linux-user/signal: Map exit signals in SIGCHLD siginfo_t

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>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <81534fde7cdfc6acea4889d886fbefdd606630fb.1635019124.git.mschiffer@universe-factory.net>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

1 files changed, 6 insertions, 1 deletions

diff --git a/linux-user/signal.c b/linux-user/signal.c
index 510db73..1229fec 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -406,7 +406,12 @@ 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;