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

Aktemur, Tankut Baris
2023-12-05T08:35:47Z

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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