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

[Guinevere Larsen <guinevere@redhat.com>]

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)