btrfs-progs: fix unaligned accesses v2

gcc optimizes out the memcpy calls at -O2 and -Os.

Replacing memcpy with memmove does't work - gcc treats memmove
the same way it treats memcpy.

This patch brings in {get|put}_unaligned_le{16|32|64} (using the
packed struct method), and uses them in the failing get/set calls.

On architectures where unaligned accesses are cheap, these unaligned
macros should be optimized out by the compiler.

Signed-off-by: Ben Peddell <klightspeed@killerwolves.net>

diff --git a/ctree.h b/ctree.h
index 0675989..1f5a795 100644 (file)
--- a/ctree.h
+++ b/ctree.h
@@ -1086,19 +1086,15 @@ static inline u##bits btrfs_##name(struct extent_buffer *eb,            \
                                   type *s)                             \
 {                                                                      \
        unsigned long offset = (unsigned long)s;                        \
-       u##bits m;                                                      \
        type *p = (type *) (eb->data + offset);                         \
-       memcpy(&m, &p->member, sizeof(m));                              \
-       return le##bits##_to_cpu(m);                                    \
+       return get_unaligned_le##bits(&p->member);                      \
 }                                                                      \
 static inline void btrfs_set_##name(struct extent_buffer *eb,          \
                                    type *s, u##bits val)               \
 {                                                                      \
        unsigned long offset = (unsigned long)s;                        \
-       u##bits m;                                                      \
        type *p = (type *) (eb->data + offset);                         \
-       m = cpu_to_le##bits(val);                                       \
-       memcpy(&p->member, &m, sizeof(m));                              \
+       put_unaligned_le##bits(val, &p->member);                        \
 }
 
 #define BTRFS_SETGET_STACK_FUNCS(name, type, member, bits)             \

diff --git a/kerncompat.h b/kerncompat.h
index d60f722..a38a9b0 100644 (file)
--- a/kerncompat.h
+++ b/kerncompat.h
@@ -267,6 +267,19 @@ typedef u64 __bitwise __be64;
 #define cpu_to_le16(x) ((__force __le16)(u16)(x))
 #define le16_to_cpu(x) ((__force u16)(__le16)(x))
 #endif
+
+struct __una_u16 { u16 x; } __attribute__((__packed__));
+struct __una_u32 { u32 x; } __attribute__((__packed__));
+struct __una_u64 { u64 x; } __attribute__((__packed__));
+
+#define get_unaligned_le8(p) (*((u8 *)(p)))
+#define put_unaligned_le8(val,p) ((*((u8 *)(p))) = (val))
+#define get_unaligned_le16(p) le16_to_cpu(((const struct __una_u16 *)(p))->x)
+#define put_unaligned_le16(val,p) (((struct __una_u16 *)(p))->x = cpu_to_le16(val))
+#define get_unaligned_le32(p) le32_to_cpu(((const struct __una_u32 *)(p))->x)
+#define put_unaligned_le32(val,p) (((struct __una_u32 *)(p))->x = cpu_to_le32(val))
+#define get_unaligned_le64(p) le64_to_cpu(((const struct __una_u64 *)(p))->x)
+#define put_unaligned_le64(val,p) (((struct __una_u64 *)(p))->x = cpu_to_le64(val))
 #endif
 
 #ifndef noinline