From ecdc3a72c89e43e0e13c5478723b4f70b3964e9f Mon Sep 17 00:00:00 2001 From: Pedro Alves Date: Thu, 28 Jun 2018 16:57:18 +0100 Subject: [PATCH] Fix follow-exec regression / crash After commit 00431a78b28f ("Use thread_info and inferior pointers more throughout"), following an exec can result in gdb crashing. On some systems, this is visible with gdb.multi/multi-arch-exec.exp and gdb.base/foll-exec-mode.exp. E.g.: $ make check TESTS="gdb.multi/multi-arch-exec.exp gdb.base/foll-exec-mode.exp" [snip] FAIL: gdb.multi/multi-arch-exec.exp: first_arch=1: selected_thread=1: follow_exec_mode=new: continue across exec that changes architecture (GDB internal error) ERROR: : spawn id exp10 not open while executing Running multi-arch-exec under Valgrind we easily spot the problem: process 16305 is executing new program: ..../gdb.multi/multi-arch-exec/1-multi-arch-exec-hello [New inferior 2 (process 0)] [New process 16305] ==16129== Invalid read of size 8 ==16129== at 0x7FA14D: get_thread_regcache(thread_info*) (regcache.c:399) ==16129== by 0x75E54B: handle_inferior_event_1(execution_control_state*) (infrun.c:5292) ==16129== by 0x75E82D: handle_inferior_event(execution_control_state*) (infrun.c:5382) ==16129== by 0x75BC6A: fetch_inferior_event(void*) (infrun.c:3918) ==16129== by 0x748DA3: inferior_event_handler(inferior_event_type, void*) (inf-loop.c:43) ==16129== by 0x464B5D: handle_target_event(int, void*) (linux-nat.c:4359) ==16129== by 0x7047E0: handle_file_event(file_handler*, int) (event-loop.c:733) ==16129== by 0x704D83: gdb_wait_for_event(int) (event-loop.c:859) ==16129== by 0x703BF6: gdb_do_one_event() (event-loop.c:322) ==16129== by 0x703CA2: start_event_loop() (event-loop.c:371) ==16129== by 0x791D95: captured_command_loop() (main.c:330) ==16129== by 0x79311C: captured_main(void*) (main.c:1157) ==16129== Address 0x15a5bad0 is 32 bytes inside a block of size 600 free'd ==16129== at 0x4C2E1E8: operator delete(void*) (vg_replace_malloc.c:576) ==16129== by 0x8A15D0: delete_thread_1(thread_info*, bool) (thread.c:465) ==16129== by 0x8A15FA: delete_thread(thread_info*) (thread.c:476) ==16129== by 0x8A0D43: add_thread_silent(ptid_t) (thread.c:291) ==16129== by 0x8A0DF0: add_thread_with_info(ptid_t, private_thread_info*) (thread.c:317) ==16129== by 0x8A0E79: add_thread(ptid_t) (thread.c:331) ==16129== by 0x75764C: follow_exec(ptid_t, char*) (infrun.c:1233) ==16129== by 0x75E534: handle_inferior_event_1(execution_control_state*) (infrun.c:5290) ==16129== by 0x75E82D: handle_inferior_event(execution_control_state*) (infrun.c:5382) ==16129== by 0x75BC6A: fetch_inferior_event(void*) (infrun.c:3918) ==16129== by 0x748DA3: inferior_event_handler(inferior_event_type, void*) (inf-loop.c:43) ==16129== by 0x464B5D: handle_target_event(int, void*) (linux-nat.c:4359) The problem is that handle_inferior_event_1 is reading the stop_pc off of a thread that was deleted by follow_exec. Before commit 00431a78b28f, we didn't crash because we were passing down a ptid to get_thread_regcache instead of ecs->event_thread. Fix this by simply moving the stop_pc reading until after ecs->event_thread is refreshed. gdb/ChangeLog: 2018-06-28 Pedro Alves * infrun.c (handle_inferior_event_1) : Moving fetching stop_pc until after ecs->event_thread is refreshed. --- gdb/ChangeLog | 5 +++++ gdb/infrun.c | 4 ++-- 2 files changed, 7 insertions(+), 2 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 81fae4924a5..417c563849a 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,8 @@ +2018-06-28 Pedro Alves + + * infrun.c (handle_inferior_event_1) : + Moving fetching stop_pc until after ecs->event_thread is refreshed. + 2018-06-28 Tom Tromey * coffread.c (coff_symfile_finish): Update. diff --git a/gdb/infrun.c b/gdb/infrun.c index 9548f9cafdb..4c732340d1e 100644 --- a/gdb/infrun.c +++ b/gdb/infrun.c @@ -5289,13 +5289,13 @@ Cannot fill $_exitsignal with the correct signal number.\n")); stop. */ follow_exec (inferior_ptid, ecs->ws.value.execd_pathname); - stop_pc = regcache_read_pc (get_thread_regcache (ecs->event_thread)); - /* In follow_exec we may have deleted the original thread and created a new one. Make sure that the event thread is the execd thread for that case (this is a nop otherwise). */ ecs->event_thread = inferior_thread (); + stop_pc = regcache_read_pc (get_thread_regcache (ecs->event_thread)); + ecs->event_thread->control.stop_bpstat = bpstat_stop_status (get_current_regcache ()->aspace (), stop_pc, ecs->event_thread, &ecs->ws); -- 2.30.2