Use malloc by default but allow bounded alloca

Signed-off-by: Mattias Andrée <maandree@kth.se>

1 files changed, 32 insertions, 0 deletions

diff --git a/sum_fd.c b/sum_fd.c
index bc2761d..a61bf71 100644
--- a/sum_fd.c
+++ b/sum_fd.c
@@ -16,17 +16,42 @@ libsha1_sum_fd(int fd, enum libsha1_algorithm algorithm, void *restrict hashsum)
 {
 	struct libsha1_state state;
 	ssize_t r;
+#ifndef _WIN32
 	struct stat attr;
+#endif
 	size_t blksize = 4096;
 	char *restrict chunk;
 
 	if (libsha1_init(&state, algorithm) < 0)
 		return -1;
 
+#ifndef _WIN32
 	if (fstat(fd, &attr) == 0 && attr.st_blksize > 0)
 		blksize = (size_t)(attr.st_blksize);
+#endif
 
+#if ALLOCA_LIMIT > 0
+	if (blksize > (size_t)ALLOCA_LIMIT) {
+		blksize = (size_t)ALLOCA_LIMIT;
+		blksize -= blksize % sizeof(((struct libsha1_state)NULL)->chunk);
+		if (!blksize)
+			blksize = sizeof(((struct libsha1_state)NULL)->chunk);
+	}
+# if defined(__clang__)
+	/* We are using a limit so it's just like declaring an array
+	 * in a function, except we might use less of the stack. */
+#  pragma clang diagnostic push
+#  pragma clang diagnostic ignored "-Walloca"
+# endif
 	chunk = alloca(blksize);
+# if defined(__clang__)
+#  pragma clang diagnostic pop
+# endif
+#else
+	chunk = malloc(blksize);
+	if (!chunk)
+		return -1;
+#endif
 
 	for (;;) {
 		r = read(fd, chunk, blksize);
@@ -35,11 +60,18 @@ libsha1_sum_fd(int fd, enum libsha1_algorithm algorithm, void *restrict hashsum)
 				break;
 			if (errno == EINTR)
 				continue;
+#if ALLOCA_LIMIT <= 0
+	free(chunk);
+#endif
 			return -1;
 		}
 		libsha1_update(&state, chunk, (size_t)r * 8);
 	}
 
 	libsha1_digest(&state, NULL, 0, hashsum);
+
+#if ALLOCA_LIMIT <= 0
+	free(chunk);
+#endif
 	return 0;
 }