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Subject[PATCH 1/9] arm64: entry: use the callee-saved registers to save some registers
Date
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.huang@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
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