Re: RFC: close-on-exec internal file descriptors

[Joel Brobecker <brobecker at adacore dot com>]

Hi Tom,

> Tom> 2013-01-03  Tom Tromey  <tromey@redhat.com>
> 
> Tom> 	PR gdb/7912:
> Tom> 	* Makefile.in (SFILES): Add filestuff.c
> Tom> 	(COMMON_OBS): Add filestuff.o.
> Tom> 	(filestuff.o): New target.
> [...]

Unfortunately, this is causing problems on Darwin and HP/UX,
because both platforms use pipes to synchronize parent and
child during the fork/exec. See for instance darwin-nat.c:

    /* The child must synchronize with gdb: gdb must set the exception port
       before the child call PTRACE_SIGEXC.  We use a pipe to achieve this.
       FIXME: is there a lighter way ?  */
    static int ptrace_fds[2];

Same mechanism, and therefore problem, with HP/UX targets:

    /* File descriptors for pipes used as semaphores during initial
       startup of an inferior.  */
    static int inf_ttrace_pfd1[2];
    static int inf_ttrace_pfd2[2];

In terms of behavior, GDB either hangs during process creation, or
reports a fatal failure during one of the system calls.

I don't think there is a way of opening a FD with the intention
of protecting them from the close-at-exec, is there? So, the solution
would seem to add an interface to setup the protection, as well
as a function to remove that protection (necessary when we close
the fd).

What do you think?

-- 
Joel