Re: [PATCH v2 06/12] bsd-user: Helper routines h2t_old_sysctl

[Richard Henderson]

On 2/13/23 14:27, Warner Losh wrote:
> +/*
> + * Convert the old value from host to target.

host vs guest is clearer language; "target" gets overloaded, even though still present in 
the code base.

> + *
> + * For LONG and ULONG on ABI32, we need to 'down convert' the 8 byte quantities
> + * to 4 bytes. The caller setup a buffer in host memory to get this data from
> + * the kernel and pass it to us. We do the down conversion and adjust the 
> length
> + * so the caller knows what to write as the returned length into the target 
> when
> + * it copies the down converted values into the target.
> + *
> + * For normal integral types, we just need to byte swap. No size changes.
> + *
> + * For strings and node data, there's no conversion needed.
> + *
> + * For opaque data, per sysctl OID converts take care of it.
> + */
> +static void G_GNUC_UNUSED h2t_old_sysctl(void *holdp, size_t *holdlen, 
> uint32_t kind)

h2g.

> +    /*
> +     * hlen == 0 for CTLTYPE_STRING and CTLTYPE_NODE, which need no conversion
> +     * as well as CTLTYPE_OPAQUE, which needs special converters.
> +     */
> +    if (hlen == 0) {
> +        return;
> +    }
> +
> +    while (len < *holdlen) {
> +        if (hlen == tlen) {
> +            switch (hlen) {
> +            case 1:
> +                /* Nothing needed: no byteswapping and assigning in place */
> +                break;
> +            case 2:
> +                *(uint16_t *)tp = tswap16(*(uint16_t *)hp);
> +                break;
> +            case 4:
> +                *(uint32_t *)tp = tswap32(*(uint32_t *)hp);
> +                break;
> +            case 8:
> +                *(uint64_t *)tp = tswap64(*(uint64_t *)hp);
> +                break;
> +            }

default: g_assert_not_reached().

> +        }
> +#ifdef TARGET_ABI32
> +        else {
> +            /*
> +             * Saturating assignment for the only two types that differ between
> +             * 32-bit and 64-bit machines. All other integral types have the
> +             * same, fixed size and will be converted w/o loss of precision
> +             * in the above switch.
> +             */
> +            switch (kind & CTLTYPE) {
> +            case CTLTYPE_LONG:
> +                *(abi_long *)tp = tswap32(h2t_long_sat(*(long *)hp));
> +                break;
> +            case CTLTYPE_ULONG:
> +                *(abi_ulong *)tp = tswap32(h2t_ulong_sat(*(u_long *)hp));
> +                break;
> +            }

default: g_assert_not_reached().

> +        }
> +#endif

#else
    g_assert_not_reached();


r~