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* [binutils-gdb] Fix "b f(std::string)", always use DMGL_VERBOSE
@ 2022-05-10 13:18 Pedro Alves
  0 siblings, 0 replies; only message in thread
From: Pedro Alves @ 2022-05-10 13:18 UTC (permalink / raw)
  To: gdb-cvs;h=cb2cd8cba82a0a5480a147d95b16098ad74d33c6

commit cb2cd8cba82a0a5480a147d95b16098ad74d33c6
Author: Pedro Alves <>
Date:   Fri Apr 29 23:21:18 2022 +0100

    Fix "b f(std::string)", always use DMGL_VERBOSE
    Currently, on any remotely modern GNU/Linux system,
    gdb.cp/no-dmgl-verbose.exp fails like so:
      break 'f(std::string)'
      Function "f(std::string)" not defined.
      (gdb) FAIL: gdb.cp/no-dmgl-verbose.exp: gdb_breakpoint: set breakpoint at 'f(std::string)'
      break 'f(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)'
      Function "f(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)" not defined.
      (gdb) PASS: gdb.cp/no-dmgl-verbose.exp: DMGL_VERBOSE-demangled f(std::string) is not defined
    This testcase was added back in 2011, here:
      [patch] Remove DMGL_VERBOSE
    Back then, the testcase would pass cleanly.  It turns out that the
    reason it fails today is that the testcase is exercising something in
    GDB that only makes sense if the program is built for the pre-C++11
    libstc++ ABI.  Back then the C++11 ABI didn't exist yet, but nowadays,
    you need to compile with -D_GLIBCXX_USE_CXX11_ABI=0 to use the old
    ABI.  See "Dual ABI" in the libstdc++ manual, at
    If we tweak the gdb.cp/no-dmgl-verbose.exp testcase to force the old
    ABI with -D_GLIBCXX_USE_CXX11_ABI=0, then it passes cleanly.
    So why is it that setting a breakpoint at "f(std::string)" fails with
    modern ABI, but passes with old ABI?
    This is where libiberty demangler's DMGL_VERBOSE option comes in.  The
    Itanium ABI mangling scheme has a shorthand form for std::string (and
    some other types).  See
      "In addition, the following catalog of abbreviations of the form "Sx" are used:
         <substitution> ::= St # ::std::
         <substitution> ::= Sa # ::std::allocator
         <substitution> ::= Sb # ::std::basic_string
         <substitution> ::= Ss # ::std::basic_string < char,
                                                       ::std::allocator<char> >
         <substitution> ::= Si # ::std::basic_istream<char,  std::char_traits<char> >
         <substitution> ::= So # ::std::basic_ostream<char,  std::char_traits<char> >
         <substitution> ::= Sd # ::std::basic_iostream<char, std::char_traits<char> >
    When the libiberty demangler encounters such a abbreviation, by
    default, it expands it to the user-friendly typedef "std::string",
    "std::iostream", etc..  If OTOH DMGL_VERBOSE is specified, the
    abbreviation is expanded to the underlying, non-typedefed fullname
    "std::basic_string<char, std::char_traits<char>, std::allocator<char> >"
    etc. as documented in the Itanium ABI, and pasted above.  You can see
    the standard abbreviations/substitutions in
    Back before Jan's patch in 2011, there were parts of GDB that used
    DMGL_VERBOSE, and others that did not, leading to mismatches.  The
    solution back then was to stop using DMGL_VERBOSE throughout.
    GDB has code in place to let users set a breakpoint at a function with
    typedefs in its parameters, like "b f(uint32_t)".  Demangled function
    names as they appear in the symbol tables almost (more on this is in a
    bit) never have typedefs in them, so when processing "b f(uint32_t)"
    GDB first replaces "uint32_t" for its underlying type, and then sets a
    breakpoint on the resulting prototype, in this case "f(unsigned int)".
    Now, if DMGL_VERBOSE is _not_ used, then the demangler demangles the
    mangled name of a function such as "void f(std::string)" that was
    mangled using the standard abbreviations mentioned above really as:
      "void f(std::string)".
    For example, the mangled name of "void f(std::string)" if you compile
    with old pre-C++11 ABI is "_Z1fSs".  That uses the abbreviation "Ss",
    so if you demangle that without DMGL_VERBOSE, you get:
      $ echo "_Z1fSs" | c++filt --no-verbose
    while with DMGL_VERBOSE you'd get:
      $ echo "_Z1fSs" | c++filt
      f(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)
    If, when the user sets a breakpoint at "f(std::string)", GDB would
    replace the std::string typedef for its underlying type using the same
    mechanism I mentioned for the "f(uint32_t)" example above, then GDB
    would really try to set a breakpoint at "f(std::basic_string<char,
    std::char_traits<char>, std::allocator<char> >)", and that would fail,
    as the function symbol GDB knows about for that function, given no
    DMGL_VERBOSE, is "f(std::string)".
    For this reason, the code that expands typedefs in function parameter
    names has an exception for std::string (and other standard
    abbreviation types), such that "std::string" is never
    And here lies the problem when you try to do "b f(std::string)" with a
    program compiled with the C++11 ABI.  In that case, std::string
    expands to a different underlying type, like so:
      f(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)
    and this symbol naturally mangles differently, as:
    and then because this doesn't use the shorthand mangling abbreviation
    for "std::string" anymore, it always demangles as:
      f(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)
    Now, when using the C++11 ABI, and you set a breakpoint at
    "f(std::string)", GDB's typedefs-in-parameters expansion code hits the
    exception for "std::string" and doesn't expand it, so the breakpoint
    fails to be inserted, because the symbol that exists is really the
      f(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)
    one, not "f(std::string)".
    So to fix things for C++11 ABI, clearly we need to remove the
    "std::string" exception from the typedef-in-parameters expansion
    logic.  If we do just that, then "b f(std::string)" starts working
    with the C++11 ABI.
    However, if we do _just_ that, and nothing else, then we break
    pre-C++11 ABI...
    The solution is then to in addition switch GDB to always use
    DMGL_VERBOSE.  If we do this, then pre-C++11 ABI symbols works the
    same as C++11 ABI symbols overall -- the demangler expands the
    standard abbreviation for "std::string" as "std::basic_string<char,
    std::char_traits<char>, std::allocator<char> >" and letting GDB expand
    the "std::string" typedef (etc.) too is no longer a problem.
    To avoid getting in the situation where some parts of GDB use
    DMGL_VERBOSE and others not, this patch adds wrappers around the
    demangler's entry points that GDB uses, and makes those force
    The point of the gdb.cp/no-dmgl-verbose.exp testcase was to try to
    ensure that DMGL_VERBOSE doesn't creep back in:
     gdb_test {break 'f(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)'} \
              {Function ".*" not defined\.} \
              "DMGL_VERBOSE-demangled f(std::string) is not defined"
    This obviously no longer makes sense to have, since we now depend on
    DMGL_VERBOSE.  So the patch replaces gdb.cp/no-dmgl-verbose.exp with a
    new gdb.cp/break-f-std-string.exp testcase whose purpose is to make
    sure that setting a breakpoint at "f(std::string)" works.  It
    exercises both pre-C++11 ABI and C++11 ABI.
    Change-Id: Ib54fab4cf0fd307bfd55bf1dd5056830096a653b

 gdb/cp-name-parser.y                               |  12 +--
 gdb/cp-support.c                                   |  45 +++++----
 gdb/cp-support.h                                   |  16 ++++
 .../{ =>}  |   0
 gdb/testsuite/gdb.cp/break-f-std-string.exp        | 105 +++++++++++++++++++++
 gdb/testsuite/gdb.cp/no-dmgl-verbose.exp           |  35 -------
 6 files changed, 154 insertions(+), 59 deletions(-)

diff --git a/gdb/cp-name-parser.y b/gdb/cp-name-parser.y
index 6410363c87f..34c691ddabb 100644
--- a/gdb/cp-name-parser.y
+++ b/gdb/cp-name-parser.y
@@ -1948,19 +1948,15 @@ allocate_info (void)
   return info;
-/* Convert RESULT to a string.  The return value is allocated
-   using xmalloc.  ESTIMATED_LEN is used only as a guide to the
-   length of the result.  This functions handles a few cases that
-   cplus_demangle_print does not, specifically the global destructor
-   and constructor labels.  */
+/* See cp-support.h.  */
 cp_comp_to_string (struct demangle_component *result, int estimated_len)
   size_t err;
-  char *res = cplus_demangle_print (DMGL_PARAMS | DMGL_ANSI,
-				    result, estimated_len, &err);
+  char *res = gdb_cplus_demangle_print (DMGL_PARAMS | DMGL_ANSI,
+					result, estimated_len, &err);
   return gdb::unique_xmalloc_ptr<char> (res);
@@ -2060,7 +2056,7 @@ cp_print (struct demangle_component *result)
   char *str;
   size_t err = 0;
-  str = cplus_demangle_print (DMGL_PARAMS | DMGL_ANSI, result, 64, &err);
+  str = gdb_cplus_demangle_print (DMGL_PARAMS | DMGL_ANSI, result, 64, &err);
   if (str == NULL)
diff --git a/gdb/cp-support.c b/gdb/cp-support.c
index f52055893d2..71c14635e38 100644
--- a/gdb/cp-support.c
+++ b/gdb/cp-support.c
@@ -70,18 +70,16 @@ static void add_symbol_overload_list_qualified
 struct cmd_list_element *maint_cplus_cmd_list = NULL;
-/* A list of typedefs which should not be substituted by replace_typedefs.  */
-static const char * const ignore_typedefs[] =
-  {
-    "std::istream", "std::iostream", "std::ostream", "std::string"
-  };
 static void
   replace_typedefs (struct demangle_parse_info *info,
 		    struct demangle_component *ret_comp,
 		    canonicalization_ftype *finder,
 		    void *data);
+static struct demangle_component *
+  gdb_cplus_demangle_v3_components (const char *mangled,
+				    int options, void **mem);
 /* A convenience function to copy STRING into OBSTACK, returning a pointer
    to the newly allocated string and saving the number of bytes saved in LEN.
@@ -146,13 +144,6 @@ inspect_type (struct demangle_parse_info *info,
   memcpy (name, ret_comp->u.s_name.s, ret_comp->u.s_name.len);
   name[ret_comp->u.s_name.len] = '\0';
-  /* Ignore any typedefs that should not be substituted.  */
-  for (const char *ignorable : ignore_typedefs)
-    {
-      if (strcmp (name, ignorable) == 0)
-	return 0;
-    }
   sym = NULL;
@@ -670,8 +661,8 @@ mangled_name_to_comp (const char *mangled_name, int options,
       struct demangle_component *ret;
-      ret = cplus_demangle_v3_components (mangled_name,
-					  options, memory);
+      ret = gdb_cplus_demangle_v3_components (mangled_name,
+					      options, memory);
       if (ret)
 	  std::unique_ptr<demangle_parse_info> info (new demangle_parse_info);
@@ -1635,7 +1626,7 @@ gdb_demangle (const char *name, int options)
   if (crash_signal == 0)
-    result.reset (bfd_demangle (NULL, name, options));
+    result.reset (bfd_demangle (NULL, name, options | DMGL_VERBOSE));
   if (catch_demangler_crashes)
@@ -1670,6 +1661,28 @@ gdb_demangle (const char *name, int options)
 /* See cp-support.h.  */
+char *
+gdb_cplus_demangle_print (int options,
+			  struct demangle_component *tree,
+			  int estimated_length,
+			  size_t *p_allocated_size)
+  return cplus_demangle_print (options | DMGL_VERBOSE, tree,
+			       estimated_length, p_allocated_size);
+/* A wrapper for cplus_demangle_v3_components that forces
+static struct demangle_component *
+gdb_cplus_demangle_v3_components (const char *mangled,
+				  int options, void **mem)
+  return cplus_demangle_v3_components (mangled, options | DMGL_VERBOSE, mem);
+/* See cp-support.h.  */
 unsigned int
 cp_search_name_hash (const char *search_name)
diff --git a/gdb/cp-support.h b/gdb/cp-support.h
index 4fbd53c8923..2e0ad50d2b9 100644
--- a/gdb/cp-support.h
+++ b/gdb/cp-support.h
@@ -175,6 +175,9 @@ struct type *cp_find_type_baseclass_by_name (struct type *parent_type,
 extern std::unique_ptr<demangle_parse_info> cp_demangled_name_to_comp
      (const char *demangled_name, std::string *errmsg);
+/* Convert RESULT to a string.  ESTIMATED_LEN is used only as a guide
+   to the length of the result.  */
 extern gdb::unique_xmalloc_ptr<char> cp_comp_to_string
   (struct demangle_component *result, int estimated_len);
@@ -186,10 +189,23 @@ extern void cp_merge_demangle_parse_infos (struct demangle_parse_info *,
 extern struct cmd_list_element *maint_cplus_cmd_list;
+/* Wrappers for bfd and libiberty demangling entry points.  Note they
+   all force DMGL_VERBOSE so that callers don't need to.  This is so
+   that GDB consistently uses DMGL_VERBOSE throughout -- we want
+   libiberty's demangler to expand standard substitutions to their
+   full template name.  */
 /* A wrapper for bfd_demangle.  */
 gdb::unique_xmalloc_ptr<char> gdb_demangle (const char *name, int options);
+/* A wrapper for cplus_demangle_print.  */
+extern char *gdb_cplus_demangle_print (int options,
+				       struct demangle_component *tree,
+				       int estimated_length,
+				       size_t *p_allocated_size);
 /* Find an instance of the character C in the string S that is outside
    of all parenthesis pairs, single-quoted strings, and double-quoted
    strings.  Also, ignore the char within a template name, like a ','
diff --git a/gdb/testsuite/gdb.cp/ b/gdb/testsuite/gdb.cp/
similarity index 100%
rename from gdb/testsuite/gdb.cp/
rename to gdb/testsuite/gdb.cp/
diff --git a/gdb/testsuite/gdb.cp/break-f-std-string.exp b/gdb/testsuite/gdb.cp/break-f-std-string.exp
new file mode 100644
index 00000000000..0869912bb29
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/break-f-std-string.exp
@@ -0,0 +1,105 @@
+# Copyright 2022 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
+# 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 <>.  */
+# Test setting a breakpoint at "f(std::string)".
+# GDB should be able to expand the std::string typedef, and then set
+# the breakpoint using the resulting name.  In the Itanium ABI's
+# mangling scheme, "std::string", "std::istream", "std::iostream",
+# "std::ostream" are special, though, they have corresponding standard
+# abbreviations.  The libiberty demangler only expands these standard
+# abbreviations to their full non-typedef underlying type if the
+# DMGL_VERBOSE option is requested.  By default it expands them to the
+# user-friendly "std::string", etc. typedefs.  GDB didn't use to use
+# that option, and would instead prevent expansion of the
+# "std::string" (etc.) standard-abbreviation typedefs at
+# breakpoint-set type, such that the function name used for function
+# lookup would match the "std::string" present in the function's
+# non-DMGL_VERBOSE demangled name.
+# For example (DMGL_VERBOSE):
+#  $ echo "_Z1fSs" | c++filt
+#  f(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)
+# vs (no DMGL_VERBOSE):
+#  $ echo "_Z1fSs" | c++filt --no-verbose
+#  f(std::string)
+# This design broke setting a breakpoint at "f(std::string)" when the
+# libstdc++ C++11 ABI was introduced, as the "f(std::string)"
+# function's mangled name no longer uses a standard substitution for
+# std::string...
+# I.e., with the libstdc++ C++11 ABI, we now have (and DMGL_VERBOSE
+# makes no difference):
+#  $ echo _Z1fNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE | c++filt
+#  f(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)
+# So nowadays, GDB always uses DMGL_VERBOSE and no longer prevents
+# std::string (etc.) typedef expansion.  This test exercises both
+# pre-C++11 and C++11 ABIs for this reason.  On non-libstdc++ systems
+# where _GLIBCXX_USE_CXX11_ABI has no effect, we just end up running
+# the test twice with whatever ABI is used.
+standard_testfile .cc
+if { [skip_cplus_tests] } { continue }
+# CXX11_ABI specifies the value to define _GLIBCXX_USE_CXX11_ABI as.
+proc test {cxx11_abi} {
+    global srcdir subdir srcfile binfile testfile
+    set options \
+	[list c++ debug additional_flags=-D_GLIBCXX_USE_CXX11_ABI=$cxx11_abi]
+    if { [gdb_compile \
+	      "${srcdir}/${subdir}/${srcfile}" "${binfile}-${cxx11_abi}.o" \
+	      object $options] != "" } {
+	untested "failed to compile"
+	return -1
+    }
+    clean_restart ${testfile}-${cxx11_abi}.o
+    # Since we're debugging an .o file, GDB doesn't figure out we're
+    # debugging C++ code and the current language when auto, is
+    # guessed as C.
+    gdb_test_no_output "set language c++"
+    # Get the type std::string is a typedef for.  We'll try to set a
+    # breakpoint using the expanded type too.
+    set realtype ""
+    set type "std::string"
+    gdb_test_multiple "whatis /r $type" "" {
+	-re -wrap "type = (\[^\r\n\]+)" {
+	    set realtype $expect_out(1,string)
+	    gdb_assert {![string eq "$realtype" "$type"]} \
+		$gdb_test_name
+	}
+    }
+    gdb_test "break f($type)" "$srcfile, line $::decimal\\."
+    if { $realtype != "" } {
+	gdb_test "break f($realtype)" "$srcfile, line $::decimal\\."
+    }
+foreach_with_prefix _GLIBCXX_USE_CXX11_ABI {0 1} {
+    test $_GLIBCXX_USE_CXX11_ABI
diff --git a/gdb/testsuite/gdb.cp/no-dmgl-verbose.exp b/gdb/testsuite/gdb.cp/no-dmgl-verbose.exp
deleted file mode 100644
index 14f11ddcf04..00000000000
--- a/gdb/testsuite/gdb.cp/no-dmgl-verbose.exp
+++ /dev/null
@@ -1,35 +0,0 @@
-# Copyright 2011-2022 Free Software Foundation, Inc.
-# This program is free software; you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation; either version 3 of the License, or
-# (at your option) any later version.
-# This program is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# GNU General Public License for more details.
-# You should have received a copy of the GNU General Public License
-# along with this program.  If not, see <>.  */
-# Test loading symbols from unrelocated C++ object files.
-standard_testfile .cc
-if { [skip_cplus_tests] } { continue }
-if { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}.o" object {c++ debug}] != "" } {
-     untested "failed to compile"
-     return -1
-clean_restart ${testfile}.o
-gdb_test_no_output "set breakpoint pending off"
-gdb_breakpoint {'f(std::string)'}
-gdb_test {break 'f(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)'} \
-	 {Function ".*" not defined\.} \
-	 "DMGL_VERBOSE-demangled f(std::string) is not defined"

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2022-05-10 13:18 [binutils-gdb] Fix "b f(std::string)", always use DMGL_VERBOSE Pedro Alves

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