Re: [PATCH] Watchpoints + conditionals problem

[Vladimir Prus <ghost@cs.msu.su>]

Luis Machado wrote:

> Hi folks,
> 
> There is an unexpected behavior when we use software watchpoints (also
> hardware in some cases) attached to conditional expressions, such as:
> "watch x if x == <number>", considering "x" a simple "int" type
> variable.
> 
> When that watchpoint goes out of scope, it's marked for disposal at the
> next stop as obviously there's no way to evaluate the expression "x"
> anymore. But GDB is still trying to evaluate the conditional part of the
> watchpoint, even though "x" is out of scope already. Thus, GDB is
> failing to find correct frame information and ends up in an internal
> error.

I've run into same problem yesterday.

> I've tracked down this issue and it seems we need to check for the
> disposition field of the watchpoint whenever we check for the return
> value of a conditional expression.
> 
> Attached is a simple patch of what i have in mind to fix this issue. The
> testcase can be a simple "Hello world"-like binary with a few variables
> to watch.
> 
> Any other ideas?

I guess ideally we need to:

1. Don't check condition at all if bs->stop is already 0.
2. Immediately delete watchpoint, don't bother with del_at_next_stop

But for now, your approach is probably fine -- can anybody approve it?

- Volodya