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authorPedro Alves <palves@redhat.com>2015-04-10 13:08:32 +0100
committerPedro Alves <palves@redhat.com>2015-04-10 15:55:15 +0100
commitcb71640d030500888726d54a310c434a4d23b7b3 (patch)
tree3c8a06bd374efc6e69489e262fabb6cf0c6f36a1 /gdb
parentc79d856c88fbc58584d811c04b4812618aa6ac7b (diff)
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PPC64: Fix step-over-trips-on-watchpoint.exp with displaced stepping on
PPC64 currently fails this test like: FAIL: gdb.threads/step-over-trips-on-watchpoint.exp: displaced=on: no thread-specific bp: step: step FAIL: gdb.threads/step-over-trips-on-watchpoint.exp: displaced=on: no thread-specific bp: next: next FAIL: gdb.threads/step-over-trips-on-watchpoint.exp: displaced=on: no thread-specific bp: continue: continue (the program exited) FAIL: gdb.threads/step-over-trips-on-watchpoint.exp: displaced=on: with thread-specific bp: step: step FAIL: gdb.threads/step-over-trips-on-watchpoint.exp: displaced=on: with thread-specific bp: next: next FAIL: gdb.threads/step-over-trips-on-watchpoint.exp: displaced=on: with thread-specific bp: continue: continue (the program exited) The problem is that PPC is a non-continuable watchpoints architecture and the displaced stepping code isn't coping with that correctly. On such targets/architectures, a watchpoint traps _before_ the instruction executes/completes. On a watchpoint trap, the PC points at the instruction that triggers the watchpoint (side effects haven't happened yet). In order to move past the watchpoint, GDB needs to remove the watchpoint, single-step, and reinsert the watchpoint, just like when stepping past a breakpoint. The trouble is that if GDB is stepping over a breakpoint with displaced stepping, and the instruction under the breakpoint triggers a watchpoint, we get the watchpoint SIGTRAP, expecting a finished (hard or software) step trap. Even though the thread's PC hasn't advanced yet (must remove watchpoint for that), since we get a SIGTRAP, displaced_step_fixup thinks the single-step finished successfuly anyway, and calls gdbarch_displaced_step_fixup, which then adjusts the thread's registers incorrectly. The fix is to cancel the displaced step if we trip on a watchpoint. handle_inferior_event then processes the watchpoint event, and starts a new step-over, here: ... /* At this point, we are stopped at an instruction which has attempted to write to a piece of memory under control of a watchpoint. The instruction hasn't actually executed yet. If we were to evaluate the watchpoint expression now, we would get the old value, and therefore no change would seem to have occurred. ... ecs->event_thread->stepping_over_watchpoint = 1; keep_going (ecs); return; ... but this time, since we have a watchpoint to step over, watchpoints are removed from the target, so the step-over succeeds. The keep_going/resume changes are necessary because if we're stepping over a watchpoint, we need to remove it from the target - displaced stepping doesn't help, the copy of the instruction in the scratch pad reads/writes to the same addresses, thus triggers the watchpoint too... So without those changes we keep triggering the watchpoint forever, never making progress. With non-stop that means we'll need to pause all threads momentarily, which we can't today. We could avoid that by removing the watchpoint _only_ from the thread that is moving past the watchpoint, but GDB is not prepared for that today either. For remote targets, that would need new packets, so good to be able to step over it in-line as fallback anyway. gdb/ChangeLog: 2015-04-10 Pedro Alves <palves@redhat.com> * infrun.c (displaced_step_fixup): Switch to the event ptid earlier. If the thread stopped for a watchpoint and the target/arch has non-continuable watchpoints, cancel the displaced step. (resume): Don't start a displaced step if in-line step-over info is valid.
Diffstat (limited to 'gdb')
-rw-r--r--gdb/ChangeLog9
-rw-r--r--gdb/infrun.c25
2 files changed, 27 insertions, 7 deletions
diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 3de085a..73f8610 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,14 @@
2015-04-10 Pedro Alves <palves@redhat.com>
+ * infrun.c (displaced_step_fixup): Switch to the event ptid
+ earlier. If the thread stopped for a watchpoint and the
+ target/arch has non-continuable watchpoints, cancel the displaced
+ step.
+ (resume): Don't start a displaced step if in-line step-over info
+ is valid.
+
+2015-04-10 Pedro Alves <palves@redhat.com>
+
* infrun.c (displaced_step_in_progress): New function.
(do_target_resume): Advise target to report all signals if
displaced stepping.
diff --git a/gdb/infrun.c b/gdb/infrun.c
index c7567c6..c406183 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1810,13 +1810,17 @@ displaced_step_fixup (ptid_t event_ptid, enum gdb_signal signal)
displaced_step_restore (displaced, displaced->step_ptid);
+ /* Fixup may need to read memory/registers. Switch to the thread
+ that we're fixing up. Also, target_stopped_by_watchpoint checks
+ the current thread. */
+ switch_to_thread (event_ptid);
+
/* Did the instruction complete successfully? */
- if (signal == GDB_SIGNAL_TRAP)
+ if (signal == GDB_SIGNAL_TRAP
+ && !(target_stopped_by_watchpoint ()
+ && (gdbarch_have_nonsteppable_watchpoint (displaced->step_gdbarch)
+ || target_have_steppable_watchpoint)))
{
- /* Fixup may need to read memory/registers. Switch to the
- thread that we're fixing up. */
- switch_to_thread (event_ptid);
-
/* Fix up the resulting state. */
gdbarch_displaced_step_fixup (displaced->step_gdbarch,
displaced->step_closure,
@@ -2247,6 +2251,7 @@ resume (enum gdb_signal sig)
step software breakpoint. */
if (use_displaced_stepping (gdbarch)
&& tp->control.trap_expected
+ && !step_over_info_valid_p ()
&& sig == GDB_SIGNAL_0
&& !current_inferior ()->waiting_for_vfork_done)
{
@@ -2392,7 +2397,8 @@ resume (enum gdb_signal sig)
if (debug_displaced
&& use_displaced_stepping (gdbarch)
- && tp->control.trap_expected)
+ && tp->control.trap_expected
+ && !step_over_info_valid_p ())
{
struct regcache *resume_regcache = get_thread_regcache (tp->ptid);
struct gdbarch *resume_gdbarch = get_regcache_arch (resume_regcache);
@@ -6271,7 +6277,12 @@ keep_going (struct execution_control_state *ecs)
remove_wps = (ecs->event_thread->stepping_over_watchpoint
&& !target_have_steppable_watchpoint);
- if (remove_bp && !use_displaced_stepping (get_regcache_arch (regcache)))
+ /* We can't use displaced stepping if we need to step past a
+ watchpoint. The instruction copied to the scratch pad would
+ still trigger the watchpoint. */
+ if (remove_bp
+ && (remove_wps
+ || !use_displaced_stepping (get_regcache_arch (regcache))))
{
set_step_over_info (get_regcache_aspace (regcache),
regcache_read_pc (regcache), remove_wps);