Re: [PATCH 4/9] bsd-user: Two helper routines oidfmt and sysctl_oldcvt

[Warner Losh <imp@bsdimp.com>]

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On Sat, Feb 11, 2023 at 3:17 PM Richard Henderson <
richard.henderson@linaro.org> wrote:

> On 2/10/23 13:18, Warner Losh wrote:
> > +static int sysctl_oldcvt(void *holdp, size_t *holdlen, uint32_t kind)
> > +{
> > +    switch (kind & CTLTYPE) {
> > +    case CTLTYPE_INT:
> > +    case CTLTYPE_UINT:
> > +        *(uint32_t *)holdp = tswap32(*(uint32_t *)holdp);
> > +        break;
> > +
> > +#ifdef TARGET_ABI32
> > +    case CTLTYPE_LONG:
> > +    case CTLTYPE_ULONG:
> > +        /*
> > +         * If the sysctl has a type of long/ulong but seems to be
> bigger than
> > +         * these data types, its probably an array.  Double check that
> its
> > +         * evenly divisible by the size of long and convert holdp to a
> series of
> > +         * 32bit elements instead, adjusting holdlen to the new size.
> > +         */
> > +        if ((*holdlen > sizeof(abi_ulong)) &&
> > +            ((*holdlen % sizeof(abi_ulong)) == 0)) {
> > +            int array_size = *holdlen / sizeof(long);
> > +            int i;
> > +            if (holdp) {
> > +                for (i = 0; i < array_size; i++) {
> > +                    ((uint32_t *)holdp)[i] = tswap32(((long
> *)holdp)[i]);
> > +                }
> > +                *holdlen = array_size * sizeof(abi_ulong);
> > +            } else {
> > +                *holdlen = sizeof(abi_ulong);
> > +            }
> > +        } else {
> > +            *(uint32_t *)holdp = tswap32(*(long *)holdp);
> > +            *holdlen = sizeof(uint32_t);
>
> This is totally confusing.  Why would it ever be an array?
> Why is this section the only place we ever assign back into holdlen?
>
> Can you point to anything similar in the freebsd source?  The whole thing
> is pretty hard
> to track, starting from sys/kern/kern_sysctl.c.
>

I need to understand this... I've been looking for where we export an
array, and we just don't.

I've asked the original author who said it had something to do with
different size longs. I'll
look into that a bit and get back to this.

I think we assign back into holdlen in a weird attempt adjust for the
difference of LONG between
the two. But I'm not sure that that's where we should assign.

Warner

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