In article <m0t9v5Y-00005tC@flatlin.ka.sub.org>,
Christoph Badura <bad@flatlin.ka.sub.org> wrote:
> John Birrel writes:
> >We're living with a threaded version of NetBSD's libc where errno is thread
> >specific. By changing errno.h to define errno as:
> 
> >extern  int *__error();
> >#define errno (*__error())
> 
> I believe POSIX requires errno to be writeable in order to detect the
> indeterminate cases of sysconf()/pathconf().

The above does makes errno writable, since the function returns a
pointer to it, not the value. The question is, is this safe in other
cases, and do POSIX or other standards allow errno to be a macro?

(I've done something like this before, which is why this interests me.
Worked fine for what I was doing, but it was much less pervasive and
potentially dangerous as changing the whole C library)