widl: Handle C++ aggregate returns in a MSVC compatible way.

This mainly affects 64-bit winelib applications, and potentially mingw-w64 usage of the Wine headers. As explained in commit fabfa59a, MSVC returns aggregates through an implicit parameter immediately after the this/interface pointer. GCC's "ms_abi" attribute is supposed to match this, but unfortunately current versions of g++ (confirmed up to at least g++ 6.3) place the implicit return pointer before the this/interface pointer. See also https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52792. This commit takes an approach similar to the earlier commit fabfa59a: For ABI compatibility the return pointer is listed as an explicit parameter in the vtbl entry, while an inline helper is provided for source code compatibility. Signed-off-by: Henri Verbeet <hverbeet@codeweavers.com> Signed-off-by: Alexandre Julliard <julliard@winehq.org>

widl: Handle C++ aggregate returns in a MSVC compatible way.
b42a1551 · Henri Verbeet · Alexandre Julliard · f91b4bd4 · b42a1551
Commit b42a1551 authored Jul 21, 2017 by Henri Verbeet Committed by Alexandre Julliard Jul 24, 2017
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header.c tools/widl/header.c +50 -1

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--- a/tools/widl/header.c
+++ b/tools/widl/header.c
@@ -1043,13 +1043,62 @@ static void write_cpp_method_def(FILE *header, const type_t *iface)
    const var_t *func = stmt->u.var;
    if (!is_callas(func->attrs)) {
      const char *callconv = get_attrp(func->type->attrs, ATTR_CALLCONV);
+      const var_list_t *args = type_get_function_args(func->type);
+      const var_t *arg;
+
      if (!callconv) callconv = "STDMETHODCALLTYPE";
+
+      if (is_aggregate_return(func)) {
+        fprintf(header, "#ifdef WIDL_EXPLICIT_AGGREGATE_RETURNS\n");
+
+        indent(header, 0);
+        fprintf(header, "virtual ");
+        write_type_decl_left(header, type_function_get_rettype(func->type));
+        fprintf(header, "* %s %s(\n", callconv, get_name(func));
+        ++indentation;
+        indent(header, 0);
+        write_type_decl_left(header, type_function_get_rettype(func->type));
+        fprintf(header, " *__ret");
+        --indentation;
+        if (args) {
+          fprintf(header, ",\n");
+          write_args(header, args, iface->name, 2, TRUE);
+        }
+        fprintf(header, ") = 0;\n");
+
+        indent(header, 0);
+        write_type_decl_left(header, type_function_get_rettype(func->type));
+        fprintf(header, " %s %s(\n", callconv, get_name(func));
+        write_args(header, args, iface->name, 2, TRUE);
+        fprintf(header, ")\n");
+        indent(header, 0);
+        fprintf(header, "{\n");
+        ++indentation;
+        indent(header, 0);
+        write_type_decl_left(header, type_function_get_rettype(func->type));
+        fprintf(header, " __ret;\n");
+        indent(header, 0);
+        fprintf(header, "return *%s(&__ret", get_name(func));
+        if (args)
+            LIST_FOR_EACH_ENTRY(arg, args, const var_t, entry)
+                fprintf(header, ", %s", arg->name);
+        fprintf(header, ");\n");
+        --indentation;
+        indent(header, 0);
+        fprintf(header, "}\n");
+
+        fprintf(header, "#else\n");
+      }
+
      indent(header, 0);
      fprintf(header, "virtual ");
      write_type_decl_left(header, type_function_get_rettype(func->type));
      fprintf(header, " %s %s(\n", callconv, get_name(func));
-      write_args(header, type_get_function_args(func->type), iface->name, 2, TRUE);
+      write_args(header, args, iface->name, 2, TRUE);
      fprintf(header, ") = 0;\n");
+
+      if (is_aggregate_return(func))
+        fprintf(header, "#endif\n");
      fprintf(header, "\n");
    }
  }