Re: Your change to can_use_hardware_watchpoint breaks hw wp

[hjl@varesearch.com (H.J. Lu)]

> 
> 
> > 	* breakpoint.c (can_use_hardware_watchpoint): Call
> > 	TARGET_REGION_OK_FOR_HW_WATCHPOINT; if it returns zero,
> > 	return zero immediately.
> > 
> > I can no longer set hardware watchpoint like
> > 
> > int foo [20];
> > 
> > (gdb) watch foo[1];
> > 
> > on x86.
> 
> As far as I can see, this is another incarnation of a bug in GDB
> whereby GDB wants to watch the entire array/structure when you only
> need to watch one array element or one struct member.  See my message

I knew this one.

> to gdb-patches on 15 Aug with the Subject "Watching a struct member"
> and Jim Blandy's reply on 16 Aug.
> 
> So the problem is not the above change, it is simply another bug that
> was previously hiding behind the code in can_use_hardware_watchpoint.

I have a modified gdb. I use a kludge to watch the struct member.
Could you please tell me what bug your patch tried to fix?

> 
> > Do you have a patch to get it to work again?
> 
> The code that evaluates expressions is very complicated, and I haven't
> yet figured out how to fix it.  Perhaps someone who knows more about
> that could suggest a patch.
> 
> For now, I only have a work-around: 
> 
>  (gdb) p &foo[2]
>  $1 = (int *) 0x9880
>  (gdb) watch *(int *)0x9880
>  Hardware watchpoint 1: *(int *) 39040
> 

I don't like this work around. BTW, if you use Linux, you can try
my modified gdb at

ftp://ftp.valinux.com/pub/support/hjl/gdb

to see if it works for you. I also have a patch for gdb snapshot
which

1. Adds linuxthreads support for alpha and ppc.
2. Changes the hardware watchpoint such that I can watch array
element and struct member among other things.


-- 
H.J. Lu (hjl@gnu.org)