Put single-step breakpoints on the bp_location chain
authorPedro Alves <palves@redhat.com>
Wed, 15 Oct 2014 19:18:31 +0000 (20:18 +0100)
committerPedro Alves <palves@redhat.com>
Wed, 15 Oct 2014 19:18:31 +0000 (20:18 +0100)
commit7c16b83e0521a007e4d86fc30e334b41b01668b4
tree4b2b8fbdaf92625694dfa3b894e7b74665dd718a
parent0cbcdb96eaba80fe8e94ccc2b6f1f382a467a04e
Put single-step breakpoints on the bp_location chain

This patch makes single-step breakpoints "real" breakpoints on the
global location list.

There are several benefits to this:

- It removes the currently limitation that only 2 single-step
  breakpoints can be inserted.  See an example here of a discussion
  around a case that wants more than 2, possibly unbounded:

  https://sourceware.org/ml/gdb-patches/2014-03/msg00663.html

- makes software single-step work on read-only code regions.

  The logic to convert a software breakpoint to a hardware breakpoint
  if the memory map says the breakpoint address is in read only memory
  is in insert_bp_location.  Because software single-step breakpoints
  bypass all that go and straight to target_insert_breakpoint, we
  can't software single-step over read only memory.  This patch
  removes that limitation, and adds a test that makes sure that works,
  by forcing a code region to read-only with "mem LOW HIGH ro" and
  then stepping through that.

- Fixes PR breakpoints/9649

  This is an assertion failure in insert_single_step_breakpoint in
  breakpoint.c, because we may leave stale single-step breakpoints
  behind on error.

  The tests for stepping through read-only regions exercise the root
  cause of the bug, which is that we leave single-step breakpoints
  behind if we fail to insert any single-step breakpoint.  Deleting
  the single-step breakpoints in resume_cleanups,
  delete_just_stopped_threads_infrun_breakpoints, and
  fetch_inferior_event fixes this.  Without that, we'd no longer hit
  the assertion, as that code is deleted, but we'd instead run into
  errors/warnings trying to insert/remove the stale breakpoints on
  next resume.

- Paves the way to have multiple threads software single-stepping at
  the same time, leaving update_global_location_list to worry about
  duplicate locations.

- Makes the moribund location machinery aware of software single-step
  breakpoints, paving the way to enable software single-step on
  non-stop, instead of forcing serialized displaced stepping for all
  single steps.

- It's generaly cleaner.

  We no longer have to play games with single-step breakpoints
  inserted at the same address as regular breakpoints, like we
  recently had to do for 7.8.  See this discussion:

  https://sourceware.org/ml/gdb-patches/2014-06/msg00052.html.

Tested on x86_64 Fedora 20, on top of my 'single-step breakpoints on
x86' series.

gdb/
2014-10-15  Pedro Alves  <palves@redhat.com>

PR breakpoints/9649
* breakpoint.c (single_step_breakpoints, single_step_gdbarch):
Delete array globals.
(single_step_breakpoints): New global.
(breakpoint_xfer_memory): Remove special handling for single-step
breakpoints.
(update_breakpoints_after_exec): Delete bp_single_step
breakpoints.
(detach_breakpoints): Remove special handling for single-step
breakpoints.
(breakpoint_init_inferior): Delete bp_single_step breakpoints.
(bpstat_stop_status): Add comment.
(bpstat_what, bptype_string, print_one_breakpoint_location)
(adjust_breakpoint_address, init_bp_location): Handle
bp_single_step.
(new_single_step_breakpoint): New function.
(set_momentary_breakpoint, bkpt_remove_location): Remove special
handling for single-step breakpoints.
(insert_single_step_breakpoint, single_step_breakpoints_inserted)
(remove_single_step_breakpoints, cancel_single_step_breakpoints):
Rewrite.
(detach_single_step_breakpoints, find_single_step_breakpoint):
Delete functions.
(breakpoint_has_location_inserted_here): New function.
(single_step_breakpoint_inserted_here_p): Rewrite.
* breakpoint.h: Remove FIXME.
(enum bptype) <bp_single_step>: New enum value.
(insert_single_step_breakpoint): Update comment.
* infrun.c (resume_cleanups)
(delete_step_thread_step_resume_breakpoint): Remove single-step
breakpoints.
(fetch_inferior_event): Install a cleanup that removes infrun
breakpoints.
(switch_back_to_stepped_thread) <expect thread advanced also>:
Clear step-over info.

gdb/testsuite/
2014-10-15  Pedro Alves  <palves@redhat.com>

PR breakpoints/9649
* gdb.base/breakpoint-in-ro-region.c (main): Add more instructions.
* gdb.base/breakpoint-in-ro-region.exp
(probe_target_hardware_step): New procedure.
(top level): Probe hardware stepping and hardware breakpoint
support.  Test stepping through a read-only region, with both
"breakpoint auto-hw" on and off and both "always-inserted" on and
off.
gdb/ChangeLog
gdb/breakpoint.c
gdb/breakpoint.h
gdb/infrun.c
gdb/testsuite/ChangeLog
gdb/testsuite/gdb.base/breakpoint-in-ro-region.c
gdb/testsuite/gdb.base/breakpoint-in-ro-region.exp