[ARM] 2865/2: fix fadvise64_64 syscall argument passing

Patch from Nicolas Pitre

The prototype for sys_fadvise64_64() is:
    long sys_fadvise64_64(int fd, loff_t offset, loff_t len, int advice)
The argument list is therefore as follows on legacy ABI:
	fd: type int (r0)
	offset: type long long (r1-r2)
	len: type long long (r3-sp[0])
	advice: type int (sp[4])
With EABI this becomes:
	fd: type int (r0)
	offset: type long long (r2-r3)
	len: type long long (sp[0]-sp[4])
	advice: type int (sp[8])
Not only do we have ABI differences here, but the EABI version requires
one additional word on the syscall stack.
To avoid the ABI mismatch and the extra stack space required with EABI
this syscall is now defined with a different argument ordering
on ARM as follows:
    long sys_arm_fadvise64_64(int fd, int advice, loff_t offset, loff_t len)
This gives us the following ABI independent argument distribution:
	fd: type int (r0)
	advice: type int (r1)
	offset: type long long (r2-r3)
	len: type long long (sp[0]-sp[4])
Now, since the syscall entry code takes care of 5 registers only by
default including the store of r4 to the stack, we need a wrapper to
store r5 to the stack as well.  Because that wrapper was missing and was
always required this means that sys_fadvise64_64 never worked on ARM and
therefore we can safely reuse its syscall number for our new
sys_arm_fadvise64_64 interface.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/calls.S

@@ -284,7 +284,7 @@ __syscall_start:
 		.long	sys_fstatfs64
 		.long	sys_tgkill
 		.long	sys_utimes
-/* 270 */	.long	sys_fadvise64_64
+/* 270 */	.long	sys_arm_fadvise64_64_wrapper
 		.long	sys_pciconfig_iobase
 		.long	sys_pciconfig_read
 		.long	sys_pciconfig_write

arch/arm/kernel/entry-common.S

@@ -265,6 +265,10 @@ sys_futex_wrapper:
 		str	r5, [sp, #4]		@ push sixth arg
 		b	sys_futex
 
+sys_arm_fadvise64_64_wrapper:
+		str	r5, [sp, #4]		@ push r5 to stack
+		b	sys_arm_fadvise64_64
+
 /*
  * Note: off_4k (r5) is always units of 4K.  If we can't do the requested
  * offset, we return EINVAL.

arch/arm/kernel/sys_arm.c

@@ -311,3 +311,13 @@ long execve(const char *filename, char **argv, char **envp)
 	return ret;
 }
 EXPORT_SYMBOL(execve);
+
+/*
+ * Since loff_t is a 64 bit type we avoid a lot of ABI hastle
+ * with a different argument ordering.
+ */
+asmlinkage long sys_arm_fadvise64_64(int fd, int advice,
+				     loff_t offset, loff_t len)
+{
+	return sys_fadvise64_64(fd, offset, len, advice);
+}

include/asm-arm/unistd.h

@@ -295,7 +295,7 @@
 #define __NR_fstatfs64			(__NR_SYSCALL_BASE+267)
 #define __NR_tgkill			(__NR_SYSCALL_BASE+268)
 #define __NR_utimes			(__NR_SYSCALL_BASE+269)
-#define __NR_fadvise64_64		(__NR_SYSCALL_BASE+270)
+#define __NR_arm_fadvise64_64		(__NR_SYSCALL_BASE+270)
 #define __NR_pciconfig_iobase		(__NR_SYSCALL_BASE+271)
 #define __NR_pciconfig_read		(__NR_SYSCALL_BASE+272)
 #define __NR_pciconfig_write		(__NR_SYSCALL_BASE+273)