From: Pranith Kumar <bobby.prani@gmail.com>
To: "Paolo Bonzini" <pbonzini@redhat.com>,
"Emilio G. Cota" <cota@braap.org>,
"Alex Bennée" <alex.bennee@linaro.org>,
"Richard Henderson" <rth@twiddle.net>,
"Markus Armbruster" <armbru@redhat.com>,
"open list:All patches CC here" <qemu-devel@nongnu.org>
Cc: peter.maydell@linaro.org
Subject: [Qemu-devel] [PATCH 1/5] atomic: strip "const" from variables declared with typeof
Date: Tue, 9 Aug 2016 15:02:24 -0400 [thread overview]
Message-ID: <20160809190229.27871-1-bobby.prani@gmail.com> (raw)
From: Paolo Bonzini <pbonzini@redhat.com>
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>
---
include/qemu/atomic.h | 54 +++++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 48 insertions(+), 6 deletions(-)
diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h
index 7e13fca..43b0645 100644
--- a/include/qemu/atomic.h
+++ b/include/qemu/atomic.h
@@ -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; \
--
2.9.2
next reply other threads:[~2016-08-09 19:02 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-09 19:02 Pranith Kumar [this message]
2016-08-09 19:02 ` [Qemu-devel] [PATCH 2/5] softfloat: Fix warn about implicit conversion from int to int8_t Pranith Kumar
2016-08-09 19:16 ` Aurelien Jarno
2016-08-09 21:12 ` Peter Maydell
2016-08-10 12:27 ` Aurelien Jarno
2016-08-10 10:32 ` Richard Henderson
2016-08-10 10:37 ` Peter Maydell
2016-08-10 12:12 ` Paolo Bonzini
2016-08-09 19:02 ` [Qemu-devel] [PATCH 3/5] Disable warn about left shifts of negative values Pranith Kumar
2016-08-09 19:02 ` [Qemu-devel] [PATCH 4/5] clang: Fix warning reg. expansion to 'defined' Pranith Kumar
2016-08-09 19:02 ` [Qemu-arm] [PATCH 5/5] target-arm: Fix warn about implicit conversion Pranith Kumar
2016-08-09 19:02 ` [Qemu-devel] " Pranith Kumar
2016-08-11 10:50 ` [Qemu-arm] " Peter Maydell
2016-08-11 10:50 ` [Qemu-devel] " Peter Maydell
2016-08-12 12:20 ` Peter Maydell
2016-08-12 12:20 ` Peter Maydell
2016-08-09 20:14 ` [Qemu-devel] [PATCH 1/5] atomic: strip "const" from variables declared with typeof Paolo Bonzini
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