From: xndcn <xndchn@gmail.com>
To: gcc-patches@gcc.gnu.org
Subject: [PATCH] libstdc++: atomic: Add missing clear_padding in __atomic_float constructor
Date: Mon, 8 Jan 2024 09:01:48 +0800 [thread overview]
Message-ID: <CAJ=gGT3=TCsF2GcsawmbOReDjwVPmxpSLw1_CTZX5NE6HUtu+g@mail.gmail.com> (raw)
[-- Attachment #1: Type: text/plain, Size: 1541 bytes --]
Hi, I found __atomic_float constructor does not clear padding,
while __compare_exchange assumes it as zeroed padding. So it is easy to
reproducing a infinite loop in X86-64 with long double type like:
---
-O0 -std=c++23 -mlong-double-80
#include <stdio.h>
#include <atomic>
#define T long double
int main() {
std::atomic<T> t(0.5);
t.fetch_add(0.5);
float x = t;
printf("%f\n", x);
}
---
So we should add __builtin_clear_padding in __atomic_float constructor,
just like the generic atomic struct.
regtested on x86_64-linux. Is it OK for trunk?
---
libstdc++: atomic: Add missing clear_padding in __atomic_float constructor.
libstdc++-v3/ChangeLog:
* include/bits/atomic_base.h: add __builtin_clear_padding in __atomic_float
constructor.
---
libstdc++-v3/include/bits/atomic_base.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/include/bits/atomic_base.h
b/libstdc++-v3/include/bits/atomic_base.h
index f4ce0fa53..d59c2209e 100644
--- a/libstdc++-v3/include/bits/atomic_base.h
+++ b/libstdc++-v3/include/bits/atomic_base.h
@@ -1283,7 +1283,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr
__atomic_float(_Fp __t) : _M_fp(__t)
- { }
+ {
+#if __has_builtin(__builtin_clear_padding)
+ if _GLIBCXX17_CONSTEXPR (__atomic_impl::__maybe_has_padding<_Fp>())
+ __builtin_clear_padding(std::__addressof(_M_fp));
+#endif
+ }
__atomic_float(const __atomic_float&) = delete;
__atomic_float& operator=(const __atomic_float&) = delete;
--
2.25.1
next reply other threads:[~2024-01-08 1:02 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-08 1:01 xndcn [this message]
2024-01-15 0:45 ` [PING][PATCH] " xndcn
2024-01-15 3:46 ` [PATCH] " H.J. Lu
2024-01-16 9:53 ` xndcn
2024-01-16 10:12 ` Xi Ruoyao
2024-01-16 16:16 ` xndcn
2024-01-24 15:53 ` xndcn
2024-01-30 16:08 ` [PING][PATCH] " xndcn
2024-01-30 16:31 ` [PATCH] " Jonathan Wakely
2024-01-30 16:34 ` Jonathan Wakely
2024-01-30 16:50 ` Jakub Jelinek
2024-01-31 17:19 ` xndcn
2024-02-01 13:54 ` Jonathan Wakely
2024-02-02 16:52 ` xndcn
2024-02-16 12:38 ` Jonathan Wakely
2024-02-16 13:51 ` Jonathan Wakely
2024-02-16 14:10 ` Jakub Jelinek
2024-02-16 15:15 ` Jonathan Wakely
2024-03-14 15:13 ` Jonathan Wakely
2024-03-25 15:42 ` [PING][PATCH] " xndcn
2024-02-19 7:55 ` [PATCH] c-family, c++: Fix up handling of types which may have padding in __atomic_{compare_}exchange Jakub Jelinek
2024-02-20 0:12 ` Jason Merrill
2024-02-20 0:51 ` Jakub Jelinek
2024-02-20 8:01 ` Richard Biener
2024-02-20 10:02 ` [PATCH] c-family, c++, v2: " Jakub Jelinek
2024-02-20 10:11 ` Richard Biener
2024-02-20 10:27 ` Jakub Jelinek
2024-03-07 0:00 ` Jason Merrill
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