LoongArch: change global registers to local registers

LoongArch inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5OHOB

--------------------------------

From gcc commit 3f13154553f8
("df-scan: remove ad-hoc handling of global regs in asms"),
global registers will no longer be forced to add to the def-use
chain for the following inline asm :
  __asm("" : "=r"(a) : "0"(c)); /* the case for RELOC_HIDE */
  __asm("" : "=r"(b));

So we change to use $r21 $tp $sp as local registers,this way
they can be forced to add to the def-use chain.
Signed-off-by: NHongchen Zhang <zhanghongchen@loongson.cn>
Signed-off-by: NXing Li <lixing@loongson.cn>
Change-Id: I8ab88684ba8093f5ab84dec837d10594128ee16b

arch/loongarch/include/asm/entry-common.h

@@ -7,7 +7,7 @@
 
 static inline bool on_thread_stack(void)
 {
-	return !(((unsigned long)(current->stack) ^ current_stack_pointer) & ~(THREAD_SIZE - 1));
+	return !(((unsigned long)(current->stack) ^ current_stack_pointer()) & ~(THREAD_SIZE - 1));
 }
 
 #endif

arch/loongarch/include/asm/percpu.h

@@ -18,14 +18,19 @@
 #endif
 
 /* Use r21 for fast access */
-register unsigned long __my_cpu_offset __asm__("$r21");
+static inline unsigned long __kern_my_cpu_offset(void)
+{
+	register unsigned long off __asm__("$r21");
+
+	return off;
+}
+#define __my_cpu_offset __kern_my_cpu_offset()
 
 static inline void set_my_cpu_offset(unsigned long off)
 {
-	__my_cpu_offset = off;
+	asm volatile("move $r21, %0"::"r"(off));
 	csr_write64(off, PERCPU_BASE_KS);
 }
-#define __my_cpu_offset __my_cpu_offset
 
 #define PERCPU_OP(op, asm_op, c_op)					\
 static inline unsigned long __percpu_##op(void *ptr,			\

arch/loongarch/include/asm/thread_info.h

@@ -44,14 +44,19 @@ struct thread_info {
 }
 
 /* How to get the thread information struct from C. */
-register struct thread_info *__current_thread_info __asm__("$tp");
-
 static inline struct thread_info *current_thread_info(void)
 {
+	register struct thread_info *__current_thread_info __asm__("$tp");
+
 	return __current_thread_info;
 }
 
-register unsigned long current_stack_pointer __asm__("$sp");
+static inline unsigned long current_stack_pointer(void)
+{
+	register unsigned long __current_stack_pointer __asm__("$sp");
+
+	return __current_stack_pointer;
+}
 
 #endif /* !__ASSEMBLY__ */