Re: [PATCH] linux-user/signal: Map exit signals in SIGCHLD siginfo_t

[Matthias Schiffer]

On 23/10/2021 21:59, Matthias Schiffer wrote:
> When converting a siginfo_t from waitid(), the interpretation of si_status
> depends on the value of si_code: For CLD_EXITED, it is an exit code and
> should be copied verbatim. For other codes, it is a signal number
> (possibly with additional high bits from ptrace) that should be mapped.
>
> This code was previously changed in commit 1c3dfb506ea3
> ("linux-user/signal: Decode waitid si_code"), but the fix was
> incomplete.

ping

> Tested with the following test program:
>
>      #include <stdio.h>
>      #include <stdlib.h>
>      #include <unistd.h>
>      #include <sys/wait.h>
>
>      int main() {
>         pid_t pid = fork();
>         if (pid == 0) {
>                 exit(12);
>         } else {
>                 siginfo_t siginfo = {};
>                 waitid(P_PID, pid, &siginfo, WEXITED);
>                 printf("Code: %d, status: %d\n", (int)siginfo.si_code, 
> (int)siginfo.si_status);
>         }
>
>         pid = fork();
>         if (pid == 0) {
>                 raise(SIGUSR2);
>         } else {
>                 siginfo_t siginfo = {};
>                 waitid(P_PID, pid, &siginfo, WEXITED);
>                 printf("Code: %d, status: %d\n", (int)siginfo.si_code, 
> (int)siginfo.si_status);
>         }
>      }
>
> Output with an x86_64 host and mips64el target before 1c3dfb506ea3
> (incorrect: exit code 12 is translated like a signal):
>
>      Code: 1, status: 17
>      Code: 2, status: 17
>
> After 1c3dfb506ea3 (incorrect: signal number is not translated):
>
>      Code: 1, status: 12
>      Code: 2, status: 12
>
> With this patch:
>
>      Code: 1, status: 12
>      Code: 2, status: 17
>
> Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
> ---
>   linux-user/signal.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/linux-user/signal.c b/linux-user/signal.c
> index 14d8fdfde152..8e3af98ec0a7 100644
> --- a/linux-user/signal.c
> +++ b/linux-user/signal.c
> @@ -403,7 +403,12 @@ 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 = info->si_status;
> +            if (si_code == CLD_EXITED)
> +                tinfo->_sifields._sigchld._status = info->si_status;
> +            else
> +                tinfo->_sifields._sigchld._status
> +                    = host_to_target_signal(info->si_status & 0x7f)
> +                        | (info->si_status & ~0x7f);
>               tinfo->_sifields._sigchld._utime = info->si_utime;
>               tinfo->_sifields._sigchld._stime = info->si_stime;
>               si_type = QEMU_SI_CHLD;

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