469 lines
17 KiB
C++
469 lines
17 KiB
C++
//===-- sanitizer_stoptheworld_linux_libcdep.cc ---------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// See sanitizer_stoptheworld.h for details.
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// This implementation was inspired by Markus Gutschke's linuxthreads.cc.
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//
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//===----------------------------------------------------------------------===//
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#include "sanitizer_platform.h"
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#if SANITIZER_LINUX && (defined(__x86_64__) || defined(__mips__))
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#include "sanitizer_stoptheworld.h"
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#include "sanitizer_platform_limits_posix.h"
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#include <errno.h>
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#include <sched.h> // for CLONE_* definitions
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#include <stddef.h>
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#include <sys/prctl.h> // for PR_* definitions
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#include <sys/ptrace.h> // for PTRACE_* definitions
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#include <sys/types.h> // for pid_t
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#if SANITIZER_ANDROID && defined(__arm__)
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# include <linux/user.h> // for pt_regs
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#else
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# include <sys/user.h> // for user_regs_struct
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#endif
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#include <sys/wait.h> // for signal-related stuff
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#ifdef sa_handler
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# undef sa_handler
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#endif
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#ifdef sa_sigaction
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# undef sa_sigaction
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#endif
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#include "sanitizer_common.h"
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#include "sanitizer_flags.h"
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#include "sanitizer_libc.h"
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#include "sanitizer_linux.h"
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#include "sanitizer_mutex.h"
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#include "sanitizer_placement_new.h"
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// This module works by spawning a Linux task which then attaches to every
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// thread in the caller process with ptrace. This suspends the threads, and
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// PTRACE_GETREGS can then be used to obtain their register state. The callback
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// supplied to StopTheWorld() is run in the tracer task while the threads are
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// suspended.
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// The tracer task must be placed in a different thread group for ptrace to
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// work, so it cannot be spawned as a pthread. Instead, we use the low-level
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// clone() interface (we want to share the address space with the caller
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// process, so we prefer clone() over fork()).
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//
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// We don't use any libc functions, relying instead on direct syscalls. There
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// are two reasons for this:
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// 1. calling a library function while threads are suspended could cause a
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// deadlock, if one of the treads happens to be holding a libc lock;
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// 2. it's generally not safe to call libc functions from the tracer task,
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// because clone() does not set up a thread-local storage for it. Any
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// thread-local variables used by libc will be shared between the tracer task
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// and the thread which spawned it.
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COMPILER_CHECK(sizeof(SuspendedThreadID) == sizeof(pid_t));
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namespace __sanitizer {
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// This class handles thread suspending/unsuspending in the tracer thread.
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class ThreadSuspender {
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public:
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explicit ThreadSuspender(pid_t pid)
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: pid_(pid) {
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CHECK_GE(pid, 0);
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}
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bool SuspendAllThreads();
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void ResumeAllThreads();
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void KillAllThreads();
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SuspendedThreadsList &suspended_threads_list() {
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return suspended_threads_list_;
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}
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private:
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SuspendedThreadsList suspended_threads_list_;
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pid_t pid_;
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bool SuspendThread(SuspendedThreadID thread_id);
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};
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bool ThreadSuspender::SuspendThread(SuspendedThreadID tid) {
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// Are we already attached to this thread?
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// Currently this check takes linear time, however the number of threads is
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// usually small.
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if (suspended_threads_list_.Contains(tid))
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return false;
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int pterrno;
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if (internal_iserror(internal_ptrace(PTRACE_ATTACH, tid, NULL, NULL),
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&pterrno)) {
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// Either the thread is dead, or something prevented us from attaching.
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// Log this event and move on.
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VReport(1, "Could not attach to thread %d (errno %d).\n", tid, pterrno);
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return false;
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} else {
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VReport(1, "Attached to thread %d.\n", tid);
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// The thread is not guaranteed to stop before ptrace returns, so we must
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// wait on it. Note: if the thread receives a signal concurrently,
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// we can get notification about the signal before notification about stop.
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// In such case we need to forward the signal to the thread, otherwise
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// the signal will be missed (as we do PTRACE_DETACH with arg=0) and
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// any logic relying on signals will break. After forwarding we need to
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// continue to wait for stopping, because the thread is not stopped yet.
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// We do ignore delivery of SIGSTOP, because we want to make stop-the-world
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// as invisible as possible.
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for (;;) {
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int status;
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uptr waitpid_status;
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HANDLE_EINTR(waitpid_status, internal_waitpid(tid, &status, __WALL));
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int wperrno;
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if (internal_iserror(waitpid_status, &wperrno)) {
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// Got a ECHILD error. I don't think this situation is possible, but it
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// doesn't hurt to report it.
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VReport(1, "Waiting on thread %d failed, detaching (errno %d).\n",
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tid, wperrno);
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internal_ptrace(PTRACE_DETACH, tid, NULL, NULL);
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return false;
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}
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if (WIFSTOPPED(status) && WSTOPSIG(status) != SIGSTOP) {
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internal_ptrace(PTRACE_CONT, tid, 0, (void*)(uptr)WSTOPSIG(status));
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continue;
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}
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break;
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}
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suspended_threads_list_.Append(tid);
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return true;
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}
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}
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void ThreadSuspender::ResumeAllThreads() {
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for (uptr i = 0; i < suspended_threads_list_.thread_count(); i++) {
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pid_t tid = suspended_threads_list_.GetThreadID(i);
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int pterrno;
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if (!internal_iserror(internal_ptrace(PTRACE_DETACH, tid, NULL, NULL),
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&pterrno)) {
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VReport(1, "Detached from thread %d.\n", tid);
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} else {
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// Either the thread is dead, or we are already detached.
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// The latter case is possible, for instance, if this function was called
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// from a signal handler.
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VReport(1, "Could not detach from thread %d (errno %d).\n", tid, pterrno);
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}
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}
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}
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void ThreadSuspender::KillAllThreads() {
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for (uptr i = 0; i < suspended_threads_list_.thread_count(); i++)
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internal_ptrace(PTRACE_KILL, suspended_threads_list_.GetThreadID(i),
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NULL, NULL);
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}
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bool ThreadSuspender::SuspendAllThreads() {
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ThreadLister thread_lister(pid_);
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bool added_threads;
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do {
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// Run through the directory entries once.
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added_threads = false;
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pid_t tid = thread_lister.GetNextTID();
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while (tid >= 0) {
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if (SuspendThread(tid))
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added_threads = true;
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tid = thread_lister.GetNextTID();
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}
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if (thread_lister.error()) {
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// Detach threads and fail.
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ResumeAllThreads();
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return false;
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}
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thread_lister.Reset();
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} while (added_threads);
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return true;
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}
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// Pointer to the ThreadSuspender instance for use in signal handler.
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static ThreadSuspender *thread_suspender_instance = NULL;
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// Synchronous signals that should not be blocked.
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static const int kSyncSignals[] = { SIGABRT, SIGILL, SIGFPE, SIGSEGV, SIGBUS,
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SIGXCPU, SIGXFSZ };
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// Structure for passing arguments into the tracer thread.
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struct TracerThreadArgument {
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StopTheWorldCallback callback;
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void *callback_argument;
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// The tracer thread waits on this mutex while the parent finishes its
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// preparations.
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BlockingMutex mutex;
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uptr parent_pid;
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};
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static DieCallbackType old_die_callback;
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// Signal handler to wake up suspended threads when the tracer thread dies.
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static void TracerThreadSignalHandler(int signum, void *siginfo, void *) {
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if (thread_suspender_instance != NULL) {
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if (signum == SIGABRT)
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thread_suspender_instance->KillAllThreads();
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else
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thread_suspender_instance->ResumeAllThreads();
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}
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internal__exit((signum == SIGABRT) ? 1 : 2);
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}
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static void TracerThreadDieCallback() {
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// Generally a call to Die() in the tracer thread should be fatal to the
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// parent process as well, because they share the address space.
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// This really only works correctly if all the threads are suspended at this
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// point. So we correctly handle calls to Die() from within the callback, but
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// not those that happen before or after the callback. Hopefully there aren't
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// a lot of opportunities for that to happen...
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if (thread_suspender_instance)
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thread_suspender_instance->KillAllThreads();
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if (old_die_callback)
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old_die_callback();
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}
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// Size of alternative stack for signal handlers in the tracer thread.
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static const int kHandlerStackSize = 4096;
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// This function will be run as a cloned task.
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static int TracerThread(void* argument) {
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TracerThreadArgument *tracer_thread_argument =
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(TracerThreadArgument *)argument;
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internal_prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
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// Check if parent is already dead.
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if (internal_getppid() != tracer_thread_argument->parent_pid)
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internal__exit(4);
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// Wait for the parent thread to finish preparations.
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tracer_thread_argument->mutex.Lock();
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tracer_thread_argument->mutex.Unlock();
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old_die_callback = GetDieCallback();
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SetDieCallback(TracerThreadDieCallback);
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ThreadSuspender thread_suspender(internal_getppid());
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// Global pointer for the signal handler.
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thread_suspender_instance = &thread_suspender;
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// Alternate stack for signal handling.
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InternalScopedBuffer<char> handler_stack_memory(kHandlerStackSize);
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struct sigaltstack handler_stack;
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internal_memset(&handler_stack, 0, sizeof(handler_stack));
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handler_stack.ss_sp = handler_stack_memory.data();
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handler_stack.ss_size = kHandlerStackSize;
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internal_sigaltstack(&handler_stack, NULL);
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// Install our handler for synchronous signals. Other signals should be
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// blocked by the mask we inherited from the parent thread.
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for (uptr i = 0; i < ARRAY_SIZE(kSyncSignals); i++) {
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__sanitizer_sigaction act;
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internal_memset(&act, 0, sizeof(act));
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act.sigaction = TracerThreadSignalHandler;
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act.sa_flags = SA_ONSTACK | SA_SIGINFO;
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internal_sigaction_norestorer(kSyncSignals[i], &act, 0);
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}
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int exit_code = 0;
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if (!thread_suspender.SuspendAllThreads()) {
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VReport(1, "Failed suspending threads.\n");
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exit_code = 3;
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} else {
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tracer_thread_argument->callback(thread_suspender.suspended_threads_list(),
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tracer_thread_argument->callback_argument);
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thread_suspender.ResumeAllThreads();
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exit_code = 0;
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}
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// Note, this is a bad race. If TracerThreadDieCallback is already started
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// in another thread and observed that thread_suspender_instance != 0,
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// it can call KillAllThreads on the destroyed variable.
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SetDieCallback(old_die_callback);
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thread_suspender_instance = NULL;
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return exit_code;
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}
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class ScopedStackSpaceWithGuard {
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public:
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explicit ScopedStackSpaceWithGuard(uptr stack_size) {
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stack_size_ = stack_size;
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guard_size_ = GetPageSizeCached();
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// FIXME: Omitting MAP_STACK here works in current kernels but might break
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// in the future.
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guard_start_ = (uptr)MmapOrDie(stack_size_ + guard_size_,
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"ScopedStackWithGuard");
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CHECK_EQ(guard_start_, (uptr)Mprotect((uptr)guard_start_, guard_size_));
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}
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~ScopedStackSpaceWithGuard() {
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UnmapOrDie((void *)guard_start_, stack_size_ + guard_size_);
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}
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void *Bottom() const {
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return (void *)(guard_start_ + stack_size_ + guard_size_);
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}
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private:
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uptr stack_size_;
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uptr guard_size_;
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uptr guard_start_;
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};
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// We have a limitation on the stack frame size, so some stuff had to be moved
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// into globals.
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static __sanitizer_sigset_t blocked_sigset;
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static __sanitizer_sigset_t old_sigset;
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class StopTheWorldScope {
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public:
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StopTheWorldScope() {
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// Make this process dumpable. Processes that are not dumpable cannot be
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// attached to.
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process_was_dumpable_ = internal_prctl(PR_GET_DUMPABLE, 0, 0, 0, 0);
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if (!process_was_dumpable_)
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internal_prctl(PR_SET_DUMPABLE, 1, 0, 0, 0);
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}
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~StopTheWorldScope() {
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// Restore the dumpable flag.
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if (!process_was_dumpable_)
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internal_prctl(PR_SET_DUMPABLE, 0, 0, 0, 0);
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}
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private:
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int process_was_dumpable_;
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};
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// When sanitizer output is being redirected to file (i.e. by using log_path),
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// the tracer should write to the parent's log instead of trying to open a new
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// file. Alert the logging code to the fact that we have a tracer.
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struct ScopedSetTracerPID {
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explicit ScopedSetTracerPID(uptr tracer_pid) {
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stoptheworld_tracer_pid = tracer_pid;
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stoptheworld_tracer_ppid = internal_getpid();
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}
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~ScopedSetTracerPID() {
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stoptheworld_tracer_pid = 0;
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stoptheworld_tracer_ppid = 0;
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}
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};
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void StopTheWorld(StopTheWorldCallback callback, void *argument) {
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StopTheWorldScope in_stoptheworld;
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// Prepare the arguments for TracerThread.
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struct TracerThreadArgument tracer_thread_argument;
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tracer_thread_argument.callback = callback;
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tracer_thread_argument.callback_argument = argument;
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tracer_thread_argument.parent_pid = internal_getpid();
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const uptr kTracerStackSize = 2 * 1024 * 1024;
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ScopedStackSpaceWithGuard tracer_stack(kTracerStackSize);
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// Block the execution of TracerThread until after we have set ptrace
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// permissions.
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tracer_thread_argument.mutex.Lock();
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// Signal handling story.
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// We don't want async signals to be delivered to the tracer thread,
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// so we block all async signals before creating the thread. An async signal
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// handler can temporary modify errno, which is shared with this thread.
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// We ought to use pthread_sigmask here, because sigprocmask has undefined
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// behavior in multithreaded programs. However, on linux sigprocmask is
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// equivalent to pthread_sigmask with the exception that pthread_sigmask
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// does not allow to block some signals used internally in pthread
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// implementation. We are fine with blocking them here, we are really not
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// going to pthread_cancel the thread.
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// The tracer thread should not raise any synchronous signals. But in case it
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// does, we setup a special handler for sync signals that properly kills the
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// parent as well. Note: we don't pass CLONE_SIGHAND to clone, so handlers
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// in the tracer thread won't interfere with user program. Double note: if a
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// user does something along the lines of 'kill -11 pid', that can kill the
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// process even if user setup own handler for SEGV.
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// Thing to watch out for: this code should not change behavior of user code
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// in any observable way. In particular it should not override user signal
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// handlers.
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internal_sigfillset(&blocked_sigset);
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for (uptr i = 0; i < ARRAY_SIZE(kSyncSignals); i++)
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internal_sigdelset(&blocked_sigset, kSyncSignals[i]);
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int rv = internal_sigprocmask(SIG_BLOCK, &blocked_sigset, &old_sigset);
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CHECK_EQ(rv, 0);
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uptr tracer_pid = internal_clone(
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TracerThread, tracer_stack.Bottom(),
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CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_UNTRACED,
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&tracer_thread_argument, 0 /* parent_tidptr */, 0 /* newtls */, 0
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/* child_tidptr */);
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internal_sigprocmask(SIG_SETMASK, &old_sigset, 0);
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int local_errno = 0;
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if (internal_iserror(tracer_pid, &local_errno)) {
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VReport(1, "Failed spawning a tracer thread (errno %d).\n", local_errno);
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tracer_thread_argument.mutex.Unlock();
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} else {
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ScopedSetTracerPID scoped_set_tracer_pid(tracer_pid);
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// On some systems we have to explicitly declare that we want to be traced
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// by the tracer thread.
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#ifdef PR_SET_PTRACER
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internal_prctl(PR_SET_PTRACER, tracer_pid, 0, 0, 0);
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#endif
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// Allow the tracer thread to start.
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tracer_thread_argument.mutex.Unlock();
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// Since errno is shared between this thread and the tracer thread, we
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// must avoid using errno while the tracer thread is running.
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// At this point, any signal will either be blocked or kill us, so waitpid
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// should never return (and set errno) while the tracer thread is alive.
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uptr waitpid_status = internal_waitpid(tracer_pid, NULL, __WALL);
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if (internal_iserror(waitpid_status, &local_errno))
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VReport(1, "Waiting on the tracer thread failed (errno %d).\n",
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local_errno);
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}
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}
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// Platform-specific methods from SuspendedThreadsList.
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#if SANITIZER_ANDROID && defined(__arm__)
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typedef pt_regs regs_struct;
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#define REG_SP ARM_sp
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#elif SANITIZER_LINUX && defined(__arm__)
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typedef user_regs regs_struct;
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#define REG_SP uregs[13]
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#elif defined(__i386__) || defined(__x86_64__)
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typedef user_regs_struct regs_struct;
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#if defined(__i386__)
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#define REG_SP esp
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#else
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#define REG_SP rsp
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#endif
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#elif defined(__powerpc__) || defined(__powerpc64__)
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typedef pt_regs regs_struct;
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#define REG_SP gpr[PT_R1]
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#elif defined(__mips__)
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typedef struct user regs_struct;
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#define REG_SP regs[EF_REG29]
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#else
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#error "Unsupported architecture"
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#endif // SANITIZER_ANDROID && defined(__arm__)
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int SuspendedThreadsList::GetRegistersAndSP(uptr index,
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uptr *buffer,
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uptr *sp) const {
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pid_t tid = GetThreadID(index);
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regs_struct regs;
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int pterrno;
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if (internal_iserror(internal_ptrace(PTRACE_GETREGS, tid, NULL, ®s),
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&pterrno)) {
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VReport(1, "Could not get registers from thread %d (errno %d).\n", tid,
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pterrno);
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return -1;
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}
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*sp = regs.REG_SP;
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internal_memcpy(buffer, ®s, sizeof(regs));
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return 0;
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}
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uptr SuspendedThreadsList::RegisterCount() {
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return sizeof(regs_struct) / sizeof(uptr);
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}
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} // namespace __sanitizer
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#endif // SANITIZER_LINUX && (defined(__x86_64__) || defined(__mips__))
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