* [committed] libstdc++: Fix misuse of alloca in std::bitset [PR108214]
@ 2023-01-06 14:12 Jonathan Wakely
0 siblings, 0 replies; only message in thread
From: Jonathan Wakely @ 2023-01-06 14:12 UTC (permalink / raw)
To: libstdc++, gcc-patches
I done a silly. Tested x86_64-linux, pushed to trunk.
-- >8 --
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.
---
libstdc++-v3/include/std/bitset | 24 +++++++++++--------
.../testsuite/20_util/bitset/io/input.cc | 21 ++++++++++++++++
2 files changed, 35 insertions(+), 10 deletions(-)
diff --git a/libstdc++-v3/include/std/bitset b/libstdc++-v3/include/std/bitset
index 1f3f68fefce..edda0776629 100644
--- a/libstdc++-v3/include/std/bitset
+++ b/libstdc++-v3/include/std/bitset
@@ -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
diff --git a/libstdc++-v3/testsuite/20_util/bitset/io/input.cc b/libstdc++-v3/testsuite/20_util/bitset/io/input.cc
index 0f22cefbb5b..4f7e6281ac5 100644
--- a/libstdc++-v3/testsuite/20_util/bitset/io/input.cc
+++ b/libstdc++-v3/testsuite/20_util/bitset/io/input.cc
@@ -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;
}
--
2.39.0
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2023-01-06 14:12 [committed] libstdc++: Fix misuse of alloca in std::bitset [PR108214] Jonathan Wakely
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