[PATCHv6,05/10] gdb: don't display inferior list for pending breakpoints

  I noticed that in the 'info breakpoints' output, GDB sometimes prints
the inferior list for pending breakpoints, this doesn't seem right to
me.  A pending breakpoint has no locations (at least, as far as we
display things in the 'info breakpoints' output), so including an
inferior list seems odd.

Here's what I see right now:

  (gdb) info breakpoint 5
  Num     Type           Disp Enb Address            What
  5       breakpoint     keep y   <PENDING>          foo inf 1
  (gdb)

It's the 'inf 1' at the end of the line that I'm objecting too.

To trigger this behaviour we need to be in a multi-inferior debug
session.  The breakpoint must have been non-pending at some point in
the past, and so have a location assigned to it.

The breakpoint becomes pending again as a result of a shared library
being unloaded.  When this happens the location itself is marked
pending (via bp_location::shlib_disabled).

In print_one_breakpoint_location, in order to print the inferior list
we check that the breakpoint has a location, and that we have multiple
inferiors, but we don't check if the location itself is pending.

This commit adds that check, which means the output is now:

  (gdb) info breakpoint 5
  Num     Type           Disp Enb Address            What
  5       breakpoint     keep y   <PENDING>          foo
  (gdb)

Which I think makes more sense -- indeed, the format without the
inferior list is what we display for a pending breakpoint that has
never had any locations assigned, so I think this change in behaviour
makes GDB more consistent.
---
 gdb/breakpoint.c                         |   2 +-
 gdb/testsuite/gdb.multi/pending-bp-lib.c |  22 ++++
 gdb/testsuite/gdb.multi/pending-bp.c     |  66 ++++++++++++
 gdb/testsuite/gdb.multi/pending-bp.exp   | 130 +++++++++++++++++++++++
 4 files changed, 219 insertions(+), 1 deletion(-)
 create mode 100644 gdb/testsuite/gdb.multi/pending-bp-lib.c
 create mode 100644 gdb/testsuite/gdb.multi/pending-bp.c
 create mode 100644 gdb/testsuite/gdb.multi/pending-bp.exp
  

On Saturday, December 2, 2023 11:42 AM, Andrew Burgess wrote:
> I noticed that in the 'info breakpoints' output, GDB sometimes prints
> the inferior list for pending breakpoints, this doesn't seem right to
> me.  A pending breakpoint has no locations (at least, as far as we
> display things in the 'info breakpoints' output), so including an
> inferior list seems odd.
> 
> Here's what I see right now:
> 
>   (gdb) info breakpoint 5
>   Num     Type           Disp Enb Address            What
>   5       breakpoint     keep y   <PENDING>          foo inf 1
>   (gdb)
> 
> It's the 'inf 1' at the end of the line that I'm objecting too.
> 
> To trigger this behaviour we need to be in a multi-inferior debug
> session.  The breakpoint must have been non-pending at some point in
> the past, and so have a location assigned to it.
> 
> The breakpoint becomes pending again as a result of a shared library
> being unloaded.  When this happens the location itself is marked
> pending (via bp_location::shlib_disabled).
> 
> In print_one_breakpoint_location, in order to print the inferior list
> we check that the breakpoint has a location, and that we have multiple
> inferiors, but we don't check if the location itself is pending.
> 
> This commit adds that check, which means the output is now:
> 
>   (gdb) info breakpoint 5
>   Num     Type           Disp Enb Address            What
>   5       breakpoint     keep y   <PENDING>          foo
>   (gdb)
> 
> Which I think makes more sense -- indeed, the format without the
> inferior list is what we display for a pending breakpoint that has
> never had any locations assigned, so I think this change in behaviour
> makes GDB more consistent.
> ---
>  gdb/breakpoint.c                         |   2 +-
>  gdb/testsuite/gdb.multi/pending-bp-lib.c |  22 ++++
>  gdb/testsuite/gdb.multi/pending-bp.c     |  66 ++++++++++++
>  gdb/testsuite/gdb.multi/pending-bp.exp   | 130 +++++++++++++++++++++++
>  4 files changed, 219 insertions(+), 1 deletion(-)
>  create mode 100644 gdb/testsuite/gdb.multi/pending-bp-lib.c
>  create mode 100644 gdb/testsuite/gdb.multi/pending-bp.c
>  create mode 100644 gdb/testsuite/gdb.multi/pending-bp.exp
> 
> diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
> index c1440a6921f..3ee23af83d6 100644
> --- a/gdb/breakpoint.c
> +++ b/gdb/breakpoint.c
> @@ -6597,7 +6597,7 @@ print_one_breakpoint_location (struct breakpoint *b,
>  	}
>      }
> 
> -  if (loc != NULL && !header_of_multiple)
> +  if (loc != NULL && !header_of_multiple && !loc->shlib_disabled)

Since you're touching the line, would you consider turning NULL
into nullptr?

>      {
>        std::vector<int> inf_nums;
>        int mi_only = 1;
> diff --git a/gdb/testsuite/gdb.multi/pending-bp-lib.c b/gdb/testsuite/gdb.multi/pending-bp-
> lib.c
> new file mode 100644
> index 00000000000..15d1b9833dd
> --- /dev/null
> +++ b/gdb/testsuite/gdb.multi/pending-bp-lib.c
> @@ -0,0 +1,22 @@
> +/* Copyright 2023 Free Software Foundation, Inc.
> +
> +   This program is free software; you can redistribute it and/or modify
> +   it under the terms of the GNU General Public License as published by
> +   the Free Software Foundation; either version 3 of the License, or
> +   (at your option) any later version.
> +
> +   This program is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +   GNU General Public License for more details.
> +
> +   You should have received a copy of the GNU General Public License
> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
> +
> +int global_var = 0;
> +
> +void
> +foo (int arg)
> +{
> +  global_var = arg;
> +}
> diff --git a/gdb/testsuite/gdb.multi/pending-bp.c b/gdb/testsuite/gdb.multi/pending-bp.c
> new file mode 100644
> index 00000000000..ca8a3c20b72
> --- /dev/null
> +++ b/gdb/testsuite/gdb.multi/pending-bp.c
> @@ -0,0 +1,66 @@
> +/* Copyright 2023 Free Software Foundation, Inc.
> +
> +   This program is free software; you can redistribute it and/or modify
> +   it under the terms of the GNU General Public License as published by
> +   the Free Software Foundation; either version 3 of the License, or
> +   (at your option) any later version.
> +
> +   This program is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +   GNU General Public License for more details.
> +
> +   You should have received a copy of the GNU General Public License
> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
> +
> +#include <dlfcn.h>
> +#include <stdlib.h>
> +
> +void
> +breakpt ()
> +{
> +  /* Nothing.  */
> +}
> +
> +volatile int global_counter = 0;
> +
> +volatile int call_count = 1;
> +
> +int
> +main (void)
> +{
> +  void *handle;
> +  void (*func)(int);
> +
> +  /* Some filler work so that we don't initially stop on the breakpt call
> +     below.  */
> +  ++global_counter;
> +
> +  breakpt ();	/* Break before open.  */
> +
> +  /* Now load the shared library.  */
> +  handle = dlopen (SHLIB_NAME, RTLD_LAZY);
> +  if (handle == NULL)
> +    abort ();
> +
> +  breakpt ();	/* Break after open.  */
> +
> +  /* Find the function symbol.  */
> +  func = (void (*)(int)) dlsym (handle, "foo");
> +
> +  for (; call_count > 0; --call_count)
> +    {
> +      /* Call the library function.  */
> +      func (1);
> +    }
> +
> +  breakpt ();	/* Break before close.  */
> +
> +  /* Unload the shared library.  */
> +  if (dlclose (handle) != 0)
> +    abort ();
> +
> +  breakpt ();	/* Break after close.  */
> +
> +  return 0;
> +}
> diff --git a/gdb/testsuite/gdb.multi/pending-bp.exp b/gdb/testsuite/gdb.multi/pending-bp.exp
> new file mode 100644
> index 00000000000..e4f0aa2e38a
> --- /dev/null
> +++ b/gdb/testsuite/gdb.multi/pending-bp.exp
> @@ -0,0 +1,130 @@
> +# Copyright 2023 Free Software Foundation, Inc.
> +
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
> +
> +# Tests related to pending breakpoints in a multi-inferior environment.
> +
> +require allow_shlib_tests !use_gdb_stub
> +
> +standard_testfile
> +
> +set libname $testfile-lib
> +set srcfile_lib $srcdir/$subdir/$libname.c
> +set binfile_lib [standard_output_file $libname.so]
> +
> +if { [gdb_compile_shlib $srcfile_lib $binfile_lib {}] != "" } {
> +    untested "failed to compile shared library 1"
> +    return -1
> +}
> +
> +set binfile_lib_target [gdb_download_shlib $binfile_lib]
> +
> +if { [build_executable "failed to prepare" $testfile $srcfile \
> +	  [list debug \
> +	       additional_flags=-DSHLIB_NAME=\"$binfile_lib_target\" \
> +	       shlib_load pthreads]] } {

Is pthreads needed?

> +    return -1
> +}
> +
> +# Used to override delete_breakpoints when we don't want breakpoints
> +# deleted.
> +proc do_nothing {} {}
> +
> +# Start two inferiors, both running the same test binary.  The arguments
> +# INF_1_STOP and INF_2_STOP are source code patterns that are passed to
> +# gdb_get_line_number to figure out where each inferior should be stopped.
> +#
> +# This proc does a clean_restart and leaves inferior 2 selected.  Also the
> +# 'breakpoint pending' flag is enabled, so pending breakpoints can be created
> +# without GDB prompting the user.
> +proc do_test_setup { inf_1_stop inf_2_stop } {
> +    clean_restart ${::binfile}
> +
> +    gdb_locate_shlib $::binfile_lib
> +
> +    if ![runto_main] {

Braces can be added for consistency with the other if-statements.

> +	return false
> +    }
> +
> +    gdb_breakpoint [gdb_get_line_number ${inf_1_stop}] temporary
> +    gdb_continue_to_breakpoint "move inferior 1 into position"
> +
> +    gdb_test "add-inferior -exec ${::binfile}" \
> +	"Added inferior 2.*" "add inferior 2"
> +    gdb_test "inferior 2" "Switching to inferior 2 .*" "switch to inferior 2"
> +
> +    with_override delete_breakpoints do_nothing {

I'm not sure why this is needed.  The BP at inf_1_stop was already
defined temporary.  Is there any breakpoint left that we want to retain?

> +	if {![runto_main]} {
> +	    return false
> +	}
> +    }
> +
> +    gdb_breakpoint [gdb_get_line_number ${inf_2_stop}] temporary
> +    gdb_continue_to_breakpoint "move inferior 2 into position"
> +
> +    gdb_test_no_output "set breakpoint pending on"
> +
> +    return true
> +}
> +
> +# Check that when a breakpoint is in the pending state, but that breakpoint
> +# does have some locations (those locations themselves are pending), GDB
> +# doesn't display the inferior list in the 'info breakpoints' output.
> +proc_with_prefix test_no_inf_display {} {
> +    do_test_setup "Break before open" "Break before open"
> +
> +    # Create a breakpoint on 'foo'.  As the shared library (that contains
> +    # foo) has not been loaded into any inferior yet, then there will be no
> +    # locations and the breakpoint will be created pending.
> +    gdb_breakpoint "foo" allow-pending

We already did "set breakpoint pending on" in setup.  Do we need "allow-pending"?

> +    set bpnum [get_integer_valueof "\$bpnum" "*INVALID*" \
> +		   "get foo breakpoint number"]
> +
> +    # Check the 'info breakpoints' output; the breakpoint is pending with
> +    # not 'inf X' appearing at the end of the line.

"not" -> "no"

Regards
-Baris


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