PR 8507 - Remote watchpoint limit really large

[Mark Kettenis]

> From: Pedro Alves <pedro@codesourcery.com>
> Date: Mon, 29 Dec 2008 05:25:11 +0000
> 
> PR 8507 is about this command:
> 
>  (gdb) help show remote hardware-watchpoint-limit
>  Show the maximum number of target hardware watchpoints.
>  Specify a negative limit for unlimited.
> 
> And the fact that a negative value (default is -1), shows
> through as a large positive value, which is somewhat confusing:
> 
>  (gdb) show remote hardware-watchpoint-limit 
>  The maximum number of target hardware watchpoints is 4294967295.
> 
> Notice that the "show" help explicitly mentioned "Specify a negative
> limit for unlimited.".
> 
> This patch fixes it to show:
> 
>  (gdb) set remote hardware-watchpoint-limit -1
>  (gdb) show remote hardware-watchpoint-limit
>  The maximum number of target hardware watchpoints is unlimited.
> 
> There's no current enum var_types for this integer usage, where
> 0 really means zero, and negatives mean unlimited, so I've added one.

Hmm, I'm not sure I like the name.  How about var_zuinteger, for
zeroable unsigned Integer?

Interesting enough, the existing usage of var_zinteger in alpha-tdep.c
and mips-tdep.c looks like it should really be var_zuinteger too.  I
bet there are more cases.

I'm also not sure your implementation will actually work.  Especially
the statement:

> +	      *(int *) c->var = UINT_MAX;

looks very suspicious to me.  I suspect you are having problems
converting the variables set by this command from 'int' to 'unsigned
int'.  I actually think it would make sense to treat var_uinteger and
var_zuinteger variables as 'int' ans set them to INT_MAX to mean
unlimited.  I don't think the loss of range is a big loss.  For all
practical purposes INT_MAX is just as much infinty as UINT_MAX.

This would probably fix a few bugs as well, since eventually you're
going to compare these to signed integers anyway, and having your
"unsigned" integers in the range [0, INT_MAX] prevents a lot of
accidents from happening there.  (Do you fully understand the C rules
for integer type promotion?).

Mark