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Re: [Qemu-devel] [PATCH 1/1] seqlock: Fix warning reg. incompatible cast
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 1/1] seqlock: Fix warning reg. incompatible cast |
Date: |
Mon, 8 Aug 2016 11:55:26 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 |
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 <address@hidden>
>> 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