Re: [PATCH] PPC sim: Don't close file descriptors 0, 1, or 2

[Kevin Buettner <kevinb at redhat dot com>]

On Mon, 16 Nov 2015 18:53:17 -0500
Mike Frysinger <vapier@gentoo.org> wrote:

> On 16 Nov 2015 14:58, Kevin Buettner wrote:
> > This occurs because the powerpc simulator closes, on behalf of the
> > testcase, the file descriptors associated with stdin, stdout, and
> > stderr.  GDB still needs these descriptors to communicate with the
> > user or, in this case, with the testing framework.
> 
> special casing this logic in the sim looks wrong to me.  why
> is the testcase itself trying to close stdin/stdout/stderr ?

It's not just one test case, but a bunch of them, 229 to be exact.

I haven't investigated all of them, but in many (if not all) of them,
close() is being called during exit().  This problem arises when
GDB runs the testcase to completion.

sim/common achieves the same result by placing file descriptors 0, 1,
2, and MAX_CALLBACK_FDS together in a circular fd_buddy list.  (See
os_init() in sim/common/callback.c.) close() is never called on any of
these descriptors due to the fact that they're in a (circular) list of
greater than one element.  When one of these descriptors (0, 1, or 2)
is closed (in os_close()), it is simply removed from the fd_buddy
list, with no close() operation actually being performed.  Note that
when the final one is "closed", it is still on an fd_buddy list with
MAX_CALLBACK_FDS - hence it won't be closed either.

So sim/common is doing the same thing as my proposed patch for ppc;
sim/common is just using a more elegant mechanism to avoid calling
close() on these three file descriptors.

Kevin