This patch introduces __gnu_cxx::__gnat_exception, a class derived
from abi::__foreign_exception, that can be used to catch GNAT
exceptions and obtain information from them, such as the exception
name and message:
try {
try {
raise_gnat_exception (1);
} catch (__gnu_cxx::__gnat_exception& e) {
__builtin_printf("caught gnat %p\n", &e);
__builtin_printf("what: %s\n", e.what ());
auto msg = e.__msg ();
__builtin_printf("msg: %*s\n", msg.__len, msg.__ptr);
throw;
}
} catch (abi::__foreign_exception& f) {
__builtin_printf("caught foreign %p\n", &f);
}
prints:
caught gnat 0x<_Unwind_Exception*>
what: <GNAT Exception name>
msg: <GNAT Exception message>
caught foreign 0x<_Unwind_Exception*>
I'm not entirely happy with the C++ API WRT how internal Ada strings
are exposed as {len,ptr}, but something like std::string is probably
undersirable in libsupc++, more so because it would require a hosted
libstdc++.
It would be cool to expose GNAT exceptions' backtraces as well, but
System.Params.Default_Exception_Msg_Max_Length might conceivably vary,
and that would offset the backtrace data, and we presumably don't want
libstdc++ to depend on libgnat to get runtime access to that param and
behave accordingly, and a #define that might go out of sync feels
risky.
Regstrapped on x86_64-linux-gnu; also tested on arm-eabi with gcc-15. I
wasn't sure whether to bump the CXXABI version; 1.3.17 is present in the
GCC 16 branch, but adding symbols might be permissible. I wasn't sure
whether to add the new symbols to gnu-versioned-namespace.ver, but I
did, and removed a duplicate pair of symbols there while at that. Ok to
install?
for libstdc++-v3/ChangeLog
* config/abi/pre/gnu-versioned-namespace.ver (CXXABI_2.0):
Drop duplicates. Add __gnat_exception symbols.
* config/abi/pre/gnu.ver (CXXABI_1.3.18): New. Add
__gnat_exception symbols.
* testsuite/util/testsuite_abi.cc: Update known_versions and
latestp.
* libsupc++/Makefile.am (sources): Add gnat_exception.cc.
* libsupc++/Makefile.in: Rebuild.
* libsupc++/cxxabi.h (__gnu_cxx::__gnat_exception): New.
(__cxxabiv1::__foreign_exception): Befriend it.
* libsupc++/eh_personality.cc (PERSONALITY_FUNCTION): Select
__gnat_exception for GNAT exceptions.
* libsupc++/eh_arm.cc (__cxa_type_match): Likewise.
* libsupc++/eh_catch.cc (__cxxabiv1::__cxa_begin_catch):
Return unwindHeader for GNAT exceptions.
* libsupc++/gnat_exception.cc: New.
* libsupc++/unwind-cxx.h (__is_gnat_exception_class): New, for
__ARM_EABI_UNWINDER__ and generic.
(__gnat_exception_class) [!__ARM_EABI_UNWINDER__]: New.
---
.../config/abi/pre/gnu-versioned-namespace.ver | 7 +-
libstdc++-v3/config/abi/pre/gnu.ver | 10 ++
libstdc++-v3/libsupc++/Makefile.am | 1
libstdc++-v3/libsupc++/Makefile.in | 5 +
libstdc++-v3/libsupc++/cxxabi.h | 16 ++++
libstdc++-v3/libsupc++/eh_arm.cc | 6 +
libstdc++-v3/libsupc++/eh_catch.cc | 5 +
libstdc++-v3/libsupc++/eh_personality.cc | 2
libstdc++-v3/libsupc++/gnat_exception.cc | 91 ++++++++++++++++++++
libstdc++-v3/libsupc++/unwind-cxx.h | 31 +++++++
libstdc++-v3/testsuite/util/testsuite_abi.cc | 3 -
11 files changed, 171 insertions(+), 6 deletions(-)
create mode 100644 libstdc++-v3/libsupc++/gnat_exception.cc
diff --git a/libstdc++-v3/config/abi/pre/gnu-versioned-namespace.ver
b/libstdc++-v3/config/abi/pre/gnu-versioned-namespace.ver
index 7c5059944272e..6298a9ddeb289 100644
--- a/libstdc++-v3/config/abi/pre/gnu-versioned-namespace.ver
+++ b/libstdc++-v3/config/abi/pre/gnu-versioned-namespace.ver
@@ -286,8 +286,6 @@ CXXABI_2.0 {
_ZTIN10__cxxabiv121__vmi_class_type_infoE;
_ZTIN10__cxxabiv115__forced_unwindE;
_ZTIN10__cxxabiv119__foreign_exceptionE;
- _ZTIN10__cxxabiv115__forced_unwindE;
- _ZTIN10__cxxabiv119__foreign_exceptionE;
# typeinfo name
_ZTS[a-z];
@@ -372,6 +370,11 @@ CXXABI_2.0 {
_ZdaPvSt11align_val_t;
_ZdaPvSt11align_val_tRKSt9nothrow_t;
_ZdaPv[jmy]St11align_val_t;
+
+ # __gnu_cxx::__gnat_exception typeinfo and member functions
+ _ZNK9__gnu_cxx16__gnat_exception*;
+ _ZTIN9__gnu_cxx16__gnat_exceptionE;
+ _ZTSN9__gnu_cxx16__gnat_exceptionE;
};
# Symbols in the support library (libsupc++) supporting trans-mem.
diff --git a/libstdc++-v3/config/abi/pre/gnu.ver
b/libstdc++-v3/config/abi/pre/gnu.ver
index 3a6afac830873..ab26420f9a67b 100644
--- a/libstdc++-v3/config/abi/pre/gnu.ver
+++ b/libstdc++-v3/config/abi/pre/gnu.ver
@@ -2999,6 +2999,16 @@ CXXABI_1.3.17 {
} CXXABI_1.3.15;
#endif
+CXXABI_1.3.18 {
+
+ global:
+ # __gnu_cxx::__gnat_exception typeinfo and member functions
+ _ZNK9__gnu_cxx16__gnat_exception*;
+ _ZTIN9__gnu_cxx16__gnat_exceptionE;
+ _ZTSN9__gnu_cxx16__gnat_exceptionE;
+
+} CXXABI_1.3.17;
+
# Symbols in the support library (libsupc++) supporting transactional memory.
CXXABI_TM_1 {
diff --git a/libstdc++-v3/libsupc++/Makefile.am
b/libstdc++-v3/libsupc++/Makefile.am
index a3dc60f39458f..3523366fc13f7 100644
--- a/libstdc++-v3/libsupc++/Makefile.am
+++ b/libstdc++-v3/libsupc++/Makefile.am
@@ -80,6 +80,7 @@ sources = \
enum_type_info.cc \
function_type_info.cc \
fundamental_type_info.cc \
+ gnat_exception.cc \
guard.cc \
guard_error.cc \
hash_bytes.cc \
diff --git a/libstdc++-v3/libsupc++/Makefile.in
b/libstdc++-v3/libsupc++/Makefile.in
index db5e83803d52e..ec4dd4af3d296 100644
--- a/libstdc++-v3/libsupc++/Makefile.in
+++ b/libstdc++-v3/libsupc++/Makefile.in
@@ -161,8 +161,8 @@ am__objects_1 = array_type_info.lo atexit_arm.lo
atexit_thread.lo \
eh_catch.lo eh_exception.lo eh_globals.lo eh_personality.lo \
eh_ptr.lo eh_term_handler.lo eh_terminate.lo eh_tm.lo \
eh_throw.lo eh_type.lo eh_unex_handler.lo enum_type_info.lo \
- function_type_info.lo fundamental_type_info.lo guard.lo \
- guard_error.lo hash_bytes.lo nested_exception.lo \
+ function_type_info.lo fundamental_type_info.lo gnat_exception.lo \
+ guard.lo guard_error.lo hash_bytes.lo nested_exception.lo \
new_handler.lo new_op.lo new_opnt.lo new_opv.lo new_opvnt.lo \
new_opa.lo new_opant.lo new_opva.lo new_opvant.lo del_opa.lo \
del_opant.lo del_opsa.lo del_opva.lo del_opvant.lo \
@@ -546,6 +546,7 @@ sources = \
enum_type_info.cc \
function_type_info.cc \
fundamental_type_info.cc \
+ gnat_exception.cc \
guard.cc \
guard_error.cc \
hash_bytes.cc \
diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
index 244b21fc9db36..09e48bd2a866a 100644
--- a/libstdc++-v3/libsupc++/cxxabi.h
+++ b/libstdc++-v3/libsupc++/cxxabi.h
@@ -54,6 +54,10 @@
#include <bits/cxxabi_init_exception.h>
#ifdef __cplusplus
+namespace __gnu_cxx
+{
+ class __gnat_exception;
+}
namespace __cxxabiv1
{
extern "C"
@@ -662,6 +666,7 @@ namespace __cxxabiv1
{
virtual ~__foreign_exception() throw();
virtual void __pure_dummy() = 0; // prevent catch by value
+ friend class __gnu_cxx::__gnat_exception;
};
} // namespace __cxxabiv1
@@ -690,6 +695,17 @@ namespace abi = __cxxabiv1;
namespace __gnu_cxx
{
+ // A magic placeholder class that can be caught by reference
+ // to recognize GNAT exceptions.
+ class __gnat_exception : public abi::__foreign_exception
+ {
+ virtual ~__gnat_exception() throw();
+ public:
+ const char *what() const _GLIBCXX_TXN_SAFE_DYN _GLIBCXX_NOTHROW;
+ struct __ada_str { unsigned __len; const char *__ptr; };
+ __ada_str __msg() const _GLIBCXX_TXN_SAFE_DYN _GLIBCXX_NOTHROW;
+ };
+
/**
* @brief Exception thrown by __cxa_guard_acquire.
* @ingroup exceptions
diff --git a/libstdc++-v3/libsupc++/eh_arm.cc b/libstdc++-v3/libsupc++/eh_arm.cc
index 7008ce60f6df1..5d0ed1d789fe4 100644
--- a/libstdc++-v3/libsupc++/eh_arm.cc
+++ b/libstdc++-v3/libsupc++/eh_arm.cc
@@ -56,7 +56,11 @@ __cxa_type_match(_Unwind_Exception* ue_header,
if (forced_unwind)
throw_type = &typeid(abi::__forced_unwind);
else if (foreign_exception)
- throw_type = &typeid(abi::__foreign_exception);
+ {
+ throw_type = &typeid(abi::__foreign_exception);
+ if (__is_gnat_exception_class(ue_header->exception_class))
+ throw_type = &typeid(__gnu_cxx::__gnat_exception);
+ }
else
{
if (dependent_exception)
diff --git a/libstdc++-v3/libsupc++/eh_catch.cc
b/libstdc++-v3/libsupc++/eh_catch.cc
index 424dbc724b6a4..650c75e177d05 100644
--- a/libstdc++-v3/libsupc++/eh_catch.cc
+++ b/libstdc++-v3/libsupc++/eh_catch.cc
@@ -58,6 +58,11 @@ __cxxabiv1::__cxa_begin_catch (void *exc_obj_in)
_GLIBCXX_NOTHROW
// Remember for end_catch and rethrow.
globals->caughtExceptions = header;
+ // For GNAT exceptions, return the address of the unwind header.
+ // __gnat_exception member functions rely on that.
+ if (__is_gnat_exception_class(header->unwindHeader.exception_class))
+ return &header->unwindHeader;
+
// ??? No sensible value to return; we don't know what the
// object is, much less where it is in relation to the header.
return 0;
diff --git a/libstdc++-v3/libsupc++/eh_personality.cc
b/libstdc++-v3/libsupc++/eh_personality.cc
index 10458318f88ef..ff242872d6587 100644
--- a/libstdc++-v3/libsupc++/eh_personality.cc
+++ b/libstdc++-v3/libsupc++/eh_personality.cc
@@ -571,6 +571,8 @@ PERSONALITY_FUNCTION (int version,
else if (foreign_exception)
{
throw_type = &typeid(abi::__foreign_exception);
+ if (__is_gnat_exception_class(exception_class))
+ throw_type = &typeid(__gnu_cxx::__gnat_exception);
}
else
#endif
diff --git a/libstdc++-v3/libsupc++/gnat_exception.cc
b/libstdc++-v3/libsupc++/gnat_exception.cc
new file mode 100644
index 0000000000000..a1b6d1ee71fc3
--- /dev/null
+++ b/libstdc++-v3/libsupc++/gnat_exception.cc
@@ -0,0 +1,91 @@
+// -*- C++ -*- __gnu_cxx::__gnat_exception implementation.
+// Copyright (C) 2026 Free Software Foundation, Inc.
+//
+// This file is part of GCC.
+//
+// GCC 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, or (at your option)
+// any later version.
+//
+// GCC 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.
+//
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
+// <http://www.gnu.org/licenses/>.
+
+#include "exception"
+#include <cxxabi.h>
+#include "unwind.h"
+
+namespace {
+
+#if __ARM_EABI_UNWINDER__ && ! __USING_SJLJ_EXCEPTIONS__
+ typedef _Unwind_Control_Block GNAT_Unwind_Header;
+#else
+ typedef struct
+ {
+ _Unwind_Exception_Class exception_class;
+ _Unwind_Exception_Cleanup_Fn exception_cleanup;
+ _Unwind_Word private_[6];
+ } GNAT_Unwind_Header;
+#endif
+
+ struct GNAT_Exception_Data
+ {
+ bool not_handled_by_others;
+ char lang;
+ unsigned name_length;
+ const char *full_name; /* NULL terminated string. */
+ /* ... */
+ };
+
+ struct GNAT_Exception_Occurrence
+ {
+ GNAT_Exception_Data *eid;
+ GNAT_Unwind_Header *header;
+ unsigned msg_length;
+ char msg[/*msg_[max_]length*/];
+ /* ... */
+ };
+
+ struct GNAT_Exception
+ {
+ GNAT_Unwind_Header header;
+ GNAT_Exception_Occurrence occurrence;
+ };
+}
+
+__gnu_cxx::__gnat_exception::~__gnat_exception() throw()
+{
+}
+
+const char*
+__gnu_cxx::__gnat_exception::what()
+ const _GLIBCXX_TXN_SAFE_DYN _GLIBCXX_USE_NOEXCEPT
+{
+ GNAT_Exception const *ex = reinterpret_cast<GNAT_Exception const *>(this);
+ if (ex->occurrence.eid)
+ return ex->occurrence.eid->full_name;
+ return "GNAT exception";
+}
+
+struct __gnu_cxx::__gnat_exception::__ada_str
+__gnu_cxx::__gnat_exception::__msg()
+ const _GLIBCXX_TXN_SAFE_DYN _GLIBCXX_USE_NOEXCEPT
+{
+ GNAT_Exception const *ex = reinterpret_cast<GNAT_Exception const *>(this);
+ __ada_str str = {
+ ex->occurrence.msg_length,
+ ex->occurrence.msg
+ };
+ return str;
+}
diff --git a/libstdc++-v3/libsupc++/unwind-cxx.h
b/libstdc++-v3/libsupc++/unwind-cxx.h
index b6030f0d19784..6e69c1ff9c5be 100644
--- a/libstdc++-v3/libsupc++/unwind-cxx.h
+++ b/libstdc++-v3/libsupc++/unwind-cxx.h
@@ -250,6 +250,20 @@ __is_gxx_exception_class(_Unwind_Exception_Class c)
&& (c[7] == '\0' || c[7] == '\x01');
}
+static inline bool
+__is_gnat_exception_class(_Unwind_Exception_Class c)
+{
+ // TODO: Take advantage of the fact that c will always be word aligned.
+ return c[0] == 'G'
+ && c[1] == 'N'
+ && c[2] == 'U'
+ && c[3] == '-'
+ && c[4] == 'A'
+ && c[5] == 'd'
+ && c[6] == 'a'
+ && c[7] == '\0';
+}
+
// Only checks for primary or dependent, but not that it is a C++ exception at
// all.
static inline bool
@@ -346,6 +360,23 @@ __is_gxx_exception_class(_Unwind_Exception_Class c)
|| c == __gxx_dependent_exception_class;
}
+// GNAT reports exceptions as "GNU-Ada\0"
+const _Unwind_Exception_Class __gnat_exception_class
+= ((((((((_Unwind_Exception_Class) 'G'
+ << 8 | (_Unwind_Exception_Class) 'N')
+ << 8 | (_Unwind_Exception_Class) 'U')
+ << 8 | (_Unwind_Exception_Class) '-')
+ << 8 | (_Unwind_Exception_Class) 'A')
+ << 8 | (_Unwind_Exception_Class) 'd')
+ << 8 | (_Unwind_Exception_Class) 'a')
+ << 8 | (_Unwind_Exception_Class) '\0');
+
+static inline bool
+__is_gnat_exception_class(_Unwind_Exception_Class c)
+{
+ return c == __gnat_exception_class;
+}
+
// Only checks for primary or dependent, but not that it is a C++ exception at
// all.
static inline bool
diff --git a/libstdc++-v3/testsuite/util/testsuite_abi.cc
b/libstdc++-v3/testsuite/util/testsuite_abi.cc
index 4e80c5f184a68..aaa8212b71cf2 100644
--- a/libstdc++-v3/testsuite/util/testsuite_abi.cc
+++ b/libstdc++-v3/testsuite/util/testsuite_abi.cc
@@ -243,6 +243,7 @@ check_version(symbol& test, bool added)
known_versions.push_back("CXXABI_1.3.16");
#endif
known_versions.push_back("CXXABI_1.3.17");
+ known_versions.push_back("CXXABI_1.3.18");
known_versions.push_back("CXXABI_IEEE128_1.3.13");
known_versions.push_back("CXXABI_TM_1");
known_versions.push_back("CXXABI_FLOAT128");
@@ -262,7 +263,7 @@ check_version(symbol& test, bool added)
// Check that added symbols are added in the latest pre-release version.
bool latestp = (test.version_name == "GLIBCXX_3.4.36"
- || test.version_name == "CXXABI_1.3.17"
+ || test.version_name == "CXXABI_1.3.18"
|| test.version_name == "CXXABI_FLOAT128"
|| test.version_name == "CXXABI_TM_1");
if (added && !latestp)
--
Alexandre Oliva, happy hacker https://blog.lx.oliva.nom.br/
Free Software Activist FSFLA co-founder GNU Toolchain Engineer
More tolerance and less prejudice are key for inclusion and diversity.
Excluding neuro-others for not behaving ""normal"" is *not* inclusive!
