From: Paolo Bonzini <pbonzini@redhat.com>
To: "Pranith Kumar" <bobby.prani@gmail.com>,
"Richard Henderson" <rth@twiddle.net>,
"Emilio G. Cota" <cota@braap.org>,
"Alex Bennée" <alex.bennee@linaro.org>,
"Sergey Fedorov" <sergey.fedorov@linaro.org>,
"Markus Armbruster" <armbru@redhat.com>,
"open list:All patches CC here" <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] [PATCH 1/1] seqlock: Fix warning reg. incompatible cast
Date: Mon, 8 Aug 2016 11:55:26 +0200 [thread overview]
Message-ID: <561336e2-41b3-d2a8-600e-e777747cac62@redhat.com> (raw)
In-Reply-To: <f26958a6-5b37-0cf0-2166-16bb4c673fa8@redhat.com>
On 08/08/2016 11:27, Paolo Bonzini wrote:
>
>
> On 08/08/2016 11:05, Paolo Bonzini wrote:
>>>> /home/pranith/devops/code/qemu/include/qemu/seqlock.h:62:21: warning: passing 'typeof (*&sl->sequence) *' (aka 'const unsigned int *') to parameter of type 'unsigned int *' discards qualifier
>>>> s [-Wincompatible-pointer-types-discards-qualifiers]
>>>> return unlikely(atomic_read(&sl->sequence) != start);
>>>> ^~~~~~~~~~~~~~~~~~~~~~~~~~
>>>> /home/pranith/devops/code/qemu/include/qemu/atomic.h:58:25: note: expanded from macro 'atomic_read'
>>>> __atomic_load(ptr, &_val, __ATOMIC_RELAXED); \
>>>> ^~~~~
>>>> /home/pranith/devops/code/qemu/include/qemu/compiler.h:62:43: note: expanded from macro 'unlikely'
>>>> #define unlikely(x) __builtin_expect(!!(x), 0)
>>>>
>>>> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
>> This is a compiler bug, isn't it? Atomic loads of a const pointer
>> should be allowed.
>
> Oh, this is &_val having a const type. That makes more sense indeed,
> but it should be worked around in qemu/atomic.h.
>
> Can you check if this works?
Better:
diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h
index 7e13fca..81cd33d 100644
--- a/include/qemu/atomic.h
+++ b/include/qemu/atomic.h
@@ -18,6 +18,26 @@
/* Compiler barrier */
#define barrier() ({ asm volatile("" ::: "memory"); (void)0; })
+#define typeof_strip_const(expr) \
+ typeof( \
+ __builtin_choose_expr( \
+ __builtin_types_compatible_p(typeof(expr), const short) || \
+ __builtin_types_compatible_p(typeof(expr), short), \
+ (short)1, \
+ __builtin_choose_expr( \
+ __builtin_types_compatible_p(typeof(expr), const unsigned short) || \
+ __builtin_types_compatible_p(typeof(expr), unsigned short), \
+ (unsigned short)1, \
+ __builtin_choose_expr( \
+ __builtin_types_compatible_p(typeof(expr), const char) || \
+ __builtin_types_compatible_p(typeof(expr), char), \
+ (char)1, \
+ __builtin_choose_expr( \
+ __builtin_types_compatible_p(typeof(expr), const unsigned char) || \
+ __builtin_types_compatible_p(typeof(expr), unsigned char), \
+ (unsigned char)1, \
+ expr+0)))))
+
#ifdef __ATOMIC_RELAXED
/* For C11 atomic ops */
@@ -54,7 +74,7 @@
#define atomic_read(ptr) \
({ \
QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
- typeof(*ptr) _val; \
+ typeof_strip_const(*ptr) _val; \
__atomic_load(ptr, &_val, __ATOMIC_RELAXED); \
_val; \
})
@@ -80,7 +100,7 @@
#define atomic_rcu_read(ptr) \
({ \
QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
- typeof(*ptr) _val; \
+ typeof_strip_const(*ptr) _val; \
atomic_rcu_read__nocheck(ptr, &_val); \
_val; \
})
@@ -103,7 +123,7 @@
#define atomic_mb_read(ptr) \
({ \
QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
- typeof(*ptr) _val; \
+ typeof_strip_const(*ptr) _val; \
__atomic_load(ptr, &_val, __ATOMIC_RELAXED); \
smp_rmb(); \
_val; \
@@ -120,7 +140,7 @@
#define atomic_mb_read(ptr) \
({ \
QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
- typeof(*ptr) _val; \
+ typeof_strip_const(*ptr) _val; \
__atomic_load(ptr, &_val, __ATOMIC_SEQ_CST); \
_val; \
})
@@ -137,7 +157,7 @@
#define atomic_xchg(ptr, i) ({ \
QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
- typeof(*ptr) _new = (i), _old; \
+ typeof_strip_const(*ptr) _new = (i), _old; \
__atomic_exchange(ptr, &_new, &_old, __ATOMIC_SEQ_CST); \
_old; \
})
@@ -146,7 +166,7 @@
#define atomic_cmpxchg(ptr, old, new) \
({ \
QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
- typeof(*ptr) _old = (old), _new = (new); \
+ typeof_strip_const(*ptr) _old = (old), _new = (new); \
__atomic_compare_exchange(ptr, &_old, &_new, false, \
__ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \
_old; \
Paolo
next prev parent reply other threads:[~2016-08-08 9:55 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-07 1:41 [Qemu-devel] [PATCH 1/1] seqlock: Fix warning reg. incompatible cast Pranith Kumar
2016-08-08 9:05 ` Paolo Bonzini
2016-08-08 9:27 ` Paolo Bonzini
2016-08-08 9:55 ` Paolo Bonzini [this message]
2016-08-08 10:00 ` Richard Henderson
2016-08-08 10:02 ` Paolo Bonzini
2016-08-08 10:25 ` Richard Henderson
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