fast-export: avoid NULL pointer arithmetic

rscharfe · gitster · commit c112084af965 · 2018-05-10T18:29:57.000+09:00
Clang 6 reports the following warning, which is turned into an error in a DEVELOPER build: builtin/fast-export.c:162:28: error: performing pointer arithmetic on a null pointer has undefined behavior [-Werror,-Wnull-pointer-arithmetic] return ((uint32_t *)NULL) + mark; ~~~~~~~~~~~~~~~~~~ ^ 1 error generated. The compiler is correct, and the error message speaks for itself. There is no need for any undefined operation -- just cast mark to void * or uint32_t after an intermediate cast to uintptr_t. That encodes the integer value into a pointer and later decodes it as intended. While at it remove an outdated comment -- intptr_t has been used since ffe659f (parse-options: make some arguments optional, add callbacks), committed in October 2007. Signed-off-by: Rene Scharfe <l.s.r@web.de> Acked-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/fast-export.c b/builtin/fast-export.c
@@ -154,15 +154,14 @@ static void anonymize_path(struct strbuf *out, const char *path,
 	}
 }
 
-/* Since intptr_t is C99, we do not use it here */
-static inline uint32_t *mark_to_ptr(uint32_t mark)
+static inline void *mark_to_ptr(uint32_t mark)
 {
-	return ((uint32_t *)NULL) + mark;
+	return (void *)(uintptr_t)mark;
 }
 
 static inline uint32_t ptr_to_mark(void * mark)
 {
-	return (uint32_t *)mark - (uint32_t *)NULL;
+	return (uint32_t)(uintptr_t)mark;
 }
 
 static inline void mark_object(struct object *object, uint32_t mark)

Original file line number	Diff line number	Diff line change
`@@ -154,15 +154,14 @@ static void anonymize_path(struct strbuf out, const char path,`
`154`	`154`	`}`
`155`	`155`	`}`
`156`	`156`
`157`		`-/* Since intptr_t is C99, we do not use it here */`
`158`		`-static inline uint32_t *mark_to_ptr(uint32_t mark)`
	`157`	`+static inline void *mark_to_ptr(uint32_t mark)`
`159`	`158`	`{`
`160`		`- return ((uint32_t *)NULL) + mark;`
	`159`	`+ return (void *)(uintptr_t)mark;`
`161`	`160`	`}`
`162`	`161`
`163`	`162`	`static inline uint32_t ptr_to_mark(void * mark)`
`164`	`163`	`{`
`165`		`- return (uint32_t )mark - (uint32_t )NULL;`
	`164`	`+ return (uint32_t)(uintptr_t)mark;`
`166`	`165`	`}`
`167`	`166`
`168`	`167`	`static inline void mark_object(struct object *object, uint32_t mark)`