linux-kernel - [RFC PATCH 2/6] x86/entry: reverse arguments to do_syscall

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Message-Id: <20210510174509.3039991-3-hpa@zytor.com>
Date:   Mon, 10 May 2021 10:45:05 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH 2/6] x86/entry: reverse arguments to do_syscall_64()

From: "H. Peter Anvin (Intel)" <hpa@...or.com>

Reverse the order of arguments to do_syscall_64() so that the first
argument is the pt_regs pointer. This is not only consistent with
*all* other entry points from assembly, but it actually makes the
compiled code slightly better.

Signed-off-by: H. Peter Anvin (Intel) <hpa@...or.com>
---
 arch/x86/entry/common.c        | 2 +-
 arch/x86/entry/entry_64.S      | 4 ++--
 arch/x86/include/asm/syscall.h | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 7b2542b13ebd..00da0f5420de 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -36,7 +36,7 @@
 #include <asm/irq_stack.h>
 
 #ifdef CONFIG_X86_64
-__visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs)
+__visible noinstr void do_syscall_64(struct pt_regs *regs, unsigned long nr)
 {
 	add_random_kstack_offset();
 	nr = syscall_enter_from_user_mode(regs, nr);
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index a16a5294d55f..1d9db15fdc69 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -107,8 +107,8 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL)
 	PUSH_AND_CLEAR_REGS rax=$-ENOSYS
 
 	/* IRQs are off. */
-	movq	%rax, %rdi
-	movq	%rsp, %rsi
+	movq	%rsp, %rdi
+	movq	%rax, %rsi
 	call	do_syscall_64		/* returns with IRQs disabled */
 
 	/*
diff --git a/arch/x86/include/asm/syscall.h b/arch/x86/include/asm/syscall.h
index 7cbf733d11af..4e20054d7533 100644
--- a/arch/x86/include/asm/syscall.h
+++ b/arch/x86/include/asm/syscall.h
@@ -160,7 +160,7 @@ static inline int syscall_get_arch(struct task_struct *task)
 		? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
 }
 
-void do_syscall_64(unsigned long nr, struct pt_regs *regs);
+void do_syscall_64(struct pt_regs *regs, unsigned long nr);
 void do_int80_syscall_32(struct pt_regs *regs);
 long do_fast_syscall_32(struct pt_regs *regs);
 
-- 
2.31.1