Re: [RFA]: Modified Watchthreads Patch

[Jeff Johnston <jjohnstn@redhat.com>]

Daniel Jacobowitz wrote:
> On Fri, Dec 10, 2004 at 06:52:37PM -0500, Jeff Johnston wrote:
> 
>>Interesting results.  Applying my previous patch and just changing the 
>>FIXME code in dr_get_register and dr_set_register to use the standard:
>>
>>tid = TIDGET (inferior_ptid);
>>if (tid == 0)
>>  tid = PIDGET (inferior_ptid);
>>
>>allows watchthreads.exp to work for both x86 and x86_64.  For x86, I used 
>>an fc3 system with a 2.6.9-1.667smp kernel.  I had to use an RHEL3 2.4 
>>kernel for x86-64.
> 
> 
> As Eli says, there are some design issues with the rest of the x86
> watchpoint code that make me nervous about doing this.
> 
> 
>>The test sets two watchpoints that will be triggered once in the main 
>>thread and thereafter in two distinct threads.  The test verifies that each 
>>value is incremented as it should in the correct thread.  It makes sure 
>>there are no missing jumps.  I have witnessed multiple watchpoint events 
>>and thread creation events requiring processing at the same time (i.e. 
>>deferred events required) and it handles these correctly.
>>
>>I tried an experiment and broke in the thread function in one of the 
>>threads.  I then watched a variable that can only be triggered in a 
>>separate thread.  That also worked which was cool.
>>
>>As I observed before, the actual watchpoint only needs to be set on one 
>>thread and it will trigger in other threads.  I can send you the additional 
>>patch if you want to experiment with it.  I am still waiting for a machine 
>>with the latest RH kernel on it.  I'll let you know if that works the same.
> 
> 
> I'm glad to hear that it works for you.  However, since the kernel
> sources that I have here patently say that it shouldn't, we need to
> understand why.  Do the RHEL kernels have local changes to watchpoint
> support?  arch/i386/kernel/ptrace.c and arch/i386/kernel/process.c
> should have all the relevant bits.
>

There's no comments in the kernel patches (try not to laugh) and I don't know by 
looking at the patches whether any of them are affecting the watchpoint support. 
  I will ask one of the kernel folks here if they know of any local patch that 
might do this.  There are no changes to ptrace.c in the patches I have for fc3.

-- Jeff J.