I believe this problem occurs when ddb is enabled and the in-kernel symbol 
table is not populated. Make sure you have enough space set aside in your 
kernel for the symbol table with "options SYMTAB_SPACE=xxxxx" and execute 
dbsym on your kernel with "dbsym mykernel" (powerpc--netbsd2.0-dbsym in your 
case).

>When '[no symbols available]' message comes out while booting, what
>options should I set for compiling a kernel with symbols?