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Re: [PATCH 2/8] Fix follow-fork latent bug
On 04/13/2017 10:58 AM, Yao Qi wrote:
> Pedro Alves <palves@redhat.com> writes:
>
>> - old_chain = save_inferior_ptid ();
>> - save_current_program_space ();
>> + old_chain = save_current_space_and_thread ();
>>
>> inferior_ptid = child_ptid;
>> add_thread (inferior_ptid);
>> + set_current_inferior (child_inf);
>> child_inf->symfile_flags = SYMFILE_NO_READ;
>
> Can we set up child thread_info inferior and pspace first, and then,
> call switch_to_thread_no_regs to switch them in one go?
Although it seemingly works, and I tried this patch on top
of the series:
diff --git c/gdb/infrun.c w/gdb/infrun.c
index fcafdc1..3c5f583 100644
--- c/gdb/infrun.c
+++ w/gdb/infrun.c
@@ -500,9 +500,7 @@ holding the child stopped. Try \"set detach-on-fork\" or \
old_chain = save_current_space_and_thread ();
- inferior_ptid = child_ptid;
- add_thread (inferior_ptid);
- set_current_inferior (child_inf);
+ add_thread (child_ptid);
child_inf->symfile_flags = SYMFILE_NO_READ;
/* If this is a vfork child, then the address-space is
@@ -629,9 +627,7 @@ holding the child stopped. Try \"set detach-on-fork\" or \
this new thread, before cloning the program space, and
informing the solib layer about this new process. */
- inferior_ptid = child_ptid;
- add_thread (inferior_ptid);
- set_current_inferior (child_inf);
+ add_thread (child_ptid);
/* If this is a vfork child, then the address-space is shared
with the parent. If we detached from the parent, then we can
@@ -657,6 +653,8 @@ holding the child stopped. Try \"set detach-on-fork\" or \
the core, this wouldn't be required. */
solib_create_inferior_hook (0);
}
+
+ switch_to_thread (child_ptid);
}
return target_follow_fork (follow_child, detach_fork);
I don't think I'd like to do that (at least not now), because it doesn't
look like clone_program_space and solib_create_inferior_hook really
work correctly if called without switching the current inferior to
point to the child.
For example, I set a breakpoint on current_inferior, active
while GDB is running clone_program_space, and with
"set detach-on-fork off" for example, we get many hits
which currently (it looks to me incorrectly) refer to the
parent inferior instead of the child inferior that is
loading symbols. Here's a sample:
(top-gdb) bt
#0 0x00000000006c2baa in current_inferior() () at src/gdb/inferior.c:59
#1 0x00000000006a5026 in set_target_gdbarch(gdbarch*) (new_gdbarch=0x19aba30) at src/gdb/gdbarch.c:5438
#2 0x00000000005b21ac in set_gdbarch_from_file(bfd*) (abfd=0x1193540) at src/gdb/arch-utils.c:620
#3 0x000000000067f2a8 in exec_file_attach(char const*, int) (filename=0x1894a30, from_tty=0) at src/gdb/exec.c:383
#4 0x0000000000729985 in clone_program_space(program_space*, program_space*) (dest=0x1c8d3a0, src=0x11e8de0)
at src/gdb/progspace.c:193
#5 0x00000000006c571a in follow_fork_inferior(int, int) (follow_child=0, detach_fork=0)
at infrun.c:527
(top-gdb) bt
#0 0x00000000006c2baa in current_inferior() () at src/gdb/inferior.c:59
#1 0x00000000005b66f5 in invalidate_auxv_cache() () at src/gdb/auxv.c:345
#2 0x000000000070f705 in observer_executable_changed_notification_stub(void const*, void const*) (data=0x5b66ec <invalidate_auxv_cache()>, args_data=0x7fffffffd028) at ./observer.inc:364
#3 0x000000000070ef72 in generic_observer_notify(observer_list*, void const*) (subject=0x11085e0, args=0x7fffffffd028)
at src/gdb/observer.c:167
#4 0x000000000070f796 in observer_notify_executable_changed() () at ./observer.inc:387
#5 0x000000000067f316 in exec_file_attach(char const*, int) (filename=0x1894a30 "gdb/testsuite/outputs/gdb.base/foll-fork/foll-fork", from_tty=0) at src/gdb/exec.c:399
#6 0x0000000000729985 in clone_program_space(program_space*, program_space*) (dest=0x1c8d3a0, src=0x11e8de0)
at src/gdb/progspace.c:193
I'd rather not have to dig into this area too deeply at this point.
Thanks,
Pedro Alves