with the help of John Bowler, track down the ugly ABI change between 2.4 / 2.6 on big endian arm kernels and work around it best we can at runtime

1 files changed, 69 insertions, 3 deletions

diff --git a/libc/sysdeps/linux/common/xstatconv.c b/libc/sysdeps/linux/common/xstatconv.c
index 60ec25bd5..325b70550 100644
--- a/libc/sysdeps/linux/common/xstatconv.c
+++ b/libc/sysdeps/linux/common/xstatconv.c
@@ -55,26 +55,92 @@ void __xstat_conv(struct kernel_stat *kbuf, struct stat *buf)
 #endif
 }
 
- #if defined(__UCLIBC_HAS_LFS__)
+#if defined(__UCLIBC_HAS_LFS__)
+
+/* OK, this is ugly, but not much we can do about it.
+ *
+ * The issue at hand is that the kernel introduced an ABI change between 
+ * 2.4 and 2.6 for big endian machines on some architectures in stat64 with 
+ * st_dev and st_rdev fields.   Older kernels used 'short' but newer kernels 
+ * use a 'long'.  As if that wasn't fun enough, the location of st_blocks and 
+ * its padding have swapped.  So, when applicable, we need to detect and shift 
+ * bits around and hope for the best.  The kernel at least helps us out a bit 
+ * because it will be sure to zero out all padding fields.
+ *
+ * Unimportant Note About Mis-detections:
+ * - if user is running a 2.4 system with the old ABI and they stat a file on 
+ *   a system which major 0 / minor 0.  We can ignore this though because the 
+ *   kernel has major 0 reserved for non mountable devices (wh00t!)
+ * - if user is running a 2.6 system with the new ABI and they stat a file on 
+ *   a device whose st_dev fills up the lower 6 bytes into the upper 2 bytes 
+ *   which overlap.  Again we should be able to safely ignore this because 
+ *   that means it'd be a pretty big ass (read: uncommon) major/minor combo :).
+
+ Old [2.4]:
+struct stat64 {
+    unsigned short  st_dev;
+    unsigned char   __pad0[10];
+    ...
+    unsigned long   st_blocks;
+    unsigned long   __pad4;
+    ...
+ New [2.6]:
+struct stat64 {
+    unsigned long long  st_dev;
+    unsigned char   __pad0[4];
+    ...
+    unsigned long   __pad4;
+    unsigned long   st_blocks;
+    ...
+
+ * sizeof(unsigned short) = 2
+ * sizeof(unsigned long long) = 8
+ */
+#include <endian.h>
+#include <sys/utsname.h>
+#if BYTE_ORDER == BIG_ENDIAN && \
+    (defined(__ARMEB__)) /* || defined(__sh__) || defined(__sparc__))*/
+# define NEED_ABI_CHECK 1
+#else
+# define NEED_ABI_CHECK 0
+#endif
+
 void __xstat64_conv(struct kernel_stat64 *kbuf, struct stat64 *buf)
 {
     /* Convert to current kernel version of `struct stat64'.  */
+
+#if NEED_ABI_CHECK
+	if (!kbuf->st_dev.old_abi) {
+		/* new 2.6 ABI */
+		buf->st_dev = kbuf->st_dev.new_abi;
+		buf->st_rdev = kbuf->st_rdev.new_abi;
+		buf->st_blocks = kbuf->st_blocks;
+	} else {
+		/* old 2.4 ABI */
+		buf->st_dev = kbuf->st_dev.old_abi;
+		buf->st_rdev = kbuf->st_dev.old_abi;
+		buf->st_blocks = kbuf->__pad_st_blocks;
+	}
+#else
     buf->st_dev = kbuf->st_dev;
     buf->st_ino = kbuf->st_ino;
+    buf->st_rdev = kbuf->st_rdev;
+#endif
+
 #ifdef _HAVE_STAT64___ST_INO
     buf->__st_ino = kbuf->__st_ino;
 #endif
+
     buf->st_mode = kbuf->st_mode;
     buf->st_nlink = kbuf->st_nlink;
     buf->st_uid = kbuf->st_uid;
     buf->st_gid = kbuf->st_gid;
-    buf->st_rdev = kbuf->st_rdev;
     buf->st_size = kbuf->st_size;
     buf->st_blksize = kbuf->st_blksize;
-    buf->st_blocks = kbuf->st_blocks;
     buf->st_atime = kbuf->st_atime;
     buf->st_mtime = kbuf->st_mtime;
     buf->st_ctime = kbuf->st_ctime;
+
 #ifdef STAT_HAVE_NSEC
 	buf->st_atime_nsec = kbuf->st_atime_nsec;
 	buf->st_mtime_nsec = kbuf->st_mtime_nsec;