In order to support c source code level debugging, it is a must to enable debugging option during compile

    mips-openwrt-linux-objdump -g vmlinux | grep -i DW_AT_comp_dir | grep -i indirect |  grep '\/'

Its output is like:

    <bb2043>   DW_AT_comp_dir : (indirect string, offset: 0x171): /disk/fs1/tmp2/openwrt/core/kernel_tree

• Discover vmlinux entry point

     mips-openwrt-linux-objdump -t vmlinux | grep -w "_text"

Its output in my setup: 60020000 g .text 00000000 _text

• Discover kernel_entry

    mips-openwrt-linux-objdump -f vmlinux

Its output in my setup: start address 0x6002df00

    mips-openwrt-linux-nm -n vmlinux | grep -v '\( [aNUw] \)\|\(__crc_\)\|\( \$[adt]\)' > System.map

    mips-openwrt-linux-objdump -t vmlinux | grep dp_xmit

Suppose below working environment: