OpenE2K/gcc
2
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

libstdc++: Make std::rethrow_if_nested work without RTTI

Browse Source 
This allows std::rethrow_if_nested to work with -fno-rtti by not
attempting the dynamic_cast if it requires RTTI, since that's ill-formed
with -fno-rtti. The cast will still work if a static upcast to
std::nested_exception is allowed.

Also use if-constexpr to avoid the compile-time overload resolution (and
SFINAE) and run-time dispatching for std::rethrow_if_nested and
std::throw_with_nested.

Also add better doxygen comments throughout the file.

libstdc++-v3/ChangeLog:

	* libsupc++/nested_exception.h (throw_with_nested) [C++17]: Use
	if-constexpr instead of tag dispatching.
	(rethrow_if_nested) [C++17]: Likewise.
	(rethrow_if_nested) [!__cpp_rtti]: Do not use dynamic_cast if it
	would require RTTI.
	* testsuite/18_support/nested_exception/rethrow_if_nested-term.cc:
	New test.
This commit is contained in:
Jonathan Wakely 2022-05-12 14:18:06 +01:00
parent e97e992965
commit c470f3ea86
2 changed files with 129 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

114
libstdc++-v3/libsupc++/nested_exception.h
View File

@ -35,6 +35,7 @@
#else
#include <bits/move.h>
#include <bits/exception_ptr.h>
extern "C++" {
@ -45,12 +46,22 @@ namespace std _GLIBCXX_VISIBILITY(default)
* @{
*/
/// Exception class with exception_ptr data member.
/** Mixin class that stores the current exception.
*
* This type can be used via `std::throw_with_nested` to store
* the current exception nested within another exception.
*
* @headerfile exception
* @since C++11
* @see std::throw_with_nested
* @ingroup exceptions
*/
class nested_exception
{
exception_ptr _M_ptr;
public:
/// The default constructor stores the current exception (if any).
nested_exception() noexcept : _M_ptr(current_exception()) { }
nested_exception(const nested_exception&) noexcept = default;
@ -59,6 +70,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
virtual ~nested_exception() noexcept;
/// Rethrow the stored exception, or terminate if none was stored.
[[noreturn]]
void
rethrow_nested() const
@ -68,6 +80,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
std::terminate();
}
/// Access the stored exception.
exception_ptr
nested_ptr() const noexcept
{ return _M_ptr; }
@ -87,6 +100,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
{ }
};
#if __cplusplus < 201703L || ! defined __cpp_if_constexpr
// [except.nested]/8
// Throw an exception of unspecified type that is publicly derived from
// both remove_reference_t<_Tp> and nested_exception.
@ -95,8 +109,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
inline void
__throw_with_nested_impl(_Tp&& __t, true_type)
{
using _Up = typename remove_reference<_Tp>::type;
throw _Nested_exception<_Up>{std::forward<_Tp>(__t)};
throw _Nested_exception<__remove_cvref_t<_Tp>>{std::forward<_Tp>(__t)};
}
template<typename _Tp>
@ -104,11 +117,31 @@ namespace std _GLIBCXX_VISIBILITY(default)
inline void
__throw_with_nested_impl(_Tp&& __t, false_type)
{ throw std::forward<_Tp>(__t); }
#endif
/// @endcond
/// If @p __t is derived from nested_exception, throws @p __t.
/// Else, throws an implementation-defined object derived from both.
/** Throw an exception that also stores the currently active exception.
*
* If `_Tp` is derived from `std::nested_exception` or is not usable
* as a base-class, throws a copy of `__t`.
* Otherwise, throws an object of an implementation-defined type derived
* from both `_Tp` and `std::nested_exception`, containing a copy of `__t`
* and the result of `std::current_exception()`.
*
* In other words, throws the argument as a new exception that contains
* the currently active exception nested within it. This is intended for
* use in a catch handler to replace the caught exception with a different
* type, while still preserving the original exception. When the new
* exception is caught, the nested exception can be rethrown by using
* `std::rethrow_if_nested`.
*
* This can be used at API boundaries, for example to catch a library's
* internal exception type and rethrow it nested with a `std::runtime_error`,
* or vice versa.
*
* @since C++11
*/
template<typename _Tp>
[[noreturn]]
inline void
@ -119,25 +152,27 @@ namespace std _GLIBCXX_VISIBILITY(default)
= __and_<is_copy_constructible<_Up>, is_move_constructible<_Up>>;
static_assert(_CopyConstructible::value,
"throw_with_nested argument must be CopyConstructible");
#if __cplusplus >= 201703L && __cpp_if_constexpr
if constexpr (is_class_v<_Up>)
if constexpr (!is_final_v<_Up>)
if constexpr (!is_base_of_v<nested_exception, _Up>)
throw _Nested_exception<_Up>{std::forward<_Tp>(__t)};
throw std::forward<_Tp>(__t);
#else
using __nest = __and_<is_class<_Up>, __bool_constant<!__is_final(_Up)>,
__not_<is_base_of<nested_exception, _Up>>>;
std::__throw_with_nested_impl(std::forward<_Tp>(__t), __nest{});
#endif
}
#if __cplusplus < 201703L || ! defined __cpp_if_constexpr
/// @cond undocumented
// Determine if dynamic_cast<const nested_exception&> would be well-formed.
template<typename _Tp>
using __rethrow_if_nested_cond = typename enable_if<
__and_<is_polymorphic<_Tp>,
__or_<__not_<is_base_of<nested_exception, _Tp>>,
is_convertible<_Tp*, nested_exception*>>>::value
>::type;
// Attempt dynamic_cast to nested_exception and call rethrow_nested().
template<typename _Ex>
inline __rethrow_if_nested_cond<_Ex>
__rethrow_if_nested_impl(const _Ex* __ptr)
inline void
__rethrow_if_nested_impl(const _Ex* __ptr, true_type)
{
if (auto __ne_ptr = dynamic_cast<const nested_exception*>(__ptr))
__ne_ptr->rethrow_nested();
@ -145,16 +180,59 @@ namespace std _GLIBCXX_VISIBILITY(default)
// Otherwise, no effects.
inline void
__rethrow_if_nested_impl(const void*)
__rethrow_if_nested_impl(const void*, false_type)
{ }
/// @endcond
#endif
/// If @p __ex is derived from nested_exception, @p __ex.rethrow_nested().
/** Rethrow a nested exception
*
* If `__ex` contains a `std::nested_exception` object, call its
* `rethrow_nested()` member to rethrow the stored exception.
*
* After catching an exception thrown by a call to `std::throw_with_nested`
* this function can be used to rethrow the exception that was active when
* `std::throw_with_nested` was called.
*
* @since C++11
*/
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2484. rethrow_if_nested() is doubly unimplementable
// 2784. Resolution to LWG 2484 is missing "otherwise, no effects" and [...]
template<typename _Ex>
# if ! __cpp_rtti
[[__gnu__::__always_inline__]]
#endif
inline void
rethrow_if_nested(const _Ex& __ex)
{ std::__rethrow_if_nested_impl(std::__addressof(__ex)); }
{
const _Ex* __ptr = __builtin_addressof(__ex);
#if __cplusplus < 201703L || ! defined __cpp_if_constexpr
# if __cpp_rtti
using __cast = __and_<is_polymorphic<_Ex>,
__or_<__not_<is_base_of<nested_exception, _Ex>>,
is_convertible<_Ex*, nested_exception*>>>;
# else
using __cast = __and_<is_polymorphic<_Ex>,
is_base_of<nested_exception, _Ex>,
is_convertible<_Ex*, nested_exception*>>;
# endif
std::__rethrow_if_nested_impl(__ptr, __cast{});
#else
if constexpr (!is_polymorphic_v<_Ex>)
return;
else if constexpr (is_base_of_v<nested_exception, _Ex>
&& !is_convertible_v<_Ex*, nested_exception*>)
return; // nested_exception base class is inaccessible or ambiguous.
# if ! __cpp_rtti
else if constexpr (!is_base_of_v<nested_exception, _Ex>)
return; // Cannot do polymorphic casts without RTTI.
# endif
else if (auto __ne_ptr = dynamic_cast<const nested_exception*>(__ptr))
__ne_ptr->rethrow_nested();
#endif
}
/// @} group exceptions
} // namespace std

33
libstdc++-v3/testsuite/18_support/nested_exception/rethrow_if_nested-term.cc Normal file
View File

@ -0,0 +1,33 @@
// { dg-do run { target c++11 } }
// { dg-skip-if "" { *-*-* } { "-fno-exceptions" } }
#include <exception>
#include <cstdlib>
[[noreturn]] void terminate_cleanly() noexcept { std::exit(0); }
struct A { virtual ~A() = default; };
int main()
{
try
{
// At this point std::current_exception() == nullptr so the
// std::nested_exception object is empty.
std::throw_with_nested(A{});
}
catch (const A& a)
{
std::set_terminate(terminate_cleanly);
std::rethrow_if_nested(a);
#if __cpp_rtti
// No nested exception, so trying to rethrow it calls std::terminate()
// which calls std::exit(0). Shoud not reach this point.
std::abort();
#else
// Without RTTI we can't dynamic_cast<const std::nested_exception*>(&a)
// so std::rethrow_if_nested(a) just returns normally.
return 0;
#endif
}
}