Re: Conformance problem in system()

[Rich Felker <dalias@libc.org>]

On Sun, Dec 31, 2017 at 12:23:42AM +0100, Markus Wichmann wrote:
> On Sat, Dec 30, 2017 at 05:22:04PM -0500, Rich Felker wrote:
> > I think you're right that there's a problem here, but I don't think
> > the patch correctly or fully fixes it. A simpler version of what
> > you're doing would be to just initialize status to -1 instead of
> > 0x7f00, since your patch is returning -1 in all cases where waitpid
> > did not complete successfully. But that ignores the POSIX requirement
> > to behave as if the interpreter exited with status 127 when it was
> > possibel to make the child process but the command interpreter could
> > not be executed.
> > 
> 
> Actually, I noticed another problem: waitpid() returns the PID of the
> changed child process on success, so the
> 
> if (wr) status = wr;
> 
> should be
> 
> if (wr < 0) status = wr;
> 
> The initialization of status would only change something if the kernel
> did not write to status on waitpid() failure. Is that guarenteed ABI, or
> does this just happen to be the case on current kernels?
> 
> > musl's posix_spawn does not succeed when exec fails in the child;
> > instead the exec error is returned. This behavior is permitted but not
> > required by POSIX. I think it would actually be preferable to system
> > to return -1 and set errno in this case too, but POSIX doesn't seem to
> > allow that.
> 
> Actually, the requirement to return exit status 127 on exec failure
> sounds mighty specific to me. As if someone wanted to codify behavior
> they needed in their utility. Which means there may be software out
> there that depends on this behavior.
> 
> There is the possibility of not considering a posix_spawn()ed child
> process as "created" unless posix_spawn() itself did return success,
> though. But that might run counter to what the POSIX was going for,
> here.

I think this is an acceptable interpretation for now. So just changing
default initialization of status to -1 should work, right?

Rich