fix regression in alignment of dirent structs produced by readdir

commit 32482f61da7650ff10741bd5aedd66bbc3ea165b reduced the number of
int members before the dirent buf from 4 to 3, thereby misaligning it
mod sizeof(off_t), producing invalid accesses on any arch where
alignof(off_t)==sizeof(off_t).

rather than re-adding wasted padding, reorder the struct to meet the
requirement and add a comment and static assertion to prevent this
from getting broken again.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/dirent/__dirent.h b/src/dirent/__dirent.h
index 101b0368..828a5f17 100644
--- a/src/dirent/__dirent.h
+++ b/src/dirent/__dirent.h
@@ -1,9 +1,11 @@
 struct __dirstream
 {
-	int fd;
 	off_t tell;
+	int fd;
 	int buf_pos;
 	int buf_end;
 	volatile int lock[1];
+	/* Any changes to this struct must preserve the property:
+	 * offsetof(struct __dirent, buf) % sizeof(off_t) == 0 */
 	char buf[2048];
 };