This removes the overload of __throw_bad_variant_access that must be
called with a string literal. This avoids a potential source of
undefined behaviour if that function got misused. The other overload
that takes a bool parameter can be adjusted to take an integer index
selecting one of the four possible string literals to use, ensuring
that the std::bad_variant_access constructor is only called with those
literals.
Passing an index outside the range [0,3] is bogus, but will still select
a valid string literal and avoid undefined behaviour.
libstdc++-v3/ChangeLog:
* include/std/variant (__throw_bad_variant_access(unsigned)):
Define new function as inline friend, with namespace-scope
declaration using noreturn attribute.
(__throw_bad_variant_access(const char*)): Remove.
(__throw_bad_variant_access(bool)): Remove.
(visit, visit<R>): Adjust calls to __throw_bad_variant_access.
Reviewed-by: Patrick Palka <[email protected]>
---
Patch v2 based on Patrick's review comments at:
https://forge.sourceware.org/gcc/gcc-TEST/pulls/3
Changes:
- Changed parameter type to unsigned.
- Added [[maybe_unused]] to the parameter and array.
- Added [[noreturn]] (which required declaring it before the
class and then defining it as an inline friend).
- Made the array static constexpr.
- Added a trailing comma after the last array element.
Tested x86_64-linux.
Pushed to trunk.
libstdc++-v3/include/std/variant | 32 +++++++++++++++-----------------
1 file changed, 15 insertions(+), 17 deletions(-)
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index cf532126d79..bd0f9c3252a 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -1402,6 +1402,8 @@ namespace __detail::__variant
&& (is_swappable_v<_Types> && ...))>
swap(variant<_Types...>&, variant<_Types...>&) = delete;
+ [[noreturn]] void __throw_bad_variant_access(unsigned);
+
class bad_variant_access : public exception
{
public:
@@ -1411,28 +1413,24 @@ namespace __detail::__variant
{ return _M_reason; }
private:
+ // Must only be called with a string literal
bad_variant_access(const char* __reason) noexcept : _M_reason(__reason) { }
// Must point to a string with static storage duration:
const char* _M_reason = "bad variant access";
- friend void __throw_bad_variant_access(const char* __what);
+ friend void __throw_bad_variant_access([[maybe_unused]] unsigned __n)
+ {
+ [[maybe_unused]] static constexpr const char* __reasons[] = {
+ "std::get: wrong index for variant",
+ "std::get: variant is valueless",
+ "std::visit: variant is valueless",
+ "std::visit<R>: variant is valueless",
+ };
+ _GLIBCXX_THROW_OR_ABORT(bad_variant_access(__reasons[__n % 4u]));
+ }
};
- // Must only be called with a string literal
- inline void
- __throw_bad_variant_access(const char* __what)
- { _GLIBCXX_THROW_OR_ABORT(bad_variant_access(__what)); }
-
- inline void
- __throw_bad_variant_access(bool __valueless)
- {
- if (__valueless) [[__unlikely__]]
- __throw_bad_variant_access("std::get: variant is valueless");
- else
- __throw_bad_variant_access("std::get: wrong index for variant");
- }
-
template<typename... _Types>
class variant
: private __detail::__variant::_Variant_base<_Types...>,
@@ -1941,7 +1939,7 @@ namespace __detail::__variant
namespace __variant = std::__detail::__variant;
if ((__variant::__as(__variants).valueless_by_exception() || ...))
- __throw_bad_variant_access("std::visit: variant is valueless");
+ __throw_bad_variant_access(2);
using _Result_type
= __detail::__variant::__visit_result_t<_Visitor, _Variants...>;
@@ -1981,7 +1979,7 @@ namespace __detail::__variant
namespace __variant = std::__detail::__variant;
if ((__variant::__as(__variants).valueless_by_exception() || ...))
- __throw_bad_variant_access("std::visit<R>: variant is valueless");
+ __throw_bad_variant_access(3);
return std::__do_visit<_Res>(std::forward<_Visitor>(__visitor),
__variant::__as(std::forward<_Variants>(__variants))...);
--
2.47.0
