Re: [PATCHv2 4/6] gdb: error if 'thread' or 'task' keywords are overused

[Pedro Alves <pedro@palves.net>]

On 2023-01-20 9:46 a.m., Andrew Burgess via Gdb-patches wrote:
> When creating a breakpoint or watchpoint, the 'thread' and 'task'
> keywords can be used to create a thread or task specific breakpoint or
> watchpoint.
> 
> Currently, a thread or task specific breakpoint can only apply for a
> single thread or task, if multiple threads or tasks are specified when
> creating the breakpoint (or watchpoint), then the last specified id
> will be used.
> 
> The exception to the above is that when the 'thread' keyword is used
> during the creation of a watchpoint, GDB will give an error if
> 'thread' is given more than once.
> 
> In this commit I propose making this behaviour consistent, if the
> 'thread' or 'task' keywords are used more than once when creating
> either a breakpoint or watchpoint, then GDB will give an error.

The patch looks fine, but does it make sense to allow both thread and task
at the same time?

For instance, with gdb.ada/tasks.exp :

(gdb) b foo thread 1 task 2
Breakpoint 1 at 0x555555557bd6: file /home/pedro/gdb/rocm/gdb/src/gdb/testsuite/gdb.ada/tasks/foo.adb, line 16.
(gdb) info breakpoints 
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x0000555555557bd6 in foo at /home/pedro/gdb/rocm/gdb/src/gdb/testsuite/gdb.ada/tasks/foo.adb:16 thread 1
        stop only in thread 1

Pedro Alves

> 
> I haven't updated the manual, we don't explicitly say that these
> keywords can be repeated, and (to me), given the keyword takes a
> single id, I don't think it makes much sense to repeat the keyword.
> As such, I see this more as adding a missing error to GDB, rather than
> making some big change.  However, I have added an entry to the NEWS
> file as I guess it is possible that some people might hit this new
> error with an existing (I claim, badly written) GDB script.
> 
> I've added some new tests to check for the new error.
> 
> Just one test needed updating, gdb.linespec/keywords.exp, this test
> did use the 'thread' keyword twice, and expected the breakpoint to be
> created.  Looking at what this test was for though, it was checking
> the use of '-force-condition', and I don't think that being able to
> repeat 'thread' was actually a critical part of this test.
> 
> As such, I've updated this test to expect the error when 'thread' is
> repeated.
> ---
>  gdb/NEWS                                         |  9 +++++++++
>  gdb/breakpoint.c                                 |  9 +++++++++
>  gdb/testsuite/gdb.ada/tasks.exp                  |  4 ++++
>  gdb/testsuite/gdb.linespec/keywords.exp          | 10 ++++++++--
>  gdb/testsuite/gdb.threads/thread-specific-bp.exp |  4 ++++
>  gdb/testsuite/gdb.threads/watchthreads2.exp      |  3 +++
>  6 files changed, 37 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/NEWS b/gdb/NEWS
> index c0aac212e30..fb49f62f7e6 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -9,6 +9,15 @@
>    This support requires that GDB be built with Python scripting
>    enabled.
>  
> +* For the break command, multiple uses of the 'thread' or 'task'
> +  keywords will now give an error instead of just using the thread or
> +  task id from the last instance of the keyword.
> +
> +* For the watch command, multiple uses of the 'task' keyword will now
> +  give an error instead of just using the task id from the last
> +  instance of the keyword.  The 'thread' keyword already gave an error
> +  when used multiple times with the watch command, this remains unchanged.
> +
>  * New commands
>  
>  maintenance print record-instruction [ N ]
> diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
> index b2cd89511fb..1400fd49642 100644
> --- a/gdb/breakpoint.c
> +++ b/gdb/breakpoint.c
> @@ -8801,6 +8801,9 @@ find_condition_and_thread (const char *tok, CORE_ADDR pc,
>  	  const char *tmptok;
>  	  struct thread_info *thr;
>  
> +	  if (*thread != -1)
> +	    error(_("You can specify only one thread."));
> +
>  	  tok = end_tok + 1;
>  	  thr = parse_thread_id (tok, &tmptok);
>  	  if (tok == tmptok)
> @@ -8812,6 +8815,9 @@ find_condition_and_thread (const char *tok, CORE_ADDR pc,
>  	{
>  	  char *tmptok;
>  
> +	  if (*task != 0)
> +	    error(_("You can specify only one task."));
> +
>  	  tok = end_tok + 1;
>  	  *task = strtol (tok, &tmptok, 0);
>  	  if (tok == tmptok)
> @@ -10094,6 +10100,9 @@ watch_command_1 (const char *arg, int accessflag, int from_tty,
>  	    {
>  	      char *tmp;
>  
> +	      if (task != 0)
> +		error(_("You can specify only one task."));
> +
>  	      task = strtol (value_start, &tmp, 0);
>  	      if (tmp == value_start)
>  		error (_("Junk after task keyword."));
> diff --git a/gdb/testsuite/gdb.ada/tasks.exp b/gdb/testsuite/gdb.ada/tasks.exp
> index 23bf3937a20..4441d92719c 100644
> --- a/gdb/testsuite/gdb.ada/tasks.exp
> +++ b/gdb/testsuite/gdb.ada/tasks.exp
> @@ -39,6 +39,10 @@ gdb_test "info tasks" \
>                 "\r\n"] \
>           "info tasks before inserting breakpoint"
>  
> +# Check that multiple uses of the 'task' keyword will give an error.
> +gdb_test "break break_me task 1 task 3" "You can specify only one task\\."
> +gdb_test "watch j task 1 task 3" "You can specify only one task\\."
> +
>  # Insert a breakpoint that should stop only if task 1 stops.  Since
>  # task 1 never calls break_me, this shouldn't actually ever trigger.
>  # The fact that this breakpoint is created _before_ the next one
> diff --git a/gdb/testsuite/gdb.linespec/keywords.exp b/gdb/testsuite/gdb.linespec/keywords.exp
> index bff64249542..dc66e32237c 100644
> --- a/gdb/testsuite/gdb.linespec/keywords.exp
> +++ b/gdb/testsuite/gdb.linespec/keywords.exp
> @@ -80,8 +80,14 @@ foreach prefix {"" "thread 1 "} {
>      foreach suffix {"" " " " thread 1"} {
>  	foreach cond {"" " if 1"} {
>  	    with_test_prefix "prefix: '$prefix', suffix: '$suffix', cond: '$cond'" {
> -		gdb_breakpoint "main ${prefix}-force-condition${suffix}${cond}"\
> -		    "message"
> +
> +		if { [regexp thread $prefix] && [regexp thread $suffix] } {
> +		    gdb_test "break main ${prefix}-force-condition${suffix}${cond}" \
> +			"You can specify only one thread\\."
> +		} else {
> +		    gdb_breakpoint "main ${prefix}-force-condition${suffix}${cond}"\
> +			"message"
> +		}
>  	    }
>  	}
>      }
> diff --git a/gdb/testsuite/gdb.threads/thread-specific-bp.exp b/gdb/testsuite/gdb.threads/thread-specific-bp.exp
> index d33b4f47258..008ae5ed05e 100644
> --- a/gdb/testsuite/gdb.threads/thread-specific-bp.exp
> +++ b/gdb/testsuite/gdb.threads/thread-specific-bp.exp
> @@ -63,6 +63,10 @@ proc check_thread_specific_breakpoint {non_stop} {
>  	return -1
>      }
>  
> +    # Check that multiple uses of 'thread' keyword give an error.
> +    gdb_test "break main thread $start_thre thread $main_thre" \
> +	"You can specify only one thread\\."
> +
>      # Set a thread-specific breakpoint at "main".  This can't ever
>      # be hit, but that's OK.
>      gdb_breakpoint "main thread $start_thre"
> diff --git a/gdb/testsuite/gdb.threads/watchthreads2.exp b/gdb/testsuite/gdb.threads/watchthreads2.exp
> index 09858aee486..a1398d668a4 100644
> --- a/gdb/testsuite/gdb.threads/watchthreads2.exp
> +++ b/gdb/testsuite/gdb.threads/watchthreads2.exp
> @@ -71,6 +71,9 @@ if { $nr_started == $NR_THREADS } {
>      return -1
>  }
>  
> +# Check that multiple uses of the 'thread' keyword will give an error.
> +gdb_test "watch x thread 1 thread 2" "You can specify only one thread\\."
> +
>  # Watch X, it will be modified by all threads.
>  # We want this watchpoint to be set *after* all threads are running.
>  gdb_test "watch x" "Hardware watchpoint 3: x"
>