[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-devel] [PATCH for 2.7] atomic: strip "const" from variables declar
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH for 2.7] atomic: strip "const" from variables declared with typeof |
Date: |
Mon, 8 Aug 2016 14:19:34 +0200 |
With the latest clang, we have the following warning:
/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 qualifiers
[-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); \
^~~~~
Stripping const is a bit tricky due to promotions, but it is doable
with either C11 _Generic or GCC extensions. Use the latter.
Reported-by: Pranith Kumar <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
---
include/qemu/atomic.h | 48 ++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 42 insertions(+), 6 deletions(-)
diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h
index 7e13fca..fc9cfa2 100644
--- a/include/qemu/atomic.h
+++ b/include/qemu/atomic.h
@@ -18,6 +18,42 @@
/* Compiler barrier */
#define barrier() ({ asm volatile("" ::: "memory"); (void)0; })
+/* The variable that receives the old value of an atomically-accessed
+ * variable must be non-qualified, because atomic builtins return values
+ * through a pointer-type argument as in __atomic_load(&var, &old, MODEL).
+ *
+ * This macro has to handle types smaller than int manually, because of
+ * implicit promotion. int and larger types, as well as pointers, can be
+ * converted to a non-qualified type just by applying a binary operator.
+ */
+#define typeof_strip_qual(expr)
\
+ typeof(
\
+ __builtin_choose_expr(
\
+ __builtin_types_compatible_p(typeof(expr), signed char) ||
\
+ __builtin_types_compatible_p(typeof(expr), const signed char) ||
\
+ __builtin_types_compatible_p(typeof(expr), volatile signed char) ||
\
+ __builtin_types_compatible_p(typeof(expr), const volatile signed
char), \
+ (signed char)1,
\
+ __builtin_choose_expr(
\
+ __builtin_types_compatible_p(typeof(expr), unsigned char) ||
\
+ __builtin_types_compatible_p(typeof(expr), const unsigned char) ||
\
+ __builtin_types_compatible_p(typeof(expr), volatile unsigned char)
|| \
+ __builtin_types_compatible_p(typeof(expr), const volatile unsigned
char), \
+ (unsigned char)1,
\
+ __builtin_choose_expr(
\
+ __builtin_types_compatible_p(typeof(expr), signed short) ||
\
+ __builtin_types_compatible_p(typeof(expr), const signed short) ||
\
+ __builtin_types_compatible_p(typeof(expr), volatile signed short)
|| \
+ __builtin_types_compatible_p(typeof(expr), const volatile signed
short), \
+ (signed short)1,
\
+ __builtin_choose_expr(
\
+ __builtin_types_compatible_p(typeof(expr), unsigned short) ||
\
+ __builtin_types_compatible_p(typeof(expr), const unsigned short)
|| \
+ __builtin_types_compatible_p(typeof(expr), volatile unsigned
short) || \
+ __builtin_types_compatible_p(typeof(expr), const volatile
unsigned short), \
+ (unsigned short)1,
\
+ (expr)+0)))))
+
#ifdef __ATOMIC_RELAXED
/* For C11 atomic ops */
@@ -54,7 +90,7 @@
#define atomic_read(ptr) \
({ \
QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
- typeof(*ptr) _val; \
+ typeof_strip_qual(*ptr) _val; \
__atomic_load(ptr, &_val, __ATOMIC_RELAXED); \
_val; \
})
@@ -80,7 +116,7 @@
#define atomic_rcu_read(ptr) \
({ \
QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
- typeof(*ptr) _val; \
+ typeof_strip_qual(*ptr) _val; \
atomic_rcu_read__nocheck(ptr, &_val); \
_val; \
})
@@ -103,7 +139,7 @@
#define atomic_mb_read(ptr) \
({ \
QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
- typeof(*ptr) _val; \
+ typeof_strip_qual(*ptr) _val; \
__atomic_load(ptr, &_val, __ATOMIC_RELAXED); \
smp_rmb(); \
_val; \
@@ -120,7 +156,7 @@
#define atomic_mb_read(ptr) \
({ \
QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
- typeof(*ptr) _val; \
+ typeof_strip_qual(*ptr) _val; \
__atomic_load(ptr, &_val, __ATOMIC_SEQ_CST); \
_val; \
})
@@ -137,7 +173,7 @@
#define atomic_xchg(ptr, i) ({ \
QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
- typeof(*ptr) _new = (i), _old; \
+ typeof_strip_qual(*ptr) _new = (i), _old; \
__atomic_exchange(ptr, &_new, &_old, __ATOMIC_SEQ_CST); \
_old; \
})
@@ -146,7 +182,7 @@
#define atomic_cmpxchg(ptr, old, new) \
({ \
QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
- typeof(*ptr) _old = (old), _new = (new); \
+ typeof_strip_qual(*ptr) _old = (old), _new = (new); \
__atomic_compare_exchange(ptr, &_old, &_new, false, \
__ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \
_old; \
--
2.7.4
- [Qemu-devel] [PATCH for 2.7] atomic: strip "const" from variables declared with typeof,
Paolo Bonzini <=