linux-user: Trace wait4()'s and waitpid()'s wstatus

Borrow the code for formatting the most frequent WIFEXITED() and
WIFSIGNALED() special cases from from the strace's printstatus().

Output examples:

    474729 wait4(-1,0x7f00767ff0a0,0,(nil)) = 474733 (wstatus={WIFEXITED(s) && WEXITSTATUS(s) == 1})
    475833 wait4(-1,0x7f7de61ff0a0,0,(nil)) = 475837 (wstatus={WIFSIGNALED(s) && WTERMSIG(s) == SIGKILL})
    1168 waitpid(1171,0x7f44eea00340,0) = 1171 (wstatus={WIFSIGNALED(s) && WTERMSIG(s) == SIGKILL})

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-ID: <20241001193244.14939-1-iii@linux.ibm.com>
[rth: Drop extra output for NULL wstatus or error reading.]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

linux-user/strace.c

@@ -4215,6 +4215,63 @@ print_ioctl(CPUArchState *cpu_env, const struct syscallname *name,
 }
 #endif
 
+#if defined(TARGET_NR_wait4) || defined(TARGET_NR_waitpid)
+static void print_wstatus(int wstatus)
+{
+    if (WIFSIGNALED(wstatus)) {
+        qemu_log("{WIFSIGNALED(s) && WTERMSIG(s) == ");
+        print_signal(WTERMSIG(wstatus), 1);
+        if (WCOREDUMP(wstatus)) {
+            qemu_log(" && WCOREDUMP(s)");
+        }
+        qemu_log("}");
+    } else if (WIFEXITED(wstatus)) {
+        qemu_log("{WIFEXITED(s) && WEXITSTATUS(s) == %d}",
+                 WEXITSTATUS(wstatus));
+    } else {
+        print_number(wstatus, 1);
+    }
+}
+
+static void print_ret_wstatus(abi_long ret, abi_long wstatus_addr)
+{
+    int wstatus;
+
+    if (!print_syscall_err(ret)
+        && wstatus_addr
+        && get_user_s32(wstatus, wstatus_addr)) {
+        qemu_log(TARGET_ABI_FMT_ld " (wstatus=", ret);
+        print_wstatus(wstatus);
+        qemu_log(")");
+    }
+    qemu_log("\n");
+}
+#endif
+
+#ifdef TARGET_NR_wait4
+static void
+print_syscall_ret_wait4(CPUArchState *cpu_env,
+                        const struct syscallname *name,
+                        abi_long ret, abi_long arg0, abi_long arg1,
+                        abi_long arg2, abi_long arg3, abi_long arg4,
+                        abi_long arg5)
+{
+    print_ret_wstatus(ret, arg1);
+}
+#endif
+
+#ifdef TARGET_NR_waitpid
+static void
+print_syscall_ret_waitpid(CPUArchState *cpu_env,
+                          const struct syscallname *name,
+                          abi_long ret, abi_long arg0, abi_long arg1,
+                          abi_long arg2, abi_long arg3, abi_long arg4,
+                          abi_long arg5)
+{
+    print_ret_wstatus(ret, arg1);
+}
+#endif
+
 /*
  * An array of all of the syscalls we know about
  */

linux-user/strace.list

@@ -1662,13 +1662,15 @@
 { TARGET_NR_vserver, "vserver" , NULL, NULL, NULL },
 #endif
 #ifdef TARGET_NR_wait4
-{ TARGET_NR_wait4, "wait4" , "%s(%d,%p,%d,%p)", NULL, NULL },
+{ TARGET_NR_wait4, "wait4" , "%s(%d,%p,%d,%p)", NULL,
+                   print_syscall_ret_wait4 },
 #endif
 #ifdef TARGET_NR_waitid
 { TARGET_NR_waitid, "waitid" , "%s(%#x,%d,%p,%#x)", NULL, NULL },
 #endif
 #ifdef TARGET_NR_waitpid
-{ TARGET_NR_waitpid, "waitpid" , "%s(%d,%p,%#x)", NULL, NULL },
+{ TARGET_NR_waitpid, "waitpid", "%s(%d,%p,%#x)", NULL,
+                     print_syscall_ret_waitpid },
 #endif
 #ifdef TARGET_NR_write
 { TARGET_NR_write, "write" , "%s(%d,%#x,%d)", NULL, NULL },