cxx-ada-visible-type-method-names

C++ Ada visible type/method names

A C++ method can collide with a type made use-visible from another generated class package, making later Ada profiles ambiguous.

AcceptedApplies in patchset orderSince 1.2.0

Bundle JSON Repository directory

Where it applies.

How each patchset treats this bundle on each GCC major
PatchsetGCC 13GCC 14GCC 15GCC 16
1.2.0 (latest)Patchedgcc-13-1413.2.0Patchedgcc-13-1414.2.0Patchedgcc-15-1615.3.0Patchedgcc-15-1616.2.0
1.1.0Not applicable13.2.0Not applicable14.2.0Not applicable15.3.0Not applicable16.2.0
1.0.1Not applicable13.2.0Not applicable14.2.0Not applicable15.3.0Not applicable16.1.0
1.0.0Not applicable13.2.0Not applicable14.2.0Not applicable15.3.0Not applicable16.1.0

Explanation.

Every generated C++ class is placed in a nested Ada package followed by a use clause. A method in one class can therefore collide case-insensitively with a type imported from another class package, even though the C++ names belong to unrelated scopes.

For example, Result becomes directly visible through use Class_Result, then result becomes directly visible through use Class_Widget:

struct Result
{
  int get ();
  int value;
};

struct Widget
{
  int result ();
  int value;
};

extern "C" Result *cpp_create_result (int value);

The unpatched mapper emits both identifiers unchanged. GNAT cannot resolve the result type in the later function profile because both use-visible names are homographs:

package Class_Result is
   type Result is limited record ... end record;
end;
use Class_Result;

package Class_Widget is
   function result (this : access Widget) return int;
end;
use Class_Widget;

function cpp_create_result (value : int) return access Result;

The corrected mapper compares every method name with all types collected for the generated unit. Only a colliding method receives the same stable suffix used for an enclosing-type collision:

package Class_Widget is
   function result_Method (this : access Widget) return int
   with Import => True,
        Convention => CPP,
        External_Name => "_ZN6Widget6resultEv";
end;

function cpp_create_result (value : int) return access Result;

The executable regression runs at -O0 and -O2. Stock GCC must produce a specification GNAT rejects for the two use-visible names. With the patch, Ada calls the renamed C++ method, reads the unrelated result object, and releases both objects through C++.

Patch.

Variant gcc-13-14

Applies to 13.2.0, 14.2.0. Source flavors: linux, darwin_arm64.

+49 −16 2 files

SHA-256
504c1639d8cb2068bc6e2f3fe46a74f9b2a7f8f18a600dfc7e7ee79323c6c02f
Patch
bundles/cxx-ada-visible-type-method-names/patches/gcc-13-14.patch

Download the patch

gcc/c-family/c-ada-spec.cc +13−16modified
@@ -3717 +3717 @@print_method_qualifiers (pretty_printer *buffer, tree t)
37173717 pp_string (buffer, "_Rvalue");
37183718}
37193719
3720/* Return true if METHOD_NAME collides with the enclosing C++ TYPE name after
3721 Ada's case-insensitive identifier conversion. */
3720/* Return true if METHOD_NAME collides with the enclosing class or another
3721 type made directly visible by a generated class-package use clause. */
37223722
37233723static bool
3724method_name_matches_type (tree method_name, tree type)
3724method_name_matches_visible_type (tree method_name, tree type)
37253725{
3726 if (!method_name || !RECORD_OR_UNION_TYPE_P (type) || !TYPE_NAME (type))
3726 if (!method_name)
37273727 return false;
37283728
3729 tree type_decl = TYPE_NAME (type);
3730 tree type_name_node = TREE_CODE (type_decl) == TYPE_DECL
3731 ? DECL_NAME (type_decl) : type_decl;
3732 if (!type_name_node || TREE_CODE (type_name_node) != IDENTIFIER_NODE)
3733 return false;
3729 if (identifier_matches_type (method_name, type))
3730 return true;
37343731
3735 char *method_ada = to_ada_name (IDENTIFIER_POINTER (method_name), NULL);
3736 char *type_ada = to_ada_name (IDENTIFIER_POINTER (type_name_node), NULL);
3737 const bool matches = !strcasecmp (method_ada, type_ada);
3738 free (method_ada);
3739 free (type_ada);
3740 return matches;
3732 for (int i = 0; i < to_dump_count; i++)
3733 if (TREE_CODE (to_dump[i]) == TYPE_DECL
3734 && identifier_matches_type (method_name, TREE_TYPE (to_dump[i])))
3735 return true;
3736
3737 return false;
37413738}
37423739
37433740/* Return the name of type T. */
@@ -4084 +4081 @@dump_ada_declaration (pretty_printer *buffer, tree t, tree type, int spc)
40844081 if (is_method)
40854082 {
40864083 print_method_qualifiers (buffer, t);
4087 if (method_name_matches_type (decl_name, type))
4084 if (method_name_matches_visible_type (decl_name, type))
40884085 pp_string (buffer, "_Method");
40894086 }
40904087 if (suffix > 1)
gcc/testsuite/g++.dg/ada-spec/visible-type-method-names.C +36−0new file
@@ -0 +1 @@
1/* { dg-do compile } */
2/* { dg-options "-fdump-ada-spec-slim" } */
3/* { dg-final { scan-file visible_type_method_names_c.ads "function result_Method" } } */
4
5struct Result
6{
7 int get ();
8 int value;
9};
10
11class Widget
12{
13public:
14 int result ();
15 int value;
16};
17
18int Result::get () { return value; }
19int Widget::result () { return value; }
20
21extern "C" Widget *cpp_create_widget (int value)
22{
23 Widget *object = new Widget;
24 object->value = value;
25 return object;
26}
27
28extern "C" Result *cpp_create_result (int value)
29{
30 return new Result { value };
31}
32
33extern "C" void cpp_delete_widget (Widget *object) { delete object; }
34extern "C" void cpp_delete_result (Result *object) { delete object; }
35
36/* { dg-final { cleanup-ada-spec } } */
37
138
239

Variant gcc-15-16

Applies to 15.3.0, 16.1.0, 16.2.0. Source flavors: linux, darwin_arm64.

+49 −16 2 files

SHA-256
afbd2983b7d3f967c388db9a18c897659b92be96a742fdf230c19bec1f065149
Patch
bundles/cxx-ada-visible-type-method-names/patches/gcc-15-16.patch

Download the patch

gcc/c-family/c-ada-spec.cc +13−16modified
@@ -3717 +3717 @@print_method_qualifiers (pretty_printer *pp, tree t)
37173717 pp_string (pp, "_Rvalue");
37183718}
37193719
3720/* Return true if METHOD_NAME collides with the enclosing C++ TYPE name after
3721 Ada's case-insensitive identifier conversion. */
3720/* Return true if METHOD_NAME collides with the enclosing class or another
3721 type made directly visible by a generated class-package use clause. */
37223722
37233723static bool
3724method_name_matches_type (tree method_name, tree type)
3724method_name_matches_visible_type (tree method_name, tree type)
37253725{
3726 if (!method_name || !RECORD_OR_UNION_TYPE_P (type) || !TYPE_NAME (type))
3726 if (!method_name)
37273727 return false;
37283728
3729 tree type_decl = TYPE_NAME (type);
3730 tree type_name_node = TREE_CODE (type_decl) == TYPE_DECL
3731 ? DECL_NAME (type_decl) : type_decl;
3732 if (!type_name_node || TREE_CODE (type_name_node) != IDENTIFIER_NODE)
3733 return false;
3729 if (identifier_matches_type (method_name, type))
3730 return true;
37343731
3735 char *method_ada = to_ada_name (IDENTIFIER_POINTER (method_name), NULL);
3736 char *type_ada = to_ada_name (IDENTIFIER_POINTER (type_name_node), NULL);
3737 const bool matches = !strcasecmp (method_ada, type_ada);
3738 free (method_ada);
3739 free (type_ada);
3740 return matches;
3732 for (int i = 0; i < to_dump_count; i++)
3733 if (TREE_CODE (to_dump[i]) == TYPE_DECL
3734 && identifier_matches_type (method_name, TREE_TYPE (to_dump[i])))
3735 return true;
3736
3737 return false;
37413738}
37423739
37433740/* Return the name of type T. */
@@ -4084 +4081 @@dump_ada_declaration (pretty_printer *pp, tree t, tree type, int spc)
40844081 if (is_method)
40854082 {
40864083 print_method_qualifiers (pp, t);
4087 if (method_name_matches_type (decl_name, type))
4084 if (method_name_matches_visible_type (decl_name, type))
40884085 pp_string (pp, "_Method");
40894086 }
40904087 if (suffix > 1)
gcc/testsuite/g++.dg/ada-spec/visible-type-method-names.C +36−0new file
@@ -0 +1 @@
1/* { dg-do compile } */
2/* { dg-options "-fdump-ada-spec-slim" } */
3/* { dg-final { scan-file visible_type_method_names_c.ads "function result_Method" } } */
4
5struct Result
6{
7 int get ();
8 int value;
9};
10
11class Widget
12{
13public:
14 int result ();
15 int value;
16};
17
18int Result::get () { return value; }
19int Widget::result () { return value; }
20
21extern "C" Widget *cpp_create_widget (int value)
22{
23 Widget *object = new Widget;
24 object->value = value;
25 return object;
26}
27
28extern "C" Result *cpp_create_result (int value)
29{
30 return new Result { value };
31}
32
33extern "C" void cpp_delete_widget (Widget *object) { delete object; }
34extern "C" void cpp_delete_result (Result *object) { delete object; }
35
36/* { dg-final { cleanup-ada-spec } } */
37
138

Tests.

Before the patch
GNAT rejects a later profile because a method and a type from different generated class packages are both use-visible under the same Ada identifier.
After the patch
Only a method matching any visible generated type receives a stable Method suffix, retains its C++ external symbol, and executes at -O0 and -O2.
visible-type-method-names.C C++ · 36 lines 
/* { dg-do compile } */
/* { dg-options "-fdump-ada-spec-slim" } */
/* { dg-final { scan-file visible_type_method_names_c.ads "function result_Method" } } */

struct Result
{
  int get ();
  int value;
};

class Widget
{
public:
  int result ();
  int value;
};

int Result::get () { return value; }
int Widget::result () { return value; }

extern "C" Widget *cpp_create_widget (int value)
{
  Widget *object = new Widget;
  object->value = value;
  return object;
}

extern "C" Result *cpp_create_result (int value)
{
  return new Result { value };
}

extern "C" void cpp_delete_widget (Widget *object) { delete object; }
extern "C" void cpp_delete_result (Result *object) { delete object; }

/* { dg-final { cleanup-ada-spec } } */

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visible_type_method_names_consumer.adb Ada · 22 lines 
with Ada.Text_IO;
with Interfaces.C; use Interfaces.C;
with Visible_Type_Method_Names_C;

procedure Visible_Type_Method_Names_Consumer is
   package Bindings renames Visible_Type_Method_Names_C;
   Widget_Object : access Bindings.Class_Widget.Widget :=
     Bindings.cpp_create_widget (41);
   Result_Object : access Bindings.Class_Result.Result :=
     Bindings.cpp_create_result (73);
begin
   if Widget_Object = null or else Result_Object = null
     or else Bindings.Class_Widget.result_Method (Widget_Object) /= 41
     or else Result_Object.value /= 73
   then
      raise Program_Error with "visible type/method collision changed values";
   end if;

   Bindings.cpp_delete_widget (Widget_Object);
   Bindings.cpp_delete_result (Result_Object);
   Ada.Text_IO.Put_Line ("MATCH visible type and method names");
end Visible_Type_Method_Names_Consumer;

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run-test.sh shell · 33 lines 
#!/usr/bin/env bash
set -euo pipefail

if [[ $# -ne 3 ]]; then echo "usage: $0 TOOLCHAIN_ROOT GCC_VERSION unpatched|patched" >&2; exit 2; fi
root=$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)
source "$root/scripts/regression-common.sh"
resolve_regression_toolchain "$1"
version=$2
state=$3
[[ "$state" == unpatched || "$state" == patched ]] || exit 2
gxx="$REGRESSION_TOOLCHAIN/bin/g++"
cxx="$root/bundles/cxx-ada-visible-type-method-names/tests/visible-type-method-names.C"
ada="$root/bundles/cxx-ada-visible-type-method-names/tests/visible_type_method_names_consumer.adb"
work=$(mktemp -d "${TMPDIR:-/tmp}/gnat-cxx-ada-visible-method.XXXXXX")
trap 'rm -rf "$work"' EXIT

for optimization in 0 2; do
  dir="$work/O$optimization"; mkdir -p "$dir"; cp "$cxx" "$ada" "$dir/"
  (cd "$dir"; "${REGRESSION_ENV[@]}" "$gxx" -c "-O$optimization" -fdump-ada-spec-slim visible-type-method-names.C)
  if [[ "$state" == unpatched ]]; then
    set +e
    (cd "$dir"; "${REGRESSION_ENV[@]}" "$REGRESSION_GCC" -c visible_type_method_names_c.ads) >"$dir/build.log" 2>&1
    status=$?; set -e
    [[ $status -ne 0 ]] || { echo "error: unpatched visible type/method binding compiled" >&2; exit 1; }
    grep -Eiq '(result).*not visible|multiple use clauses cause hiding' "$dir/build.log"
    echo "cxx-ada-visible-type-method-names -O$optimization: expected hiding (GCC $version)"
  else
    grep -F "function result_Method" "$dir/visible_type_method_names_c.ads"
    (cd "$dir"; "${REGRESSION_ENV[@]}" "$REGRESSION_GNATMAKE" -q -f "-O$optimization" visible_type_method_names_consumer.adb -largs visible-type-method-names.o -lstdc++; "${REGRESSION_ENV[@]}" ./visible_type_method_names_consumer) >"$dir/output.log" 2>&1 || { cat "$dir/output.log"; exit 1; }
    grep -Fx "MATCH visible type and method names" "$dir/output.log"
    echo "cxx-ada-visible-type-method-names -O$optimization: patched (GCC $version)"
  fi
done

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Commands.

Apply the patch
patch --fuzz=0 -p1 -i bundles/cxx-ada-visible-type-method-names/patches/VARIANT.patch
Build the compiler
PATH=/path/to/bootstrap/bin:$PATH ./scripts/build-gnat.sh SOURCE BUILD INSTALL
Run the regression
./scripts/run-regressions.sh INSTALL 1.2.0 GCC_MAJOR patched

Metadata.

Affected releases
  • 13.2.0
  • 14.2.0
  • 15.3.0
  • 16.1.0
  • 16.2.0
Known-good releases

None.

Files modified
  • gcc/c-family/c-ada-spec.cc
  • gcc/testsuite/g++.dg/ada-spec/visible-type-method-names.C
Regression tests
  • gcc/testsuite/g++.dg/ada-spec/visible-type-method-names.C
Before the patch
GNAT rejects a later profile because a method and a type from different generated class packages are both use-visible under the same Ada identifier.
After the patch
Only a method matching any visible generated type receives a stable Method suffix, retains its C++ external symbol, and executes at -O0 and -O2.
Upstream issue
Pending GCC Bugzilla filing.
Upstream submission
Not yet filed or submitted upstream.
Provenance
Repository-authored GCC patch and executable regression; exact application verified locally against the pinned Darwin patchset inputs. Pinned FSF release application is required by Linux CI.
Licensing
GCC-derived compiler hunks remain GPL-3.0-or-later. The new test is proposed for the GCC testsuite under GCC project terms.
Repository fixture
bundles/cxx-ada-visible-type-method-names/tests/visible-type-method-names.C
Fixture SHA-256
c1f347b7a4588c023f7c0e266f97966bc0f89ce377add6ac3cafbb9566776fca
Test runner
bundles/cxx-ada-visible-type-method-names/run-test.sh