Hi!
On 2025-03-21T15:46:01+0100, I wrote:
> On 2025-03-19T14:25:49+0000, Jonathan Wakely <jwakely....@gmail.com> wrote:
>> On Wed, 19 Mar 2025 at 14:21, Marek Polacek <pola...@redhat.com> wrote:
>>> On Wed, Mar 19, 2025 at 12:38:31PM +0100, Thomas Schwinge wrote:
>>> > In 2001 Subversion r40924 (Git commit
>>> > 52a11cbfcf0cfb32628b6953588b6af4037ac0b6)
>>> > "IA-64 ABI Exception Handling", '__cxa_bad_cast' changed from 'void *' to
>>> > 'void' return type:
>>> >
>>> > --- libstdc++-v3/libsupc++/exception_support.cc
>>> > +++ /dev/null
>>> > @@ -1,388 +0,0 @@
>>> > -[...]
>>> > -// Helpers for rtti. Although these don't return, we give them
>>> > return types so
>>> > -// that the type system is not broken.
>>> > -extern "C" void *
>>> > -__cxa_bad_cast ()
>>> > -{
>>> > - [...]
>>> > -}
>>> > -[...]
>>> >
>>> > --- /dev/null
>>> > +++ libstdc++-v3/libsupc++/unwind-cxx.h
>>> > @@ -0,0 +1,163 @@
>>> > +[...]
>>> > +extern "C" void __cxa_bad_cast ();
>>> > +[...]
>>> >
>>> > --- /dev/null
>>> > +++ libstdc++-v3/libsupc++/eh_aux_runtime.cc
>>> > @@ -0,0 +1,56 @@
>>> > +[...]
>>> > +extern "C" void
>>> > +__cxa_bad_cast ()
>>> > +{
>>> > + [...]
>>> > +}
>>> > +[...]
>>> >
>>> > The implicit prototype in the C++ front end however wasn't likewise
>>> > adjusted,
>>> > and so for nvptx we generate code for 'void *' return type:
>>> >
>>> > // BEGIN GLOBAL FUNCTION DECL: __cxa_bad_cast
>>> > .extern .func (.param .u64 %value_out) __cxa_bad_cast;
>>> >
>>> > {
>>> > .param .u64 %value_in;
>>> > call (%value_in),__cxa_bad_cast;
>>> > trap;
>>> > // (noreturn)
>>> > exit;
>>> > // (noreturn)
>>> > ld.param.u64 %r30,[%value_in];
>>> > }
>>> >
>>> > ..., which is in conflict with the library code with 'void' return type:
>>> >
>>> > // BEGIN GLOBAL FUNCTION DECL: __cxa_bad_cast
>>> > .visible .func __cxa_bad_cast;
>>> >
>>> > // BEGIN GLOBAL FUNCTION DEF: __cxa_bad_cast
>>> > .visible .func __cxa_bad_cast
>>> > {
>>> > [...]
>>> > }
>>> >
>>> > ..., and we thus get execution test FAIL for 'g++.dg/rtti/dyncast2.C':
>>> >
>>> > error : Prototype doesn't match for '__cxa_bad_cast' in 'input file
>>> > 7 at offset 51437', first defined in 'input file 7 at offset 51437'
>>> > nvptx-run: cuLinkAddData failed: device kernel image is invalid
>>> > (CUDA_ERROR_INVALID_SOURCE, 300)
>>> >
>>> > With this patched, we get the expected: [...]
>>> > --- a/gcc/cp/rtti.cc
>>> > +++ b/gcc/cp/rtti.cc
>>> > @@ -198,7 +198,7 @@ throw_bad_cast (void)
>>> > fn = get_global_binding (name);
>>> > if (!fn)
>>> > fn = push_throw_library_fn
>>> > - (name, build_function_type_list (ptr_type_node, NULL_TREE));
>>> > + (name, build_function_type_list (void_type_node, NULL_TREE));
>>> > }
>>> >
>>> > return build_cxx_call (fn, 0, NULL, tf_warning_or_error);
>>>
>>> LGTM, matches what I see in abi-eh.html from the itanium-cxx-abi.
> [...] I've now pushed to trunk branch:
> commit 618c42d23726be6e2086d452d6718abe5e0daca8
> "C++: Adjust implicit '__cxa_bad_cast' prototype to reality", [...]
So, a similar problem exists for '__cxa_bad_typeid'. See the attached
"[WIP] C++: Adjust implicit '__cxa_bad_typeid' prototype to reality" for
what seemed to be the corresponding patch for that one. However, that
isn't sufficient; we run into internal errors like:
[...]/g++.dg/rtti/typeid1.C: In function 'int main()':
[...]/g++.dg/rtti/typeid1.C:9:12: error: lvalue required as unary '&'
operand
I got lost in the C++ front end code trying to understand how to resolve
this mismatch. Anyone able to advise, please?
Grüße
Thomas
> By the way, I've also tested this with 'fn = get_global_binding (name);'
> commented out, to force always using the C++ front end-synthesized
> prototype (per my understanding).
>
> I've just realized that we might check if some users of 'throw_bad_cast'
> have special code to handle the case of 'void *' return type in addition
> to 'void', which can now be simplified -- I'll try to look into that next
> week.
>
>
> Grüße
> Thomas
>From a9e2942f2bbfc70343a26b73bb11c2b591c96b8f Mon Sep 17 00:00:00 2001
From: Thomas Schwinge <tschwi...@baylibre.com>
Date: Wed, 19 Mar 2025 12:18:26 +0100
Subject: [PATCH] [WIP] C++: Adjust implicit '__cxa_bad_typeid' prototype to
reality
In 2001 Subversion r40924 (Git commit 52a11cbfcf0cfb32628b6953588b6af4037ac0b6)
"IA-64 ABI Exception Handling", '__cxa_bad_typeid' changed from
'std::type_info const &' to 'void' return type:
--- libstdc++-v3/libsupc++/exception_support.cc
+++ /dev/null
@@ -1,388 +0,0 @@
-[...]
-// Helpers for rtti. Although these don't return, we give them return types so
-// that the type system is not broken.
-[...]
-extern "C" std::type_info const &
-__cxa_bad_typeid ()
-{
- [...]
-}
-[...]
--- /dev/null
+++ libstdc++-v3/libsupc++/unwind-cxx.h
@@ -0,0 +1,163 @@
+[...]
+extern "C" void __cxa_bad_typeid ();
+[...]
--- /dev/null
+++ libstdc++-v3/libsupc++/eh_aux_runtime.cc
@@ -0,0 +1,56 @@
+[...]
+extern "C" void
+__cxa_bad_typeid ()
+{
+ [...]
+}
The implicit prototype in the C++ front end however wasn't likewise adjusted,
and so for nvptx we generate code for 'std::type_info const &' return type:
// BEGIN GLOBAL FUNCTION DECL: __cxa_bad_typeid
.extern .func (.param .u64 %value_out) __cxa_bad_typeid;
{
.param .u64 %value_in;
call (%value_in),__cxa_bad_typeid;
trap;
// (noreturn)
exit;
// (noreturn)
ld.param.u64 %r39,[%value_in];
}
..., which is in conflict with the library code with 'void' return type:
// BEGIN GLOBAL FUNCTION DECL: __cxa_bad_typeid
.visible .func __cxa_bad_typeid;
// BEGIN GLOBAL FUNCTION DEF: __cxa_bad_typeid
.visible .func __cxa_bad_typeid
{
[...]
}
..., and we thus get execution test FAILs for 'g++.dg/rtti/typeid11.C', for
example:
error : Prototype doesn't match for '__cxa_bad_typeid' in 'input file 4 at offset 22204', first defined in 'input file 4 at offset 22204'
nvptx-run: cuLinkAddData failed: unknown error (CUDA_ERROR_UNKNOWN, 999)
---
gcc/cp/rtti.cc | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)
diff --git a/gcc/cp/rtti.cc b/gcc/cp/rtti.cc
index 158b5ba13979..a55b8611cdaf 100644
--- a/gcc/cp/rtti.cc
+++ b/gcc/cp/rtti.cc
@@ -204,8 +204,7 @@ throw_bad_cast (void)
return build_cxx_call (fn, 0, NULL, tf_warning_or_error);
}
-/* Return an expression for "__cxa_bad_typeid()". The expression
- returned is an lvalue of type "const std::type_info". */
+/* See 'libstdc++-v3/libsupc++/eh_aux_runtime.cc' for '__cxa_bad_typeid'. */
static tree
throw_bad_typeid (void)
@@ -216,11 +215,8 @@ throw_bad_typeid (void)
tree name = get_identifier ("__cxa_bad_typeid");
fn = get_global_binding (name);
if (!fn)
- {
- tree t = build_reference_type (const_type_info_type_node);
- t = build_function_type_list (t, NULL_TREE);
- fn = push_throw_library_fn (name, t);
- }
+ fn = push_throw_library_fn
+ (name, build_function_type_list (void_type_node, NULL_TREE));
}
return build_cxx_call (fn, 0, NULL, tf_warning_or_error);
--
2.34.1
