RE: errno variable on the Hurd (was: Re: Postgresql question)
> On Fri, Jan 28, 2000 at 09:36:30AM -0800, Brent Fulgham wrote:
> > Errno seems problematic on the Hurd for some reason. I've seen
> > a few cases where the header has needed to be added to source
> > files for a clean compile, whereas it was not needed on other
> > environments (such as Linux).
> Of course, using errno without including <errno.h> is the
> Wrong Thing (tm).
> There is a good reason, too:
> /* Declare the `errno' variable, unless it's defined as a macro by
> bits/errno.h. This is the case in GNU, where it is a per-thread
> variable. This redeclaration using the macro still works, but it
> will be a function declaration without a prototype and may trigger
> a -Wstrict-prototypes warning. */
> #ifndef errno
> extern int errno;
> and in bits/errno.h:
> /* errno is a per-thread variable. */
> #include <hurd/threadvar.h>
> #define errno (*__hurd_errno_location ())
> #define __set_errno(val) errno = (val)
> So it is a macro and not an extern int variable, which is why
> the linker can't see it.
Ahh -- this makes a lot of sense now. So we should probably file
bugs upstream against software that makes use of errno without including
the errno header file in a particular module/source file. I think
there's a lot of stuff out there that relies on the belief that it's
an `extern int`, which is (as we now know) not always the case.