LoongArch: Remove unused kernel stack padding

The current LoongArch kernel stack is padded as if obeying the MIPS o32
calling convention (32 bytes), signifying the port's MIPS lineage but no
longer making sense. Remove the padding for clarity.
Reviewed-by: NWANG Xuerui <git@xen0n.name>
Signed-off-by: NJinyang He <hejinyang@loongson.cn>
Signed-off-by: NHuacai Chen <chenhuacai@loongson.cn>

arch/loongarch/include/asm/processor.h

@@ -191,7 +191,7 @@ static inline void flush_thread(void)
 unsigned long __get_wchan(struct task_struct *p);
 
 #define __KSTK_TOS(tsk) ((unsigned long)task_stack_page(tsk) + \
-			 THREAD_SIZE - 32 - sizeof(struct pt_regs))
+			 THREAD_SIZE - sizeof(struct pt_regs))
 #define task_pt_regs(tsk) ((struct pt_regs *)__KSTK_TOS(tsk))
 #define KSTK_EIP(tsk) (task_pt_regs(tsk)->csr_era)
 #define KSTK_ESP(tsk) (task_pt_regs(tsk)->regs[3])

arch/loongarch/include/asm/ptrace.h

@@ -133,7 +133,7 @@ static inline void die_if_kernel(const char *str, struct pt_regs *regs)
 #define current_pt_regs()						\
 ({									\
 	unsigned long sp = (unsigned long)__builtin_frame_address(0);	\
-	(struct pt_regs *)((sp | (THREAD_SIZE - 1)) + 1 - 32) - 1;	\
+	(struct pt_regs *)((sp | (THREAD_SIZE - 1)) + 1) - 1;		\
 })
 
 /* Helpers for working with the user stack pointer */

arch/loongarch/kernel/head.S

@@ -84,10 +84,9 @@ SYM_CODE_START(kernel_entry)			# kernel entry point
 
 	la.pcrel	tp, init_thread_union
 	/* Set the SP after an empty pt_regs.  */
-	PTR_LI		sp, (_THREAD_SIZE - 32 - PT_SIZE)
+	PTR_LI		sp, (_THREAD_SIZE - PT_SIZE)
 	PTR_ADD		sp, sp, tp
 	set_saved_sp	sp, t0, t1
-	PTR_ADDI	sp, sp, -4 * SZREG	# init stack pointer
 
 	bl		start_kernel
 	ASM_BUG()

arch/loongarch/kernel/process.c

@@ -129,7 +129,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 	unsigned long clone_flags = args->flags;
 	struct pt_regs *childregs, *regs = current_pt_regs();
 
-	childksp = (unsigned long)task_stack_page(p) + THREAD_SIZE - 32;
+	childksp = (unsigned long)task_stack_page(p) + THREAD_SIZE;
 
 	/* set up new TSS. */
 	childregs = (struct pt_regs *) childksp - 1;
@@ -236,7 +236,7 @@ bool in_task_stack(unsigned long stack, struct task_struct *task,
 			struct stack_info *info)
 {
 	unsigned long begin = (unsigned long)task_stack_page(task);
-	unsigned long end = begin + THREAD_SIZE - 32;
+	unsigned long end = begin + THREAD_SIZE;
 
 	if (stack < begin || stack >= end)
 		return false;

arch/loongarch/kernel/switch.S

@@ -26,7 +26,7 @@ SYM_FUNC_START(__switch_to)
 	move	tp, a2
 	cpu_restore_nonscratch a1
 
-	li.w		t0, _THREAD_SIZE - 32
+	li.w		t0, _THREAD_SIZE
 	PTR_ADD		t0, t0, tp
 	set_saved_sp	t0, t1, t2