problem looking up some symbols when they have a linkage name

This patch fixes a known failure in gdb.ada/maint_with_ada.exp
(maintenance check-psymtabs). Another way to witness the same
issue is by considering the following Ada declarations...

   type Wrapper is record
      A : Integer;
   end record;
   u00045 : constant Wrapper := (A => 16#060287af#);
   pragma Export (C, u00045, "symada__cS");

... which declares a variable name "u00045" but with a linkage
name which is "symada__cS". This variable is a record with one
component, the Ada equivalent of a struct with one field in C.
Trying to print that variable's value currently yields:

    (gdb) p /x <symada__cS>
    'symada(char, signed)' has unknown type; cast it to its declared type

This indicates that GDB was only able to find the minimal symbol,
but not the full symbol. The expected output is:

    (gdb) print /x <symada__cS>
    $1 = (a => 0x60287af)

The error message gives a hint about what's happening: We processed
the symbol through gdb_demangle, which in the case of this particular
symbol name, ends up matching the C++ naming scheme. As a result,
the demangler transforms our symbol name into 'symada(char, signed)',
thus breaking Ada lookups.

This patch fixes the issue by first introducing a new language_defn
attribute called la_store_sym_names_in_linkage_form_p, which is a boolean
to be set to true for the few languages that do not want their symbols
to have their names stored in demangled form, and false otherwise.
We then use this language attribute to skip the call to gdb_demangle
for all languages whose la_store_sym_names_in_linkage_form_p is true.

In terms of the selection of languages for which the new attribute
is set to true, the selection errs on the side of preserving the
existing behavior, and only changes the behavior for the languages
where we are certain storing symbol names in demangling form is not
needed. It is conceivable that other languages might be in the same
situation, but I not knowing in detail the symbol name enconding
strategy, I decided to play it safe and let other language maintainers
potentially adjust their language if it makes sense to do so.

gdb/ChangeLog:

        PR gdb/22670
        * dwarf2read.c (dwarf2_physname): Do not return the demangled
        symbol name if the CU's language stores symbol names in linkage
        format.
        * language.h (struct language_defn)
        <la_store_sym_names_in_linkage_form_p>: New field.  Adjust
        all instances of this struct.

gdb/testsuite/ChangeLog:

        * gdb.ada/maint_with_ada.exp: Remove PR gdb/22670 setup_kfail.

        * gdb.ada/notcplusplus: New testcase.

        * gdb.base/c-linkage-name.c: New file.
        * gdb.base/c-linkage-name.exp: New testcase.

Tested on x86_64-linux.
This also passes AdaCore's internal GDB testsuite.

gdb/ChangeLog

@@ -1,3 +1,13 @@
+2018-03-27  Joel Brobecker  <brobecker@adacore.com>
+
+	PR gdb/22670
+	* dwarf2read.c (dwarf2_physname): Do not return the demangled
+	symbol name if the CU's language stores symbol names in linkage
+	format.
+	* language.h (struct language_defn)
+	<la_store_sym_names_in_linkage_form_p>: New field.  Adjust
+	all instances of this struct.
+
 2018-03-26  Tom Tromey  <tom@tromey.com>
 
 	* stack.c (backtrace_command_1): Remove verbose code.

gdb/ada-lang.c

@@ -14518,6 +14518,7 @@ extern const struct language_defn ada_language_defn = {
   ada_read_var_value,		/* la_read_var_value */
   NULL,                         /* Language specific skip_trampoline */
   NULL,                         /* name_of_this */
+  true,                         /* la_store_sym_names_in_linkage_form_p */
   ada_lookup_symbol_nonlocal,   /* Looking up non-local symbols.  */
   basic_lookup_transparent_type,        /* lookup_transparent_type */
   ada_la_decode,                /* Language specific symbol demangler */

gdb/c-lang.c

@@ -853,6 +853,7 @@ extern const struct language_defn c_language_defn =
   default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   NULL,				/* name_of_this */
+  true,				/* la_store_sym_names_in_linkage_form_p */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
   basic_lookup_transparent_type,/* lookup_transparent_type */
   NULL,				/* Language specific symbol demangler */
@@ -998,6 +999,7 @@ extern const struct language_defn cplus_language_defn =
   default_read_var_value,	/* la_read_var_value */
   cplus_skip_trampoline,	/* Language specific skip_trampoline */
   "this",                       /* name_of_this */
+  false,			/* la_store_sym_names_in_linkage_form_p */
   cp_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
   cp_lookup_transparent_type,   /* lookup_transparent_type */
   gdb_demangle,			/* Language specific symbol demangler */
@@ -1052,6 +1054,7 @@ extern const struct language_defn asm_language_defn =
   default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   NULL,				/* name_of_this */
+  true,				/* la_store_sym_names_in_linkage_form_p */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
   basic_lookup_transparent_type,/* lookup_transparent_type */
   NULL,				/* Language specific symbol demangler */
@@ -1106,6 +1109,7 @@ extern const struct language_defn minimal_language_defn =
   default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   NULL,				/* name_of_this */
+  true,				/* la_store_sym_names_in_linkage_form_p */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
   basic_lookup_transparent_type,/* lookup_transparent_type */
   NULL,				/* Language specific symbol demangler */

gdb/d-lang.c

@@ -229,6 +229,7 @@ extern const struct language_defn d_language_defn =
   default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline.  */
   "this",
+  false,			/* la_store_sym_names_in_linkage_form_p */
   d_lookup_symbol_nonlocal,
   basic_lookup_transparent_type,
   d_demangle,			/* Language specific symbol demangler.  */

gdb/dwarf2read.c

@@ -11492,7 +11492,11 @@ dwarf2_physname (const char *name, struct die_info *die, struct dwarf2_cu *cu)
   if (mangled != NULL)
     {
 
-      if (cu->language == language_go)
+      if (language_def (cu->language)->la_store_sym_names_in_linkage_form_p)
+	{
+	  /* Do nothing (do not demangle the symbol name).  */
+	}
+      else if (cu->language == language_go)
 	{
 	  /* This is a lie, but we already lie to the caller new_symbol.
 	     new_symbol assumes we return the mangled name.

gdb/f-lang.c

@@ -269,6 +269,7 @@ extern const struct language_defn f_language_defn =
   default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   NULL,                    	/* name_of_this */
+  false,			/* la_store_sym_names_in_linkage_form_p */
   cp_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
   basic_lookup_transparent_type,/* lookup_transparent_type */
 

gdb/go-lang.c

@@ -590,6 +590,7 @@ extern const struct language_defn go_language_defn =
   default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline.  */
   NULL,				/* name_of_this */
+  false,			/* la_store_sym_names_in_linkage_form_p */
   basic_lookup_symbol_nonlocal, 
   basic_lookup_transparent_type,
   go_demangle,			/* Language specific symbol demangler.  */

gdb/language.c

@@ -864,6 +864,7 @@ const struct language_defn unknown_language_defn =
   default_read_var_value,	/* la_read_var_value */
   unk_lang_trampoline,		/* Language specific skip_trampoline */
   "this",        	    	/* name_of_this */
+  true,				/* store_sym_names_in_linkage_form_p */
   basic_lookup_symbol_nonlocal, /* lookup_symbol_nonlocal */
   basic_lookup_transparent_type,/* lookup_transparent_type */
   unk_lang_demangle,		/* Language specific symbol demangler */
@@ -915,6 +916,7 @@ const struct language_defn auto_language_defn =
   default_read_var_value,	/* la_read_var_value */
   unk_lang_trampoline,		/* Language specific skip_trampoline */
   "this",		        /* name_of_this */
+  false,			/* store_sym_names_in_linkage_form_p */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
   basic_lookup_transparent_type,/* lookup_transparent_type */
   unk_lang_demangle,		/* Language specific symbol demangler */

gdb/language.h

@@ -264,6 +264,26 @@ struct language_defn
 
     const char *la_name_of_this;
 
+    /* True if the symbols names should be stored in GDB's data structures
+       for minimal/partial/full symbols using their linkage (aka mangled)
+       form; false if the symbol names should be demangled first.
+
+       Most languages implement symbol lookup by comparing the demangled
+       names, in which case it is advantageous to store that information
+       already demangled, and so would set this field to false.
+
+       On the other hand, some languages have opted for doing symbol
+       lookups by comparing mangled names instead, for reasons usually
+       specific to the language.  Those languages should set this field
+       to true.
+
+       And finally, other languages such as C or Asm do not have
+       the concept of mangled vs demangled name, so those languages
+       should set this field to true as well, to prevent any accidental
+       demangling through an unrelated language's demangler.  */
+
+    const bool la_store_sym_names_in_linkage_form_p;
+
     /* This is a function that lookup_symbol will call when it gets to
        the part of symbol lookup where C looks up static and global
        variables.  */

gdb/m2-lang.c

@@ -377,6 +377,7 @@ extern const struct language_defn m2_language_defn =
   default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   NULL,		                /* name_of_this */
+  false,			/* la_store_sym_names_in_linkage_form_p */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
   basic_lookup_transparent_type,/* lookup_transparent_type */
   NULL,				/* Language specific symbol demangler */

gdb/objc-lang.c

@@ -389,6 +389,7 @@ extern const struct language_defn objc_language_defn = {
   default_read_var_value,	/* la_read_var_value */
   objc_skip_trampoline, 	/* Language specific skip_trampoline */
   "self",		        /* name_of_this */
+  false,			/* la_store_sym_names_in_linkage_form_p */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
   basic_lookup_transparent_type,/* lookup_transparent_type */
   objc_demangle,		/* Language specific symbol demangler */

gdb/opencl-lang.c

@@ -1065,6 +1065,7 @@ extern const struct language_defn opencl_language_defn =
   default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   NULL,                         /* name_of_this */
+  false,			/* la_store_sym_names_in_linkage_form_p */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
   basic_lookup_transparent_type,/* lookup_transparent_type */
   NULL,				/* Language specific symbol demangler */

gdb/p-lang.c

@@ -439,6 +439,7 @@ extern const struct language_defn pascal_language_defn =
   default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   "this",		        /* name_of_this */
+  false,			/* la_store_sym_names_in_linkage_form_p */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
   basic_lookup_transparent_type,/* lookup_transparent_type */
   NULL,				/* Language specific symbol demangler */

gdb/rust-lang.c

@@ -2070,6 +2070,7 @@ extern const struct language_defn rust_language_defn =
   default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   NULL,				/* name_of_this */
+  false,			/* la_store_sym_names_in_linkage_form_p */
   rust_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
   basic_lookup_transparent_type,/* lookup_transparent_type */
   gdb_demangle,			/* Language specific symbol demangler */

gdb/testsuite/ChangeLog

@@ -1,3 +1,12 @@
+2018-03-27  Joel Brobecker  <brobecker@adacore.com>
+
+	* gdb.ada/maint_with_ada.exp: Remove PR gdb/22670 setup_kfail.
+
+	* gdb.ada/notcplusplus: New testcase.
+
+	* gdb.base/c-linkage-name.c: New file.
+	* gdb.base/c-linkage-name.exp: New testcase.
+
 2018-03-26  Tom Tromey  <tom@tromey.com>
 
 	* gdb.python/py-framefilter.exp: Add test for KeyboardInterrupt.

gdb/testsuite/gdb.ada/maint_with_ada.exp

@@ -32,7 +32,6 @@ gdb_breakpoint "adainit"
 gdb_breakpoint "Var_Arr_Typedef"
 gdb_breakpoint "Do_Nothing"
 
-setup_kfail gdb/22670 "*-*-*"
 gdb_test_no_output "maintenance check-psymtabs"
 
 gdb_test_no_output "maintenance check-symtabs"

gdb/testsuite/gdb.ada/notcplusplus.exp

@@ -0,0 +1,45 @@
+# Copyright 2018 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/>.
+
+load_lib "ada.exp"
+
+if { [skip_ada_tests] } { return -1 }
+
+standard_ada_testfile foo
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable {debug}] != ""} {
+    return -1
+}
+
+clean_restart ${testfile}
+
+gdb_test "print /x <symada__cS>" \
+         "= \\(a => 0x60287af\\)" \
+         "print <symada__cS> before loading symbols from ver.ads"
+
+# Force the partial symbosl from ver.ads to be expanded into full symbols.
+
+gdb_test \
+     "list ver.ads:16" \
+     [multi_line ".*" \
+                 "16\\s+package Ver is" \
+                 "17\\s+type Wrapper is record" \
+                 "18\\s+A : Integer;" \
+                 "19\\s+end record;" \
+                 "20\\s+u00045 : constant Wrapper := \\(A => 16#060287af#\\);"]
+
+gdb_test "print /x <symada__cS>" \
+         "= \\(a => 0x60287af\\)" \
+         "print <symada__cS> after loading symbols from ver.ads"

gdb/testsuite/gdb.ada/notcplusplus/foo.adb

@@ -0,0 +1,21 @@
+--  Copyright 2018 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/>.
+
+with Pck; use Pck;
+with Ver; use Ver;
+procedure Foo is
+begin
+   Do_Nothing (u00045'Address);
+end Foo;

gdb/testsuite/gdb.ada/notcplusplus/pck.adb

@@ -0,0 +1,21 @@
+--  Copyright 2018 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/>.
+
+package body Pck is
+   procedure Do_Nothing (A : System.Address) is
+   begin
+      null;
+   end Do_Nothing;
+end Pck;

gdb/testsuite/gdb.ada/notcplusplus/pck.ads

@@ -0,0 +1,19 @@
+--  Copyright 2018 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/>.
+
+with System;
+package Pck is
+   procedure Do_Nothing (A : System.Address);
+end Pck;

gdb/testsuite/gdb.ada/notcplusplus/ver.ads

@@ -0,0 +1,22 @@
+--  Copyright 2018 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/>.
+
+package Ver is
+   type Wrapper is record
+      A : Integer;
+   end record;
+   u00045 : constant Wrapper := (A => 16#060287af#);
+   pragma Export (C, u00045, "symada__cS");
+end Ver;

gdb/testsuite/gdb.base/c-linkage-name.c

@@ -0,0 +1,44 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2018 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/>.  */
+
+struct wrapper
+{
+  int a;
+};
+
+/* Create a global variable whose name in the assembly code
+   (aka the "linkage name") is different from the name in
+   the source code.  The goal is to create a symbol described
+   in DWARF using a DW_AT_linkage_name attribute, with a name
+   which follows the C++ mangling.
+
+   In this particular case, we chose "symada__cS" which, if it were
+   demangled, would translate to "symada (char, signed)".  */
+struct wrapper mundane asm ("symada__cS") = {0x060287af};
+
+void
+do_something (struct wrapper *w)
+{
+  w->a++;
+}
+
+int
+main (void)
+{
+  do_something (&mundane);
+  return 0;
+}

gdb/testsuite/gdb.base/c-linkage-name.exp

@@ -0,0 +1,47 @@
+# Copyright 2018 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 is intended to test that
+# gdb can correctly print arrays with indexes for each element of the
+# array.
+
+standard_testfile .c
+
+if { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug}] != "" } {
+    untested "failed to compile"
+    return -1
+}
+
+clean_restart ${binfile}
+
+# Try to print MUNDANE, but using its linkage name.
+
+gdb_test "print symada__cS" \
+         " = {a = 100829103}" \
+         "print symada__cS before partial symtab expansion"
+
+# Force the symbols to be expanded for the unit that contains
+# our symada__cS symbol by, e.g. inserting a breakpoint on one
+# of the founction also provided by the same using.
+
+gdb_test "break main" \
+         "Breakpoint $decimal at $hex: file .*$srcfile, line $decimal\\."
+
+# Try to print MUNDANE using its linkage name again, after partial
+# symtab expansion.
+
+gdb_test "print symada__cS" \
+         " = {a = 100829103}" \
+         "print symada__cS after partial symtab expansion"