ptrace single-stepping change breaks Wine

[Daniel Jacobowitz]

On Thu, Dec 30, 2004 at 03:17:01PM -0800, Linus Torvalds wrote:
> 
> 
> On Thu, 30 Dec 2004, Daniel Jacobowitz wrote:
> > 
> > does not look right to me.  Before, we'd get an 0x80|SIGTRAP result
> > from wait.  Now, you've moved the 0x80 to live only inside the siginfo.
> > This is accessible to the debugger via ptrace, but only very recently
> > (late 2.5.x).  So this will probably break users of PT_TRACESYSGOOD.
> 
> I don't see how to easily emulate the old behaviour 100% - see
> ptrace_notify. We always sent the signal SIGTRAP to the process, and then
> set "exit_code" tp have the 0x80 marker by calling ptrace_stop() by hand.
> However, if we make it a real signal (which we need to do to get the 
> continue semantics right), we no longer have that out-of-band info 
> available to us.
> 
> We could make "get_signal_to_deliver()" pass in some other exit_code to 
> ptrace_stop() than just signr. It would have to pick it up from the 
> siginfo structure, but then we'd have to make sure that _other_ signal 
> users do that properly..
> 
> Patches/suggestions welcome.

Well, you put SIGTRAP|0x80 in si_code.  Coincidentally, 0x80 is
SI_KERNEL.  So testing for SI_KERNEL | 0x80 is probably OK in the
signal path, since most of its other arbitrary values would be either
negative or not include SI_KERNEL.

-- 
Daniel Jacobowitz