Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64

Peter Zijlstra
2018-11-29T16:49:32Z

On Thu, Nov 29, 2018 at 10:33:42AM -0600, Josh Poimboeuf wrote:
> > can't we 'fix' that again? The alternative is moving that IRET-frame and
> > fixing everything up, which is going to be fragile, ugly and such
> > things more.

> This seems to work...

That's almost too easy... nice!

> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index ce25d84023c0..184523447d35 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -876,7 +876,7 @@ apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt
> * @paranoid == 2 is special: the stub will never switch stacks. This is for
> * #DF: if the thread stack is somehow unusable, we'll still get a useful OOPS.
> */
> -.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1
> +.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 create_gap=0
> ENTRY(\sym)
> UNWIND_HINT_IRET_REGS offset=\has_error_code*8
>
> @@ -891,6 +891,12 @@ ENTRY(\sym)
> pushq $-1 /* ORIG_RAX: no syscall to restart */
> .endif
>
> + .if \create_gap == 1
> + .rept 6
> + pushq 5*8(%rsp)
> + .endr
> + .endif
> +
> .if \paranoid == 1
> testb $3, CS-ORIG_RAX(%rsp) /* If coming from userspace, switch stacks */
> jnz .Lfrom_usermode_switch_stack_\@
> @@ -1126,7 +1132,7 @@ apicinterrupt3 HYPERV_STIMER0_VECTOR \
> #endif /* CONFIG_HYPERV */
>
> idtentry debug do_debug has_error_code=0 paranoid=1 shift_ist=DEBUG_STACK
> -idtentry int3 do_int3 has_error_code=0
> +idtentry int3 do_int3 has_error_code=0 create_gap=1
> idtentry stack_segment do_stack_segment has_error_code=1
>
> #ifdef CONFIG_XEN_PV