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atomic: strip "const" from variables declared with typeof

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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 <bobby.prani@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[pranith: Add conversion for bool type]
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2016-08-09 15:02:24 -04:00
parent 9d4cd7b4ed
commit 5927ed846a
1 changed files with 48 additions and 6 deletions
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54
include/qemu/atomic.h
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@ -18,6 +18,48 @@
/* 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), bool) || \
__builtin_types_compatible_p(typeof(expr), const bool) || \
__builtin_types_compatible_p(typeof(expr), volatile bool) || \
__builtin_types_compatible_p(typeof(expr), const volatile bool), \
(bool)1, \
__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 +96,7 @@
#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 +122,7 @@
#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 +145,7 @@
#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 +162,7 @@
#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 +179,7 @@
#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 +188,7 @@
#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; \