You used --decode_raw correctly, but your input does not seem to be a protobuf.
For --decode, you need to specify the type name, like:
protoc --decode header my.proto < b.bin
However, if --decode_raw reports a parse error than --decode will too.
It would seem that the bytes you extracted via gdb are not a valid protobuf. Perhaps your addresses aren’t exactly right: if you added or removed a byte at either end, it probably won’t parse.
I note that according to the addresses you specified, the protobuf is only 9 bytes long, which is only enough space for three or four of the fields to be set. Is that what you are expecting? Perhaps you could post the bytes here.
EDIT:
The 10 bytes you added to your question appear to decode successfully using --decode_raw:
$ echo 08ffff01100840f7d438 | xxd -r -p | protoc --decode_raw
1: 32767
2: 8
8: 928375
Cross-referencing the field numbers, we get:
u1: 32767
u2: 8
u6: 928375