执行nasm -o kernel.bat kernel.asm  报错

以下是错误：

write_vga_desktop_keyboard_bu.asm:414: error: symbol `keybuf' not defined write_vga_desktop_keyboard_bu.asm:420: error: symbol `keybuf' not defined write_vga_desktop_keyboard_bu.asm:421: error: symbol `keybuf' not defined write_vga_desktop_keyboard_bu.asm:424: error: symbol `keybuf' not defined write_vga_desktop_keyboard_bu.asm:433: error: symbol `keybuf' not defined write_vga_desktop_keyboard_bu.asm:435: error: symbol `keybuf' not defined write_vga_desktop_keyboard_bu.asm:437: error: symbol `keybuf' not defined write_vga_desktop_keyboard_bu.asm:896: error: symbol `keybuf' not defined write_vga_desktop_keyboard_bu.asm:899: error: symbol `keybuf' not defined write_vga_desktop_keyboard_bu.asm:901: error: symbol `keybuf' not defined write_vga_desktop_keyboard_bu.asm:902: error: symbol `keybuf' not defined write_vga_desktop_keyboard_bu.asm:904: error: symbol `keybuf' not defined write_vga_desktop_keyboard_bu.asm:905: error: symbol `keybuf' not defined write_vga_desktop_keyboard_bu.asm:914: error: symbol `keybuf' not defined write_vga_desktop_keyboard_bu.asm:1024: warning: uninitialized space declared in .s32 section: zeroing [-w+zeroing] write_vga_desktop_keyboard_bu.asm:1027: warning: uninitialized space declared in .s32 section: zeroing [-w+zeroing] write_vga_desktop_keyboard_bu.asm:1029: warning: uninitialized space declared in .s32 section: zeroing [-w+zeroing] write_vga_desktop_keyboard_bu.asm:1031: warning: uninitialized space declared in .s32 section: zeroing [-w+zeroing] write_vga_desktop_keyboard_bu.asm:1034: warning: uninitialized space declared in .s32 section: zeroing [-w+zeroing]