linux-kernel - Re: [PATCH] x86/cpu/vmware: use the full form of inl in VMWARE

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Message-ID: <201910071743.1C48038A@keescook>
Date:   Mon, 7 Oct 2019 17:44:14 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Thomas Hellstrom <thellstrom@...are.com>, pv-drivers@...are.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        hpa@...or.com, x86@...nel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH] x86/cpu/vmware: use the full form of inl in VMWARE_PORT

On Mon, Oct 07, 2019 at 12:21:29PM -0700, Sami Tolvanen wrote:
> LLVM's assembler doesn't accept the short form inl (%%dx) instruction,
> but instead insists on the output register to be explicitly specified:
> 
>   <inline asm>:1:7: error: invalid operand for instruction
>           inl (%dx)
>              ^
>   LLVM ERROR: Error parsing inline asm
> 
> Use the full form of the instruction to fix the build.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  arch/x86/kernel/cpu/vmware.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
> index 9735139cfdf8..46d732696c1c 100644
> --- a/arch/x86/kernel/cpu/vmware.c
> +++ b/arch/x86/kernel/cpu/vmware.c
> @@ -49,7 +49,7 @@
>  #define VMWARE_CMD_VCPU_RESERVED 31
>  
>  #define VMWARE_PORT(cmd, eax, ebx, ecx, edx)				\
> -	__asm__("inl (%%dx)" :						\
> +	__asm__("inl (%%dx), %%eax" :					\
>  		"=a"(eax), "=c"(ecx), "=d"(edx), "=b"(ebx) :		\
>  		"a"(VMWARE_HYPERVISOR_MAGIC),				\
>  		"c"(VMWARE_CMD_##cmd),					\
> -- 
> 2.23.0.581.g78d2f28ef7-goog
> 

-- 
Kees Cook