8310265: (process) jspawnhelper should not use argv[0]

Backport-of: cd6cb730c934d8e16d4bd8e3342e59e806f158f9

Author: luhenry

src/java.base/unix/native/jspawnhelper/jspawnhelper.c

@@ -134,10 +134,10 @@ int main(int argc, char *argv[]) {
     ChildStuff c;
     int t;
     struct stat buf;
-    /* argv[0] contains the fd number to read all the child info */
+    /* argv[1] contains the fd number to read all the child info */
     int r, fdin, fdout;
 
-    r = sscanf (argv[argc-1], "%d:%d", &fdin, &fdout);
+    r = sscanf (argv[1], "%d:%d", &fdin, &fdout);
     if (r == 2 && fcntl(fdin, F_GETFD) != -1) {
         fstat(fdin, &buf);
         if (!S_ISFIFO(buf.st_mode))

src/java.base/unix/native/libjava/ProcessImpl_md.c

@@ -394,16 +394,20 @@ spawnChild(JNIEnv *env, jobject process, ChildStuff *c, const char *helperpath)
     jboolean isCopy;
     int i, offset, rval, bufsize, magic;
     char *buf, buf1[16];
-    char *hlpargs[2];
+    char *hlpargs[3];
     SpawnInfo sp;
 
     /* need to tell helper which fd is for receiving the childstuff
      * and which fd to send response back on
      */
     snprintf(buf1, sizeof(buf1), "%d:%d", c->childenv[0], c->fail[1]);
-    /* put the fd string as argument to the helper cmd */
-    hlpargs[0] = buf1;
-    hlpargs[1] = 0;
+    /* NULL-terminated argv array.
+     * argv[0] contains path to jspawnhelper, to follow conventions.
+     * argv[1] contains the fd string as argument to jspawnhelper
+     */
+    hlpargs[0] = (char*)helperpath;
+    hlpargs[1] = buf1;
+    hlpargs[2] = NULL;
 
     /* Following items are sent down the pipe to the helper
      * after it is spawned.