LoongArch: optimize for syscall return

LoongArch inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I6BWFP

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

If the syscall is not rt_sigreturn,there is no need to do
RESTORE_STATIC and RESTORE_TEMP.
Signed-off-by: NHongchen Zhang <zhanghongchen@loongson.cn>
Change-Id: I61804bb16ce678dd39e9f197bd88d91e13b972cb
(cherry picked from commit eba5f68c)

arch/loongarch/kernel/entry.S

@@ -14,13 +14,14 @@
 #include <asm/regdef.h>
 #include <asm/stackframe.h>
 #include <asm/thread_info.h>
+#include <asm/unistd.h>
 
 	.text
 	.cfi_sections	.debug_frame
 	.align	5
 SYM_FUNC_START(handle_syscall)
 	csrrd	t0, PERCPU_BASE_KS
-	la.abs	t1, kernelsp
+	la.pcrel t1, kernelsp
 	add.d	t1, t1, t0
 	move	t2, sp
 	ld.d	sp, t1, 0
@@ -28,11 +29,10 @@ SYM_FUNC_START(handle_syscall)
 	addi.d	sp, sp, -PT_SIZE
 	cfi_st	t2, PT_R3
 	cfi_rel_offset	sp, PT_R3
-	st.d	zero, sp, PT_R0
 	csrrd	t2, LOONGARCH_CSR_PRMD
 	st.d	t2, sp, PT_PRMD
 	cfi_st	ra, PT_R1
-	cfi_st	a0, PT_R4
+	cfi_st	a0, PT_ORIG_A0
 	cfi_st	a1, PT_R5
 	cfi_st	a2, PT_R6
 	cfi_st	a3, PT_R7
@@ -41,6 +41,7 @@ SYM_FUNC_START(handle_syscall)
 	cfi_st	a6, PT_R10
 	cfi_st	a7, PT_R11
 	csrrd	ra, LOONGARCH_CSR_ERA
+	addi.d	ra, ra, 4
 	st.d	ra, sp, PT_ERA
 	cfi_rel_offset	ra, PT_ERA
 
@@ -55,9 +56,17 @@ SYM_FUNC_START(handle_syscall)
 	and	tp, tp, sp
 
 	move	a0, sp
+	move	a1, a7
 	bl	do_syscall
 
-	RESTORE_ALL_AND_RET
+	addi.w	t0, zero, __NR_rt_sigreturn
+	bne	a0, t0, 1f
+
+	RESTORE_STATIC
+	RESTORE_TEMP
+1:
+	RESTORE_SOME
+	RESTORE_SP_AND_RET
 SYM_FUNC_END(handle_syscall)
 
 SYM_CODE_START(ret_from_fork)

arch/loongarch/kernel/syscall.c

@@ -37,18 +37,16 @@ void *sys_call_table[__NR_syscalls] = {
 typedef long (*sys_call_fn)(unsigned long, unsigned long,
 	unsigned long, unsigned long, unsigned long, unsigned long);
 
-void noinstr do_syscall(struct pt_regs *regs)
+unsigned long noinstr do_syscall(struct pt_regs *regs, unsigned long nr)
 {
-	unsigned long nr;
 	sys_call_fn syscall_fn;
 
-	nr = regs->regs[11];
 	/* Set for syscall restarting */
 	if (nr < NR_syscalls)
 		regs->regs[0] = nr + 1;
+	else
+		regs->regs[0] = 0;
 
-	regs->csr_era += 4;
-	regs->orig_a0 = regs->regs[4];
 	regs->regs[4] = -ENOSYS;
 
 	nr = syscall_enter_from_user_mode(regs, nr);
@@ -60,4 +58,6 @@ void noinstr do_syscall(struct pt_regs *regs)
 	}
 
 	syscall_exit_to_user_mode(regs);
+
+	return nr;
 }