Re: [PATCH v5] [PR python/29603] Disable out-of-scope watchpoints

[Simon Marchi <simark@simark.ca>]

On 4/23/23 05:54, Johnson Sun wrote:
> Currently, when a local software watchpoint goes out of scope, GDB sets
> the watchpoint's disposition to `delete at next stop' and then normal
> stops (i.e., stop and wait for the next GDB command). When GDB normal
> stops, it automatically deletes the breakpoints with their disposition
> set to `delete at next stop'.
> 
> Suppose a Python script decides not to normal stop when a local
> software watchpoint goes out of scope, the watchpoint will not be
> automatically deleted even when its disposition is set to
> `delete at next stop'.
> 
> Since GDB single-steps the program and tests the watched expression
> after each instruction, not deleting the watchpoint causes the
> watchpoint to be hit many more times than it should, as reported in
> PR python/29603.
> 
> This was happening because the watchpoint is not deleted or disabled
> when going out of scope.
> 
> This commit fixes this issue by disabling the watchpoint when going out
> of scope. It also adds a test to ensure this feature isn't regressed in
> the future.
> 
> Calling `breakpoint_auto_delete' on all kinds of stops (in
> `fetch_inferior_event') seem to solve this issue, but is in fact
> inappropriate, since `breakpoint_auto_delete' goes over all breakpoints
> instead of just going through the bpstat chain (which only contains the
> breakpoints that were hit right now).
> 
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29603

Hi,

Hmm, re-testing the patch, it now just times out like this:

    (gdb) PASS: gdb.python/py-watchpoint.exp: check modified BP count
    continue
    Continuing.
    Watchpoint Hit: 1
    FAIL: gdb.python/py-watchpoint.exp: run until program stops (timeout)
    python print(bpt.n)

It basically hangs there.  Do you see this?

Simon