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    SubjectRe: [PATCH] kvm/emulate: fix a -Werror=cast-function-type
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    On Fri, 2020-02-14 at 09:40 -0800, Jim Mattson wrote:
    > On Fri, Feb 14, 2020 at 9:08 AM Qian Cai <cai@lca.pw> wrote:
    > >
    > > On Fri, 2020-02-14 at 08:59 -0800, Sean Christopherson wrote:
    > > > 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@lca.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.
    > >
    > > I am doing W=1 on linux-next where some of the warnings might be silly but the
    > > recent commit changes all warnings to errors forces me having to silence those
    > > somehow.
    > >
    > > >
    > > > If not, will either of these work?
    > > >
    > > > rc = fastop(ctxt, (void *)ctxt->execute);
    > > >
    > > > or
    > > > rc = fastop(ctxt, (fastop_t)(void *)ctxt->execute);
    > >
    > > I have no strong preference. I originally thought just to go back the previous
    > > code style where might be more acceptable, but it is up to maintainers.
    >
    > It seems misguided to define a local variable just to get an implicit
    > cast from (void *) to (fastop_t). Sean's first suggestion gives you
    > the same implicit cast without the local variable. The second
    > suggestion makes both casts explicit.

    OK, I'll do a v2 using the first suggestion which looks simpler once it passed
    compilations.

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