[RFC v2 PATCH 2/7] x86/entry: reverse arguments to do_syscall_64()

From: H. Peter Anvin
Date: Mon May 10 2021 - 14:53:50 EST


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

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@xxxxxxxxx>
---
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