[PATCH 1/9] arm64: entry: use the callee-saved registers to save some registers

[Huang Shijie]

This patch uses the callee-saved registers x19/x20/scno to save the
x0/x7/x8 which will be used in the syscall path.

This patch makes preparation for the trace code.

Signed-off-by: Huang Shijie <shijie.hu...@arm.com>
---
 arch/arm64/kernel/entry.S | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index d70a9e4..7dcfd49 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -119,6 +119,16 @@
        .endif
 
        /*
+        * Save the x0/x7/x8 in the Callee-saved registers.
+        * We will use them in the syscall path.
+        */
+       .if     \el == 0
+       mov     x19, x0
+       mov     x20, x7
+       mov     scno, x8
+       .endif
+
+       /*
         * Registers that may be useful after this macro is invoked:
         *
         * x21 - aborted SP
@@ -500,7 +510,7 @@ el0_svc_compat:
         * AArch32 syscall handling
         */
        adrp    stbl, compat_sys_call_table     // load compat syscall table 
pointer
-       uxtw    scno, w7                        // syscall number in w7 (r7)
+       uxtw    scno, w20                       // syscall number in w7 (r7)
        mov     sc_nr, #__NR_compat_syscalls
        b       el0_svc_naked
 
@@ -712,10 +722,10 @@ ENDPROC(ret_from_fork)
        .align  6
 el0_svc:
        adrp    stbl, sys_call_table            // load syscall table pointer
-       uxtw    scno, w8                        // syscall number in w8
+       uxtw    scno, w26                       // syscall number in w8
        mov     sc_nr, #__NR_syscalls
 el0_svc_naked:                                 // compat entry point
-       stp     x0, scno, [sp, #S_ORIG_X0]      // save the original x0 and 
syscall number
+       stp     x19, scno, [sp, #S_ORIG_X0]     // save the original x0 and 
syscall number
        enable_dbg_and_irq
        ct_user_exit 1
 
-- 
2.5.5