[patch] Multi-architecture debugging regression (Re: performance of multithreading gets gradually worse under gdb)

["Ulrich Weigand" <uweigand at de dot ibm dot com>]

Pedro Alves wrote:

> 2011-02-04  Pedro Alves  <pedro@codesourcery.com>
> 
> 	gdb/
> 	* regcache.c (registers_changed_ptid): Don't explictly always
> 	clear `current_regcache'.  Only clear current_thread_ptid and
> 	current_thread_arch when PTID matches.  Only reinit the frame
> 	cache if PTID matches the current inferior_ptid.  Move alloca(0)
> 	call to ...
> 	(registers_changed): ... here.

It seems this patch broke multi-architecture debugging on Cell/B.E. since
the cached thread architecture is sometimes not invalidated when it should
be.  This happens when resume is called with a PTID that refers to all
threads of a process.

The problem is that your patch specifically handles PTIDs that refer to
one particular thread, and also handles a wildcard PTID that refers to
all threads of all processes.  But it does not handle PTIDs that refer
to all threads of one single process.

I think the code should simply use ptid_match here (as is already done
elsewhere, even in this same function).  This fixes the problem on
Cell/B.E. for me ...

Tested on powerpc-linux (Cell/B.E.).
Does this look OK to you?

Bye,
Ulrich


ChangeLog:

	* regcache.c (registers_changed_ptid): Invalidate thread architecture
	and frame caches if PTID refers to all threads of a process.


Index: gdb/regcache.c
===================================================================
RCS file: /cvs/src/src/gdb/regcache.c,v
retrieving revision 1.194
diff -u -p -r1.194 regcache.c
--- gdb/regcache.c	11 Oct 2011 18:35:25 -0000	1.194
+++ gdb/regcache.c	24 Oct 2011 11:02:46 -0000
@@ -548,7 +548,6 @@ void
 registers_changed_ptid (ptid_t ptid)
 {
   struct regcache_list *list, **list_link;
-  int wildcard = ptid_equal (ptid, minus_one_ptid);
 
   list = current_regcache;
   list_link = &current_regcache;
@@ -569,13 +568,13 @@ registers_changed_ptid (ptid_t ptid)
       list = *list_link;
     }
 
-  if (wildcard || ptid_equal (ptid, current_thread_ptid))
+  if (ptid_match (current_thread_ptid, ptid))
     {
       current_thread_ptid = null_ptid;
       current_thread_arch = NULL;
     }
 
-  if (wildcard || ptid_equal (ptid, inferior_ptid))
+  if (ptid_match (inferior_ptid, ptid))
     {
       /* We just deleted the regcache of the current thread.  Need to
 	 forget about any frames we have cached, too.  */

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com