Message ID | 1446130862-12824-3-git-send-email-yao.qi@linaro.org |
---|---|
State | New, archived |
Headers |
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Commit Message
Yao Qi
Oct. 29, 2015, 3:01 p.m. UTC
Hi, Some tests in gdb.threads/multiple-step-overs.exp fail on arm target when the displaced stepping on, but they pass when displaced stepping is off. FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: step: step FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: next: next FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: continue: continue FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: signal thr1: continue to sigusr1_handler when displaced stepping is on, Sending packet: $vCont;c#a8...infrun: infrun_async(1)^M <--- [1] infrun: prepare_to_wait^M infrun: target_wait (-1.0.0, status) =^M infrun: -1.0.0 [Thread 0],^M infrun: status->kind = ignore^M infrun: TARGET_WAITKIND_IGNORE^M infrun: prepare_to_wait^M Packet received: T05swbreak:;0b:f8faffbe;0d:409ee7b6;0f:d0880000;thread:p635.636;core:0;^M infrun: target_wait (-1.0.0, status) =^M infrun: 1589.1590.0 [Thread 1590],^M infrun: status->kind = stopped, signal = GDB_SIGNAL_TRAP^M infrun: TARGET_WAITKIND_STOPPED^M infrun: stop_pc = 0x88d0^M infrun: context switch^M infrun: Switching context from Thread 1591 to Thread 1590^ GDB resumes the whole process (all threads) rather than the specific thread it wants to single step (as shown in [1]). That is wrong. when displaced stepping is off, GDB behaves correctly, only resumes the specific thread (as shown in [2]). Sending packet: $vCont;c:p611.613#b2...infrun: infrun_async(1)^M <-- [2] infrun: prepare_to_wait^M infrun: target_wait (-1.0.0, status) =^M infrun: -1.0.0 [Thread 0],^M infrun: status->kind = ignore^M infrun: TARGET_WAITKIND_IGNORE^M infrun: prepare_to_wait^M Packet received: T05swbreak:;0b:f8faffbe;0d:409e67b6;0f:48880000;thread:p611.613;core:1;^M infrun: target_wait (-1.0.0, status) =^M infrun: 1553.1555.0 [Thread 1555],^M infrun: status->kind = stopped, signal = GDB_SIGNAL_TRAP^M infrun: TARGET_WAITKIND_STOPPED^M infrun: clear_step_over_info^M infrun: stop_pc = 0x8848 The current logic in GDB on deciding the set of threads to resume is: /* Decide the set of threads to ask the target to resume. */ if ((step || thread_has_single_step_breakpoints_set (tp)) && tp->control.trap_expected) { /* We're allowing a thread to run past a breakpoint it has hit, by single-stepping the thread with the breakpoint removed. In which case, we need to single-step only this thread, and keep others stopped, as they can miss this breakpoint if allowed to run. */ resume_ptid = inferior_ptid; } else resume_ptid = internal_resume_ptid (user_step); it doesn't handle the case correctly that GDB continue (instead of single step) the thread for displaced stepping. I also update the comment below to reflect the code. I remove the "with the breakpoint removed" comment, because GDB doesn't remove breakpoints in displaced stepping, so we don't have to worry that other threads may miss the breakpoint. Patch is regression tested on both x86_64-linux and arm-linux. gdb: 2015-10-28 Yao Qi <yao.qi@linaro.org> * infrun.c (resume): Check displaced_step_in_progress_thread when deciding the set of threads to resume. --- gdb/infrun.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-)
Comments
On 10/29/2015 03:01 PM, Yao Qi wrote: > Hi, > Some tests in gdb.threads/multiple-step-overs.exp fail on arm target > when the displaced stepping on, but they pass when displaced stepping > is off. > > FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: step: step > FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: next: next > FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: continue: continue > FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: signal thr1: continue to sigusr1_handler > > when displaced stepping is on, > > Sending packet: $vCont;c#a8...infrun: infrun_async(1)^M <--- [1] > infrun: prepare_to_wait^M > infrun: target_wait (-1.0.0, status) =^M > infrun: -1.0.0 [Thread 0],^M > infrun: status->kind = ignore^M > infrun: TARGET_WAITKIND_IGNORE^M > infrun: prepare_to_wait^M > Packet received: T05swbreak:;0b:f8faffbe;0d:409ee7b6;0f:d0880000;thread:p635.636;core:0;^M > infrun: target_wait (-1.0.0, status) =^M > infrun: 1589.1590.0 [Thread 1590],^M > infrun: status->kind = stopped, signal = GDB_SIGNAL_TRAP^M > infrun: TARGET_WAITKIND_STOPPED^M > infrun: stop_pc = 0x88d0^M > infrun: context switch^M > infrun: Switching context from Thread 1591 to Thread 1590^ > > GDB resumes the whole process (all threads) rather than the specific > thread it wants to single step (as shown in [1]). That is wrong. (I understand this, but I think it'd make it clearer to explicitly state _why_ that is wrong.) > > when displaced stepping is off, GDB behaves correctly, only resumes > the specific thread (as shown in [2]). > > Sending packet: $vCont;c:p611.613#b2...infrun: infrun_async(1)^M <-- [2] > infrun: prepare_to_wait^M > infrun: target_wait (-1.0.0, status) =^M > infrun: -1.0.0 [Thread 0],^M > infrun: status->kind = ignore^M > infrun: TARGET_WAITKIND_IGNORE^M > infrun: prepare_to_wait^M > Packet received: T05swbreak:;0b:f8faffbe;0d:409e67b6;0f:48880000;thread:p611.613;core:1;^M > infrun: target_wait (-1.0.0, status) =^M > infrun: 1553.1555.0 [Thread 1555],^M > infrun: status->kind = stopped, signal = GDB_SIGNAL_TRAP^M > infrun: TARGET_WAITKIND_STOPPED^M > infrun: clear_step_over_info^M > infrun: stop_pc = 0x8848 > > The current logic in GDB on deciding the set of threads to resume is: > > /* Decide the set of threads to ask the target to resume. */ > if ((step || thread_has_single_step_breakpoints_set (tp)) > && tp->control.trap_expected) > { > /* We're allowing a thread to run past a breakpoint it has > hit, by single-stepping the thread with the breakpoint > removed. In which case, we need to single-step only this > thread, and keep others stopped, as they can miss this > breakpoint if allowed to run. */ > resume_ptid = inferior_ptid; > } > else > resume_ptid = internal_resume_ptid (user_step); > > it doesn't handle the case correctly that GDB continue (instead of > single step) the thread for displaced stepping. > > I also update the comment below to reflect the code. I remove the > "with the breakpoint removed" comment, because GDB doesn't remove > breakpoints in displaced stepping, so we don't have to worry that > other threads may miss the breakpoint. > > Patch is regression tested on both x86_64-linux and arm-linux. > > gdb: > > 2015-10-28 Yao Qi <yao.qi@linaro.org> > > * infrun.c (resume): Check displaced_step_in_progress_thread > when deciding the set of threads to resume. > --- > gdb/infrun.c | 8 +++----- > 1 file changed, 3 insertions(+), 5 deletions(-) > > diff --git a/gdb/infrun.c b/gdb/infrun.c > index 0265d35..c619b61 100644 > --- a/gdb/infrun.c > +++ b/gdb/infrun.c > @@ -2631,14 +2631,12 @@ resume (enum gdb_signal sig) > gdb_assert (!(thread_has_single_step_breakpoints_set (tp) && step)); > > /* Decide the set of threads to ask the target to resume. */ > - if ((step || thread_has_single_step_breakpoints_set (tp)) > + if ((step || thread_has_single_step_breakpoints_set (tp) > + || displaced_step_in_progress_thread (tp->ptid)) > && tp->control.trap_expected) I wonder, can't we just remove the "step" check, like: if (tp->control.trap_expected) { > { > /* We're allowing a thread to run past a breakpoint it has > - hit, by single-stepping the thread with the breakpoint > - removed. In which case, we need to single-step only this > - thread, and keep others stopped, as they can miss this > - breakpoint if allowed to run. */ > + hit, by single-stepping (in-line or out-of-line) the thread. */ The change looks good to me, though I think we should clarify the comment here. How about: /* We're allowing a thread to run past a breakpoint it has hit, either by single-stepping the thread with the breakpoint removed, or by displaced stepping, with the breakpoint inserted. In the former case, we need to single-step only this thread, and keep others stopped, as they can miss this breakpoint if allowed to run. That's not really a problem for displaced stepping, but, we still keep other threads stopped, in case another thread is also stopped for a breakpoint waiting for its turn in the displaced stepping queue. */ I think we could optimize this by checking for thread_step_over_chain_next (tp) == NULL, because if no other thread is waiting for a step-over, then we could resume all threads, but that's maybe not worth it. > resume_ptid = inferior_ptid; > } > else Thanks, Pedro Alves
diff --git a/gdb/infrun.c b/gdb/infrun.c index 0265d35..c619b61 100644 --- a/gdb/infrun.c +++ b/gdb/infrun.c @@ -2631,14 +2631,12 @@ resume (enum gdb_signal sig) gdb_assert (!(thread_has_single_step_breakpoints_set (tp) && step)); /* Decide the set of threads to ask the target to resume. */ - if ((step || thread_has_single_step_breakpoints_set (tp)) + if ((step || thread_has_single_step_breakpoints_set (tp) + || displaced_step_in_progress_thread (tp->ptid)) && tp->control.trap_expected) { /* We're allowing a thread to run past a breakpoint it has - hit, by single-stepping the thread with the breakpoint - removed. In which case, we need to single-step only this - thread, and keep others stopped, as they can miss this - breakpoint if allowed to run. */ + hit, by single-stepping (in-line or out-of-line) the thread. */ resume_ptid = inferior_ptid; } else