ptrace single-stepping change breaks Wine

Linus Torvalds torvalds at
Fri Nov 19 15:53:38 CST 2004

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 
 - 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.


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