Re: ptrace single-stepping change breaks Wine

Linus Torvalds
2004-11-19T22:02:52Z

On Fri, 19 Nov 2004, Daniel Jacobowitz wrote:
>
> I'm getting the feeling that the question of whether to step into
> signal handlers is orthogonal to single-stepping; maybe it should be a
> separate ptrace operation.

I really don't see why. If a controlling process is asking for
single-stepping, then it damn well should get it. It it doesn't want to
single-step through a signal handler, then it could decide to just put a
breakpoint on the return point (possibly by modifying the signal handler
save area).

It's not like single-stepping into the signal handler in any way removes
any information (while _not_ single-stepping into it clearly does).

With the patch I just posted (assuming it works for people), Wine should
at least have the choice. The behaviour now should be:

- if the app sets TF on its own, it will cause a SIGTRAP which it can
catch.
- if the debugger sets TF with SINGLESTEP, it will single-step into a
signal handler.
- it the app sets TF _and_ you ptrace it, you the ptracer will see the
debug event and catch it. However, doing a "continue" at that point
will remove the TF flag (and always has), the app will normally then
never see the trap. You can do a "signal SIGTRAP" to actually force
the trap handler to tun, but that one won't actually single-step (it's
a "continue" in all other senses).

It sounds like the third case is what wine wants.

Linus