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028a46039a
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.
255 lines
5.4 KiB
C++
255 lines
5.4 KiB
C++
/* Inferior process information for the remote server for GDB.
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Copyright (C) 2002-2020 Free Software Foundation, Inc.
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Contributed by MontaVista Software.
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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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#include "server.h"
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#include "gdbsupport/common-inferior.h"
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#include "gdbthread.h"
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#include "dll.h"
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std::list<process_info *> all_processes;
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std::list<thread_info *> all_threads;
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struct thread_info *current_thread;
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/* The current working directory used to start the inferior. */
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static const char *current_inferior_cwd = NULL;
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struct thread_info *
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add_thread (ptid_t thread_id, void *target_data)
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{
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struct thread_info *new_thread = XCNEW (struct thread_info);
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new_thread->id = thread_id;
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new_thread->last_resume_kind = resume_continue;
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new_thread->last_status.kind = TARGET_WAITKIND_IGNORE;
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all_threads.push_back (new_thread);
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if (current_thread == NULL)
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current_thread = new_thread;
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new_thread->target_data = target_data;
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return new_thread;
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}
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/* See gdbthread.h. */
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struct thread_info *
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get_first_thread (void)
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{
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if (!all_threads.empty ())
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return all_threads.front ();
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else
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return NULL;
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}
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struct thread_info *
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find_thread_ptid (ptid_t ptid)
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{
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return find_thread ([&] (thread_info *thread) {
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return thread->id == ptid;
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});
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}
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/* Find a thread associated with the given PROCESS, or NULL if no
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such thread exists. */
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static struct thread_info *
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find_thread_process (const struct process_info *const process)
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{
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return find_any_thread_of_pid (process->pid);
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}
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/* See gdbthread.h. */
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struct thread_info *
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find_any_thread_of_pid (int pid)
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{
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return find_thread (pid, [] (thread_info *thread) {
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return true;
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});
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}
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static void
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free_one_thread (thread_info *thread)
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{
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free_register_cache (thread_regcache_data (thread));
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free (thread);
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}
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void
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remove_thread (struct thread_info *thread)
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{
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if (thread->btrace != NULL)
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target_disable_btrace (thread->btrace);
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discard_queued_stop_replies (ptid_of (thread));
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all_threads.remove (thread);
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free_one_thread (thread);
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if (current_thread == thread)
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current_thread = NULL;
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}
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void *
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thread_target_data (struct thread_info *thread)
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{
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return thread->target_data;
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}
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struct regcache *
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thread_regcache_data (struct thread_info *thread)
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{
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return thread->regcache_data;
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}
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void
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set_thread_regcache_data (struct thread_info *thread, struct regcache *data)
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{
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thread->regcache_data = data;
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}
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void
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clear_inferiors (void)
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{
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for_each_thread (free_one_thread);
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all_threads.clear ();
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clear_dlls ();
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current_thread = NULL;
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}
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struct process_info *
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add_process (int pid, int attached)
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{
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process_info *process = new process_info (pid, attached);
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all_processes.push_back (process);
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return process;
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}
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/* Remove a process from the common process list and free the memory
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allocated for it.
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The caller is responsible for freeing private data first. */
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void
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remove_process (struct process_info *process)
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{
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clear_symbol_cache (&process->symbol_cache);
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free_all_breakpoints (process);
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gdb_assert (find_thread_process (process) == NULL);
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all_processes.remove (process);
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delete process;
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}
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process_info *
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find_process_pid (int pid)
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{
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return find_process ([&] (process_info *process) {
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return process->pid == pid;
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});
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}
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/* Get the first process in the process list, or NULL if the list is empty. */
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process_info *
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get_first_process (void)
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{
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if (!all_processes.empty ())
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return all_processes.front ();
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else
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return NULL;
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}
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/* Return non-zero if there are any inferiors that we have created
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(as opposed to attached-to). */
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int
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have_started_inferiors_p (void)
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{
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return find_process ([] (process_info *process) {
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return !process->attached;
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}) != NULL;
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}
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/* Return non-zero if there are any inferiors that we have attached to. */
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int
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have_attached_inferiors_p (void)
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{
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return find_process ([] (process_info *process) {
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return process->attached;
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}) != NULL;
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}
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struct process_info *
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get_thread_process (const struct thread_info *thread)
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{
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return find_process_pid (thread->id.pid ());
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}
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struct process_info *
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current_process (void)
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{
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gdb_assert (current_thread != NULL);
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return get_thread_process (current_thread);
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}
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/* See gdbsupport/common-gdbthread.h. */
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void
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switch_to_thread (process_stratum_target *ops, ptid_t ptid)
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{
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gdb_assert (ptid != minus_one_ptid);
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current_thread = find_thread_ptid (ptid);
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}
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/* See inferiors.h. */
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void
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switch_to_process (process_info *proc)
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{
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int pid = pid_of (proc);
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current_thread = find_any_thread_of_pid (pid);
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}
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/* See gdbsupport/common-inferior.h. */
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const char *
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get_inferior_cwd ()
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{
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return current_inferior_cwd;
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}
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/* See gdbsupport/common-inferior.h. */
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void
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set_inferior_cwd (const char *cwd)
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{
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xfree ((void *) current_inferior_cwd);
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if (cwd != NULL)
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current_inferior_cwd = xstrdup (cwd);
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else
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current_inferior_cwd = NULL;
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}
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