Re: [PING][PATCH v8] gdb: Print linker namespace when showing a frame

[Guinevere Larsen <guinevere@redhat.com>]

Ping :)

On 6/22/26 5:34 PM, Guinevere Larsen wrote:
> Ping :)
>
> On 5/7/26 10:48 AM, Guinevere Larsen wrote:
>> When a user is stopped in a private linker namespace, the only way for
>> them to realize that is using the _linker_namespace convenience
>> variable. While serviceable, this is a sub-optimal solution, as most
>> users are unaware of convenience variables.
>>
>> This commit introduces a new way for users to be informed of the linker
>> namespace of a function, by printing it along with the function name.
>> This is done by using the proposed syntax for symbols and locations,
>> like so:
>>
>>    #0  [[0]]::main ()
>>
>> This is done by introducing a new function on solib.h,
>> linker_namespace_prefix, that returns either an empty string (if only
>> one namespace is active, or we can't determine the PC for the frame), or
>> the correct identifier. This should be printed manually every time GDB
>> will print a frame, so that we don't confuse other systems that look at
>> function names.
>>
>> A previous revision would break GDB's ability to strip the parameters of
>> C++ symbols, so this commit also adds a C++ SO to the test. However,
>> libstdc++ never gets unloaded, so many changes were required to make the
>> rest of the test still valid.
>>
>> Reviewed-By: Eli Zaretskii <eliz@gnu.org>
>> ---
>>   gdb/NEWS                                      |  4 +
>>   gdb/doc/gdb.texinfo                           |  9 +++
>>   gdb/solib.c                                   | 43 ++++++++---
>>   gdb/solib.h                                   | 13 ++++
>>   gdb/stack.c                                   |  2 +
>>   .../gdb.base/dlmopen-ns-ids-framefilter.py    | 31 ++++++++
>>   .../gdb.base/dlmopen-ns-ids-libc++.cc         | 36 +++++++++
>>   gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c  | 19 ++++-
>>   gdb/testsuite/gdb.base/dlmopen-ns-ids.exp     | 74 ++++++++++++++++---
>>   gdb/testsuite/gdb.mi/mi-dlmopen.exp           |  2 +-
>>   10 files changed, 206 insertions(+), 27 deletions(-)
>>   create mode 100644 
>> gdb/testsuite/gdb.base/dlmopen-ns-ids-framefilter.py
>>   create mode 100644 gdb/testsuite/gdb.base/dlmopen-ns-ids-libc++.cc
>>
>> diff --git a/gdb/NEWS b/gdb/NEWS
>> index 480e1854002..941178c06a4 100644
>> --- a/gdb/NEWS
>> +++ b/gdb/NEWS
>> @@ -78,6 +78,10 @@
>>   * The Windows native target now supports non-stop mode.  This feature
>>     requires Windows 10 or later.
>>   +* When debugging an inferior with multiple linker namespaces, 
>> functions
>> +  will be printed like so [[N]]::foo, where N is the namespace that
>> +  contains foo.  For example [[0]]::main.
>> +
>>   * New targets
>>     GNU/Linux/MicroBlaze (gdbserver) microblazeel-*linux*
>> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
>> index ab0216ff477..98a43f3a57e 100644
>> --- a/gdb/doc/gdb.texinfo
>> +++ b/gdb/doc/gdb.texinfo
>> @@ -22431,6 +22431,15 @@ possibility that those objects may 
>> cross-talk.  Each set of isolated
>>   shared objects is said to belong to a ``namespace'', and linker 
>> related
>>   actions such as relocations do not cross namespace boundaries.
>>   +When multiple linker namespaces are active, @value{GDBN} will 
>> print the
>> +identifier of the namespace that contains the function, when a function
>> +is printed.  It will look like this:
>> +
>> +@smallexample
>> +#0  [[1]]::inc (n=0) at dlmopen-ns-ids-lib.c
>> +#1  0x0000000000400591 in [[0]]::main () at dlmopen-ns-ids-main.c
>> +@end smallexample
>> +
>>   @kindex info dll
>>   @item info dll @var{regex}
>>   This is an alias of @code{info sharedlibrary}.
>> diff --git a/gdb/solib.c b/gdb/solib.c
>> index 782b844aa2f..add842b5771 100644
>> --- a/gdb/solib.c
>> +++ b/gdb/solib.c
>> @@ -1796,6 +1796,36 @@ solib_linker_namespace_count (program_space 
>> *pspace)
>>     return 0;
>>   }
>>   +/* See solib.h.  */
>> +
>> +int
>> +linker_namespace_for_addr (CORE_ADDR addr, program_space *pspace)
>> +{
>> +  for (const solib &so : pspace->solibs ())
>> +    if (solib_contains_address_p (so, addr))
>> +      {
>> +    if (so.ops ().supports_namespaces ())
>> +      return so.ops ().find_solib_ns (so);
>> +    break;
>> +      }
>> +
>> +  return 0;
>> +}
>> +
>> +/* See solib.h.  */
>> +
>> +std::string
>> +linker_namespace_prefix (const frame_info_ptr &frame)
>> +{
>> +  std::optional<CORE_ADDR> pc = get_frame_pc_if_available (frame);
>> +  program_space *pspace = get_frame_program_space (frame);
>> +  if (!pc.has_value () || solib_linker_namespace_count (pspace) <= 1)
>> +    return std::string ("");
>> +
>> +  return string_printf ("[[%d]]::", linker_namespace_for_addr 
>> (pc.value (),
>> +                                   pspace));
>> +}
>> +
>>   /* Implementation of the linker_namespace convenience variable.
>>        This returns the GDB internal identifier of the linker namespace,
>> @@ -1804,19 +1834,10 @@ solib_linker_namespace_count (program_space 
>> *pspace)
>>     static value *
>>   linker_namespace_make_value (gdbarch *gdbarch, internalvar *var,
>> -                     void *ignore)
>> +                 void *ignore)
>>   {
>> -  int nsid = 0;
>>     CORE_ADDR curr_pc = get_frame_pc (get_selected_frame ());
>> -
>> -  for (const solib &so : current_program_space->solibs ())
>> -    if (solib_contains_address_p (so, curr_pc))
>> -      {
>> -    if (so.ops ().supports_namespaces ())
>> -      nsid = so.ops ().find_solib_ns (so);
>> -
>> -    break;
>> -      }
>> +  int nsid = linker_namespace_for_addr (curr_pc, 
>> current_program_space);
>>       /* If the PC is not in an SO, or the solib_ops doesn't support
>>        linker namespaces, the inferior is in the default namespace.  */
>> diff --git a/gdb/solib.h b/gdb/solib.h
>> index 564655c4a57..39931bb1b93 100644
>> --- a/gdb/solib.h
>> +++ b/gdb/solib.h
>> @@ -334,6 +334,19 @@ extern const char *solib_name_from_address 
>> (struct program_space *, CORE_ADDR);
>>     extern bool solib_contains_address_p (const solib &, CORE_ADDR);
>>   +/* Given the address ADDR, return which linker namespace contains
>> +   this address in PSPACE.  If ADDR is present in multiple namespaces,
>> +   an arbitrary one is returned.  If ADDR is not present in any
>> +   namespace, or if the target doesn't support linker namespaces,
>> +   returns 0.  */
>> +
>> +extern int linker_namespace_for_addr (CORE_ADDR addr, program_space 
>> *pspace);
>> +
>> +/* Calculate the linker namespace identifier, and turn it into a prefix
>> +   to be used to print a frame.  */
>> +
>> +extern std::string linker_namespace_prefix (const frame_info_ptr 
>> &frame);
>> +
>>   /* Return whether the data starting at VADDR, size SIZE, must be kept
>>      in a core file for shared libraries loaded before "gcore" is used
>>      to be handled correctly when the core file is loaded.  This only
>> diff --git a/gdb/stack.c b/gdb/stack.c
>> index 7329430adab..ac270718a91 100644
>> --- a/gdb/stack.c
>> +++ b/gdb/stack.c
>> @@ -1306,6 +1306,7 @@ print_frame (struct ui_out *uiout,
>>       annotate_frame_function_name ();
>>         string_file stb;
>> +    gdb_puts (linker_namespace_prefix (frame).c_str (), &stb);
>>       gdb_puts (funname ? funname.get () : "??", &stb);
>>       uiout->field_stream ("func", stb, function_name_style.style ());
>>       uiout->wrap_hint (3);
>> @@ -1466,6 +1467,7 @@ info_frame_command_core (const frame_info_ptr 
>> &fi, bool selected_frame_p)
>>       fputs_styled ("<unavailable>", metadata_style.style (), 
>> gdb_stdout);
>>       gdb_stdout->wrap_here (3);
>> +  gdb_puts (linker_namespace_prefix (fi).c_str ());
>>     if (funname.get () != nullptr)
>>       {
>>         gdb_puts (" in ");
>> diff --git a/gdb/testsuite/gdb.base/dlmopen-ns-ids-framefilter.py 
>> b/gdb/testsuite/gdb.base/dlmopen-ns-ids-framefilter.py
>> new file mode 100644
>> index 00000000000..11d96fcfbc4
>> --- /dev/null
>> +++ b/gdb/testsuite/gdb.base/dlmopen-ns-ids-framefilter.py
>> @@ -0,0 +1,31 @@
>> +# Copyright (C) 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 file is part of the GDB testsuite.  It tests if printing the
>> +# linker namespace id is affected by a null frame filter
>> +
>> +import gdb
>> +
>> +
>> +class NullFilter:
>> +    def __init__(self):
>> +        self.name = "null filter"
>> +        self.priority = 100
>> +        self.enabled = True
>> +        gdb.frame_filters[self.name] = self
>> +
>> +    def filter(self, iterator):
>> +        return iterator
>> diff --git a/gdb/testsuite/gdb.base/dlmopen-ns-ids-libc++.cc 
>> b/gdb/testsuite/gdb.base/dlmopen-ns-ids-libc++.cc
>> new file mode 100644
>> index 00000000000..9abf3f25096
>> --- /dev/null
>> +++ b/gdb/testsuite/gdb.base/dlmopen-ns-ids-libc++.cc
>> @@ -0,0 +1,36 @@
>> +/* This testcase is part of GDB, the GNU debugger.
>> +
>> +   Copyright 2025-2026 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/>.
>> +
>> +*/
>> +
>> +int gdb_dlmopen_glob = 0;
>> +
>> +int
>> +cpp_inc (int n)
>> +{
>> +    int amount = gdb_dlmopen_glob;
>> +    return n + amount;  /* bp.inc.  */
>> +}
>> +
>> +extern "C" {
>> +  __attribute__((visibility ("default")))
>> +  int
>> +  inc (int n)
>> +  {
>> +    return cpp_inc (n);
>> +  }
>> +}
>> diff --git a/gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c 
>> b/gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c
>> index 4f08a5135b2..f13eb9168de 100644
>> --- a/gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c
>> +++ b/gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c
>> @@ -27,7 +27,7 @@
>>   int
>>   main (void)
>>   {
>> -  void *handle[4];
>> +  void *handle[5];
>>     int (*fun) (int);
>>     Lmid_t lmid;
>>     int dl;
>> @@ -41,20 +41,31 @@ main (void)
>>     handle[2] = dlmopen (LM_ID_NEWLM, DSO_NAME, RTLD_LAZY | RTLD_LOCAL);
>>     assert (handle[2] != NULL);
>>   +  /* We open the C++ SO on the main namespace because libstdc++ 
>> marks a
>> +     lot of objects as GNU_UNIQUE meaning that they effectively 
>> can't be
>> +     unloaded, so the final namespace would never be fully 
>> unloaded.  */
>> +  handle[3] = dlmopen (LM_ID_BASE, CPP_DSO_NAME, RTLD_LAZY | 
>> RTLD_LOCAL);
>> +  assert (handle[3] != NULL);
>> +
>>     for (dl = 2; dl >= 0; dl--)
>>       {
>>         fun = dlsym (handle[dl], "inc");
>>         fun (dl);
>>       }
>> +  /* C++ call, to make sure the linker namespace doesn't break anything
>> +     of the C++ handling of symbols.  */
>> +  fun = dlsym (handle[3], "inc");
>> +  fun (-1);
>>       dlclose (handle[0]); /* TAG: first dlclose */
>>     dlclose (handle[1]); /* TAG: second dlclose */
>>     dlclose (handle[2]); /* TAG: third dlclose */
>> +  dlclose (handle[3]); /* TAG: fourth dlclose */
>>   -  handle[3] = dlmopen (LM_ID_NEWLM, DSO_NAME, RTLD_LAZY | 
>> RTLD_LOCAL);
>> -  dlinfo (handle[3], RTLD_DI_LMID, &lmid);
>> +  handle[4] = dlmopen (LM_ID_NEWLM, DSO_NAME, RTLD_LAZY | RTLD_LOCAL);
>> +  dlinfo (handle[4], RTLD_DI_LMID, &lmid);
>>   -  dlclose (handle[3]); /* TAG: fourth dlclose */
>> +  dlclose (handle[4]); /* TAG: final dlclose */
>>       return 0;
>>   }
>> diff --git a/gdb/testsuite/gdb.base/dlmopen-ns-ids.exp 
>> b/gdb/testsuite/gdb.base/dlmopen-ns-ids.exp
>> index e40bc213454..cc1696f4229 100644
>> --- a/gdb/testsuite/gdb.base/dlmopen-ns-ids.exp
>> +++ b/gdb/testsuite/gdb.base/dlmopen-ns-ids.exp
>> @@ -21,20 +21,29 @@
>>     require allow_dlmopen_tests
>>   -standard_testfile -main.c -lib.c
>> +standard_testfile -main.c -lib.c -framefilter.py -libc++.cc
>>     set srcfile_lib $srcfile2
>> +set srcfile_libcpp $srcfile4
>>   set so_name dlmopen-lib.so
>> +set cpp_so_name dlmopen-libc++.so
>>   set binfile_lib [standard_output_file $so_name]
>> +set binfile_libcpp [standard_output_file $cpp_so_name]
>>     if { [build_executable "build shlib" $binfile_lib $srcfile_lib \
>>         [list debug shlib]] == -1 } {
>>       return
>>   }
>>   +if { [build_executable "build shlib" $binfile_libcpp 
>> $srcfile_libcpp \
>> +      [list debug shlib c++]] == -1 } {
>> +    return
>> +}
>> +
>>   if { [build_executable "failed to build" $testfile $srcfile \
>>         [list additional_flags=-DDSO_NAME=\"$binfile_lib\" \
>> -           shlib_load debug]] } {
>> +        additional_flags=-DCPP_DSO_NAME=\"$binfile_libcpp\" \
>> +        shlib_load debug]] } {
>>       return
>>   }
>>   @@ -107,11 +116,13 @@ proc check_no_duplicates {} {
>>   proc get_first_so_ns {} {
>>       set ns -1
>>       set lib_regexp [string_to_regexp ${::binfile_lib}]
>> +    set libcpp_regexp [string_to_regexp ${::binfile_libcpp}]
>> +    set both_regexp "($lib_regexp|$libcpp_regexp)"
>>       gdb_test_multiple "info sharedlibrary $::so_name" "get SO 
>> namespace" -lbl {
>>       -re "\r\nFrom\\s+To\\s+\(Linker NS\\s+\)?Syms\\s+Read\\s+Shared 
>> Object Library(?=\r\n)" {
>>           exp_continue
>>       }
>> -    -re 
>> "\r\n$::hex\\s+$::hex\\s+($::decimal)\\s+\[^\r\n]+${lib_regexp}(?=\r\n)" 
>> {
>> +    -re 
>> "\r\n$::hex\\s+$::hex\\s+($::decimal)\\s+\[^\r\n]+${both_regexp}(?=\r\n)" 
>> {
>>           if {$ns == -1} {
>>           set ns $expect_out(1,string)
>>           }
>> @@ -155,8 +166,8 @@ proc test_info_shared {} {
>>       gdb_test "next" ".*third dlclose.*" "close second library"
>>       gdb_assert {[get_first_so_ns] == 3} "before closing two libraries"
>>   -    gdb_breakpoint [gdb_get_line_number "TAG: fourth dlclose"]
>> -    gdb_continue_to_breakpoint "TAG: fourth dlclose"
>> +    gdb_breakpoint [gdb_get_line_number "TAG: final dlclose"]
>> +    gdb_continue_to_breakpoint "TAG: final dlclose"
>>       # As of writing this test, glibc's LMID is just an index on an 
>> array of
>>       # namespaces.  After closing a namespace, requesting a new one 
>> will
>>       # return the index of the lowest-closed namespace, so this will 
>> likely
>> @@ -192,6 +203,11 @@ proc_with_prefix test_conv_vars {} {
>>       gdb_test "print \$_linker_namespace" ".* = 0" \
>>       "Still in the default namespace"
>>   +    # There should be no namespace ID visible, since there's
>> +    # only one namespace loaded.
>> +    gdb_test "backtrace" "\#0\\s+main .*" \
>> +    "No namespace ID in backtrace"
>> +
>>       gdb_breakpoint "inc" allow-pending
>>       gdb_breakpoint [gdb_get_line_number "TAG: first dlclose"]
>>   @@ -200,14 +216,41 @@ proc_with_prefix test_conv_vars {} {
>>         gdb_test "print \$_linker_namespace" ".* = $dl" \
>>           "Verify we're in namespace $dl"
>> +
>> +    gdb_test "frame" "\#0\\s+\\\[\\\[$dl\\\]\\\]::inc.*" \
>> +        "Namespace ID in the frame"
>>       }
>>         # Check that we display the namespace of the selected
>>       # frame, not the lowermost one.
>> -    gdb_test "up" "\#1.*in main.*"
>> +    gdb_test "up" "\#1.*in \\\[\\\[0\\\]\\\]::main.*"
>>       gdb_test "print \$_linker_namespace" ".* = 0" \
>>       "print namespace of selected frame"
>>   +    gdb_test "backtrace" [multi_line \
>> +        "\#0\\s+\\\[\\\[1\\\]\\\]::inc \[^\r\n\]*" \
>> +        "\#1\\s+$::hex in \\\[\\\[0\\\]\\\]::main \[^\r\n\]*" ] \
>> +    "raw backtrace"
>> +
>> +    set remote_python_file [gdb_remote_download host \
>> +                $::srcdir/$::subdir/$::srcfile3]
>> +    gdb_test_no_output "source $remote_python_file" "load frame filter"
>> +    gdb_test "backtrace" [multi_line \
>> +        "\#0\\s+\\\[\\\[1\\\]\\\]::inc \[^\r\n\]*" \
>> +        "\#1\\s+$::hex in \\\[\\\[0\\\]\\\]::main \[^\r\n\]*" ] \
>> +    "With null frame filter"
>> +
>> +    # Ensure that the code for identifying and removing parameters for
>> +    # C++ symbols still works with linker namespace IDs.
>> +    gdb_continue_to_breakpoint "inc on c++ SO"
>> +    gdb_test "step" "\\\[\\\[0\\\]\\\]::cpp_inc \\\(n=-1\\\).*" 
>> "step into c++ symbol"
>> +    gdb_test "backtrace" [multi_line \
>> +        "\#0\\s+\\\[\\\[0\\\]\\\]::cpp_inc \\\(n=-1\\\)\[^\r\n\]*" \
>> +        "\#1\\s+$::hex in \\\[\\\[0\\\]\\\]::inc 
>> \\\(n=-1\\\)\[^\r\n\]*" \
>> +        "\#2\\s+$::hex in \\\[\\\[0\\\]\\\]::main \[^\r\n\]*" ] \
>> +    "bt through c++ symbols"
>> +
>> +    # Check that everything still works as we close namespaces.
>>       gdb_continue_to_breakpoint "first dlclose"
>>       gdb_test "print \$_linker_namespace_count" "4" "all SOs loaded"
>>   @@ -264,15 +307,23 @@ proc test_info_linker_namespaces {} {
>>         # Some systems may add libc and libm to every loaded namespace,
>>       # others may load only one or neither, because the SO doesn't
>> -    # actually use either library.  The best we can do is check if
>> -    # we found the dynamic linker, and up to 2 more libraries.
>> -    gdb_assert {$n_libraries <= 3}  "the correct number of libraries 
>> was reported"
>> +    # actually use either library.  Similarly, because of the c++
>> +    # SO, libstdc++ and libgcc_s may be included.  The best we can
>> +    # do is check if  we found the dynamic linker, the SO, and up to
>> +    # 4 more libraries.  Ensuring that only the right one shows up is
>> +    # in the foreach block.
>> +    gdb_assert {$n_libraries <= 6}  "the correct number of libraries 
>> was reported"
>>         set binfile_lib_re [string_to_regexp $::binfile_lib]
>>   -    foreach_with_prefix ns {1 2 3} {
>> +    foreach_with_prefix ns {1 2 3 0} {
>>       set found_test_so false
>>       set n_libraries 999
>> +    set expected_libs 4
>> +    if {$ns == 0} {
>> +        set expected_libs 6
>> +        set binfile_lib_re [string_to_regexp $::binfile_libcpp]
>> +    }
>>         gdb_test_multiple "info linker-namespaces $ns" "print 
>> namespace $ns" {
>>           -re ".*($::decimal) librar(?:y|ies) loaded in linker 
>> namespace $ns:\r\n" {
>> @@ -290,7 +341,8 @@ proc test_info_linker_namespaces {} {
>>       # actually use either library.  The best we can do is check if
>>       # we found the dynamic linker, the test SO, and maybe up to 2
>>       # more libraries.
>> -    gdb_assert {$n_libraries <= 4} "the correct number of libraries 
>> was reported"
>> +    gdb_assert {$n_libraries <= $expected_libs} \
>> +        "the correct number of libraries was reported"
>>       gdb_assert {$found_test_so} "this testfile's SO was reported"
>>       }
>>   diff --git a/gdb/testsuite/gdb.mi/mi-dlmopen.exp 
>> b/gdb/testsuite/gdb.mi/mi-dlmopen.exp
>> index ff854ac7dd4..832c6ea6fe6 100644
>> --- a/gdb/testsuite/gdb.mi/mi-dlmopen.exp
>> +++ b/gdb/testsuite/gdb.mi/mi-dlmopen.exp
>> @@ -156,7 +156,7 @@ proc check_solib_unload_events {} {
>>       -disp keep -func main -file ".*$::srcfile" -line $::bp_main
>>         # Run past all the dlopen and dlmopen calls.
>> -    mi_execute_to "exec-continue" "breakpoint-hit" main "" ".*" 
>> $::bp_loaded \
>> +    mi_execute_to "exec-continue" "breakpoint-hit" {\[\[0\]\]::main} 
>> "" ".*" $::bp_loaded \
>>       {"" "disp=\"keep\""} "continue until all libraries are loaded"
>>         # Check that the dynamic linker has now been loaded multiple 
>> times.
>>
>> base-commit: 9e6e0c3cd9e6d5ee4953f72a805cff5f150aa2fd
>
>

-- 
Cheers,
Guinevere Larsen
it/its
she/her (deprecated)