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?