linux-kernel - [RFC PATCH v2 2/2] LoongArch: No need to call RESTORE_ALL_AND

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Date:   Wed, 15 Jun 2022 14:37:59 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>
Cc:     Xuefeng Li <lixuefeng@...ngson.cn>,
        Jianmin Lv <lvjianmin@...ngson.cn>, Jun Yi <yijun@...ngson.cn>,
        Rui Wang <wangrui@...ngson.cn>, linux-kernel@...r.kernel.org
Subject: [RFC PATCH v2 2/2] LoongArch: No need to call RESTORE_ALL_AND_RET for all syscalls

In handle_syscall, it is unnecessary to call RESTORE_ALL_AND_RET
for all syscalls.

(1) If syscall number is __NR_clone and __NR_clone3,
    call RESTORE_STATIC_SOME_SP_AND_RET.
(2) If syscall number is __NR_rt_sigreturn and __NR_rt_sigsuspend,
    call RESTORE_TEMP_SOME_SP_AND_RET.
(3) The other syscalls call RESTORE_SOME_SP_AND_RET.

With this patch, it can reduce many load instructions.

Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
---
 arch/loongarch/include/asm/stackframe.h | 17 +++++++++++++++++
 arch/loongarch/kernel/entry.S           | 24 +++++++++++++++++++++++-
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/arch/loongarch/include/asm/stackframe.h b/arch/loongarch/include/asm/stackframe.h
index 4ca9530..52649a5f 100644
--- a/arch/loongarch/include/asm/stackframe.h
+++ b/arch/loongarch/include/asm/stackframe.h
@@ -216,4 +216,21 @@
 	RESTORE_SP_AND_RET \docfi
 	.endm
 
+	.macro	RESTORE_SOME_SP_AND_RET docfi=0
+	RESTORE_SOME \docfi
+	RESTORE_SP_AND_RET \docfi
+	.endm
+
+	.macro	RESTORE_STATIC_SOME_SP_AND_RET docfi=0
+	RESTORE_STATIC \docfi
+	RESTORE_SOME \docfi
+	RESTORE_SP_AND_RET \docfi
+	.endm
+
+	.macro	RESTORE_TEMP_SOME_SP_AND_RET docfi=0
+	RESTORE_TEMP \docfi
+	RESTORE_SOME \docfi
+	RESTORE_SP_AND_RET \docfi
+	.endm
+
 #endif /* _ASM_STACKFRAME_H */
diff --git a/arch/loongarch/kernel/entry.S b/arch/loongarch/kernel/entry.S
index 53ce2cb..58fe507 100644
--- a/arch/loongarch/kernel/entry.S
+++ b/arch/loongarch/kernel/entry.S
@@ -79,7 +79,29 @@ SYM_FUNC_START(handle_syscall)
 	move	a0, sp
 	bl	do_syscall
 
-	RESTORE_ALL_AND_RET
+	/*
+	 * Syscall number held in a7 which is stored in PT_R11.
+	 * If syscall number is __NR_clone and __NR_clone3,
+	 * call RESTORE_STATIC_SOME_SP_AND_RET.
+	 * If syscall number is __NR_rt_sigreturn and __NR_rt_sigsuspend,
+	 * call RESTORE_TEMP_SOME_SP_AND_RET.
+	 * The other syscalls call RESTORE_SOME_SP_AND_RET.
+	 */
+	cfi_ld	t3, PT_R11
+	li.w	t4, __NR_clone
+	beq	t3, t4, 3f
+	li.w	t4, __NR_clone3
+	beq	t3, t4, 3f
+	li.w	t4, __NR_rt_sigreturn
+	beq	t3, t4, 4f
+	li.w	t4, __NR_rt_sigsuspend
+	beq	t3, t4, 4f
+
+	RESTORE_SOME_SP_AND_RET
+3:
+	RESTORE_STATIC_SOME_SP_AND_RET
+4:
+	RESTORE_TEMP_SOME_SP_AND_RET
 SYM_FUNC_END(handle_syscall)
 
 SYM_CODE_START(ret_from_fork)
-- 
2.1.0