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

["Andreas K. Huettel" <dilfridge@gentoo.org>]

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Well, the original fix 1c3dfb506ea3 did clearly improve things for me, but it wasn't
complete yet. At some point I gave up on finding a minimal reproducer for my remaining 
problems (futex-related hangs in a complex python+bash app).

So, this *may* be the missing piece.

Will test, but that takes a few days.

Andreas

Am Sonntag, 19. Dezember 2021, 16:55:16 CET schrieb Laurent Vivier:
> CC'ing Alistair and Andreas that were involved in original fix 1c3dfb506ea3 ("linux-user/signal: 
> Decode waitid si_code")
> 
> Thanks,
> Laurent
> 
> 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;
> > 
> 
> 
> 


-- 
Andreas K. Hüttel
dilfridge@gentoo.org
Gentoo Linux developer
(council, toolchain, base-system, perl, libreoffice)

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