[PATCH] Avoid allocating 0 bytes, was Re: [PATCH 4/4] git-compat-util.h: dietlibc-friendly x{malloc,realloc,calloc}

@@ -121,6 +121,9 @@ int sha1write_compressed(struct sha1file
 	unsigned long maxsize;
 	void *out;
 
+	if (size == 0)
+		return 0;
+
 	memset(&stream, 0, sizeof(stream));
 	deflateInit(&stream, Z_DEFAULT_COMPRESSION);
 	maxsize = deflateBound(&stream, size);

@@ -504,9 +504,9 @@ static void prepare_temp_file(const char
 		}
 		if (S_ISLNK(st.st_mode)) {
 			int ret;
-			char *buf, buf_[1024];
-			buf = ((sizeof(buf_) < st.st_size) ?
-			       xmalloc(st.st_size) : buf_);
+			char buf[MAXPATHLEN + 1];
+			if (st.st_size > MAXPATHLEN)
+				die("Unbelievably long symlink: %", name);
 			ret = readlink(name, buf, st.st_size);
 			if (ret < 0)
 				die("readlink(%s)", name);

@@ -61,6 +61,8 @@ static void prepare_order(const char *or
 		}
 		if (pass == 0) {
 			order_cnt = cnt;
+			if (cnt == 0)
+				return;
 			order = xmalloc(sizeof(*order) * cnt);
 		}
 	}

@@ -105,9 +107,13 @@ static int compare_pair_order(const void
 void diffcore_order(const char *orderfile)
 {
 	struct diff_queue_struct *q = &diff_queued_diff;
-	struct pair_order *o = xmalloc(sizeof(*o) * q->nr);
+	struct pair_order *o;
 	int i;
 
+	if (q->nr == 0)
+		return;
+
+	o = xmalloc(sizeof(*o) * q->nr);
 	prepare_order(orderfile);
 	for (i = 0; i < q->nr; i++) {
 		o[i].pair = q->queue[i];

@@ -48,10 +48,14 @@ void diffcore_pathspec(const char **path
 	for (i = 0; pathspec[i]; i++)
 		;
 	speccnt = i;
-	spec = xmalloc(sizeof(*spec) * speccnt);
-	for (i = 0; pathspec[i]; i++) {
-		spec[i].spec = pathspec[i];
-		spec[i].len = strlen(pathspec[i]);
+	if (speccnt == 0)
+		spec = NULL;
+	else {
+		spec = xmalloc(sizeof(*spec) * speccnt);
+		for (i = 0; pathspec[i]; i++) {
+			spec[i].spec = pathspec[i];
+			spec[i].len = strlen(pathspec[i]);
+		}
 	}
 
 	for (i = 0; i < q->nr; i++) {

@@ -103,7 +103,7 @@ static void *unpack_entry_data(unsigned 
 	unsigned long pack_limit = pack_size - 20;
 	unsigned long pos = *current_pos;
 	z_stream stream;
-	void *buf = xmalloc(size);
+	void *buf = xmalloc(size ? size : 1);
 
 	memset(&stream, 0, sizeof(stream));
 	stream.next_out = buf;

@@ -353,7 +353,8 @@ static void write_index_file(const char 
 {
 	struct sha1file *f;
 	struct object_entry **sorted_by_sha =
-		xcalloc(nr_objects, sizeof(struct object_entry *));
+		xcalloc(nr_objects ? nr_objects : 1,
+				sizeof(struct object_entry *));
 	struct object_entry **list = sorted_by_sha;
 	struct object_entry **last = sorted_by_sha + nr_objects;
 	unsigned int array[256];

@@ -448,8 +449,10 @@ int main(int argc, char **argv)
 
 	open_pack_file();
 	parse_pack_header();
-	objects = xcalloc(nr_objects, sizeof(struct object_entry));
-	deltas = xcalloc(nr_objects, sizeof(struct delta_entry));
+	objects = xcalloc(nr_objects ? nr_objects : 1,
+			sizeof(struct object_entry));
+	deltas = xcalloc(nr_objects ? nr_objects : 1,
+			sizeof(struct delta_entry));
 	parse_pack_objects();
 	free(deltas);
 	write_index_file(index_name, sha1);

@@ -406,7 +406,8 @@ static void prepare_pack(int window, int
 
 	fprintf(stderr, "Packing %d objects\n", nr_objects);
 
-	sorted_by_type = create_sorted_list(type_size_sort);
+	if (nr_objects > 0)
+		sorted_by_type = create_sorted_list(type_size_sort);
 	if (window && depth)
 		find_deltas(sorted_by_type, window+1, depth);
 	write_pack_file();

@@ -540,7 +541,8 @@ int main(int argc, char **argv)
 	if (non_empty && !nr_objects)
 		return 0;
 
-	sorted_by_sha = create_sorted_list(sha1_sort);
+	if (nr_objects > 0)
+		sorted_by_sha = create_sorted_list(sha1_sort);
 	SHA1_Init(&ctx);
 	list = sorted_by_sha;
 	for (i = 0; i < nr_objects; i++) {

@@ -294,17 +294,20 @@ static int unpack_trees(merge_fn_t fn)
 {
 	int indpos = 0;
 	unsigned len = object_list_length(trees);
-	struct tree_entry_list **posns = 
-		xmalloc(len * sizeof(struct tree_entry_list *));
+	struct tree_entry_list **posns;
 	int i;
 	struct object_list *posn = trees;
 	merge_size = len;
-	for (i = 0; i < len; i++) {
-		posns[i] = ((struct tree *) posn->item)->entries;
-		posn = posn->next;
+
+	if (len) {
+		posns = xmalloc(len * sizeof(struct tree_entry_list *));
+		for (i = 0; i < len; i++) {
+			posns[i] = ((struct tree *) posn->item)->entries;
+			posn = posn->next;
+		}
+		if (unpack_trees_rec(posns, len, "", fn, &indpos))
+			return -1;
 	}
-	if (unpack_trees_rec(posns, len, "", fn, &indpos))
-		return -1;
 
 	if (trivial_merges_only && nontrivial_merge)
 		die("Merge requires file-level merging");

@@ -1371,35 +1371,37 @@ int write_sha1_file(void *buf, unsigned 
 		return -1;
 	}
 
-	/* Set it up */
-	memset(&stream, 0, sizeof(stream));
-	deflateInit(&stream, Z_BEST_COMPRESSION);
-	size = deflateBound(&stream, len+hdrlen);
-	compressed = xmalloc(size);
-
-	/* Compress it */
-	stream.next_out = compressed;
-	stream.avail_out = size;
-
-	/* First header.. */
-	stream.next_in = hdr;
-	stream.avail_in = hdrlen;
-	while (deflate(&stream, 0) == Z_OK)
-		/* nothing */;
-
-	/* Then the data itself.. */
-	stream.next_in = buf;
-	stream.avail_in = len;
-	while (deflate(&stream, Z_FINISH) == Z_OK)
-		/* nothing */;
-	deflateEnd(&stream);
-	size = stream.total_out;
+	if (len + hdrlen > 0) {
+		/* Set it up */
+		memset(&stream, 0, sizeof(stream));
+		deflateInit(&stream, Z_BEST_COMPRESSION);
+		size = deflateBound(&stream, len+hdrlen);
+		compressed = xmalloc(size);
+
+		/* Compress it */
+		stream.next_out = compressed;
+		stream.avail_out = size;
 
-	if (write(fd, compressed, size) != size)
-		die("unable to write file");
+		/* First header.. */
+		stream.next_in = hdr;
+		stream.avail_in = hdrlen;
+		while (deflate(&stream, 0) == Z_OK)
+			/* nothing */;
+
+		/* Then the data itself.. */
+		stream.next_in = buf;
+		stream.avail_in = len;
+		while (deflate(&stream, Z_FINISH) == Z_OK)
+			/* nothing */;
+		deflateEnd(&stream);
+		size = stream.total_out;
+
+		if (write(fd, compressed, size) != size)
+			die("unable to write file");
+		free(compressed);
+	}
 	fchmod(fd, 0444);
 	close(fd);
-	free(compressed);
 
 	return move_temp_to_file(tmpfile, filename);
 }

@@ -1429,7 +1431,7 @@ int write_sha1_to_fd(int fd, const unsig
 		memset(&stream, 0, sizeof(stream));
 		deflateInit(&stream, Z_BEST_COMPRESSION);
 		size = deflateBound(&stream, len + hdrlen);
-		temp_obj = buf = xmalloc(size);
+		temp_obj = buf = xmalloc(size ? size : 1);
 
 		/* Compress it */
 		stream.next_out = buf;

@@ -263,6 +263,10 @@ void diff_tree_setup_paths(const char **
 
 		paths = p;
 		nr_paths = count_paths(paths);
+		if (nr_paths == 0) {
+			pathlens = NULL;
+			return;
+		}
 		pathlens = xmalloc(nr_paths * sizeof(int));
 		for (i=0; i<nr_paths; i++)
 			pathlens[i] = strlen(paths[i]);

@@ -53,7 +53,7 @@ static void use(int bytes)
 static void *get_data(unsigned long size)
 {
 	z_stream stream;
-	void *buf = xmalloc(size);
+	void *buf = xmalloc(size ? size : 1);
 
 	memset(&stream, 0, sizeof(stream));