Questions about debugging in xv6(riscv) -from MIT 6.S081/6.828 2019 OS course

I am trying to debug user programs,but when I do as follows:

open a terminal:make qemu-gdb
another terminal:
riscv64-unknown-elf-gdb 
file wc(or any other user programs)
it says:
(gdb) file wc
warning: A handler for the OS ABI "GNU/Linux" is not built into this configuration
of GDB. Attempting to continue with the default riscv settings.

warning: A handler for the OS ABI "GNU/Linux" is not built into this configuration
of GDB. Attempting to continue with the default riscv settings.

Reading symbols from wc...
(No debugging symbols found in wc)

I edit the Makefile,and add -g in both CFLAGS and LDFLAGS,but it just don't work I wonder how can I debug user programs

I'd appreciate it if you could reply and helpe me

ps:here is the MakeFile and the project tree

tree:https://paste.ubuntu.com/p/s9JGY8d4Z9/ makefile:https://paste.ubuntu.com/p/Zp6HXcF4Vq/