.c <<\EOF
extern char **environ;
int main (void)
{
  const char *newenv[] = {
    "PATH=/usr/bin:/bin",
    0,
  };
  environ = (char **)newenv;
  return 0;
}
EOF
2. $ gcc -O2 -o bar -Wall bar.c -fprofile-arcs -ftest-coverage
3. $ gdb ./bar
4. (gdb) b main
5. (gdb) r
6. (gdb) b getenv
7. (gdb) c
8. (gdb) bt

Actual results:
Method 1: the libvirt testsuite fails, with a core dump in commandtest
Method 2: gcov calls getenv, after the contents of environ have gone out of scope, which has undefined behavior (even though if the program were not compiled for gcov, then there is no use of environ that late)
#0  getenv (name=0x4023e7 "GCOV_PREFIX") at getenv.c:36
#1  0x0000000000401370 in gcov_exit ()
#2  0x0000003d15e369f1 in __run_exit_handlers (status=0) at exit.c:78
#3  exit (status=0) at exit.c:100
#4  0x0000003d15e1ee64 in __libc_start_main (main=0x400c80 <main>, argc=1, 
    ubp_av=0x7fffffffe1c8, init=<value optimized out>, 
    fini=<value optimized out>, rtld_fini=<value optimized out>, 
    stack_end=0x7fffffffe1b8) at libc-start.c:258
#5  0x0000000000400bb9 in _start ()


Expected results:
Method 1: the libvirt test should succeed
Method 2: at step 7, the getenv() breakpoint should not hit after main() has started

Additional info:
https://www.redhat.com/archives/libvir-list/2011-May/msg00679.html