Re: [PATCH v13] gdb: Add source-tracking breakpoints feature

[Andrew Burgess <aburgess@redhat.com>]

Alexandra Hájková <ahajkova@redhat.com> writes:

> When we rerun the executable after changing its source files,
> GDB would re-set all previously set breakpoints. The
> breakpoints set to the function names would remain at their initial
> locations. But the breakpoints which used filename:line notation would
> be silently shifted following the source code changes.
>
> To address this, GDB now optionally captures a small window of source
> code lines around each breakpoint set with filename:line notation,
> when it is first set. When the binary is reloaded, GDB detects the BFD
> change and tries to locate the same source context in the new file,
> and if successful, re-sets the breakpoint to the matched source code
> line.
>
> The breakpoint_source structure stores captured source code lines
> around a breakpoint location, along with a reference to the BFD
> that was current when the source was captured.
>
> When source tracking is enabled (via 'set breakpoint source-tracking
> enabled on'), GDB captures 3 lines of source context
> (BREAKPOINT_SRC_CTX_LINES) along with the current BFD when a
> breakpoint is first set.  On executable reload (detected by comparing
> BFDs), it searches within a 12-line window
> (BREAKPOINT_SRC_CTX_LINES * BREAKPOINT_SRC_SEARCH_MULTIPLIER) for
> the best match and adjusts the breakpoint location if needed.
>
> If source tracking is disabled after breakpoints have been tracked,
> all existing source tracking information is discarded and a message
> is printed.
>
> Tests added:
>   gdb.base/adjust_breakpoint.exp
>   gdb.base/adjust_breakpoint-missing-source.exp
>   gdb.base/source-tracking-inline.exp
>   gdb.base/test_source_tracking.exp
>
> adjust_breakpoint.exp covers four scenarios:
>   - adjust the breakpoint when lines are deleted
>   - adjust the breakpoint when lines are inserted
>   - the tracked line disappears entirely
>   - verify the tracking can be disabled
>
> adjust_breakpoint-missing-source.exp covers the edge case where source
> files are unavailable, verifying GDB falls back to non-tracking breakpoints.
>
> source-tracking-inline.exp covers source tracking with inline functions.
>
> test_source_tracking.exp verifies that source context is correctly captured
> when the breakpoint is on the last line of the file.
>
> Add maintenance command to print tracked source code.
> Add documentation for the new source-tracking breakpoints feature.
>
> Limitations of the current implementation:
>
> Source tracking is not enabled for pending breakpoints that become
> non-pending.  When a breakpoint is created pending (e.g. with 'set
> breakpoint pending on'), source context is not captured at creation
> time since no symtab is available yet.  When the breakpoint later
> resolves to a location, re_set_default() only updates existing tracked
> breakpoints and does not initiate tracking for newly resolved ones.
> This could be fixed in the future by initiating source tracking in
> re_set_default() when a breakpoint transitions from pending to
> non-pending.
>
> Source tracking for ranged breakpoints is not currently supported.
> Ranged breakpoints have a start and end location spec, and tracking
> both independently raises questions about whether to preserve the
> range length or track each end separately.  For now, ranged
> breakpoints will never be source-tracked.
>
> Reviewed-By: Eli Zaretskii <eliz@gnu.org>

In case you've not merged this yet, I agree with Kevin that we should
get this merged and iterate from there.  I think what you have is
looking pretty good now.

Thanks for all your work on this.

Approved-By: Andrew Burgess <aburgess@redhat.com>

Thanks,
Andrew