linux-kernel - Re: [PATCH] kvm/emulate: fix a -Werror=cast-function-type

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Date:   Fri, 14 Feb 2020 08:59:24 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Qian Cai <cai@....pw>
Cc:     pbonzini@...hat.com, vkuznets@...hat.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm/emulate: fix a -Werror=cast-function-type

On Fri, Feb 14, 2020 at 10:56:08AM -0500, Qian Cai wrote:
> arch/x86/kvm/emulate.c: In function 'x86_emulate_insn':
> arch/x86/kvm/emulate.c:5686:22: error: cast between incompatible
> function types from 'int (*)(struct x86_emulate_ctxt *)' to 'void
> (*)(struct fastop *)' [-Werror=cast-function-type]
>     rc = fastop(ctxt, (fastop_t)ctxt->execute);
> 
> Fixes: 3009afc6e39e ("KVM: x86: Use a typedef for fastop functions")
> Signed-off-by: Qian Cai <cai@....pw>
> ---
>  arch/x86/kvm/emulate.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index ddbc61984227..17ae820cf59d 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -5682,10 +5682,12 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
>  		ctxt->eflags &= ~X86_EFLAGS_RF;
>  
>  	if (ctxt->execute) {
> -		if (ctxt->d & Fastop)
> -			rc = fastop(ctxt, (fastop_t)ctxt->execute);

Alternatively, can we do -Wno-cast-function-type?  That's a silly warning
IMO.

If not, will either of these work?

			rc = fastop(ctxt, (void *)ctxt->execute);

or
			rc = fastop(ctxt, (fastop_t)(void *)ctxt->execute);

> -		else
> +		if (ctxt->d & Fastop) {
> +			fastop_t fop = (void *)ctxt->execute;
> +			rc = fastop(ctxt, fop);
> +		} else {
>  			rc = ctxt->execute(ctxt);
> +		}
>  		if (rc != X86EMUL_CONTINUE)
>  			goto done;
>  		goto writeback;
> -- 
> 1.8.3.1
>