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libstdc++: Fix misuse of alloca in std::bitset [PR108214]

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The use of alloca in a constructor is wrong, because the memory is gone
after the constructor returns, and will be overwritten by a subsequent
function call. This didn't show up in testing because function inlining
alters the stack usage.

libstdc++-v3/ChangeLog:

	PR libstdc++/108214
	* include/std/bitset (operator>>): Use alloca in the right
	scope, not in a constructor.
	* testsuite/20_util/bitset/io/input.cc: Check case from PR.
This commit is contained in:
Jonathan Wakely 2023-01-06 13:42:07 +00:00
parent 8c330fd494
commit 553332c19a
2 changed files with 35 additions and 10 deletions
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24
libstdc++-v3/include/std/bitset
View file

@ -1598,20 +1598,24 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
struct _Buffer
{
_Buffer()
: _M_base(_Nb > 256 ? new _CharT[_Nb] : (_CharT*)__builtin_alloca(_Nb))
{ }
static _GLIBCXX_CONSTEXPR bool _S_use_alloca() { return _Nb <= 256; }
explicit _Buffer(_CharT* __p) : _M_ptr(__p) { }
~_Buffer()
{
if _GLIBCXX17_CONSTEXPR (_Nb > 256)
delete[] _M_base;
if _GLIBCXX17_CONSTEXPR (!_S_use_alloca())
delete[] _M_ptr;
}
_CharT* const _M_base;
_CharT* const _M_ptr;
};
_Buffer __buf;
_CharT* __ptr = __buf._M_base;
_CharT* __ptr;
if _GLIBCXX17_CONSTEXPR (_Buffer::_S_use_alloca())
__ptr = (_CharT*)__builtin_alloca(_Nb);
else
__ptr = new _CharT[_Nb];
const _Buffer __buf(__ptr);
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 303. Bitset input operator underspecified
@ -1662,8 +1666,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
if _GLIBCXX17_CONSTEXPR (_Nb)
{
if (size_t __len = __ptr - __buf._M_base)
__x.template _M_copy_from_ptr<_CharT, _Traits>(__buf._M_base, __len,
if (size_t __len = __ptr - __buf._M_ptr)
__x.template _M_copy_from_ptr<_CharT, _Traits>(__buf._M_ptr, __len,
0, __len,
__zero, __one);
else

21
libstdc++-v3/testsuite/20_util/bitset/io/input.cc
View file

@ -42,8 +42,29 @@ void test01()
VERIFY( ss.rdstate() == ios_base::goodbit ); // LWG 3199
}
void
test02()
{
std::bitset<4> a(0b1100), b;
std::stringstream ss;
ss << a;
ss >> b; // PR libstdc++/108214
VERIFY( b == a );
ss.str("");
ss.clear();
std::bitset<4000> c, d;
for (int i = 0; i < 4000; i += 5)
c.flip(i);
ss << c;
ss >> d;
VERIFY( d == c );
}
int main()
{
test01();
test02();
return 0;
}