[RFC] Python Finish Breakpoints

[Kevin Pouget]

On Wed, Jan 4, 2012 at 6:12 PM, Ulrich Weigand <uweigand@de.ibm.com> wrote:
> Tom Tromey wrote:
>
>> We have support for "finish", and other operations in the presence of
>> exceptions.  Search for _Unwind_DebugHook (in breakpoint.c and infrun.c).
>> This code only works if you are using a new-enough version of GCC and
>> have debuginfo for libgcc (but once the stap probe patches are in, you
>> will no longer need debuginfo).
>
> Ah, I see -- that's what I was missing.  Yes, this looks like the
> way to handle this situation ...

Hello,

I would like to discuss this patch which intends to fix and improve
the handling for c++ exceptions with the Python FinishBreakpoint.

Based on what I understood of the existing mechanisms which handle
longjmps and and exception, I extended the "momentary breakpoints"
with a "nostop" flag. Indeed, their initial behavior/goal was to stop
unconditionally the execution, whereas I just wanted to receive a
notification when the relevant code location was hit (namely
infrun.c::BPSTAT_WHAT_CLEAR_LONGJMP_RESUME). The nostop flag is
propagated step by step (bp by bp) from the exception throw to its
catchpoint, where I check if the FinishBreakpoint have ran out of
their scope.

As Tom mentioned, c++ debug info are needed for this machinery to work
(otherwise, FinishBreakpoint will fail the same way GDB fails: stop at
the beginning of the catch(), never stop, ...) -- I used xfail in the
testsuite to refer to this situation, I'm not sure that's correct).

I've also fixed a bug which triggered twice the out_of_scope
notification in case of inferior exit (observer_attach_normal_stop and
observer_attach_inferior_exit are both triggered when the inferior
exits)

(This is just a preliminary patch, I'll would like to prepare some
more tests with exceptions and longjmps)

Tested with no regression on f15/X86_64

( these always fail on my system:
 Running PATH/git/gdb/gdb/testsuite/gdb.base/longjmp.exp ...
 FAIL: gdb.base/longjmp.exp: next over longjmp(1)
 FAIL: gdb.base/longjmp.exp: next over call_longjmp (2)
 FAIL: gdb.base/longjmp.exp: next over patt3
)

Thanks for your comments,

Kevin

--

2012-01-09  Kevin Pouget <kevin.pouget@st.com>

	* breakpoint.c (momentary_nostop_breakpoint_ops): New variable.
	(bpstat_what): Set field retval.is_nostop when necessary.
	(set_longjmp_breakpoint): Add parameter nostop and create nostop
	momentary breakpoint ops if necessary.
	(set_momentary_breakpoint): Likewise.
	(set_momentary_breakpoint_at_pc): Likewise.
	(momentary_breakpoint_is_nostop): New function.
	(until_break_command): Call set_momentary_breakpoint and
	set_longjmp_breakpoint with nostop not set.
	(momentary_stop_bkpt_check_status): Rename from
	momentary_bkpt_check_status.
	(momentary_bkpt_check_status): Remove.
	(momentary_nostop_bkpt_check_status): New function.
	(initialize_breakpoint_ops): Initialize
	momentary_breakpoint_ops.check_status to
	momentary_stop_bkpt_check_status, initialize
	momentary_nostop_breakpoint_ops.
	* breakpoint.h (struct bpstat_what): New field: is_nostop.
	(set_momentary_breakpoint): New parameter: nostop.
	(set_momentary_breakpoint_at_pc): Liklewise.
	(set_longjmp_breakpoint): Likewise.
	(momentary_breakpoint_is_nostop): New prototype.
	* arm-linux-tdep.c (arm_linux_copy_svc): Add nostop parameter to
        set_momentary_breakpoint call.
	* elfread.c: (elf_gnu_ifunc_resolver_stop): Likewise
	* infcall.c (call_function_by_hand): Likewise.
	* infcmd.c: (finish_forward): Likewise, add nostop parameter to
        set_longjmp_breakpoint call.
	(step_1): Add nostop parameter to set_longjmp_breakpoint call.
	(until_next_command): Likewise.
	* infrun.c: Include python/python.h.
	(insert_step_resume_breakpoint_at_sal_1): Add nostop parameter to
        set_momentary_breakpoint call.
	(insert_longjmp_resume_breakpoint): Add nostop parameter to prototype.
	Add nostop parameter to set_momentary_breakpoint_at_pc call.
	(insert_exception_resume_breakpoint): Likewise.
	(check_exception_resume): Add nostop parameter to prototype. Add nostop
        parameter to insert_exception_resume_breakpoint call.
	(process_event_stop_test): Set and use nostop to prevent GDB from
	stopping the execution, trigger gdbpy_bpfinish_handle_exception when
	necessary.
	* python/py-finishbreakpoint.c (bpfinishpy_init): Call
	set_longjmp_breakpoint.
	(bpfinishpy_detect_out_scope): Renamed from
	bpfinishpy_detect_out_scope_cb. Cleaned up. Add inc_current parameter.
	(bpfinishpy_detect_out_scope_cb): Removed.
	(bpfinishpy_detect_out_scope_bp_cb): New function.
	(bpfinishpy_detect_out_scope_exception_cb): New function.
	(bpfinishpy_handle_stop): Update with function name
	bpfinishpy_detect_out_scope_bp_cb.
	(bpfinishpy_handle_exit): Removed.
	(gdbpy_bpfinish_handle_exception): New function.
	(gdbpy_initialize_finishbreakpoints): Remove call to
	bpfinishpy_handle_exit.
	* python/python.c (gdbpy_bpfinish_handle_exception): New function.
	* python/python.h (gdbpy_bpfinish_handle_exception): New prototype.

testsuite/
	* gdb.python/py-finish-breakpoint2.exp: Strengthen the exception tests.
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