Cast 64 bit off_t to 32 bit size_t

Some systems have sizeof(off_t) == 8 while sizeof(size_t) == 4.
This implies that we are able to access and work on files whose
maximum length is around 2^63-1 bytes, but we can only malloc or
mmap somewhat less than 2^32-1 bytes of memory.

On such a system an implicit conversion of off_t to size_t can cause
the size_t to wrap, resulting in unexpected and exciting behavior.
Right now we are working around all gcc warnings generated by the
-Wshorten-64-to-32 option by passing the off_t through xsize_t().

In the future we should make xsize_t on such problematic platforms
detect the wrapping and die if such a file is accessed.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 3 insertions, 3 deletions

diff --git a/read-cache.c b/read-cache.c
index 4a972b4ab..6339a278d 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -66,7 +66,7 @@ static int ce_compare_data(struct cache_entry *ce, struct stat *st)
 	return match;
 }
 
-static int ce_compare_link(struct cache_entry *ce, unsigned long expected_size)
+static int ce_compare_link(struct cache_entry *ce, size_t expected_size)
 {
 	int match = -1;
 	char *target;
@@ -101,7 +101,7 @@ static int ce_modified_check_fs(struct cache_entry *ce, struct stat *st)
 			return DATA_CHANGED;
 		break;
 	case S_IFLNK:
-		if (ce_compare_link(ce, st->st_size))
+		if (ce_compare_link(ce, xsize_t(st->st_size)))
 			return DATA_CHANGED;
 		break;
 	default:
@@ -797,7 +797,7 @@ int read_cache_from(const char *path)
 	}
 
 	if (!fstat(fd, &st)) {
-		cache_mmap_size = st.st_size;
+		cache_mmap_size = xsize_t(st.st_size);
 		errno = EINVAL;
 		if (cache_mmap_size >= sizeof(struct cache_header) + 20)
 			cache_mmap = xmmap(NULL, cache_mmap_size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);