[PATCH 3/6] arm64: scs: Use 'scs_sp' register alias for x18

Will Deacon
2020-05-15T17:29:00Z

x18 holds the SCS stack pointer value, so introduce a register alias to
make this easier to read in assembly code.

Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/include/asm/scs.h | 6 ++++--
arch/arm64/kernel/entry.S | 10 +++++-----
arch/arm64/kernel/head.S | 2 +-
3 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/scs.h b/arch/arm64/include/asm/scs.h
index 6b8cf4352fe3..d46efdd2060a 100644
--- a/arch/arm64/include/asm/scs.h
+++ b/arch/arm64/include/asm/scs.h
@@ -7,12 +7,14 @@
#include <asm/asm-offsets.h>

#ifdef CONFIG_SHADOW_CALL_STACK
+ scs_sp .req x18
+
.macro scs_load tsk, tmp
- ldr x18, [\tsk, #TSK_TI_SCS_SP]
+ ldr scs_sp, [\tsk, #TSK_TI_SCS_SP]
.endm

.macro scs_save tsk, tmp
- str x18, [\tsk, #TSK_TI_SCS_SP]
+ str scs_sp, [\tsk, #TSK_TI_SCS_SP]
.endm
#else
.macro scs_load tsk, tmp
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index cb0516e6f963..741faf0706f1 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -394,7 +394,7 @@ alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0
.macro irq_stack_entry
mov x19, sp // preserve the original sp
#ifdef CONFIG_SHADOW_CALL_STACK
- mov x24, x18 // preserve the original shadow stack
+ mov x24, scs_sp // preserve the original shadow stack
#endif

/*
@@ -416,7 +416,7 @@ alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0

#ifdef CONFIG_SHADOW_CALL_STACK
/* also switch to the irq shadow stack */
- adr_this_cpu x18, irq_shadow_call_stack, x26
+ adr_this_cpu scs_sp, irq_shadow_call_stack, x26
#endif

9998:
@@ -430,7 +430,7 @@ alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0
.macro irq_stack_exit
mov sp, x19
#ifdef CONFIG_SHADOW_CALL_STACK
- mov x18, x24
+ mov scs_sp, x24
#endif
.endm

@@ -1071,9 +1071,9 @@ SYM_CODE_START(__sdei_asm_handler)
#ifdef CONFIG_SHADOW_CALL_STACK
/* Use a separate shadow call stack for normal and critical events */
cbnz w4, 3f
- adr_this_cpu dst=x18, sym=sdei_shadow_call_stack_normal, tmp=x6
+ adr_this_cpu dst=scs_sp, sym=sdei_shadow_call_stack_normal, tmp=x6
b 4f
-3: adr_this_cpu dst=x18, sym=sdei_shadow_call_stack_critical, tmp=x6
+3: adr_this_cpu dst=scs_sp, sym=sdei_shadow_call_stack_critical, tmp=x6
4:
#endif

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 2b01c19c5483..1293baddfd20 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -426,7 +426,7 @@ SYM_FUNC_START_LOCAL(__primary_switched)
mov x29, sp

#ifdef CONFIG_SHADOW_CALL_STACK
- adr_l x18, init_shadow_call_stack // Set shadow call stack
+ adr_l scs_sp, init_shadow_call_stack // Set shadow call stack
#endif

str_l x21, __fdt_pointer, x5 // Save FDT pointer
--
2.26.2.761.g0e0b3e54be-goog