powerpc: Add a proper syscall for switching endianness
We currently have a "special" syscall for switching endianness. This is
syscall number 0x1ebe, which is handled explicitly in the 64-bit syscall
exception entry.
That has a few problems, firstly the syscall number is outside of the
usual range, which confuses various tools. For example strace doesn't
recognise the syscall at all.
Secondly it's handled explicitly as a special case in the syscall
exception entry, which is complicated enough without it.
As a first step toward removing the special syscall, we need to add a
regular syscall that implements the same functionality.
The logic is simple, it simply toggles the MSR_LE bit in the userspace
MSR. This is the same as the special syscall, with the caveat that the
special syscall clobbers fewer registers.
This version clobbers r9-r12, XER, CTR, and CR0-1,5-7.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index d180caf2..afbc200 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -356,6 +356,11 @@
bl sys_swapcontext
b .Lsyscall_exit
+_GLOBAL(ppc_switch_endian)
+ bl save_nvgprs
+ bl sys_switch_endian
+ b .Lsyscall_exit
+
_GLOBAL(ret_from_fork)
bl schedule_tail
REST_NVGPRS(r1)
