linux-kernel - Re: [RFC][PATCH 6/7] x86/retpoline: Out-of-line retpoline

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Date:   Thu, 16 Apr 2020 17:22:42 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     jpoimboe@...hat.com, alexandre.chartre@...cle.com
Cc:     linux-kernel@...r.kernel.org, jthierry@...hat.com,
        tglx@...utronix.de, x86@...nel.org
Subject: Re: [RFC][PATCH 6/7] x86/retpoline: Out-of-line retpoline


Bah, chunks went missing, I'll make sure to push out a working version.

On Thu, Apr 16, 2020 at 05:07:58PM +0200, Peter Zijlstra wrote:
> --- a/arch/x86/lib/retpoline.S
> +++ b/arch/x86/lib/retpoline.S
> @@ -7,15 +7,30 @@
>  #include <asm/alternative-asm.h>
>  #include <asm/export.h>
>  #include <asm/nospec-branch.h>
> +#include <asm/unwind_hints.h>
> +#include <asm/frame.h>
>  
>  .macro THUNK reg
>  	.section .text.__x86.indirect_thunk
>  
> +	.align 32
>  SYM_FUNC_START(__x86_indirect_thunk_\reg)
> -	CFI_STARTPROC
> -	JMP_NOSPEC %\reg
> -	CFI_ENDPROC
> +	JMP_NOSPEC \reg
>  SYM_FUNC_END(__x86_indirect_thunk_\reg)
> +
> +SYM_FUNC_START_NOALIGN(__x86_retpoline_\reg)
> +	ANNOTATE_INTRA_FUNCTION_CALL
> +	call	.Ldo_rop_\@
> +.Lspec_trap_\@:
	UNWIND_HINT_EMPTY
> +	pause
> +	lfence
> +	jmp	.Lspec_trap_\@
> +.Ldo_rop_\@:
> +	mov	%\reg, (%_ASM_SP)
> +	UNWIND_HINT_RET_OFFSET
> +	ret
> +SYM_FUNC_END(__x86_retpoline_\reg)
> +
>  .endm
>  
>  /*