c - セグメンテーション違反 (コア ダンプ) mknode 関数の呼び出し中にエラーが発生しました

Question

YYSTYPE 構造体 node1 を定義します *

%token INT FLOAT CHAR DOUBLE VOID

start: 宣言関数 Declaration1 {$$ = mknode($1, $2, $3,NULL,0);}

|Declaration Function             {$$=mknode($1,$2,NULL,NULL,0);}   
        
| Declaration                 {$$ =mknode($1,NULL,NULL,NULL,0); }

| Function                {$$ =mknode($1,NULL,NULL,NULL,0); }
;

Declaration1 :Function           {$$ =mknode($1,NULL,NULL,NULL,NULL); }
;


Function: 

Type ID '(' ArgListOpt ')' CompoundStmt         {$$ = mknode($1,$2,$4,$6,NULL); }
;

タイプ: INT {$$ = mknode(NULL,NULL,NULL,NULL,"INT"); }

| | FLOAT {$$ = mknode(NULL,NULL,NULL,NULL,"FLOAT"); }

| | CHAR {$$ = mknode(NULL,NULL,NULL,NULL,"CHAR"); }

| | DOUBLE {$$ = mknode(NULL,NULL,NULL,NULL,"DOUBLE"); }

| | VOID {$$ = mknode(NULL,NULL,NULL,NULL,"VOID"); }

;

CompoundStmt: '{' StmtList '}'      {$$ =$2; }
;

StmtList: StmtList Stmt            {$$ = mknode($1,$2,NULL,NULL,NULL); }

|                   {$$=mknode(NULL,NULL,NULL,NULL,NULL);}
;

when i am running this on the input 

int mian()
{}


it is giving segementation fault at

char* newnode =(char*)malloc(strlen(token));



node1 *mknode(node1 *left1, node1 *left2, node1* left3,node1* left4,char *token)
{

  /* malloc the node */

  node1 *newnode = (node1 *)malloc(sizeof(node1));



  char *newstr = (char *)malloc(strlen(token));

  strcpy(newstr, token);



  newnode->left1 = left1;

  newnode->left2 = left2;

newnode->left3 = left3;

  newnode->left4 = left4;

  newnode->token = newstr;

  return(newnode);
}

ここでのエラーは何ですか？助けてください