linux-kernel - Re: [RFC][PATCH 14/22] x86,ftrace: Remove .fixup usage

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Date:   Thu, 4 Nov 2021 15:35:50 -0700
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, mark.rutland@....com,
        dvyukov@...gle.com, seanjc@...gle.com, pbonzini@...hat.com,
        mbenes@...e.cz
Subject: Re: [RFC][PATCH 14/22] x86,ftrace: Remove .fixup usage

On Thu, Nov 04, 2021 at 05:47:43PM +0100, Peter Zijlstra wrote:
> Create and use EX_TYPE_ONE_REG to load 1 into the %[faulted] register
> on exception.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  arch/x86/include/asm/extable_fixup_types.h |    1 +
>  arch/x86/kernel/ftrace.c                   |    9 ++-------
>  2 files changed, 3 insertions(+), 7 deletions(-)
> 
> --- a/arch/x86/include/asm/extable_fixup_types.h
> +++ b/arch/x86/include/asm/extable_fixup_types.h
> @@ -37,5 +37,6 @@
>  #define	EX_TYPE_EFAULT_REG		(EX_TYPE_IMM_REG | EX_TYPE_IMM(-EFAULT))
>  #define	EX_TYPE_NEG_REG			(EX_TYPE_IMM_REG | EX_TYPE_IMM(-1))
>  #define	EX_TYPE_ZERO_REG		(EX_TYPE_IMM_REG | EX_TYPE_IMM(0))
> +#define	EX_TYPE_ONE_REG			(EX_TYPE_IMM_REG | EX_TYPE_IMM(1))
>  
>  #endif
> --- a/arch/x86/kernel/ftrace.c
> +++ b/arch/x86/kernel/ftrace.c
> @@ -661,13 +661,8 @@ void prepare_ftrace_return(unsigned long
>  		"   movl $0, %[faulted]\n"
>  		"3:\n"
>  
> -		".section .fixup, \"ax\"\n"
> -		"4: movl $1, %[faulted]\n"
> -		"   jmp 3b\n"
> -		".previous\n"
> -
> -		_ASM_EXTABLE(1b, 4b)
> -		_ASM_EXTABLE(2b, 4b)
> +		_ASM_EXTABLE_TYPE_REG(1b, 3b, EX_TYPE_ONE_REG, %[faulted])
> +		_ASM_EXTABLE_TYPE_REG(2b, 3b, EX_TYPE_ONE_REG, %[faulted])
>  
>  		: [old] "=&r" (old), [faulted] "=r" (faulted)
>  		: [parent] "r" (parent), [return_hooker] "r" (return_hooker)

This fixup code seems to no longer exist in the latest.

-- 
Josh