After having spent some time digging into the origin of the strict-aliasing warnings when compiling with GCC 3.3 (brought about by Stefan Roehrich's post a couple of days ago), I came up with a couple of things that might be of interest in the development of PHP.
First of all, GCC provides an function qualifier __attribute_malloc__, which tells the compiler that the function in question is a malloc-like function, and will therefore never return values that might be aliased by other pointers in the scope of the function that called it. This is quite a boost for the effectiveness of the optimizations, because - the return type of malloc() being void* - the compiler has to take into account that every pointer in scope might be an alias of the resulting value. __attribute_malloc__ fixes that. (Disabled for non-GCC compilers)
The other thing is, that a lot of warnings are being triggered by invocations of zend_hash_find(). This function stores its result in the location pointed to by a void** argument, and returns an int specifying whether the key was found or not. As the comment in the source states, this was a conscious decision, because hashes can also be used to store null pointers.
After looking through some of the code, I found out that in a lot of cases, the pointers are expected not to be zero, and are being dereferenced in the code that immediately follows it [without checking for validity first].
Wouldn't it be more straight-forward to introduce an analogue for zend_hash_find() (eg. 'void *zend_hash_get()') which returns the stored pointer [or NULL on failure]. It could be used for applications where null pointers aren't allowed, and fix current code, where the implicit assumption is made the SUCCESS means the the pointers is non-null.
Last of all, I would like to know if we care about the warnings. Personally I don't really mind, as GCC's capabilities of accurately identifying violations of strict-aliasing rules are limited anyway.
Ard
Index: Zend/zend_alloc.h =================================================================== RCS file: /repository/ZendEngine2/zend_alloc.h,v retrieving revision 1.44 diff -u -u -r1.44 zend_alloc.h --- Zend/zend_alloc.h 18 Aug 2003 21:17:26 -0000 1.44 +++ Zend/zend_alloc.h 27 Aug 2003 13:17:13 -0000 @@ -68,6 +68,7 @@ #define PLATFORM_ALIGNMENT (__alignof__ (align_test)) #else #define PLATFORM_ALIGNMENT (sizeof(align_test)) +#define __attribute_malloc__ #endif #define MEM_HEADER_PADDING (((PLATFORM_ALIGNMENT-sizeof(zend_mem_header))%PLATFORM_ALIGNMENT+PLATFORM_ALIGNMENT)%PLATFORM_ALIGNMENT) @@ -75,15 +76,15 @@ BEGIN_EXTERN_C() -ZEND_API char *zend_strndup(const char *s, unsigned int length); +ZEND_API char *zend_strndup(const char *s, unsigned int length) __attribute_malloc__; -ZEND_API void *_emalloc(size_t size ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC); -ZEND_API void *_safe_emalloc(size_t nmemb, size_t size, size_t offset ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC); +ZEND_API void *_emalloc(size_t size ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC) __attribute_malloc__; +ZEND_API void *_safe_emalloc(size_t nmemb, size_t size, size_t offset ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC) __attribute_malloc__; ZEND_API void _efree(void *ptr ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC); -ZEND_API void *_ecalloc(size_t nmemb, size_t size ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC); -ZEND_API void *_erealloc(void *ptr, size_t size, int allow_failure ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC); -ZEND_API char *_estrdup(const char *s ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC); -ZEND_API char *_estrndup(const char *s, unsigned int length ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC); +ZEND_API void *_ecalloc(size_t nmemb, size_t size ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC) __attribute_malloc__; +ZEND_API void *_erealloc(void *ptr, size_t size, int allow_failure ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC) __attribute_malloc__; +ZEND_API char *_estrdup(const char *s ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC) __attribute_malloc__; +ZEND_API char *_estrndup(const char *s, unsigned int length ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC) __attribute_malloc__; /* Standard wrapper macros */ #define emalloc(size) _emalloc((size) ZEND_FILE_LINE_CC ZEND_FILE_LINE_EMPTY_CC)
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