Re: [PATCH 03/33] Update the definitions of __put_user and __get_user macros

[Warner Losh <imp@bsdimp.com>]

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On Tue, Aug 8, 2023 at 7:47 PM Richard Henderson <
richard.henderson@linaro.org> wrote:

> On 8/8/23 18:39, Warner Losh wrote:
> >      > +#define __put_user_e(x, hptr, e)
>             \
> >      > +    do {
>             \
> >      > +        PRAGMA_DISABLE_PACKED_WARNING;
>             \
> >      > +        (__builtin_choose_expr(sizeof(*(hptr)) == 1, stb_p,
>            \
> >      > +        __builtin_choose_expr(sizeof(*(hptr)) == 2,
> stw_##e##_p,            \
> >      > +        __builtin_choose_expr(sizeof(*(hptr)) == 4,
> stl_##e##_p,            \
> >      > +        __builtin_choose_expr(sizeof(*(hptr)) == 8, stq_##e##_p,
> abort))))  \
> >      > +            ((hptr), (x)), (void)0);
>             \
> >      > +        PRAGMA_REENABLE_PACKED_WARNING;
>            \
> >      > +    } while (0)
> >      > +
> >      > +#define __get_user_e(x, hptr, e)
>             \
> >      > +    do {
>             \
> >      > +        PRAGMA_DISABLE_PACKED_WARNING;
>             \
> >      > +        ((x) = (typeof(*hptr))(
>            \
> >      > +        __builtin_choose_expr(sizeof(*(hptr)) == 1, ldub_p,
>            \
> >      > +        __builtin_choose_expr(sizeof(*(hptr)) == 2,
> lduw_##e##_p,           \
> >      > +        __builtin_choose_expr(sizeof(*(hptr)) == 4,
> ldl_##e##_p,            \
> >      > +        __builtin_choose_expr(sizeof(*(hptr)) == 8, ldq_##e##_p,
> abort))))  \
> >      > +            (hptr)), (void)0);
>             \
> >      > +        PRAGMA_REENABLE_PACKED_WARNING;
>            \
> >      > +    } while (0)
> >
> >     Hmm.  I guess this works.  The typeof cast in __get_user_e being
> required when
> >     sizeof(x) >
> >     sizeof(*hptr) in order to get the correct extension.
> >
> >
> > This code was copied 100% from the current linux-user :)
>
> Ha ha indeed!  I should have known.
>

Yea... It's old-school crazy, and I've done a lot of that in my day, but not
here :)


> >     Is it clearer with _Generic?
> >
> >           (x) = _Generic(*(hptr),
> >                          int8_t: *(int8_t *)(hptr),
> >                          uint8_t: *(uint8_t *)(hptr),
> >                          int16_t: (int16_t)lduw_##e##_p(hptr),
> >                          uint16_t: lduw_##e##_p(hptr),
> >                          int32_t: (int32_t)ldl_##e##_p(hptr),
> >                          uint32_t: (uint32_t)ldl_##e##_p(hptr),
> >                          int64_t: (int64_t)ldq_##e##_p(hptr),
> >                          uint64_t: ldq_##e##_p(hptr));
> >
> >     In particular I believe the error message will be much prettier.
> >
> >
> > Indeed. That looks cleaner. I'll see if I can test that against the
> latest bsd-user upstream.
>
> I'll see if we can share this code via common-user.
>

It seems to work, though I still need the pragmas for clang 16 (see another
patch for that).

I tried to implement both get and put in terms of this, but found that it
broke the blitz
branch. So why don't we land this as is for bsd-user and then one of us can
try to
put it into common-user so as to not create too many waves for our GSoC
student Kariim.
There's already enough to fix in this series... Sound fair?

Warner

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