Hi,

I've noticed the following loop at 
https://git.musl-libc.org/cgit/musl/tree/src/process/posix_spawn.c#n159:

     exec(args->path, args->argv, args->envp);
     ret = -errno;

fail:
     /* Since sizeof errno < PIPE_BUF, the write is atomic. */
     ret = -ret;
     if (ret) while (__syscall(SYS_write, p, &ret, sizeof ret) < 0);
     _exit(127);

Is there any reason that write is done in a loop? If SIGPIPE is blocked 
or ignored and the parent dies before this point, the child will spin in 
it forever.

A test case is attached. It overrides execve() to abuse it as a 
callback, avoiding reliance on timings.

As an aside, perhaps it would make sense to call execve() in 
posix_spawn() implementation via a hidden symbol? This would both make 
it consistent with posix_spawnp() and avoid any trouble with user code 
executing in a vfork'ed child if execve() is overridden via e.g. 
LD_PRELOAD.

Alexey