Re: [Qemu-devel] [PATCH Risu v2 4/9] Implement lib to deal with PPC64 registers

[Peter Maydell]

On 6 November 2016 at 17:15, Jose Ricardo Ziviani
<address@hidden> wrote:
> This library is the initial effort to have PPC64 support for Risu. It
> implements functions to initialize, compare and print PPC64 registers.
>
> Signed-off-by: Jose Ricardo Ziviani <address@hidden>

Hi; I've been looking at refactoring risu to reduce the huge
code duplication between the CPU backends, and I noticed this
weirdness in the PPC code:


> +/* reginfo_is_eq: compare the reginfo structs, returns nonzero if equal */
> +int reginfo_is_eq(struct reginfo *m, struct reginfo *a, ucontext_t *uc)
> +{

> +    for (i = 0; i < 32; i++) {
> +        if (m->vrregs.vrregs[i][0] != a->vrregs.vrregs[i][0] ||
> +                m->vrregs.vrregs[i][1] != a->vrregs.vrregs[i][1] ||
> +                m->vrregs.vrregs[i][2] != a->vrregs.vrregs[i][2] ||
> +                m->vrregs.vrregs[i][3] != a->vrregs.vrregs[i][3]) {
> +
> +            if (uc != NULL && (m->gregs[CCR] & 0x10)) {
> +                uc->uc_mcontext.v_regs->vrregs[i][0] = 
> a->vrregs.vrregs[i][0];
> +                uc->uc_mcontext.v_regs->vrregs[i][1] = 
> a->vrregs.vrregs[i][1];
> +                uc->uc_mcontext.v_regs->vrregs[i][2] = 
> a->vrregs.vrregs[i][2];
> +                uc->uc_mcontext.v_regs->vrregs[i][3] = 
> a->vrregs.vrregs[i][3];
> +                return 1;
> +            }

What is this intended to be doing? reginfo_is_eq() should be
a simple "compare two structures" operation, but here we
take a ucontext_t* (which is something completely different)
and modify it. We don't even necessarily have a ucontext_t
to hand when we're trying to compare reginfo structs...

thanks
-- PMM