atomic: strip "const" from variables declared with typeof
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>
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@ -18,6 +18,48 @@
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/* Compiler barrier */
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#define barrier() ({ asm volatile("" ::: "memory"); (void)0; })
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/* The variable that receives the old value of an atomically-accessed
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* variable must be non-qualified, because atomic builtins return values
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* through a pointer-type argument as in __atomic_load(&var, &old, MODEL).
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*
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* This macro has to handle types smaller than int manually, because of
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* implicit promotion. int and larger types, as well as pointers, can be
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* converted to a non-qualified type just by applying a binary operator.
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*/
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#define typeof_strip_qual(expr) \
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typeof( \
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__builtin_choose_expr( \
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__builtin_types_compatible_p(typeof(expr), bool) || \
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__builtin_types_compatible_p(typeof(expr), const bool) || \
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__builtin_types_compatible_p(typeof(expr), volatile bool) || \
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__builtin_types_compatible_p(typeof(expr), const volatile bool), \
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(bool)1, \
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__builtin_choose_expr( \
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__builtin_types_compatible_p(typeof(expr), signed char) || \
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__builtin_types_compatible_p(typeof(expr), const signed char) || \
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__builtin_types_compatible_p(typeof(expr), volatile signed char) || \
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__builtin_types_compatible_p(typeof(expr), const volatile signed char), \
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(signed char)1, \
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__builtin_choose_expr( \
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__builtin_types_compatible_p(typeof(expr), unsigned char) || \
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__builtin_types_compatible_p(typeof(expr), const unsigned char) || \
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__builtin_types_compatible_p(typeof(expr), volatile unsigned char) || \
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__builtin_types_compatible_p(typeof(expr), const volatile unsigned char), \
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(unsigned char)1, \
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__builtin_choose_expr( \
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__builtin_types_compatible_p(typeof(expr), signed short) || \
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__builtin_types_compatible_p(typeof(expr), const signed short) || \
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__builtin_types_compatible_p(typeof(expr), volatile signed short) || \
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__builtin_types_compatible_p(typeof(expr), const volatile signed short), \
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(signed short)1, \
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__builtin_choose_expr( \
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__builtin_types_compatible_p(typeof(expr), unsigned short) || \
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__builtin_types_compatible_p(typeof(expr), const unsigned short) || \
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__builtin_types_compatible_p(typeof(expr), volatile unsigned short) || \
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__builtin_types_compatible_p(typeof(expr), const volatile unsigned short), \
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(unsigned short)1, \
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(expr)+0))))))
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#ifdef __ATOMIC_RELAXED
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/* For C11 atomic ops */
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@ -54,7 +96,7 @@
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#define atomic_read(ptr) \
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({ \
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QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
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typeof(*ptr) _val; \
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typeof_strip_qual(*ptr) _val; \
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__atomic_load(ptr, &_val, __ATOMIC_RELAXED); \
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_val; \
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})
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@ -80,7 +122,7 @@
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#define atomic_rcu_read(ptr) \
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({ \
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QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
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typeof(*ptr) _val; \
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typeof_strip_qual(*ptr) _val; \
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atomic_rcu_read__nocheck(ptr, &_val); \
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_val; \
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})
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@ -103,7 +145,7 @@
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#define atomic_mb_read(ptr) \
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({ \
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QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
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typeof(*ptr) _val; \
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typeof_strip_qual(*ptr) _val; \
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__atomic_load(ptr, &_val, __ATOMIC_RELAXED); \
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smp_rmb(); \
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_val; \
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@ -120,7 +162,7 @@
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#define atomic_mb_read(ptr) \
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({ \
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QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
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typeof(*ptr) _val; \
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typeof_strip_qual(*ptr) _val; \
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__atomic_load(ptr, &_val, __ATOMIC_SEQ_CST); \
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_val; \
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})
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@ -137,7 +179,7 @@
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#define atomic_xchg(ptr, i) ({ \
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QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
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typeof(*ptr) _new = (i), _old; \
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typeof_strip_qual(*ptr) _new = (i), _old; \
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__atomic_exchange(ptr, &_new, &_old, __ATOMIC_SEQ_CST); \
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_old; \
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})
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#define atomic_cmpxchg(ptr, old, new) \
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({ \
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QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
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typeof(*ptr) _old = (old), _new = (new); \
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typeof_strip_qual(*ptr) _old = (old), _new = (new); \
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__atomic_compare_exchange(ptr, &_old, &_new, false, \
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__ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \
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_old; \
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