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

[Laurent Vivier]

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 <address@hidden>
> ---
>  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).

Thanks,
Laurent