[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>

3 files changed, 15 insertions, 1 deletions

diff --git a/arch/arm/kernel/calls.S b/arch/arm/kernel/calls.S
index 2b6b4c786e65..db07ce42b3b2 100644
--- a/arch/arm/kernel/calls.S
+++ b/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
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 3f8d0e3aefab..6281d488ac97 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/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.
diff --git a/arch/arm/kernel/sys_arm.c b/arch/arm/kernel/sys_arm.c
index f897ce2ccf0d..42629ff84f5a 100644
--- a/arch/arm/kernel/sys_arm.c
+++ b/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);
+}