Re: AIX sysval failure

[Eric Blake]

Gary V. Vaughan <gary <at> gnu.org> writes:

> > What is sysval after this run?
> >
> > $ echo 'changequote([,])syscmd([echo "meh" && kill -9 $$ ||
> >    echo "oops: $?"])sysval' | ./src/m4
> 
> Oh yeah.  D'uh, should've thought of that myself!
> 
> % echo 'changequote([,])syscmd([echo "meh" && kill -9 $$ ||
>    echo "oops: $?"])sysval' | ./src/m4
> meh
> 127

What if you replace the || with ; in the syscmd?  Or how about:

echo 'changequote([,])syscmd([sh -c '\''kill -9 $$'\'';
 st=$?; echo $st; exit $st])sysval' | ./src/m4

Also, do you have anything like strace or truss, that can see what syscalls 
were in play during syscmd's use of system()?

Maybe this slimmed down program is helpful as a debugging aid:

$ cat foo.c
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <sys/wait.h>

int main (int argc, char **argv)
{
  int r = system (argc == 1 ? "kill -9 $$" : argv[1]);
  printf ("%04x %d\n", r, errno);
  if (fork ())
    {
      wait (&r);
      printf ("%04x %d\n", r, errno);
    }
  else
    {
      execlp ("sh", "sh", "-c",
              argc == 1 ? "kill -9 $$" : argv[1], (char*) 0);
    }
  return 0;
}
$ ./foo false
0100 0
0100 0
$ ./foo
0009 0
0009 0

On my system, the lower 7 bits represent signals, the upper 8 represent normal 
return (on some platforms, this setup is swapped).  The intent of the m4 test 
is to find some portable way to cause sysval's child process to exit with a 
signal (since we document that sysval distinguishes signals from normal exit, 
similar to Solaris m4), hence the attempt to use 'kill -9 $$' since that is 
unblockable.  I'm starting to wonder if AIX system() is massaging the return 
value from wait(); maybe the gnulib 'execute' module is worthwhile.

Similar questions apply to popen() for esyscmd.

-- 
Eric Blake