Re: [PATCH 1/3] Fix any_thread_of_inferior

[Simon Marchi <simon.marchi@polymtl.ca>]

On 2021-03-15 7:43 p.m., Pedro Alves wrote:
> Running gdb-term.exp against gdbserver with "maint set target-non-stop
> on", runs into this:
> 
>   [infrun] fetch_inferior_event: exit
>   [infrun] fetch_inferior_event: enter
>   /home/pedro/gdb/binutils-gdb/src/gdb/thread.c:72: internal-error: thread_info* inferior_thread(): Assertion `current_thread_ != nullptr' failed.
>   A problem internal to GDB has been detected,
>   further debugging may prove unreliable.
> 
>   This is a bug, please report it.  For instructions, see:
>   <https://www.gnu.org/software/gdb/bugs/>.
> 
>   FAIL: gdb.base/gdb-sigterm.exp: expect eof #2 (GDB internal error)
>   Resyncing due to internal error.
>   ERROR: : spawn id exp9 not open
>       while executing
>   "expect {
>   -i exp9 -timeout 10
> 	      -re "Quit this debugging session\\? \\(y or n\\) $" {
> 		  send_gdb "n\n" answer
> 		  incr count
> 	      }
> 	      -re "Create ..."
>       ("uplevel" body line 1)
>       invoked from within
>   "uplevel $body" NONE : spawn id exp9 not open
>   ERROR: Could not resync from internal error (timeout)
>   gdb.base/gdb-sigterm.exp: expect eof #2: stepped 0 times
>   UNRESOLVED: gdb.base/gdb-sigterm.exp: 50 SIGTERM passes
> 
> The assertion fails here:
> 
>   ...
>   #5  0x000055af4b4a7164 in internal_error (file=0x55af4b5e5de8 "/home/pedro/gdb/binutils-gdb/src/gdb/thread.c", line=72, fmt=0x55af4b5e5ce9 "%s: Assertion `%s' failed.") at /home/pedro/gdb/binutils-gdb/src/gdbsupport/errors.cc:55
>   #6  0x000055af4b25fc43 in inferior_thread () at /home/pedro/gdb/binutils-gdb/src/gdb/thread.c:72
>   #7  0x000055af4b26177e in any_thread_of_inferior (inf=0x55af4cf874f0) at /home/pedro/gdb/binutils-gdb/src/gdb/thread.c:638
>   #8  0x000055af4b26eec8 in kill_or_detach (inf=0x55af4cf874f0, from_tty=0) at /home/pedro/gdb/binutils-gdb/src/gdb/top.c:1665
>   #9  0x000055af4b26f37f in quit_force (exit_arg=0x0, from_tty=0) at /home/pedro/gdb/binutils-gdb/src/gdb/top.c:1767
>   #10 0x000055af4b2f72a7 in quit () at /home/pedro/gdb/binutils-gdb/src/gdb/utils.c:633
>   #11 0x000055af4b2f730b in maybe_quit () at /home/pedro/gdb/binutils-gdb/src/gdb/utils.c:657
>   #12 0x000055af4b1adb74 in ser_base_wait_for (scb=0x55af4d02e460, timeout=0) at /home/pedro/gdb/binutils-gdb/src/gdb/ser-base.c:236
>   #13 0x000055af4b1adf0f in do_ser_base_readchar (scb=0x55af4d02e460, timeout=0) at /home/pedro/gdb/binutils-gdb/src/gdb/ser-base.c:365
>   #14 0x000055af4b1ae06d in generic_readchar (scb=0x55af4d02e460, timeout=0, do_readchar=0x55af4b1adeb1 <do_ser_base_readchar(serial*, int)>) at /home/pedro/gdb/binutils-gdb/src/gdb/ser-base.c:444
>   ...
> 
> The bug is that any_thread_of_inferior incorrectly assumes that
> there's always a selected thread.  This fixes it.
> 
> gdb/ChangeLog:
> 
> 	* thread.c (any_thread_of_inferior): Check if there's a selected
> 	thread before calling inferior_thread().
> 
> Change-Id: Ica4b9ec746121a7a7c22bef09baea72103b3853d
> ---
>  gdb/thread.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/thread.c b/gdb/thread.c
> index 3e7d6e14bf7..fc6db96fbcb 100644
> --- a/gdb/thread.c
> +++ b/gdb/thread.c
> @@ -637,8 +637,8 @@ any_thread_of_inferior (inferior *inf)
>  {
>    gdb_assert (inf->pid != 0);
>  
> -  /* Prefer the current thread.  */
> -  if (inf == current_inferior ())
> +  /* Prefer the current thread, if there's one.  */
> +  if (inf == current_inferior () && inferior_ptid != null_ptid)
>      return inferior_thread ();
>  
>    for (thread_info *tp : inf->non_exited_threads ())
> 

Makes sense.  current_thread_ is always supposed to be in sync with
inferior_ptid because we are always supposed to use switch_to_thread or
similar function to switch thread, right?

Simon