[PATCH 07/18] x86/asm/64: Merge the fast and slow SYSRET paths

Andy Lutomirski
2017-10-26T08:27:27Z

They did almost the same thing. Remove a bunch of pointless
instructions (mostly hidden in macros) and reduce cognitive load by
merging them.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/entry/entry_64.S | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 9dafafa3e0ec..c855ee91a3a5 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -220,10 +220,9 @@ entry_SYSCALL_64_fastpath:
TRACE_IRQS_ON /* user mode is traced as IRQs on */
movq RIP(%rsp), %rcx
movq EFLAGS(%rsp), %r11
- RESTORE_C_REGS_EXCEPT_RCX_R11
- movq RSP(%rsp), %rsp
+ addq $6*8, %rsp /* skip extra regs -- they were preserved */
UNWIND_HINT_EMPTY
- USERGS_SYSRET64
+ jmp .Lpop_c_regs_except_rcx_r11_and_sysret

1:
/*
@@ -315,6 +314,7 @@ syscall_return_via_sysret:
/* rcx and r11 are already restored (see code above) */
UNWIND_HINT_EMPTY
POP_EXTRA_REGS
+.Lpop_c_regs_except_rcx_r11_and_sysret:
popq %rsi /* skip r11 */
popq %r10
popq %r9
--
2.13.6