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

[Warner Losh <imp@bsdimp.com>]

[-- Attachment #1: Type: text/plain, Size: 2996 bytes --]

On Tue, Feb 14, 2023 at 2:16 PM Richard Henderson <
richard.henderson@linaro.org> wrote:

> 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.
>

OK. Will do. We have that all over the place upstream... I'll start there
too...


>
> > + *
> > + * 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.
>

OK.


> > +    /*
> > +     * 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().
>

Ah!  I need that in several places... Thanks.


> > +        }
> > +#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();
>

Gotcha... Thanks!

Warner


>
> r~
>

[-- Attachment #2: Type: text/html, Size: 4675 bytes --]