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

[Alistair Francis <alistair.francis@wdc.com>]

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:
+                tinfo->_sifields._sigchld._status = status;
+            }
+
             tinfo->_sifields._sigchld._utime = info->si_utime;
             tinfo->_sifields._sigchld._stime = info->si_stime;
             si_type = QEMU_SI_CHLD;
-- 
2.29.2