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f3770638ca
Both PRs are triggered by the same use case.
PR18214 is about software single-step targets. On those, the 'resume'
code that detects that we're stepping over a breakpoint and delivering
a signal at the same time:
/* Currently, our software single-step implementation leads to different
results than hardware single-stepping in one situation: when stepping
into delivering a signal which has an associated signal handler,
hardware single-step will stop at the first instruction of the handler,
while software single-step will simply skip execution of the handler.
...
Fortunately, we can at least fix this particular issue. We detect
here the case where we are about to deliver a signal while software
single-stepping with breakpoints removed. In this situation, we
revert the decisions to remove all breakpoints and insert single-
step breakpoints, and instead we install a step-resume breakpoint
at the current address, deliver the signal without stepping, and
once we arrive back at the step-resume breakpoint, actually step
over the breakpoint we originally wanted to step over. */
doesn't handle the case of _another_ thread also needing to step over
a breakpoint. Because the other thread is just resumed at the PC
where it had stopped and a breakpoint is still inserted there, the
thread immediately re-traps the same breakpoint. This test exercises
that. On software single-step targets, it fails like this:
KFAIL: gdb.threads/multiple-step-overs.exp: displaced=off: signal thr3: continue to sigusr1_handler
KFAIL: gdb.threads/multiple-step-overs.exp: displaced=off: signal thr2: continue to sigusr1_handler
gdb.log (simplified):
(gdb) continue
Continuing.
Breakpoint 4, child_function_2 (arg=0x0) at src/gdb/testsuite/gdb.threads/multiple-step-overs.c:66
66 callme (); /* set breakpoint thread 2 here */
(gdb) thread 3
(gdb) queue-signal SIGUSR1
(gdb) thread 1
[Switching to thread 1 (Thread 0x7ffff7fc1740 (LWP 24824))]
#0 main () at src/gdb/testsuite/gdb.threads/multiple-step-overs.c:106
106 wait_threads (); /* set wait-threads breakpoint here */
(gdb) break sigusr1_handler
Breakpoint 5 at 0x400837: file src/gdb/testsuite/gdb.threads/multiple-step-overs.c, line 31.
(gdb) continue
Continuing.
[Switching to Thread 0x7ffff7fc0700 (LWP 24828)]
Breakpoint 4, child_function_2 (arg=0x0) at src/gdb/testsuite/gdb.threads/multiple-step-overs.c:66
66 callme (); /* set breakpoint thread 2 here */
(gdb) KFAIL: gdb.threads/multiple-step-overs.exp: displaced=off: signal thr3: continue to sigusr1_handler
For good measure, I made the test try displaced stepping too. And
then I found it crashes GDB on x86-64 (a hardware step target), but
only when displaced stepping... :
KFAIL: gdb.threads/multiple-step-overs.exp: displaced=on: signal thr1: continue to sigusr1_handler (PRMS: gdb/18216)
KFAIL: gdb.threads/multiple-step-overs.exp: displaced=on: signal thr2: continue to sigusr1_handler (PRMS: gdb/18216)
KFAIL: gdb.threads/multiple-step-overs.exp: displaced=on: signal thr3: continue to sigusr1_handler (PRMS: gdb/18216)
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0x000000000062a83a in process_event_stop_test (ecs=0x7fff847eeee0) at src/gdb/infrun.c:4964
4964 if (sr_bp->loc->permanent
Setting up the environment for debugging gdb.
Breakpoint 1 at 0x79fcfc: file src/gdb/common/errors.c, line 54.
Breakpoint 2 at 0x50a26c: file src/gdb/cli/cli-cmds.c, line 217.
(top-gdb) p sr_bp
$1 = (struct breakpoint *) 0x0
(top-gdb) bt
#0 0x000000000062a83a in process_event_stop_test (ecs=0x7fff847eeee0) at src/gdb/infrun.c:4964
#1 0x000000000062a1af in handle_signal_stop (ecs=0x7fff847eeee0) at src/gdb/infrun.c:4715
#2 0x0000000000629097 in handle_inferior_event (ecs=0x7fff847eeee0) at src/gdb/infrun.c:4165
#3 0x0000000000627482 in fetch_inferior_event (client_data=0x0) at src/gdb/infrun.c:3298
#4 0x000000000064ad7b in inferior_event_handler (event_type=INF_REG_EVENT, client_data=0x0) at src/gdb/inf-loop.c:56
#5 0x00000000004c375f in handle_target_event (error=0, client_data=0x0) at src/gdb/linux-nat.c:4658
#6 0x0000000000648c47 in handle_file_event (file_ptr=0x2e0eaa0, ready_mask=1) at src/gdb/event-loop.c:658
The all-stop-non-stop series fixes this, but meanwhile, this augments
the multiple-step-overs.exp test to cover this, KFAILed.
gdb/testsuite/ChangeLog:
2015-04-08 Pedro Alves <palves@redhat.com>
PR gdb/18214
PR gdb/18216
* gdb.threads/multiple-step-overs.c (sigusr1_handler): New
function.
(main): Install it as SIGUSR1 handler.
* gdb.threads/multiple-step-overs.exp (setup): Remove 'prefix'
parameter. Always use "setup" as prefix. Toggle "set
displaced-stepping" off/on depending on global. Don't switch to
thread 1 here.
(top level): Add displaced stepping "off/on" test axis. Update
"setup" calls. Wrap each subtest with with_test_prefix. Test
continuing with a queued signal in each thread.
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