Re: Tentative: add -location option to clear command

[Giles Atkinson <gatk at btinternet dot com>]

I did not see any responses to the message below.
If there is something more I should do for this patch to be considered,
can someone please tell me what it is.

Thanks,

Giles

On 20 Feb 2016, at 19:17, Giles Atkinson wrote:

> Greetings.
> 
> This patch adds a variation of the "clear" command, "clear -location",
> so that (some) watchpoints can be removed by expression.  The idea is
> to support setting watchpoints in dynamically-allocated memory,
> removing them automatically when the memory is released.
> Something like this:
> 
> # Break on malloc()d memory initialisation.
> break new_stuff:init
> commands
>  watch -location new->foo[0]
>  commands
>    printf "Item %d next %p\n", it->count, it->next
>    bt
>    continue
>  end
>  continue
> end
> #
> # Break just before free().
> break free_stuff:release
> commands
>  clear -location old->foo[0]
>  continue
> end
> 
> The delete command will not work here without an external mechanism to
> associate the watchpoint number with the memory address.
> 
> Some background to this is in the recent thread
> "Dynamic watchpoints in dynamic memory" on the gdb list.
> 
> The change works by pulling out bits of the watch and clear commands
> into new functions, and re-using them.  No real understanding of gdb
> internals was needed, so there may be some subtle errors.
> In making parse_expression_for_watchpoint(), I removed what looked like
> redundant stripping of whitespace from the expression.
> 
> In its current form, the change appears to pass the tests as well as
> the original.  (I get some variation with repeated runs of "make check".)
> The results for changes named "watch*" and "break*" seem identical.
> 
> If the change can be accepted in principle, I will add tests, and
> documention changes.  There is also a potential extension to other watchpoints
> (set without -location).  The clear command would only remove watchpoints
> after failing to match any breakpoints, and would probably select watchpoints
> to be removed by matching the frame and parsed expression.
> 
> Diff is relative to 7.10.1.
> 
> Thanks,
> 
> Giles
> <patch.gz>