spawn: Fix error pipe write failure handling

A short history lesson: this code (from exec.c) used to just be

    write(...);

In 649d85b, an empty if block was added to placate _FORTIFY_SOURCE's
warn_unused_result:

    if (write(...) != sizeof(error)) {
            // ...
    }

This is fine since the parent doesn't rely on receiving those writes
(e.g. the child could die before writing), and the small write to a pipe
won't fail anyway.

But when bfs_spawn() was created, the implementation changed to this:

    while (write(...) < sizeof(error));

The while loop was presumably added to mirror musl's posix_spawn()
implementation, which handles EINTR.  But musl's is actually correct:

    while (write(...) < 0);

whereas mine has a subtle bug: since sizeof(error) is unsigned, the bfs
code did an unsigned comparison, meaning -1 from write() would *not*
restart the loop.

Fix it by comparing with 0 like musl, since short writes are impossible
here.  Perhaps it's time for -Wsign-compare, despite the other 18
instances being false positives.

0 files changed, 0 insertions, 0 deletions