Re: [PATCH v2] gdb/breakpoint: remove assertion when printing internal breakpoints without locspecs

["Sébastien Darche" <sdarche@efficios.com>]

Thanks again, Andrew.

Just pushed.

Best,
Sébastien

On 2026-06-10 11:16, Andrew Burgess wrote:
> 
> Thanks, this looks great.  I have one minor nit, no need to repost though...
> 
> Sébastien Darche <sdarche@efficios.com> writes:
> 
>> When debugging gdb with `set debug breakpoint on`, gdb would crash if
>> the inferior happened to unload (through dlclose ()) a shared library
>> that contains jit debugging symbols:
>>
>> 	../../gdb/breakpoint.c:6473: internal-error: print_breakpoint_location:
>> 	Assertion `b->locspec != nullptr || (!user_breakpoint_p (b) && (b->type
>> 	== bp_shlib_event || b->type == bp_thread_event))' failed.
>> 	A problem internal to GDB has been detected [...]
>>
>> This assertion was added in commit 5770f68 ("gdb: handle empty locspec
>> when printing breakpoints"). The assumption for this assert is that the
>> user may not call any (gdb-)debugging command between the time a shared
>> library is marked (bp_location->shlib_disabled is set) and the
>> breakpoint is actually removed. This would be true if the user called
>> `maint info breakpoints` as explained in the original commit message.
>>
>> However, if `set debug breakpoint on` is called, gdb prints debugging
>> info as the shared library is being unloaded. The ~jiter_objfile_data
>> dtor deletes the breakpoint, which calls remove_breakpoint_1 on the
>> bp_location in the recently unloaded shared object. Since `debug
>> breakpoint` is enabled, we go through print_breakpoint_location with the
>> bp_location's shlib_disabled flag set, which results in the assert
>> above.
>>
>> This commit removes the assertion as it is not true in all cases. I've
>> also included a minimal test case that loads a shared library with a
>> __jit_debug_register_code symbol. The test fails with the assert.
>>
>> Change-Id: Ia19c84f194a6f0c10315548c7f423bfd86ef0266
>> ---
>>   gdb/breakpoint.c                          | 17 -------
>>   gdb/testsuite/gdb.base/jit-unload-solib.c | 21 ++++++++
>>   gdb/testsuite/gdb.base/jit-unload.c       | 45 ++++++++++++++++
>>   gdb/testsuite/gdb.base/jit-unload.exp     | 62 +++++++++++++++++++++++
>>   4 files changed, 128 insertions(+), 17 deletions(-)
>>   create mode 100644 gdb/testsuite/gdb.base/jit-unload-solib.c
>>   create mode 100644 gdb/testsuite/gdb.base/jit-unload.c
>>   create mode 100644 gdb/testsuite/gdb.base/jit-unload.exp
>>
>> diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
>> index 101dc57ee6b..85c4ffc3171 100644
>> --- a/gdb/breakpoint.c
>> +++ b/gdb/breakpoint.c
>> @@ -6457,23 +6457,6 @@ print_breakpoint_location (const breakpoint *b, const bp_location *loc)
>>       }
>>     else
>>       {
>> -      /* Internal breakpoints don't have a locspec string, but can become
>> -	 pending if the shared library the breakpoint is in is unloaded.
>> -	 For most internal breakpoint types though, after unloading the
>> -	 shared library, the breakpoint will be deleted and never recreated
>> -	 (see internal_breakpoint::re_set).  But for two internal
>> -	 breakpoint types bp_shlib_event and bp_thread_event this is not
>> -	 true.  Usually we don't expect the libraries that contain these
>> -	 breakpoints to ever be unloaded, but a buggy inferior might do
>> -	 such a thing, in which case GDB should be prepared to handle this
>> -	 case.
>> -
>> -	 If these two breakpoint types become pending then there will be no
>> -	 locspec string.  */
>> -      gdb_assert (b->locspec != nullptr
>> -		  || (!user_breakpoint_p (b)
>> -		      && (b->type == bp_shlib_event
>> -			  || b->type == bp_thread_event)));
>>         const char *locspec_str
>>   	= (b->locspec != nullptr ? b->locspec->to_string () : "");
>>         uiout->field_string ("pending", locspec_str);
>> diff --git a/gdb/testsuite/gdb.base/jit-unload-solib.c b/gdb/testsuite/gdb.base/jit-unload-solib.c
>> new file mode 100644
>> index 00000000000..3cf2c580320
>> --- /dev/null
>> +++ b/gdb/testsuite/gdb.base/jit-unload-solib.c
>> @@ -0,0 +1,21 @@
>> +/* This test program is part of GDB, the GNU debugger.
>> +
>> +   Copyright 2026 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/>.  */
>> +
>> +/* This simulates a JIT library.  */
>> +
>> +
>> +#include "jit-protocol.h"
>> diff --git a/gdb/testsuite/gdb.base/jit-unload.c b/gdb/testsuite/gdb.base/jit-unload.c
>> new file mode 100644
>> index 00000000000..92dfa16c055
>> --- /dev/null
>> +++ b/gdb/testsuite/gdb.base/jit-unload.c
>> @@ -0,0 +1,45 @@
>> +/* This test program is part of GDB, the GNU debugger.
>> +
>> +   Copyright 2026 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/>.  */
>> +
>> +/* Simulate loading of a library JIT code.  */
>> +
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +
>> +#ifdef __WIN32__
>> +#include <windows.h>
>> +#define dlopen(name, mode) LoadLibrary (TEXT (name))
>> +#define dlclose(handle) FreeLibrary (handle)
> 
> There's no definition of dlerror() here.  Similar tests do:
> 
>    #define dlerror() "an error occurred"
> 
> If you're happy to add that here then:
> 
> Approved-By: Andrew Burgess <aburgess@redhat.com>
> 
> Thanks,
> Andrew
> 
> 
>> +#else
>> +#include <dlfcn.h>
>> +#endif
>> +
>> +
>> +int
>> +main (void)
>> +{
>> +  void *handle = dlopen (SHLIB_NAME, RTLD_NOW);
>> +
>> +  if (handle == NULL)
>> +    {
>> +      fprintf (stderr, "%s\n", dlerror ());
>> +      exit (1);
>> +    }
>> +
>> +  dlclose (handle);
>> +  return 0;
>> +}
>> diff --git a/gdb/testsuite/gdb.base/jit-unload.exp b/gdb/testsuite/gdb.base/jit-unload.exp
>> new file mode 100644
>> index 00000000000..a5f9adbd76c
>> --- /dev/null
>> +++ b/gdb/testsuite/gdb.base/jit-unload.exp
>> @@ -0,0 +1,62 @@
>> +# Copyright 2026 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/>.
>> +
>> +# This test checks that gdb does not assert when unloading a shared library
>> +# that defines a __jit_debug_register_code if `set debug breakpoint on` is set.
>> +
>> +require allow_shlib_tests
>> +
>> +standard_testfile .c -solib.c
>> +set lib_testfile ${testfile}-lib
>> +set lib_binfile [standard_output_file $lib_testfile]
>> +
>> +if { [build_executable "build shlib" $lib_testfile $srcfile2 \
>> +	{debug shlib}] == -1 } {
>> +    return
>> +}
>> +
>> +set lib_testfile_on_target [gdb_download_shlib $lib_binfile]
>> +
>> +set options [list \
>> +		debug \
>> +		shlib_load \
>> +		additional_flags=-DSHLIB_NAME=\"${lib_testfile_on_target}\"]
>> +
>> +if { [prepare_for_testing "build main file" $testfile $srcfile \
>> +	$options] == -1 } {
>> +    return
>> +}
>> +
>> +if { ![runto_main] } {
>> +    return
>> +}
>> +
>> +gdb_test_no_output "set debug breakpoint on"
>> +
>> +set saw_exit false
>> +gdb_test_multiple "continue" unload {
>> +    -re "^\\\[Inferior $decimal \[^\r\n\]+ exited normally\\\]\r\n" {
>> +	set saw_exit true
>> +	exp_continue
>> +    }
>> +
>> +    -re "^$gdb_prompt $" {
>> +	gdb_assert ${saw_exit} $gdb_test_name
>> +    }
>> +
>> +    -re "^\[^\r\n\]*\r\n" {
>> +	exp_continue
>> +    }
>> +}
>> -- 
>> 2.54.0
>