[ARM] 3102/1: ARM EABI: stack pointer must be 64-bit aligned after a CPU exception

Patch from Nicolas Pitre

The ARM EABI says that the stack pointer has to be 64-bit aligned for
reasons already mentioned in patch #3101 when calling C functions.

We therefore must verify and adjust sp accordingly when taking an
exception from kernel mode since sp might not necessarily be 64-bit
aligned if the exception occurs in the middle of a kernel function.

If the exception occurs while in user mode then no sp fixup is needed as
long as sizeof(struct pt_regs) as well as any additional syscall data
stack space remain multiples of 8.

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

1 files changed, 5 insertions, 3 deletions

diff --git a/include/asm-arm/ptrace.h b/include/asm-arm/ptrace.h
index 4377e22b7e1a..f40948d54448 100644
--- a/include/asm-arm/ptrace.h
+++ b/include/asm-arm/ptrace.h
@@ -60,9 +60,11 @@
 
 #ifndef __ASSEMBLY__
 
-/* this struct defines the way the registers are stored on the
-   stack during a system call. */
-
+/*
+ * This struct defines the way the registers are stored on the
+ * stack during a system call.  Note that sizeof(struct pt_regs)
+ * has to be a multiple of 8.
+ */
 struct pt_regs {
         long uregs[18];
 };