[Xen-devel] [PATCH] x86: simplify non-atomic bitops

["Jan Beulich" <JBeulich@xxxxxxxx>]

- being non-atomic, their pointer arguments shouldn't be volatile-
  qualified
- their (half fake) memory operands can be a single "+m" instead of
  being both an output and an input

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/include/asm-x86/bitops.h
+++ b/xen/include/asm-x86/bitops.h
@@ -53,12 +53,9 @@ static inline void set_bit(int nr, volat
  * If it's called on the same region of memory simultaneously, the effect
  * may be that only one operation succeeds.
  */
-static inline void __set_bit(int nr, volatile void *addr)
+static inline void __set_bit(int nr, void *addr)
 {
-    asm volatile (
-        "btsl %1,%0"
-        : "=m" (ADDR)
-        : "Ir" (nr), "m" (ADDR) : "memory");
+    asm volatile ( "btsl %1,%0" : "+m" (ADDR) : "Ir" (nr) : "memory" );
 }
 #define __set_bit(nr, addr) ({                          \
     if ( bitop_bad_size(addr) ) __bitop_bad_size();     \
@@ -93,12 +90,9 @@ static inline void clear_bit(int nr, vol
  * If it's called on the same region of memory simultaneously, the effect
  * may be that only one operation succeeds.
  */
-static inline void __clear_bit(int nr, volatile void *addr)
+static inline void __clear_bit(int nr, void *addr)
 {
-    asm volatile (
-        "btrl %1,%0"
-        : "=m" (ADDR)
-        : "Ir" (nr), "m" (ADDR) : "memory");
+    asm volatile ( "btrl %1,%0" : "+m" (ADDR) : "Ir" (nr) : "memory" );
 }
 #define __clear_bit(nr, addr) ({                        \
     if ( bitop_bad_size(addr) ) __bitop_bad_size();     \
@@ -114,12 +108,9 @@ static inline void __clear_bit(int nr, v
  * If it's called on the same region of memory simultaneously, the effect
  * may be that only one operation succeeds.
  */
-static inline void __change_bit(int nr, volatile void *addr)
+static inline void __change_bit(int nr, void *addr)
 {
-    asm volatile (
-        "btcl %1,%0"
-        : "=m" (ADDR)
-        : "Ir" (nr), "m" (ADDR) : "memory");
+    asm volatile ( "btcl %1,%0" : "+m" (ADDR) : "Ir" (nr) : "memory" );
 }
 #define __change_bit(nr, addr) ({                       \
     if ( bitop_bad_size(addr) ) __bitop_bad_size();     \
@@ -179,14 +170,13 @@ static inline int test_and_set_bit(int n
  * If two examples of this operation race, one can appear to succeed
  * but actually fail.  You must protect multiple accesses with a lock.
  */
-static inline int __test_and_set_bit(int nr, volatile void *addr)
+static inline int __test_and_set_bit(int nr, void *addr)
 {
     int oldbit;
 
     asm volatile (
         "btsl %2,%1\n\tsbbl %0,%0"
-        : "=r" (oldbit), "=m" (ADDR)
-        : "Ir" (nr), "m" (ADDR) : "memory");
+        : "=r" (oldbit), "+m" (ADDR) : "Ir" (nr) : "memory" );
     return oldbit;
 }
 #define __test_and_set_bit(nr, addr) ({                 \
@@ -226,14 +216,13 @@ static inline int test_and_clear_bit(int
  * If two examples of this operation race, one can appear to succeed
  * but actually fail.  You must protect multiple accesses with a lock.
  */
-static inline int __test_and_clear_bit(int nr, volatile void *addr)
+static inline int __test_and_clear_bit(int nr, void *addr)
 {
     int oldbit;
 
     asm volatile (
         "btrl %2,%1\n\tsbbl %0,%0"
-        : "=r" (oldbit), "=m" (ADDR)
-        : "Ir" (nr), "m" (ADDR) : "memory");
+        : "=r" (oldbit), "+m" (ADDR) : "Ir" (nr) : "memory" );
     return oldbit;
 }
 #define __test_and_clear_bit(nr, addr) ({               \
@@ -242,14 +231,13 @@ static inline int __test_and_clear_bit(i
 })
 
 /* WARNING: non atomic and it can be reordered! */
-static inline int __test_and_change_bit(int nr, volatile void *addr)
+static inline int __test_and_change_bit(int nr, void *addr)
 {
     int oldbit;
 
     asm volatile (
         "btcl %2,%1\n\tsbbl %0,%0"
-        : "=r" (oldbit), "=m" (ADDR)
-        : "Ir" (nr), "m" (ADDR) : "memory");
+        : "=r" (oldbit), "+m" (ADDR) : "Ir" (nr) : "memory" );
     return oldbit;
 }
 #define __test_and_change_bit(nr, addr) ({              \

Attachment: x86-non-atomic-bitops.patch
Description: Text document

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