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commit df15887584f0025e7b188e408dd3c9f638d68518
Author: Dan McGee <dan@archlinux.org>
Date: Tue Nov 2 18:43:00 2010 -0500
Fix type-punning issues exposed with GCC 4.5.1
The errors below are due to pointer magic that isn't allowed if following C
strict-aliasing rules:
memcached.c: In function .complete_incr_bin.:
memcached.c:1023:16: error: dereferencing type-punned pointer will break
strict-aliasing rules
memcached.c:1044:13: error: dereferencing type-punned pointer will break
strict-aliasing rules
memcached.c:1061:17: error: dereferencing type-punned pointer will break
strict-aliasing rules
Fix this by introducing a union type that allows access to the uint64_t
member as necessary, but doesn't add any additional length to the structure.
The size remains the same before and after; the only difference is explict
casts are now refactored into union member accesses and all compilers should
be happy.
Signed-off-by: Dan McGee <dan@archlinux.org>
diff --git a/memcached.h b/memcached.h
index 4a7295b..74a6592 100644
--- a/memcached.h
+++ b/memcached.h
@@ -77,18 +77,22 @@
#define TAIL_REPAIR_TIME (3 * 3600)
/* warning: don't use these macros with a function, as it evals its arg twice */
-#define ITEM_get_cas(i) ((uint64_t)(((i)->it_flags & ITEM_CAS) ? \
- *(uint64_t*)&((i)->end[0]) : 0x0))
-#define ITEM_set_cas(i,v) { if ((i)->it_flags & ITEM_CAS) { \
- *(uint64_t*)&((i)->end[0]) = v; } }
+#define ITEM_get_cas(i) (((i)->it_flags & ITEM_CAS) ? \
+ (i)->data->cas : (uint64_t)0)
-#define ITEM_key(item) (((char*)&((item)->end[0])) \
+#define ITEM_set_cas(i,v) { \
+ if ((i)->it_flags & ITEM_CAS) { \
+ (i)->data->cas = v; \
+ } \
+}
+
+#define ITEM_key(item) (((char*)&((item)->data)) \
+ (((item)->it_flags & ITEM_CAS) ? sizeof(uint64_t) : 0))
-#define ITEM_suffix(item) ((char*) &((item)->end[0]) + (item)->nkey + 1 \
+#define ITEM_suffix(item) ((char*) &((item)->data) + (item)->nkey + 1 \
+ (((item)->it_flags & ITEM_CAS) ? sizeof(uint64_t) : 0))
-#define ITEM_data(item) ((char*) &((item)->end[0]) + (item)->nkey + 1 \
+#define ITEM_data(item) ((char*) &((item)->data) + (item)->nkey + 1 \
+ (item)->nsuffix \
+ (((item)->it_flags & ITEM_CAS) ? sizeof(uint64_t) : 0))
@@ -302,7 +306,12 @@ typedef struct _stritem {
uint8_t it_flags; /* ITEM_* above */
uint8_t slabs_clsid;/* which slab class we're in */
uint8_t nkey; /* key length, w/terminating null and padding */
- void * end[];
+ /* this odd type prevents type-punning issues when we do
+ * the little shuffle to save space when not using CAS. */
+ union {
+ uint64_t cas;
+ char end;
+ } data[];
/* if it_flags & ITEM_CAS we have 8 bytes CAS */
/* then null-terminated key */
/* then " flags length\r\n" (no terminating null) */
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