[patch 12/38] x86/entry: Make sync_regs() invocation a tail call

Thomas Gleixner
2022-07-16T23:18:05Z

From: Peter Zijlstra <peterz@infradead.org>

No point in having a call there. Spare the call/ret overhead.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/entry/entry_64.S | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1060,11 +1060,8 @@ SYM_CODE_START_LOCAL(error_entry)
UNTRAIN_RET

leaq 8(%rsp), %rdi /* arg0 = pt_regs pointer */
-.Lerror_entry_from_usermode_after_swapgs:
-
/* Put us onto the real thread stack. */
- call sync_regs
- RET
+ jmp sync_regs

/*
* There are two places in the kernel that can potentially fault with
@@ -1122,7 +1119,7 @@ SYM_CODE_START_LOCAL(error_entry)
leaq 8(%rsp), %rdi /* arg0 = pt_regs pointer */
call fixup_bad_iret
mov %rax, %rdi
- jmp .Lerror_entry_from_usermode_after_swapgs
+ jmp sync_regs
SYM_CODE_END(error_entry)

SYM_CODE_START_LOCAL(error_return)