From 27f9f649753b8c4bd4c40bde0f49d916c222a16a Mon Sep 17 00:00:00 2001 From: Simon Marchi Date: Fri, 14 Jan 2022 16:18:03 -0500 Subject: gdb: resume ongoing step after handling fork or vfork The test introduced by this patch would fail in this configuration, with the native-gdbserver or native-extended-gdbserver boards: FAIL: gdb.threads/next-fork-other-thread.exp: fork_func=fork: target-non-stop=auto: non-stop=off: displaced-stepping=auto: i=2: next to for loop The problem is that the step operation is forgotten when handling the fork/vfork. With "debug infrun" and "debug remote", it looks like this (some lines omitted for brevity). We do the next: [infrun] proceed: enter [infrun] proceed: addr=0xffffffffffffffff, signal=GDB_SIGNAL_DEFAULT [infrun] resume_1: step=1, signal=GDB_SIGNAL_0, trap_expected=0, current thread [4154304.4154304.0] at 0x5555555553bf [infrun] do_target_resume: resume_ptid=4154304.0.0, step=1, sig=GDB_SIGNAL_0 [remote] Sending packet: $vCont;r5555555553bf,5555555553c4:p3f63c0.3f63c0;c:p3f63c0.-1#cd [infrun] proceed: exit We then handle a fork event: [infrun] fetch_inferior_event: enter [remote] wait: enter [remote] Packet received: T05fork:p3f63ee.3f63ee;06:0100000000000000;07:b08e59f6ff7f0000;10:bf60e8f7ff7f0000;thread:p3f63c0.3f63c6;core:17; [remote] wait: exit [infrun] print_target_wait_results: target_wait (-1.0.0 [process -1], status) = [infrun] print_target_wait_results: 4154304.4154310.0 [Thread 4154304.4154310], [infrun] print_target_wait_results: status->kind = FORKED, child_ptid = 4154350.4154350.0 [infrun] handle_inferior_event: status->kind = FORKED, child_ptid = 4154350.4154350.0 [remote] Sending packet: $D;3f63ee#4b [infrun] resume_1: step=0, signal=GDB_SIGNAL_0, trap_expected=0, current thread [4154304.4154310.0] at 0x7ffff7e860bf [infrun] do_target_resume: resume_ptid=4154304.0.0, step=0, sig=GDB_SIGNAL_0 [remote] Sending packet: $vCont;c:p3f63c0.-1#73 [infrun] fetch_inferior_event: exit In the first snippet, we resume the stepping thread with the range-stepping (r) vCont command. But after handling the fork (detaching the fork child), we resumed the whole process freely. The stepping thread, which was paused by GDBserver while reporting the fork event, was therefore resumed freely, instead of confined to the addresses of the stepped line. Note that since this is a "next", it could be that we have entered a function, installed a step-resume breakpoint, and it's ok to continue freely the stepping thread, but that's not the case here. The two snippets shown above were next to each other in the logs. For the fork case, we can resume stepping right after handling the event. However, for the vfork case, where we are waiting for the external child process to exec or exit, we only resume the thread that called vfork, and keep the others stopped (see patch "gdb: fix handling of vfork by multi-threaded program" prior in this series). So we can't resume the stepping thread right now. Instead, do it after handling the vfork-done event. Change-Id: I92539c970397ce880110e039fe92b87480f816bd --- gdb/infrun.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) (limited to 'gdb/infrun.c') diff --git a/gdb/infrun.c b/gdb/infrun.c index 899b2ae..0b88eb8 100644 --- a/gdb/infrun.c +++ b/gdb/infrun.c @@ -5734,7 +5734,18 @@ handle_inferior_event (struct execution_control_state *ecs) ecs->ptid = inferior_ptid; if (should_resume) - keep_going (ecs); + { + /* Never call switch_back_to_stepped_thread if we are waiting for + vfork-done (waiting for an external vfork child to exec or + exit). We will resume only the vforking thread for the purpose + of collecting the vfork-done event, and we will restart any + step once the critical shared address space window is done. */ + if ((!follow_child + && detach_fork + && parent->inf->thread_waiting_for_vfork_done != nullptr) + || !switch_back_to_stepped_thread (ecs)) + keep_going (ecs); + } else stop_waiting (ecs); return; @@ -5754,9 +5765,13 @@ handle_inferior_event (struct execution_control_state *ecs) if (handle_stop_requested (ecs)) return; - /* This also takes care of reinserting breakpoints in the - previously locked inferior. */ - keep_going (ecs); + if (!switch_back_to_stepped_thread (ecs)) + { + gdb_assert (inferior_thread () == ecs->event_thread); + /* This also takes care of reinserting breakpoints in the + previously locked inferior. */ + keep_going (ecs); + } return; case TARGET_WAITKIND_EXECD: -- cgit v1.1