oss/alsa: Do not invoke UB described in 7.15.1.1

Additional argument (whether to try poll mode) is only passed with
VOICE_ENABLE command.

Thanks to Markus Armbruster for noticing the potential breakage.

1 files changed, 14 insertions, 11 deletions

diff --git a/audio/alsaaudio.c b/audio/alsaaudio.c
index a4baebcb40..b8de3a708d 100644
--- a/audio/alsaaudio.c
+++ b/audio/alsaaudio.c
@@ -861,22 +861,25 @@ static int alsa_voice_ctl (snd_pcm_t *handle, const char *typ, int pause)
 
 static int alsa_ctl_out (HWVoiceOut *hw, int cmd, ...)
 {
-    va_list ap;
-    int poll_mode;
     ALSAVoiceOut *alsa = (ALSAVoiceOut *) hw;
 
-    va_start (ap, cmd);
-    poll_mode = va_arg (ap, int);
-    va_end (ap);
-
     switch (cmd) {
     case VOICE_ENABLE:
-        ldebug ("enabling voice\n");
-        if (poll_mode && alsa_poll_out (hw)) {
-            poll_mode = 0;
+        {
+            va_list ap;
+            int poll_mode;
+
+            va_start (ap, cmd);
+            poll_mode = va_arg (ap, int);
+            va_end (ap);
+
+            ldebug ("enabling voice\n");
+            if (poll_mode && alsa_poll_out (hw)) {
+                poll_mode = 0;
+            }
+            hw->poll_mode = poll_mode;
+            return alsa_voice_ctl (alsa->handle, "playback", 0);
         }
-        hw->poll_mode = poll_mode;
-        return alsa_voice_ctl (alsa->handle, "playback", 0);
 
     case VOICE_DISABLE:
         ldebug ("disabling voice\n");