80d82c1964
This crash is observable by debugging a threaded program on LynxOS.
On the GDB side, this is what we would see:
% gdb q
(gdb) target remote machine:4444
(gdb) break q.adb:6
(gdb) cont
[gdb hits breakpoint]
(gdb) cont
Remote connection closed <<<--- expected: [Inferior 1 (Remote target) exited normally]
On the gdbserver side, which was launched as usual:
% gdbserver --once :4444 q
Segmentation fault (core dumped)
Ooops!
The problem happens while GDB is trying to handle the thread termination
event of the thread that hit the breakpoint. It started happening after
the following change was made:
commit 96e7a1eb6d
Date: Fri Oct 16 11:08:38 2015 -0400
Subject: gdbserver: Reset current_thread when the thread is removed.
Reset current_thread and make sure 'remove_process' is used
after all associated threads have been removed first.
More precisely:
. GDBserver receives the execution-resume order;
. lynx-low resumes it succesfully, and then relies on lynx_wait_1
to wait for the next event;
. We quickly receive one, which lynx_wait_1 analyzes to be
a "thread exit" event, and therefore does...
case SIGTHREADEXIT:
remove_thread (find_thread_ptid (new_ptid));
lynx_continue (new_ptid);
goto retry;
=> remove_thread causes current_thread to be set to NULL...
(that's the recent change mentioned above)
=> ... which causes problems during lynx_continue, because
it calls lynx_resume, which calls regcache_invalidate,
which unfortunately assumes that CURRENT_THREAD is not NULL:
void
regcache_invalidate (void)
{
/* Only update the threads of the current process. */
SEGV!--> int pid = ptid_get_pid (current_thread->entry.id);
find_inferior (&all_threads, regcache_invalidate_one, &pid);
}
Since the problem at hand is caused by trying to figure out which
inferior to reset the regcache for, and since lynx_resume actually
had that info, this patch fixes the problem by introducing a new
routine called regcache_invalidate_pid, which invalidates the cache
of the given pid; and then modifies lynx_resume use that new routine
rather than relying on regcache_invalidate to invalidate the regcache
of the expected inferior.
gdb/gdbserver/ChangeLog:
* regcache.h (regcache_invalidate_pid): Add declaration.
* regcache.c (regcache_invalidate_pid): New function, extracted
from regcache_invalidate.
(regcache_invalidate): Reimplement using regcache_invalidate_pid.
Add trivial documentation comment.
* lynx-low.c: Use regcache_invalidate_pid instead of
regcache_invalidate.
130 lines
4.2 KiB
C
130 lines
4.2 KiB
C
/* Register support routines for the remote server for GDB.
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Copyright (C) 2001-2015 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef REGCACHE_H
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#define REGCACHE_H
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#include "common-regcache.h"
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struct thread_info;
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struct target_desc;
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/* The register exists, it has a value, but we don't know what it is.
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Used when inspecting traceframes. */
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#define REG_UNAVAILABLE 0
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/* We know the register's value (and we have it cached). */
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#define REG_VALID 1
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/* The data for the register cache. Note that we have one per
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inferior; this is primarily for simplicity, as the performance
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benefit is minimal. */
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struct regcache
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{
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/* The regcache's target description. */
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const struct target_desc *tdesc;
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/* Whether the REGISTERS buffer's contents are valid. If false, we
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haven't fetched the registers from the target yet. Not that this
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register cache is _not_ pass-through, unlike GDB's. Note that
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"valid" here is unrelated to whether the registers are available
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in a traceframe. For that, check REGISTER_STATUS below. */
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int registers_valid;
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int registers_owned;
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unsigned char *registers;
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#ifndef IN_PROCESS_AGENT
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/* One of REG_UNAVAILBLE or REG_VALID. */
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unsigned char *register_status;
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#endif
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};
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struct regcache *init_register_cache (struct regcache *regcache,
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const struct target_desc *tdesc,
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unsigned char *regbuf);
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void regcache_cpy (struct regcache *dst, struct regcache *src);
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/* Create a new register cache for INFERIOR. */
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struct regcache *new_register_cache (const struct target_desc *tdesc);
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struct regcache *get_thread_regcache (struct thread_info *thread, int fetch);
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/* Release all memory associated with the register cache for INFERIOR. */
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void free_register_cache (struct regcache *regcache);
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/* Invalidate cached registers for one thread. */
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void regcache_invalidate_thread (struct thread_info *);
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/* Invalidate cached registers for all threads of the given process. */
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void regcache_invalidate_pid (int pid);
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/* Invalidate cached registers for all threads of the current
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process. */
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void regcache_invalidate (void);
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/* Invalidate and release the register cache of all threads of the
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current process. */
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void regcache_release (void);
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/* Convert all registers to a string in the currently specified remote
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format. */
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void registers_to_string (struct regcache *regcache, char *buf);
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/* Convert a string to register values and fill our register cache. */
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void registers_from_string (struct regcache *regcache, char *buf);
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/* For regcache_read_pc see common/common-regcache.h. */
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void regcache_write_pc (struct regcache *regcache, CORE_ADDR pc);
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/* Return a pointer to the description of register ``n''. */
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struct reg *find_register_by_number (const struct target_desc *tdesc, int n);
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int register_cache_size (const struct target_desc *tdesc);
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int register_size (const struct target_desc *tdesc, int n);
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int find_regno (const struct target_desc *tdesc, const char *name);
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void supply_register (struct regcache *regcache, int n, const void *buf);
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void supply_register_zeroed (struct regcache *regcache, int n);
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void supply_register_by_name (struct regcache *regcache,
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const char *name, const void *buf);
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void supply_regblock (struct regcache *regcache, const void *buf);
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void collect_register (struct regcache *regcache, int n, void *buf);
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void collect_register_as_string (struct regcache *regcache, int n, char *buf);
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void collect_register_by_name (struct regcache *regcache,
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const char *name, void *buf);
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#endif /* REGCACHE_H */
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