xen/arm32: cmpxchg: Simplify the cmpxchg implementation

The only difference between each case of the cmpxchg is the size of
used. Rather than duplicating the code, provide a macro to generate each
cases.

This makes the code easier to read and modify.

While doing the rework, the case for 64-bit cmpxchg is removed. This is
unused today (already commented) and it would not be possible to use
it directly.

This is part of XSA-295.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

diff --git a/xen/include/asm-arm/arm32/cmpxchg.h b/xen/include/asm-arm/arm32/cmpxchg.h
index 03e0bed3a69338a43ce09106c67cb3d69481db17..471a9e3a3fa05a7ee2fda6732b1ea42b10029024 100644 (file)
--- a/xen/include/asm-arm/arm32/cmpxchg.h
+++ b/xen/include/asm-arm/arm32/cmpxchg.h
@@ -52,72 +52,50 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size
  * indicated by comparing RETURN with OLD.
  */
 
-extern void __bad_cmpxchg(volatile void *ptr, int size);
+extern unsigned long __bad_cmpxchg(volatile void *ptr, int size);
+
+#define __CMPXCHG_CASE(sz, name)                                       \
+static inline unsigned long __cmpxchg_case_##name(volatile void *ptr,  \
+                                                 unsigned long old,    \
+                                                 unsigned long new)    \
+{                                                                      \
+       unsigned long oldval, res;                                      \
+                                                                       \
+       do {                                                            \
+               asm volatile("@ __cmpxchg_case_" #name "\n"             \
+               "       ldrex" #sz "    %1, [%2]\n"                     \
+               "       mov     %0, #0\n"                               \
+               "       teq     %1, %3\n"                               \
+               "       strex" #sz "eq %0, %4, [%2]\n"                  \
+               : "=&r" (res), "=&r" (oldval)                           \
+               : "r" (ptr), "Ir" (old), "r" (new)                      \
+               : "memory", "cc");                                      \
+       } while (res);                                                  \
+                                                                       \
+       return oldval;                                                  \
+}
+
+__CMPXCHG_CASE(b, 1)
+__CMPXCHG_CASE(h, 2)
+__CMPXCHG_CASE( , 4)
 
 static always_inline unsigned long __cmpxchg(
     volatile void *ptr, unsigned long old, unsigned long new, int size)
 {
-       unsigned long oldval, res;
-
        prefetchw((const void *)ptr);
 
        switch (size) {
        case 1:
-               do {
-                       asm volatile("@ __cmpxchg1\n"
-                       "       ldrexb  %1, [%2]\n"
-                       "       mov     %0, #0\n"
-                       "       teq     %1, %3\n"
-                       "       strexbeq %0, %4, [%2]\n"
-                               : "=&r" (res), "=&r" (oldval)
-                               : "r" (ptr), "Ir" (old), "r" (new)
-                               : "memory", "cc");
-               } while (res);
-               break;
+               return __cmpxchg_case_1(ptr, old, new);
        case 2:
-               do {
-                       asm volatile("@ __cmpxchg2\n"
-                       "       ldrexh  %1, [%2]\n"
-                       "       mov     %0, #0\n"
-                       "       teq     %1, %3\n"
-                       "       strexheq %0, %4, [%2]\n"
-                               : "=&r" (res), "=&r" (oldval)
-                               : "r" (ptr), "Ir" (old), "r" (new)
-                               : "memory", "cc");
-               } while (res);
-               break;
+               return __cmpxchg_case_2(ptr, old, new);
        case 4:
-               do {
-                       asm volatile("@ __cmpxchg4\n"
-                       "       ldrex   %1, [%2]\n"
-                       "       mov     %0, #0\n"
-                       "       teq     %1, %3\n"
-                       "       strexeq %0, %4, [%2]\n"
-                               : "=&r" (res), "=&r" (oldval)
-                               : "r" (ptr), "Ir" (old), "r" (new)
-                               : "memory", "cc");
-           } while (res);
-           break;
-#if 0
-       case 8:
-               do {
-                       asm volatile("@ __cmpxchg8\n"
-                       "       ldrexd  %1, [%2]\n"
-                       "       mov     %0, #0\n"
-                       "       teq     %1, %3\n"
-                       "       strexdeq %0, %4, [%2]\n"
-                               : "=&r" (res), "=&r" (oldval)
-                               : "r" (ptr), "Ir" (old), "r" (new)
-                               : "memory", "cc");
-               } while (res);
-               break;
-#endif
+               return __cmpxchg_case_4(ptr, old, new);
        default:
-               __bad_cmpxchg(ptr, size);
-               oldval = 0;
+               return __bad_cmpxchg(ptr, size);
        }
 
-       return oldval;
+       ASSERT_UNREACHABLE();
 }
 
 static always_inline unsigned long __cmpxchg_mb(volatile void *ptr,