csky: add arch support current_stack_pointer

To follow the existing per-arch conventions, using "current_stack_pointer"
to set sp.

This will let it be used in non-arch places(like HARDENED_USERCOPY).

Refer to the implementation of riscv commit fdecfea ("riscv: Rename
"sp_in_global" to "current_stack_pointer"").

Link: https://lore.kernel.org/lkml/[email protected]/
Signed-off-by: Tong Tiangen <[email protected]>
Signed-off-by: Guo Ren <[email protected]>

Author: Tong Tiangen

arch/csky/Kconfig

@@ -9,6 +9,7 @@ config CSKY
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_QUEUED_RWLOCKS
 	select ARCH_USE_QUEUED_SPINLOCKS
+	select ARCH_HAS_CURRENT_STACK_POINTER
 	select ARCH_INLINE_READ_LOCK if !PREEMPTION
 	select ARCH_INLINE_READ_LOCK_BH if !PREEMPTION
 	select ARCH_INLINE_READ_LOCK_IRQ if !PREEMPTION

arch/csky/include/asm/processor.h

@@ -84,4 +84,6 @@ unsigned long __get_wchan(struct task_struct *p);
 
 #define cpu_relax() barrier()
 
+register unsigned long current_stack_pointer __asm__("sp");
+
 #endif /* __ASM_CSKY_PROCESSOR_H */

arch/csky/kernel/stacktrace.c

@@ -23,10 +23,9 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
 		sp = user_stack_pointer(regs);
 		pc = instruction_pointer(regs);
 	} else if (task == NULL || task == current) {
-		const register unsigned long current_sp __asm__ ("sp");
 		const register unsigned long current_fp __asm__ ("r8");
 		fp = current_fp;
-		sp = current_sp;
+		sp = current_stack_pointer;
 		pc = (unsigned long)walk_stackframe;
 	} else {
 		/* task blocked in __switch_to */
@@ -68,8 +67,7 @@ static void notrace walk_stackframe(struct task_struct *task,
 		sp = user_stack_pointer(regs);
 		pc = instruction_pointer(regs);
 	} else if (task == NULL || task == current) {
-		const register unsigned long current_sp __asm__ ("sp");
-		sp = current_sp;
+		sp = current_stack_pointer;
 		pc = (unsigned long)walk_stackframe;
 	} else {
 		/* task blocked in __switch_to */