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On some systems, the gdb.multi/multi-target.exp testcase occasionally fails like so: Running src/gdb/testsuite/gdb.multi/multi-target.exp ... FAIL: gdb.multi/multi-target.exp: info-inferiors: multi_process=on: inferior 1: info connections FAIL: gdb.multi/multi-target.exp: info-inferiors: multi_process=on: inferior 1: info inferiors FAIL: gdb.multi/multi-target.exp: info-inferiors: multi_process=on: inferior 2: info connections FAIL: gdb.multi/multi-target.exp: info-inferiors: multi_process=on: inferior 2: info inferiors FAIL: gdb.multi/multi-target.exp: info-inferiors: multi_process=on: inferior 3: inferior 3 ... many more cascading fails. The problem starts when the testcase runs an inferior against GDBserver: (gdb) run Starting program: build/gdb/testsuite/outputs/gdb.multi/multi-target/multi-target Reading /lib64/ld-linux-x86-64.so.2 from remote target... warning: File transfers from remote targets can be slow. Use "set sysroot" to access files locally instead. Reading /lib64/ld-linux-x86-64.so.2 from remote target... Reading /lib64/ld-2.31.so from remote target... Reading /lib64/.debug/ld-2.31.so from remote target... Reading /usr/lib/debug//lib64/ld-2.31.so from remote target... Reading /usr/lib/debug/lib64//ld-2.31.so from remote target... Reading target:/usr/lib/debug/lib64//ld-2.31.so from remote target... Reading /lib/x86_64-linux-gnu/libpthread.so.0 from remote target... Reading /lib/x86_64-linux-gnu/libc.so.6 from remote target... Reading /lib/x86_64-linux-gnu/libc-2.31.so from remote target... Reading /lib/x86_64-linux-gnu/.debug/libc-2.31.so from remote target... Reading /usr/lib/debug//lib/x86_64-linux-gnu/libc-2.31.so from remote target... Reading /usr/lib/debug//lib/x86_64-linux-gnu/libc-2.31.so from remote target... Remote connection closed ... Note the "Remote connection closed" message. That means GDBserver exited abruptly. I traced it down to the fact that GDB fetches the thread list from GDBserver while the main thread of the process is still running. On my main system where I wrote the testcase, I have not observed the failure because it is slow enough that the thread stops before GDBserver fetches the thread list in the problem scenario which I'll describe below. With some --remote-debug logging from GDBserver side, we see the last packets before the connection closes: ... getpkt ("vCont;c"); [no ack sent] putpkt ("$OK#9a"); [noack mode] getpkt ("Tp10f9a.10f9a"); [no ack sent] putpkt ("$OK#9a"); [noack mode] getpkt ("Hgp0.0"); [no ack sent] putpkt ("$OK#9a"); [noack mode] getpkt ("qXfer:threads:read::0,1000"); [no ack sent] Note the vCont;c , which sets the program running, and then a qXfer:threads:read packet at the end. The problem happens when the thread list refresh (qXfer:threads:read) is sent just while the main thread is running and it still hasn't initialized its libpthread id internally. In that state, the main thread's lwp will remain with the thread_known flag clear. See in find_one_thread: /* If the new thread ID is zero, a final thread ID will be available later. Do not enable thread debugging yet. */ if (ti.ti_tid == 0) return 0; Now, back in server.cc, to handle the qXfer:threads:read, we reach handle_qxfer_threads -> handle_qxfer_threads_proper, and the latter then calls handle_qxfer_threads_worker for each known thread. In handle_qxfer_threads_worker, we call target_thread_handle. This ends up in thread_db_thread_handle, here: if (!lwp->thread_known && !find_one_thread (thread->id)) return false; Since the thread ID isn't known yet, we call find_one_thread. This calls into libthread_db.so, which accesses memory. Because the current thread is running, that fails and we throw an error, here: /* Get information about this thread. */ err = thread_db->td_ta_map_lwp2thr_p (thread_db->thread_agent, lwpid, &th); if (err != TD_OK) error ("Cannot get thread handle for LWP %d: %s", lwpid, thread_db_err_str (err)); The current design is that whenever GDB-facing packets/requests need to accesses memory, server.cc is supposed to prepare the target for the access. See gdb_read_memory / gdb_write_memory. This preparation means pausing threads if in non-stop mode (someday we could lift this requirement, but we will still need to pause to access registers or do other related ptrace accesses like PTRACE_GET_THREAD_AREA). Note that the multi-target.exp testcase forces "maint set target-non-stop on". So the fix here is to prepare the target to access memory when handling qXfer:threads:read too. gdbserver/ChangeLog: * inferiors.cc (switch_to_process): New, moved here from thread-db.cc, and made extern. * inferiors.h (switch_to_process): Declare. * server.cc: Include "gdbsupport/scoped_restore.h". (handle_qxfer_threads_proper): Now returns bool. Prepare to access memory around target calls. (handle_qxfer_threads): Handle errors. * thread-db.cc (switch_to_process): Moved to inferiors.cc.
151 lines
3.9 KiB
C++
151 lines
3.9 KiB
C++
/* Inferior process information for the remote server for GDB.
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Copyright (C) 1993-2020 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 GDBSERVER_INFERIORS_H
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#define GDBSERVER_INFERIORS_H
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#include "gdbsupport/gdb_vecs.h"
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#include <list>
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struct thread_info;
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struct regcache;
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struct target_desc;
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struct sym_cache;
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struct breakpoint;
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struct raw_breakpoint;
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struct fast_tracepoint_jump;
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struct process_info_private;
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struct process_info
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{
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process_info (int pid_, int attached_)
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: pid (pid_), attached (attached_)
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{}
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/* This process' pid. */
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int pid;
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/* Nonzero if this child process was attached rather than
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spawned. */
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int attached;
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/* True if GDB asked us to detach from this process, but we remained
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attached anyway. */
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int gdb_detached = 0;
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/* The symbol cache. */
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struct sym_cache *symbol_cache = NULL;
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/* The list of memory breakpoints. */
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struct breakpoint *breakpoints = NULL;
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/* The list of raw memory breakpoints. */
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struct raw_breakpoint *raw_breakpoints = NULL;
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/* The list of installed fast tracepoints. */
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struct fast_tracepoint_jump *fast_tracepoint_jumps = NULL;
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/* The list of syscalls to report, or just a single element, ANY_SYSCALL,
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for unfiltered syscall reporting. */
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std::vector<int> syscalls_to_catch;
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const struct target_desc *tdesc = NULL;
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/* Private target data. */
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struct process_info_private *priv = NULL;
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};
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/* Get the pid of PROC. */
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static inline int
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pid_of (const process_info *proc)
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{
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return proc->pid;
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}
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/* Return a pointer to the process that corresponds to the current
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thread (current_thread). It is an error to call this if there is
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no current thread selected. */
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struct process_info *current_process (void);
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struct process_info *get_thread_process (const struct thread_info *);
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extern std::list<process_info *> all_processes;
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/* Invoke FUNC for each process. */
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template <typename Func>
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static void
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for_each_process (Func func)
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{
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std::list<process_info *>::iterator next, cur = all_processes.begin ();
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while (cur != all_processes.end ())
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{
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next = cur;
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next++;
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func (*cur);
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cur = next;
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}
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}
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/* Find the first process for which FUNC returns true. Return NULL if no
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process satisfying FUNC is found. */
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template <typename Func>
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static process_info *
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find_process (Func func)
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{
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std::list<process_info *>::iterator next, cur = all_processes.begin ();
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while (cur != all_processes.end ())
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{
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next = cur;
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next++;
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if (func (*cur))
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return *cur;
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cur = next;
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}
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return NULL;
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}
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extern struct thread_info *current_thread;
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/* Return the first process in the processes list. */
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struct process_info *get_first_process (void);
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struct process_info *add_process (int pid, int attached);
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void remove_process (struct process_info *process);
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struct process_info *find_process_pid (int pid);
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int have_started_inferiors_p (void);
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int have_attached_inferiors_p (void);
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/* Switch to a thread of PROC. */
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void switch_to_process (process_info *proc);
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void clear_inferiors (void);
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void *thread_target_data (struct thread_info *);
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struct regcache *thread_regcache_data (struct thread_info *);
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void set_thread_regcache_data (struct thread_info *, struct regcache *);
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#endif /* GDBSERVER_INFERIORS_H */
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