Re: [Darwin 2/4] Do not crash (failed assertion) after PT_KILL ptrace error

[Mark Kettenis <mark.kettenis@xs4all.nl>]

> From: Joel Brobecker <brobecker@adacore.com>
> Date: Fri,  1 Jul 2011 12:03:24 -0700
> 
> This is something I noticed while reading the code.  Putting an
> assertion that the PT_KILL ptrace call never returns an error
> is too strong.  It might not be a debugger bug that caused the
> PT_KILL ptrace operation to fail, so a failed-assertion "crash"
> would not be justified.  It also seems easy enough to continue
> and get ready for the next debugging session.  So this patch
> changes the assertion into a warning.
> 
> This patch also tries to handle the case where ptrace return -1,
> but left errno set to zero.  According to the ptrace man page,
> it is possible for some ptrace operations to return -1 in non-error
> situations, and to detect those situations, it explains that errno
> should be set prior to calling ptrace, and then checked again after.

I think I disagree here.  PT_KILL should only fail if you pass it the
wrong process ID.  So unless there is an OS bug of some sorts, this is
going to be a GDB internal error.  Do you have actual evidence there
is a kernel bug here?

> gdb/ChangeLog:
> 
>         * darwin-nat.c (darwin_ptrace): Add documentation.
>         Set errno to zero before calling ptrace.  If ptrace returns
>         -1 and errno is zero, then change then return zero.
>         (darwin_kill_inferior): Issue a warning instead of triggering
>         a failed assertion when the PT_KILL ptrace operations returned
>         nonzero.