memdbg: improve md_realloc() compliance with plain realloc()

  -Allow reallocation of NULL pointers (equivalent to a malloc() call)
  -Allow 'size' to be 0 (equivalent to a free() call)
  -Handle case where 'size' is smaller than the original buffer length

Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>

1 files changed, 26 insertions, 12 deletions

diff --git a/accel-pppd/memdebug.c b/accel-pppd/memdebug.c
index 286ddd84..67c84985 100644
--- a/accel-pppd/memdebug.c
+++ b/accel-pppd/memdebug.c
@@ -105,23 +105,37 @@ void __export md_free(void *ptr, const char *fname, int line)
 
 void __export *md_realloc(void *ptr, size_t size, const char *fname, int line)
 {
-	struct mem_t *mem = container_of(ptr, typeof(*mem), data);
+	struct mem_t *mem = ptr ? container_of(ptr, typeof(*mem), data) : NULL;
 	struct mem_t *mem2;
-	
-	if (mem->magic1 != MAGIC1) {
-		printf("memory corruption:\nfree at %s:%i\n", fname, line);
-		abort();
-	}
 
-	if (mem->magic2 != *(uint64_t*)(mem->data + mem->size)) {
-		printf("memory corruption:\nmalloc(%lu) at %s:%i\nfree at %s:%i\n", (long unsigned)mem->size, mem->fname, mem->line, fname, line);
-		abort();
+	if (mem) {
+		if (mem->magic1 != MAGIC1) {
+			printf("memory corruption:\nfree at %s:%i\n",
+			       fname, line);
+			abort();
+		}
+
+		if (mem->magic2 != *(uint64_t*)(mem->data + mem->size)) {
+			printf("memory corruption:\nmalloc(%zu) at %s:%i\nfree at %s:%i\n",
+			       mem->size, mem->fname, mem->line, fname, line);
+			abort();
+		}
+
+		if (size == 0) {
+			md_free(mem->data, fname, line);
+			return NULL;
+		}
 	}
 
 	mem2 = _md_malloc(size, fname, line);
-	memcpy(mem2->data, mem->data, mem->size);
-	
-	md_free(mem->data, fname, line);
+	if (mem2 == NULL)
+		return NULL;
+
+	if (mem) {
+		memcpy(mem2->data, mem->data,
+		       (size < mem->size) ? size : mem->size);
+		md_free(mem->data, fname, line);
+	}
 
 	return mem2->data;
 }