On Thu, Oct 26, 2017 at 4:26 AM, Andy Lutomirski <[email protected]> wrote: > 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 <[email protected]> > --- > 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
Wouldn't it be more logical to keep the SYSRET path at the end of the fast path (reverse of what you are doing here)? That way the fast path falls through without jumping. -- Brian Gerst
