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

[Richard Henderson <richard.henderson@linaro.org>]

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.


r~