linux-kernel - Re: [PATCH 2/2] KVM: arm/arm64: Print the EC hex value with its exact width

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Message-ID: <86h85js083.wl-maz@kernel.org>
Date:   Wed, 11 Sep 2019 09:31:24 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Zenghui Yu <yuzenghui@...wei.com>
Cc:     <james.morse@....com>, <julien.thierry.kdev@...il.com>,
        <suzuki.poulose@....com>, <kvmarm@...ts.cs.columbia.edu>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <wanghaibin.wang@...wei.com>
Subject: Re: [PATCH 2/2] KVM: arm/arm64: Print the EC hex value with its exact width

On Wed, 11 Sep 2019 03:33:36 +0100,
Zenghui Yu <yuzenghui@...wei.com> wrote:
> 
> EC is the bits [31:26] of ESR_ELx on arm64 (HSR on arm). Print the
> hex value with its exact width (8).
> 
> Signed-off-by: Zenghui Yu <yuzenghui@...wei.com>
> ---
>  virt/kvm/arm/trace.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/arm/trace.h b/virt/kvm/arm/trace.h
> index 204d210d01c2..022b0a060034 100644
> --- a/virt/kvm/arm/trace.h
> +++ b/virt/kvm/arm/trace.h
> @@ -42,7 +42,7 @@ TRACE_EVENT(kvm_exit,
>  		__entry->vcpu_pc		= vcpu_pc;
>  	),
>  
> -	TP_printk("%s: HSR_EC: 0x%04x (%s), PC: 0x%08lx",
> +	TP_printk("%s: HSR_EC: 0x%02x (%s), PC: 0x%08lx",
>  		  __print_symbolic(__entry->ret, kvm_arm_exception_type),
>  		  __entry->esr_ec,
>  		  __print_symbolic(__entry->esr_ec, kvm_arm_exception_class),

Although you're right that 8 bits ought to be enough, this is a change
to the output of the tracepoint, which userspace could (does?) parse.
I'm thus reluctant to change anything there, knowing that we don't
lose any information, and just print two extra zeroes.

Am I missing anything?

Thanks,

	M.

-- 
Jazz is not dead, it just smells funny.