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Re: [RFA 4/5] Darwin: fix thread ptid started by fork_inferior
On 2018-08-22 06:11, Xavier Roirand wrote:
When debugging a program on Mac OS X Darwin, gdb stops with:
Temporary breakpoint 1 at 0x100000fb4: file /tmp/helloworld.c, line 1.
Starting program: /private/tmp/helloworld
[New Thread 0xb03 of process 65066]
[New Thread 0xd03 of process 65066]
During startup program terminated with signal SIGTRAP, Trace/breakpoint
trap.
When the inferior is started a thread with lwp=tid=0 is created
and has to be fixed later by darwin_init_thread_list(). Because
this is not done, GDB does not understand that the SIGTRAP is
coming from GDB and not the program itself.
I think I have seen this error in my testing yesterday, though it seemed
intermittent. If I started a few times in a row, I would often get that
SIGTRAP, but it would eventually work... I can't really comment on the
validity of the fix, so I will assume it's right (I am not at work right
now so I can't test on the Mac). But linux-nat does something similar
(add a pid-only thread, then change it to its real ptid), so there is a
precedent.
diff --git a/gdb/darwin-nat.c b/gdb/darwin-nat.c
index 96f70cf..9ad4a87 100644
--- a/gdb/darwin-nat.c
+++ b/gdb/darwin-nat.c
@@ -344,8 +344,22 @@ darwin_check_new_threads (struct inferior *inf)
pti->gdb_port = new_id;
pti->msg_state = DARWIN_RUNNING;
- /* Add the new thread. */
- add_thread_with_info (ptid_t (inf->pid, 0, new_id), pti);
+ if (old_nbr == 0 && new_ix == 0)
+ {
+ /* A ptid is created when the inferior is started (see
+ fork-child.c) with lwp=tid=0. This ptid will be
renamed
+ later by darwin_init_thread_list (), so find this
previous
+ thread silently added. */
+
+ struct thread_info *tp = find_thread_ptid (ptid_t
(inf->pid, 0, 0));
+ tp->priv.reset (pti);
Put a gdb_assert (tp != nullptr), so that if for some reason the thread
is not found (because of a GDB bug), we fail with a failed assertion
rather than a segfault.
+ }
+ else
+ {
+ /* Add the new thread. */
+ add_thread_with_info (ptid_t (inf->pid, 0, new_id),
pti);
+ }
+
new_thread_vec.push_back (pti);
new_ix++;
continue;
@@ -1733,6 +1747,8 @@ thread_info_from_private_thread_info
(darwin_thread_info *pti)
static void
darwin_init_thread_list (struct inferior *inf)
{
+ ptid_t new_ptid;
+
darwin_check_new_threads (inf);
darwin_inferior *priv = get_darwin_inferior (inf);
@@ -1743,7 +1759,11 @@ darwin_init_thread_list (struct inferior *inf)
struct thread_info *first_thread
= thread_info_from_private_thread_info (first_pti);
- inferior_ptid = first_thread->ptid;
+ /* Note: fork_inferior automatically add a thread but it uses a
wrong ptid.
+ Fix up. */
+ new_ptid = ptid_t (inf->pid, 0, first_pti->gdb_port);
+ thread_change_ptid (inferior_ptid, new_ptid);
+ inferior_ptid = new_ptid;
You can declare new_ptid when initializing it.
Simon