Debug using gdb on qemu.

os/Makefile

@@ -3,6 +3,7 @@ TARGET := riscv64gc-unknown-none-elf
 MODE := release
 KERNEL_ELF := target/$(TARGET)/$(MODE)/os
 KERNEL_BIN := $(KERNEL_ELF).bin
+KERNEL_ENTRY_PA := 0x80020000
 DISASM_TMP := target/$(TARGET)/$(MODE)/asm
 
 # BOARD
@@ -48,7 +49,7 @@ ifeq ($(BOARD),qemu)
 		-machine virt \
 		-nographic \
 		-bios $(BOOTLOADER) \
-		-device loader,file=$(KERNEL_BIN),addr=0x80020000
+		-device loader,file=$(KERNEL_BIN),addr=$(KERNEL_ENTRY_PA)
 else
 	@cp $(BOOTLOADER) $(BOOTLOADER).copy
 	@dd if=$(KERNEL_BIN) of=$(BOOTLOADER).copy bs=128K seek=1
@@ -58,4 +59,10 @@ else
 	miniterm --eol LF --dtr 0 --rts 0 --filter direct $(K210-SERIALPORT) 115200
 endif
 
+debug: build
+	@tmux new-session -d \
+		"qemu-system-riscv64 -machine virt -nographic -bios $(BOOTLOADER) -device loader,file=$(KERNEL_BIN),addr=$(KERNEL_ENTRY_PA) -s -S" && \
+		tmux split-window -h "riscv64-unknown-elf-gdb -ex 'file $(KERNEL_ELF)' -ex 'set arch riscv:rv64' -ex 'target remote localhost:1234'" && \
+		tmux -2 attach-session -d
+
 .PHONY: build kernel clean disasm disasm-vim run-inner