The function create_exception_master_breakpoint in gdb/breakpoint.c attempts
to set a master exception breakpoint in each objfile. It tries this using
a libgcc/unwind probe, and if that fails then using the
_Unwind_DebugHook symbol:
...
for (objfile *objfile : current_program_space->objfiles ())
{
/* Try using probes. */
if (/* successful */)
continue;
/* Try using _Unwind_DebugHook */
}
...
The preference scheme works ok both if the objfile has debug info, and if it's
stripped.
But it doesn't work when the objfile has a .gnu_debuglink to a .debug file
(and the .debug file is present). What happens is that:
- we first encounter objfile libgcc.debug
- we try using probes, and this fails
- so we try _Unwind_DebugHook, which succeeds
- next we encounter objfile libgcc
- we try using probes, and this succeeds.
So, we end up with a master exception breakpoint in both libgcc (using probes)
and libgcc.debug (using _Unwind_DebugHook).
This eventually causes:
...
(gdb) PASS: gdb.cp/nextoverthrow.exp: post-check - next over a throw 3
next^M
src/gdb/infrun.c:6384: internal-error: \
void process_event_stop_test(execution_control_state*): \
Assertion `ecs->event_thread->control.exception_resume_breakpoint != NULL' \
failed.^M
A problem internal to GDB has been detected,^M
further debugging may prove unreliable.^M
Quit this debugging session? (y or n) FAIL: gdb.cp/nextoverthrow.exp: next
past catch (GDB internal error)
...
To trigger this internal-error, we need to use gcc-10 or later to compile the
test-case, such that it contains the fix for gcc PR97774 - "Incorrect line
info for try/catch".
Fix this by only trying to install the master exception breakpoint in
libgcc.debug using the _Unwind_DebugHook method, if the install using probes
in libgcc failed.
Tested on x86_64-linux.
gdb/ChangeLog:
2021-01-08 Tom de Vries <tdevries@suse.de>
PR gdb/26881
* breakpoint.c (create_exception_master_breakpoint_probe)
(create_exception_master_breakpoint_hook): Factor out
of ...
(create_exception_master_breakpoint): ... here. Only try to install
the master exception breakpoint in objfile.debug using the
_Unwind_DebugHook method, if the install using probes in objfile
failed.
On rare occasions, we run into this ERROR/UNRESOLVED on gdb-10-branch:
...
(gdb) PASS: gdb.multi/multi-target.exp: continue: non-stop=on: inferior 2
Remote debugging from host ::1, port 34088^M
Process outputs/gdb.multi/multi-target/multi-target created; pid = 8649^M
monitor exit^M
(gdb) Killing process(es): 8649^M
ERROR: GDB process no longer exists
GDB process exited with wait status 8627 exp14 0 0 CHILDKILLED SIGABRT SIGABRT
UNRESOLVED: gdb.multi/multi-target.exp: continue: non-stop=on: inferior 5
...
A trigger patch makes the crash happen all the time:
...
diff --git a/gdb/remote.c b/gdb/remote.c
index 71f814efb365..53ff8b63a1dc 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -14161,14 +14161,12 @@ remote_target::is_async_p ()
will be able to delay notifying the client of an event until the
point where an entire packet has been received. */
-static serial_event_ftype remote_async_serial_handler;
-
static void
remote_async_serial_handler (struct serial *scb, void *context)
{
- /* Don't propogate error information up to the client. Instead let
- the client find out about the error by querying the target. */
- inferior_event_handler (INF_REG_EVENT);
+ remote_state *rs = (remote_state *) context;
+
+ mark_async_event_handler (rs->remote_async_inferior_event_token);
}
static void
...
And using -fsanitizer=address we can get a more elaborate error message:
...
==7196==ERROR: AddressSanitizer: heap-use-after-free on address \
0x6170000bf258 at pc 0x000001481755 bp 0x7fff05b20840 sp 0x7fff05b20838
READ of size 8 at 0x6170000bf258 thread T0
#0 0x1481754 in std::_Hashtable<gdbarch*, std::pair<gdbarch* const,
remote_arch_state>, std::allocator<std::pair<gdbarch* const,
remote_arch_state> >, std::__detail::_Select1st, std::equal_to<gdbarch*>,
std::hash<gdbarch*>, std::__detail::_Mod_range_hashing,
std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy,
std::__detail::_Hashtable_traits<false, false, true>
>::_M_bucket_index(unsigned long) const
/usr/include/c++/11/bits/hashtable.h:719
#1 0x147c8ab in std::_Hashtable<gdbarch*, std::pair<gdbarch* const,
remote_arch_state>, std::allocator<std::pair<gdbarch* const,
remote_arch_state> >, std::__detail::_Select1st, std::equal_to<gdbarch*>,
std::hash<gdbarch*>, std::__detail::_Mod_range_hashing,
std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy,
std::__detail::_Hashtable_traits<false, false, true> >::find(gdbarch*
const&) /usr/include/c++/11/bits/hashtable.h:1500
#2 0x147852c in std::unordered_map<gdbarch*, remote_arch_state,
std::hash<gdbarch*>, std::equal_to<gdbarch*>,
std::allocator<std::pair<gdbarch* const, remote_arch_state> >
>::find(gdbarch* const&) /usr/include/c++/11/bits/unordered_map.h:869
#3 0x14306db in remote_state::get_remote_arch_state(gdbarch*)
src/gdb/remote.c:1203
#4 0x14309dc in remote_target::get_remote_state() src/gdb/remote.c:1232
#5 0x1470c08 in remote_async_inferior_event_handler src/gdb/remote.c:14169
#6 0xaa9f6b in check_async_event_handlers() src/gdb/async-event.c:295
#7 0x1e93ab4 in gdb_do_one_event() src/gdbsupport/event-loop.cc:194
#8 0x118f5f9 in start_event_loop src/gdb/main.c:356
#9 0x118f8ed in captured_command_loop src/gdb/main.c:416
#10 0x1192d6a in captured_main src/gdb/main.c:1253
#11 0x1192dfa in gdb_main(captured_main_args*) src/gdb/main.c:1268
#12 0x97b380 in main src/gdb/gdb.c:32
#13 0x7f550c211349 in __libc_start_main ../csu/libc-start.c:308
#14 0x97b199 in _start (build/gdb/gdb+0x97b199)
0x6170000bf258 is located 600 bytes inside of 648-byte region \
[0x6170000bf000,0x6170000bf288)
freed by thread T0 here:
#0 0x7f550f516a57 in operator delete(void*, unsigned long)
(/usr/lib64/libasan.so.6+0xaea57)
#1 0x148b1fe in extended_remote_target::~extended_remote_target()
src/gdb/remote.c:958
#2 0x143b483 in remote_target::close() src/gdb/remote.c:4074
#3 0x16cb90f in target_close(target_ops*) src/gdb/target.c:3230
#4 0x16a2635 in decref_target(target_ops*) src/gdb/target.c:557
#5 0x16a2abb in target_stack::unpush(target_ops*) src/gdb/target.c:645
#6 0x16d01ef in inferior::unpush_target(target_ops*)
src/gdb/inferior.h:356
#7 0x16a2877 in unpush_target(target_ops*) src/gdb/target.c:607
#8 0x16a2adf in unpush_target_and_assert src/gdb/target.c:655
#9 0x16a2c57 in pop_all_targets_at_and_above(strata) src/gdb/target.c:678
#10 0x1442749 in remote_unpush_target src/gdb/remote.c:5522
#11 0x1458c16 in remote_target::readchar(int) src/gdb/remote.c:9137
#12 0x145b25b in remote_target::getpkt_or_notif_sane_1(std::vector<char,
gdb::default_init_allocator<char, std::allocator<char> > >*, int, int,
int*) src/gdb/remote.c:9683
#13 0x145bc9a in remote_target::getpkt_sane(std::vector<char,
gdb::default_init_allocator<char, std::allocator<char> > >*, int)
src/gdb/remote.c:9790
#14 0x145b040 in remote_target::getpkt(std::vector<char,
gdb::default_init_allocator<char, std::allocator<char> > >*, int)
src/gdb/remote.c:9623
#15 0x145780b in remote_target::remote_read_bytes_1(unsigned long,
unsigned char*, unsigned long, int, unsigned long*) src/gdb/remote.c:8860
#16 0x145805e in remote_target::remote_read_bytes(unsigned long,
unsigned char*, unsigned long, int, unsigned long*) src/gdb/remote.c:8987
#17 0x146113a in remote_target::xfer_partial(target_object, char const*,
unsigned char*, unsigned char const*, unsigned long, unsigned long,
unsigned long*) src/gdb/remote.c:10987
#18 0x16a4004 in raw_memory_xfer_partial(target_ops*, unsigned char*,
unsigned char const*, unsigned long, long, unsigned long*)
src/gdb/target.c:918
#19 0x16a4fcf in target_xfer_partial(target_ops*, target_object, char
const*, unsigned char*, unsigned char const*, unsigned long, unsigned
long, unsigned long*) src/gdb/target.c:1156
#20 0x16a5d65 in target_read_partial src/gdb/target.c:1387
#21 0x16a5f19 in target_read(target_ops*, target_object, char const*,
unsigned char*, unsigned long, long) src/gdb/target.c:1427
#22 0x16a5666 in target_read_raw_memory(unsigned long, unsigned char*,
long) src/gdb/target.c:1260
#23 0xd22f2a in dcache_read_line src/gdb/dcache.c:336
#24 0xd232b7 in dcache_peek_byte src/gdb/dcache.c:403
#25 0xd23845 in dcache_read_memory_partial(target_ops*, dcache_struct*,
unsigned long, unsigned char*, unsigned long, unsigned long*) src/gdb/dcache.c:484
#26 0x16a47da in memory_xfer_partial_1 src/gdb/target.c:1041
#27 0x16a4a1e in memory_xfer_partial src/gdb/target.c:1084
#28 0x16a4f44 in target_xfer_partial(target_ops*, target_object,
char const*, unsigned char*, unsigned char const*, unsigned long,
unsigned long, unsigned long*) src/gdb/target.c:1141
#29 0x18203d4 in read_value_memory(value*, long, int, unsigned long,
unsigned char*, unsigned long) src/gdb/valops.c:956
previously allocated by thread T0 here:
#0 0x7f550f515c37 in operator new(unsigned long)
(/usr/lib64/libasan.so.6+0xadc37)
#1 0x14429f0 in remote_target::open_1(char const*, int, int)
src/gdb/remote.c:5562
#2 0x14405e6 in extended_remote_target::open(char const*, int)
src/gdb/remote.c:4907
#3 0x16a0f3c in open_target src/gdb/target.c:242
#4 0xc19ff5 in do_sfunc src/gdb/cli/cli-decode.c:111
#5 0xc221db in cmd_func(cmd_list_element*, char const*, int)
src/gdb/cli/cli-decode.c:2181
#6 0x16feda6 in execute_command(char const*, int) src/gdb/top.c:668
#7 0xee9dc9 in command_handler(char const*) src/gdb/event-top.c:588
#8 0xeea6a8 in command_line_handler(std::unique_ptr<char,
gdb::xfree_deleter<char> >&&) src/gdb/event-top.c:773
#9 0xee8a12 in gdb_rl_callback_handler src/gdb/event-top.c:219
#10 0x7f550f24aead in rl_callback_read_char
(/lib64/libreadline.so.7+0x31ead)
...
The problem is here in remote_async_inferior_event_handler:
...
static void
remote_async_inferior_event_handler (gdb_client_data data)
{
inferior_event_handler (INF_REG_EVENT);
remote_target *remote = (remote_target *) data;
remote_state *rs = remote->get_remote_state ();
...
The remote target (passed in the data argument) can be destroyed during the
call to inferior_event_handler. If so, the call to remote->get_remote_state
() is done using a dangling pointer.
Fix this by increasing the reference count on the remote target before calling
inferior_event_handler, such that it won't get destroyed until right before
returning from remote_async_inferior_event_handler.
Tested on x86_64-linux.
Intended for gdb-10-branch.
The problem has stopped reproducing with the trigger patch since master commit
79952e6963 "Make scoped_restore_current_thread's cdtors exception free
(RFC)". We could still apply this to master though.
gdb/ChangeLog:
2021-01-07 Pedro Alves <pedro@palves.net>
Simon Marchi <simon.marchi@polymtl.ca>
Tom de Vries <tdevries@suse.de>
PR remote/26614
* remote.c (remote_async_inferior_event_handler): Hold a strong
reference to the remote target while handling an event.
This commits the result of running gdb/copyright.py as per our Start
of New Year procedure...
gdb/ChangeLog
Update copyright year range in copyright header of all GDB files.
This commit adjusts GDB's copyright.py script, following two past changes:
- gdb/gdbserver/ being move to the toplevel directory;
- gdb/common/ being renamed to gdbsupport/.
gdb/ChangeLog:
* copyright.py (get_update_list): Add "gdbserver" and "gdbsupport"
to the list of directories to update.
(cherry picked from commit ff7e39b613)
gdb/doc/ChangeLog:
2020-12-26 Jeanne Rasata <jeanne@fsf.org>
* gdb.texinfo: Fix capitalization in many sections following CMS
style-guide rules, remove period at end of a few headings.
Copyright-paperwork-exempt: yes
