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

[Laurent Vivier <laurent@vivier.eu>]

Le 23/10/2021 à 21:59, Matthias Schiffer a écrit :
> 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.
> 
> 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;

Reviewed-by: Laurent Vivier <laurent@vivier.eu>