Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 122479f4 authored by Josh Gao's avatar Josh Gao
Browse files

crash_dump: switch to PTRACE_SEIZE. 

ptrace(PTRACE_ATTACH) does not immediately put the traced process in a
stopped state. If we manage to call PTRACE_CONT on it before it
finishes, we'll fail. Switch to using PTRACE_SEIZE and PTRACE_INTERRUPT
to guarantee that the target stops immediately.

This also has the advantage of never putting the process in group-stop
state, which means if we exit prematurely (e.g. if we crash during
stack unwinding), the target process will be resumed without any
intervention needed.

Bug: http://b/34472671
Test: while true; do debuggerd -b `pidof audioserver`; done
Change-Id: I7549f67489646cf300b8c9aa8c735e5e897806ef
parent 57594111

debuggerd/crash_dump.cpp

+13 −7
Original line number Diff line number Diff line
@@ -57,8 +57,8 @@ static bool pid_contains_tid(pid_t pid, pid_t tid) { 
}



// Attach to a thread, and verify that it's still a member of the given process

static bool ptrace_attach_thread(pid_t pid, pid_t tid, std::string* error) {

  if (ptrace(PTRACE_ATTACH, tid, 0, 0) != 0) {

static bool ptrace_seize_thread(pid_t pid, pid_t tid, std::string* error) {

  if (ptrace(PTRACE_SEIZE, tid, 0, 0) != 0) {

    *error = StringPrintf("failed to attach to thread %d: %s", tid, strerror(errno));

    return false;

  }
@@ -71,6 +71,12 @@ static bool ptrace_attach_thread(pid_t pid, pid_t tid, std::string* error) { 
    *error = StringPrintf("thread %d is not in process %d", tid, pid);

    return false;

  }



  // Put the task into ptrace-stop state.

  if (ptrace(PTRACE_INTERRUPT, tid, 0, 0) != 0) {

    PLOG(FATAL) << "failed to interrupt thread " << tid;

  }



  return true;

}
@@ -254,7 +260,7 @@ int main(int argc, char** argv) { 
  check_process(target_proc_fd, target);



  std::string attach_error;

  if (!ptrace_attach_thread(target, main_tid, &attach_error)) {

  if (!ptrace_seize_thread(target, main_tid, &attach_error)) {

    LOG(FATAL) << attach_error;

  }
@@ -279,9 +285,9 @@ int main(int argc, char** argv) { 


  LOG(INFO) << "performing dump of process " << target << " (target tid = " << main_tid << ")";



  // At this point, the thread that made the request has been PTRACE_ATTACHed

  // and has the signal that triggered things queued. Send PTRACE_CONT, and

  // then wait for the signal.

  // At this point, the thread that made the request has been attached and is

  // in ptrace-stopped state. After resumption, the triggering signal that has

  // been queued will be delivered.

  if (ptrace(PTRACE_CONT, main_tid, 0, 0) != 0) {

    PLOG(ERROR) << "PTRACE_CONT(" << main_tid << ") failed";

    exit(1);
@@ -320,7 +326,7 @@ int main(int argc, char** argv) { 
    siblings.erase(main_tid);



    for (pid_t sibling_tid : siblings) {

      if (!ptrace_attach_thread(target, sibling_tid, &attach_error)) {

      if (!ptrace_seize_thread(target, sibling_tid, &attach_error)) {

        LOG(WARNING) << attach_error;

      } else {

        attached_siblings.insert(sibling_tid);