Re: [PATCH v7 3/4] linux-user: Support futex_time64

[Alistair Francis <alistair23@gmail.com>]

On Fri, Mar 13, 2020 at 1:14 AM Laurent Vivier <laurent@vivier.eu> wrote:
>
> Le 12/03/2020 à 23:13, Alistair Francis a écrit :
> > Add support for host and target futex_time64. If futex_time64 exists on
> > the host we try that first before falling back to the standard futux
> > syscall.
> >
> > Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> > ---
> >  linux-user/syscall.c | 144 +++++++++++++++++++++++++++++++++++++++----
> >  1 file changed, 131 insertions(+), 13 deletions(-)
> >
> > diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> > index 60fd775d9c..9ae7a05e38 100644
> > --- a/linux-user/syscall.c
> > +++ b/linux-user/syscall.c
> ...
> > @@ -6890,6 +6905,55 @@ static inline abi_long host_to_target_statx(struct target_statx *host_stx,
> >  }
> >  #endif
> >
> > +static int do_sys_futex(int *uaddr, int op, int val,
> > +                         const struct timespec *timeout, int *uaddr2,
> > +                         int val3)
> > +{
> > +#if HOST_LONG_BITS == 64
> > +#if defined(__NR_futex)
> > +    /* always a 64-bit time_t, it doesn't define _time64 version  */
> > +    return sys_futex(uaddr, op, val, timeout, uaddr2, val3);
> > +
> > +#endif
> > +#else /* HOST_LONG_BITS == 64 */
> > +#if defined(__NR_futex_time64)
> > +    if (sizeof(timeout->tv_sec) == 8) {
> > +        /* _time64 function on 32bit arch */
> > +        return sys_futex_time64(uaddr, op, val, timeout, uaddr2, val3);
> > +    }
> > +#endif
> > +#if defined(__NR_futex)
> > +    /* old function on 32bit arch */
> > +    return sys_futex(uaddr, op, val, timeout, uaddr2, val3);
> > +#endif
> > +#endif /* HOST_LONG_BITS == 64 */
> > +    return -TARGET_ENOSYS;
>
> You cannot return -TARGET_ENOSYS because return value is supposed to be
> a host value as you have direct value from sys_futex().
>
> ...
>
> > @@ -7505,7 +7619,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
> >              ts = cpu->opaque;
> >              if (ts->child_tidptr) {
> >                  put_user_u32(0, ts->child_tidptr);
> > -                sys_futex(g2h(ts->child_tidptr), FUTEX_WAKE, INT_MAX,
> > +                do_sys_futex(g2h(ts->child_tidptr), FUTEX_WAKE, INT_MAX,
> >                            NULL, NULL, 0);
>
> And return value is ignored. Anyway at this point we can't do anything
> if it doesn't work, but it should not happen. So I think the best to do
> is to add a g_assert_not_reached() in place of "return -TARGET_ENOSYS"
> in do_sys_futex() (or "#error" if no futex function is available).

It sounds like you applied this series, so I'm not going to fix this
up. Let me know if you would like me to.

Alistair

>
> Thanks,
> Laurent
>
>