linux-kernel - Re: [PATCH] x86/kvm: Move kvm_fastop

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Date:   Thu, 5 Oct 2017 08:54:40 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH] x86/kvm: Move kvm_fastop_exception to .fixup section

On 04/10/2017 17:39, Josh Poimboeuf wrote:
> When compiling the kernel with the '-frecord-gcc-switches' flag, objtool
> complains:
> 
>   arch/x86/kvm/emulate.o: warning: objtool: .GCC.command.line+0x0: special: can't find new instruction
> 
> And also the kernel fails to link.
> 
> The problem is that the 'kvm_fastop_exception' code gets placed into the
> throwaway '.GCC.command.line' section instead of '.text'.
> 
> Exception fixup code is conventionally placed in the '.fixup' section,
> so put it there where it belongs.
> 
> Reported-and-tested-by: Guenter Roeck <linux@...ck-us.net>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
>  arch/x86/kvm/emulate.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index a36254cbf776..d90cdc77e077 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -425,8 +425,10 @@ static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *));
>  	#op " %al \n\t" \
>  	FOP_RET
>  
> -asm(".global kvm_fastop_exception \n"
> -    "kvm_fastop_exception: xor %esi, %esi; ret");
> +asm(".pushsection .fixup, \"ax\"\n"
> +    ".global kvm_fastop_exception \n"
> +    "kvm_fastop_exception: xor %esi, %esi; ret\n"
> +    ".popsection");
>  
>  FOP_START(setcc)
>  FOP_SETCC(seto)
> 


Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>