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[pushed] Fix follow-exec regression / crash (Re: Possible regression on gdb.multi/multi-arch-exec.exp)
On 06/28/2018 01:09 PM, Pedro Alves wrote:
> I think the "gdb: Eliminate the 'stop_pc' global" patch
> (<https://sourceware.org/ml/gdb-patches/2018-06/msg00524.html>)
> will fix this, because it moves the stop_pc assignment until
> after ecs->event_thread is refreshed:
I've split that bit out of that patch and pushed it in now,
as below.
Thanks for reporting. I recall moving the stop_pc bit in the
multi-target branch a while ago after running into this crash, but when
splitting up the "Use thread_info and inferior pointers more throughout"
patch, I didn't realize that bit was needed as well.
>From ecdc3a72c89e43e0e13c5478723b4f70b3964e9f Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
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 <palves@redhat.com>
* infrun.c (handle_inferior_event_1) <TARGET_WAITKIND_EXECD>:
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 81fae4924a..417c563849 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2018-06-28 Pedro Alves <palves@redhat.com>
+
+ * infrun.c (handle_inferior_event_1) <TARGET_WAITKIND_EXECD>:
+ Moving fetching stop_pc until after ecs->event_thread is refreshed.
+
2018-06-28 Tom Tromey <tom@tromey.com>
* coffread.c (coff_symfile_finish): Update.
diff --git a/gdb/infrun.c b/gdb/infrun.c
index 9548f9cafd..4c732340d1 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);
--
2.14.4