From: Thomas Rodgers <rodg...@twrodgers.com>
This change implements P0528 which requires that padding bits not
participate in atomic compare exchange operations. All arguments to the
generic template are 'sanitized' by the __builtin_clear_padding intrinsic
before they are used in atomic compare_exchange. This alrequires that any
stores also sanitize the incoming value.
Signed-off-by: Thomas Rodgers <trodg...@redhat.com>
libstdc++=v3/ChangeLog:
* include/std/atomic (atomic<T>::atomic(_Tp) clear padding for
__cplusplus > 201703L.
(atomic<T>::store()) Clear padding.
(atomic<T>::exchange()) Likewise.
(atomic<T>::compare_exchange_weak()) Likewise.
(atomic<T>::compare_exchange_strong()) Likewise.
* testsuite/29_atomics/atomic/compare_exchange_padding.cc: New
test.
---
libstdc++-v3/include/std/atomic | 23 +++++++++-
.../atomic/compare_exchange_padding.cc | 42 +++++++++++++++++++
2 files changed, 63 insertions(+), 2 deletions(-)
create mode 100644
libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc
diff --git a/libstdc++-v3/include/std/atomic b/libstdc++-v3/include/std/atomic
index 936dd50ba1c..51450badace 100644
--- a/libstdc++-v3/include/std/atomic
+++ b/libstdc++-v3/include/std/atomic
@@ -228,7 +228,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
atomic& operator=(const atomic&) = delete;
atomic& operator=(const atomic&) volatile = delete;
- constexpr atomic(_Tp __i) noexcept : _M_i(__i) { }
+#if __cplusplus > 201703L
+ constexpr atomic(_Tp __i) noexcept : _M_i(__i)
+ { __builtin_clear_padding(std::__addressof(_M_i)); }
+#else
+ atomic(_Tp __i) noexcept : _M_i(__i)
+ { }
+#endif
operator _Tp() const noexcept
{ return load(); }
@@ -268,12 +274,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
void
store(_Tp __i, memory_order __m = memory_order_seq_cst) noexcept
{
+ __builtin_clear_padding(std::__addressof(__i));
__atomic_store(std::__addressof(_M_i), std::__addressof(__i), int(__m));
}
void
store(_Tp __i, memory_order __m = memory_order_seq_cst) volatile noexcept
{
+ __builtin_clear_padding(std::__addressof(__i));
__atomic_store(std::__addressof(_M_i), std::__addressof(__i), int(__m));
}
@@ -300,6 +308,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
alignas(_Tp) unsigned char __buf[sizeof(_Tp)];
_Tp* __ptr = reinterpret_cast<_Tp*>(__buf);
+ __builtin_clear_padding(std::__addressof(__i));
__atomic_exchange(std::__addressof(_M_i), std::__addressof(__i),
__ptr, int(__m));
return *__ptr;
@@ -311,6 +320,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
alignas(_Tp) unsigned char __buf[sizeof(_Tp)];
_Tp* __ptr = reinterpret_cast<_Tp*>(__buf);
+ __builtin_clear_padding(std::__addressof(__i));
__atomic_exchange(std::__addressof(_M_i), std::__addressof(__i),
__ptr, int(__m));
return *__ptr;
@@ -322,6 +332,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
__glibcxx_assert(__is_valid_cmpexch_failure_order(__f));
+ __builtin_clear_padding(std::__addressof(__e));
+ __builtin_clear_padding(std::__addressof(__i));
return __atomic_compare_exchange(std::__addressof(_M_i),
std::__addressof(__e),
std::__addressof(__i),
@@ -334,6 +346,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
__glibcxx_assert(__is_valid_cmpexch_failure_order(__f));
+ __builtin_clear_padding(std::__addressof(__e));
+ __builtin_clear_padding(std::__addressof(__i));
return __atomic_compare_exchange(std::__addressof(_M_i),
std::__addressof(__e),
std::__addressof(__i),
@@ -358,6 +372,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
__glibcxx_assert(__is_valid_cmpexch_failure_order(__f));
+ __builtin_clear_padding(std::__addressof(__e));
+ __builtin_clear_padding(std::__addressof(__i));
return __atomic_compare_exchange(std::__addressof(_M_i),
std::__addressof(__e),
std::__addressof(__i),
@@ -370,6 +386,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
__glibcxx_assert(__is_valid_cmpexch_failure_order(__f));
+ __builtin_clear_padding(std::__addressof(__e));
+ __builtin_clear_padding(std::__addressof(__i));
return __atomic_compare_exchange(std::__addressof(_M_i),
std::__addressof(__e),
std::__addressof(__i),
@@ -392,6 +410,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
void
wait(_Tp __old, memory_order __m = memory_order_seq_cst) const noexcept
{
+ __builtin_clear_padding(std::__addressof(__old));
std::__atomic_wait_address_v(&_M_i, __old,
[__m, this] { return this->load(__m); });
}
@@ -407,7 +426,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{ std::__atomic_notify_address(&_M_i, true); }
#endif // __cpp_lib_atomic_wait
- };
+ };
#undef _GLIBCXX20_INIT
/// Partial specialization for pointer types.
diff --git
a/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc
b/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc
new file mode 100644
index 00000000000..0875f168097
--- /dev/null
+++ b/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc
@@ -0,0 +1,42 @@
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+// { dg-add-options libatomic }
+
+#include <atomic>
+
+#include <testsuite_hooks.h>
+
+struct S { char c; short s; };
+
+void __attribute__((noinline,noipa))
+fill_struct(S& s)
+{ __builtin_memset(&s, 0xff, sizeof(S)); }
+
+bool
+compare_struct(const S& a, const S& b)
+{ return __builtin_memcmp(&a, &b, sizeof(S)) == 0; }
+
+int
+main ()
+{
+ S s;
+ fill_struct(s);
+ s.c = 'a';
+ s.s = 42;
+
+ std::atomic<S> as{ s };
+ auto ts = as.load();
+ VERIFY( !compare_struct(s, ts) ); // padding cleared on construction
+ as.exchange(s);
+ auto es = as.load();
+ VERIFY( compare_struct(ts, es) ); // padding cleared on exchange
+
+ S n;
+ fill_struct(n);
+ n.c = 'b';
+ n.s = 71;
+ // padding cleared on compexchg
+ VERIFY( as.compare_exchange_weak(s, n) );
+ VERIFY( as.compare_exchange_strong(n, s) );
+ return 0;
+}
--
2.31.1
