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Re: [Patch] Win32 gdbserver new interrupt support, and attach to process fix.


Lerele wrote:
Pedro Alves wrote:

Space around '?' and ':'. Personally, I liked the res != FALSE ? 0 : -1 version better.


Honestly, I don't really care too much. You guys decide.


I don't care much either, but I think the spaces around '?' and ':' are mandatory.

+ return res ? 0 : -1;


I was wrong, res is not a Win32 BOOL, it's plainly a 0 or a 1.

Then make it a BOOL, it makes the code clearer anyway. See attachment.



Already fixed spacing, while you were uploading your patches.
I'll send a new version for interrupt patch when I get some time to do it, I'll need get latest cvs and merge my changes, then resend patch.



I guess that would have been sufficient. But since you already changed "target->send_signal" to "target->send_interrupt" I guess that is no longer necessary.


Yep, just change it to win32_send_interrupt (void), and drop the if (sig == SIGINT) test.

I plan on eventually adding a third option to GenerateConsoleCtrlEvent
and DebugBreakProcess, that injects a thread into the debuggee, since
WinCE doesn't have any of the above.  That should make every
stoppable process stoppable, in all Windows versions.


Do you find appropriate to use this method?

It is exactly what DebugBreakProcess does internally, so if you have a problem with the approach, you shouldn't be using it :) The thread is short-lived. It is something like:

//inferior's address space
void helper_thread (void*)
{
  DebugBreak ();  // stops here.

  // and dies on resume.
}


// debugger's address space DebugBreakProcess (pid) { if (debugger_present) // we are sure of this // but this call can come from // a 3rd process. { create_remote_thread (helper_thread, pid); } }


I stumbled on the fact that on WinCE there is no CreateRemoteThread. There is an undocumented but widely used PerformCallback4 that does a pretty good hack and can be used to simulate CreateRemoteThread (haven't tested yet), but it gone in WinCE >= 5, and I don't know the a replacement, that doesn't need messing with the registry to inject a dll into the inferior's address space, and start a thread on DllMain. Still searching. Maybe it is possible to stop one thread, and manually manipulate the stack to insert a call into CreateThread with DebugBreak as entry point. Although the prototype for DebugBreak is different from what CreateThread expects, there should be no problem, since WinCE is __cdecl. It may be problematic to do this is a thread blocked inside a Win32 or kernel call, or if the inferior thread chosen to do it is in a stack corrupted state. The advantage of these approaches is that there is a real breakpoint exception being thrown. Oh, you can't just insert a breakpoint at the current PC, since it may be a ROM address (real Flash/ROM, not locked pages).

Isn't there any other way to do it on WinCE?


Probably. I would like to know how other debuggers do it.


1) May be solved by doing:

1. Create in gdbserver process as much threads as number of cpus -1 the computer has. These threads should consume all scheduled cpu for them.
2. SetPriorityClass on gdbserver process with real-time priority.
3. GetPriorityClass on child and store it to restore later on.
4. SetPriorityClass on child with below normal or idle.
5. Suspend all child threads.
Child should be stopped here.


Only problem I see with this can be if child changes its own priority class between steps 3 and 4 above, however this is a very remote possibility, because if this happens it is because child is already running in real-time priority, and in this case gdbserver possibly may not even work at all (unless you run gdbserver itself with this priority).

What do you think about this?

I was leaving something like this as a last resort, but should be possible, I guess. Would need extra logic to handle the fact that there isn't any real breakpoint exception live (in resume, for instance).

Does WinCE API have these required functions?
It may seem a quite odd way of doing it, but if it works, that's what counts I think.



Don't know about WinCE > 5. The whole security model + address space model has changed. I'm still looking at a portable way across all WinCEs from Mobile 2003 to 6, and if I can simulate a DebugBreakProcess, it would all be nicely encapsulated.

Thanks for the suggestions!

Cheers,
Pedro Alves
Index: src/gdb/gdbserver/win32-i386-low.c
===================================================================
--- src.orig/gdb/gdbserver/win32-i386-low.c	2007-03-03 19:52:56.000000000 +0000
+++ src/gdb/gdbserver/win32-i386-low.c	2007-03-05 00:01:52.000000000 +0000
@@ -673,7 +673,7 @@ win32_create_inferior (char *program, ch
 static int
 win32_attach (unsigned long pid)
 {
-  int res = 0;
+  BOOL res = FALSE;
   winapi_DebugActiveProcessStop *DebugActiveProcessStop = NULL;
 
   winapi_DebugSetProcessKillOnExit *DebugSetProcessKillOnExit = NULL;
@@ -683,7 +683,7 @@ win32_attach (unsigned long pid)
   DebugSetProcessKillOnExit = (winapi_DebugSetProcessKillOnExit *)
     GetProcAddress (kernel32, _T("DebugSetProcessKillOnExit"));
 
-  res = DebugActiveProcess (pid) ? 1 : 0;
+  res = DebugActiveProcess (pid);
 
   if (!res)
     error ("Attach to process failed.");
@@ -696,7 +696,7 @@ win32_attach (unsigned long pid)
 
   if (current_process_handle == NULL)
     {
-      res = 0;
+      res = FALSE;
       if (DebugActiveProcessStop != NULL)
 	DebugActiveProcessStop (current_process_id);
     }
@@ -707,7 +707,7 @@ win32_attach (unsigned long pid)
   if (kernel32 != NULL)
     FreeLibrary (kernel32);
 
-  return res? 0:-1;
+  return (res != FALSE) ? 0 : -1;
 }
 
 /* Handle OUTPUT_DEBUG_STRING_EVENT from child process.  */

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