[ARM] 3108/2: old ABI compat: statfs64 and fstatfs64

Patch from Nicolas Pitre

struct statfs64 has extra padding with EABI growing its size from 84 to
88. This struct is now __attribute__((packed,aligned(4))) with a small
assembly wrapper to force the sz argument to 84 if it is 88 to avoid
copying the extra padding over user space memory unexpecting it.
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/calls.S

@@ -280,8 +280,8 @@ __syscall_start:
 		.long	sys_clock_gettime
 		.long	sys_clock_getres
 /* 265 */	.long	sys_clock_nanosleep
-		.long	sys_statfs64
-		.long	sys_fstatfs64
+		.long	sys_statfs64_wrapper
+		.long	sys_fstatfs64_wrapper
 		.long	sys_tgkill
 		.long	sys_utimes
 /* 270 */	.long	sys_arm_fadvise64_64

arch/arm/kernel/entry-common.S

@@ -262,6 +262,16 @@ sys_sigaltstack_wrapper:
 		ldr	r2, [sp, #S_OFF + S_SP]
 		b	do_sigaltstack
 
+sys_statfs64_wrapper:
+		teq	r1, #88
+		moveq	r1, #84
+		b	sys_statfs64
+
+sys_fstatfs64_wrapper:
+		teq	r1, #88
+		moveq	r1, #84
+		b	sys_fstatfs64
+
 /*
  * Note: off_4k (r5) is always units of 4K.  If we can't do the requested
  * offset, we return EINVAL.

include/asm-arm/statfs.h

 #ifndef _ASMARM_STATFS_H
 #define _ASMARM_STATFS_H
 
-#include <asm-generic/statfs.h>
+#ifndef __KERNEL_STRICT_NAMES
+# include <linux/types.h>
+typedef __kernel_fsid_t	fsid_t;
+#endif
+
+struct statfs {
+	__u32 f_type;
+	__u32 f_bsize;
+	__u32 f_blocks;
+	__u32 f_bfree;
+	__u32 f_bavail;
+	__u32 f_files;
+	__u32 f_ffree;
+	__kernel_fsid_t f_fsid;
+	__u32 f_namelen;
+	__u32 f_frsize;
+	__u32 f_spare[5];
+};
+
+/*
+ * With EABI there is 4 bytes of padding added to this structure.
+ * Let's pack it so the padding goes away to simplify dual ABI support.
+ * Note that user space does NOT have to pack this structure.
+ */
+struct statfs64 {
+	__u32 f_type;
+	__u32 f_bsize;
+	__u64 f_blocks;
+	__u64 f_bfree;
+	__u64 f_bavail;
+	__u64 f_files;
+	__u64 f_ffree;
+	__kernel_fsid_t f_fsid;
+	__u32 f_namelen;
+	__u32 f_frsize;
+	__u32 f_spare[5];
+} __attribute__ ((packed,aligned(4)));
 
 #endif