fix gdbstub support for multiple threads in usermode, v3

When debugging multi-threaded programs, QEMU's gdb stub would report the
correct number of threads (the qfThreadInfo and qsThreadInfo packets).
However, the stub was unable to actually switch between threads (the T
packet), since it would report every thread except the first as being
dead.  Furthermore, the stub relied upon cpu_index as a reliable means
of assigning IDs to the threads.  This was a bad idea; if you have this
sequence of events:

initial thread created
new thread #1
new thread #2
thread #1 exits
new thread #3

thread #3 will have the same cpu_index as thread #1, which would confuse
GDB.  (This problem is partly due to the remote protocol not having a
good way to send thread creation/destruction events.)

We fix this by using the host thread ID for the identifier passed to GDB
when debugging a multi-threaded userspace program.  The thread ID might
wrap, but the same sort of problems with wrapping thread IDs would come
up with debugging programs natively, so this doesn't represent a
problem.

Signed-off-by: Nathan Froyd <froydnj@codesourcery.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index a0915a455b..59c91f8da9 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -3202,6 +3202,7 @@ static void *clone_func(void *arg)
     env = info->env;
     thread_env = env;
     info->tid = gettid();
+    env->host_tid = info->tid;
     if (info->child_tidptr)
         put_user_u32(info->tid, info->child_tidptr);
     if (info->parent_tidptr)
@@ -3792,6 +3793,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
       /* FIXME: This probably breaks if a signal arrives.  We should probably
          be disabling signals.  */
       if (first_cpu->next_cpu) {
+          TaskState *ts;
           CPUState **lastp;
           CPUState *p;
 
@@ -3809,7 +3811,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
           /* Remove the CPU from the list.  */
           *lastp = p->next_cpu;
           cpu_list_unlock();
-          TaskState *ts = ((CPUState *)cpu_env)->opaque;
+          ts = ((CPUState *)cpu_env)->opaque;
           if (ts->child_tidptr) {
               put_user_u32(0, ts->child_tidptr);
               sys_futex(g2h(ts->child_tidptr), FUTEX_WAKE, INT_MAX,