Re: [PATCH v1 1/1] linux-user/signal: Decode waitid si_code

[Laurent Vivier <laurent@vivier.eu>]

Le 19/12/2020 à 19:11, Alistair Francis a écrit :
> When mapping the host waitid status to the target status we previously
> just used decoding information in the status value. This doesn't follow
> what the waitid documentation describes, which instead suggests using
> the si_code value for the decoding. This results in the incorrect values
> seen when calling waitid. This is especially apparent on RV32 where all
> wait calls use waitid (see the bug case).
> 
> This patch uses the si_code value to map the waitid status.
> 
> Buglink: https://bugs.launchpad.net/qemu/+bug/1906193
> Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> ---
>  linux-user/signal.c | 26 ++++++++++++++++++++++++--
>  1 file changed, 24 insertions(+), 2 deletions(-)
> 
> diff --git a/linux-user/signal.c b/linux-user/signal.c
> index 73de934c65..b6c9326521 100644
> --- a/linux-user/signal.c
> +++ b/linux-user/signal.c
> @@ -305,6 +305,7 @@ static inline void host_to_target_siginfo_noswap(target_siginfo_t *tinfo,
>      int sig = host_to_target_signal(info->si_signo);
>      int si_code = info->si_code;
>      int si_type;
> +    int status = info->si_status;
>      tinfo->si_signo = sig;
>      tinfo->si_errno = 0;
>      tinfo->si_code = info->si_code;
> @@ -349,8 +350,29 @@ static inline void host_to_target_siginfo_noswap(target_siginfo_t *tinfo,
>          case TARGET_SIGCHLD:
>              tinfo->_sifields._sigchld._pid = info->si_pid;
>              tinfo->_sifields._sigchld._uid = info->si_uid;
> -            tinfo->_sifields._sigchld._status
> -                = host_to_target_waitstatus(info->si_status);
> +
> +            /*
> +             * Map host to target signal numbers for the waitid family of
> +             * syscalls. This is similar to the functionality in
> +             * host_to_target_waitstatus() except we use the si_code to
> +             * determine the operation.
> +             */
> +            switch (info->si_code) {
> +            case CLD_KILLED:
> +            case CLD_DUMPED:
> +                tinfo->_sifields._sigchld._status =
> +                    host_to_target_signal(WTERMSIG(status)) |
> +                                          (status & ~0x7f);
> +                break;
> +            case CLD_STOPPED:
> +                tinfo->_sifields._sigchld._status =
> +                (host_to_target_signal(WSTOPSIG(status)) << 8) |
> +                    (status & 0xff);
> +                break;
> +            default:

I guess the the operation is not encoded in the status coming from the host as we need to use the
si_code to decode the status, so why do we need to encode it in the status we send to the guest?

Can it be only "tinfo->_sifields._sigchld._status = status" for all the cases?

Thanks,
Laurent