搭建Linux内核开发环境

对于Linux内核开发而言使用qemu是很方便的手段，本文主要介绍linux内核开发环境的搭建过程，主要包括内核编译、使用qemu启动编译好的内核，以及构建根文件系统，使用GDB来调试内核等内容。

Linux内核编译

git clone https://github.com/torvalds/linux.git

make ARCH=x86_64 x86_64_defconfig
make ARCH=x86_64 menuconfig

使用编译选项增加debug信息

Kernel hacking
	Compile-time checks and compiler options  --->
		[*] Compile-time checks and compiler options  --->
		[ ]   Reduce debugging information
		[*]   Provide GDB scripts for kernel debugging

Qemu启动Linux内核

qemu-system-x86_64 \
        -kernel arch/x86/boot/bzImage \
        -boot c -m 2048 \
        -append "root=/dev/zero rw console=ttyS0,115200 acpi=off nokaslr" \
        -nographic

目前没有配文件系统，启动内核会提示错误

buildroot配置根文件系统

git clone https://github.com/buildroot/buildroot

make menuconfig

Target Options
	-> Target Architecture
		(X) x86_64

Filesystem images
	-> ext2/3/4 root filesystem
		(X) ext4

启动Linux内核和rootfs，登录buildroot login: 输入root即可

qemu-system-x86_64 \
        -kernel arch/x86/boot/bzImage \
        -boot c -m 2048 \
        -hda /path/to/buildroot/output/images/rootfs.ext4 \
        -append "root=/dev/sda rw console=ttyS0,115200 acpi=off nokaslr" \
        -nographic

GDB调试Linux内核

用GDB调试内核时需要在Kernel hacking中开启对应打编译选项，然后qemu启动时增加 -s -S 选项

qemu-system-x86_64 \
        -kernel arch/x86/boot/bzImage \
        -boot c -m 2048 \
        -hda /path/to/buildroot/output/images/rootfs.ext4 \
        -append "root=/dev/sda rw console=ttyS0,115200 acpi=off nokaslr" \
        -nographic \
        -s -S

启动后再开启一个shell启动gdb

gdb ./vmlinux

(gdb) target remote localhost:1234
Remote debugging using localhost:1234
0x000000000000fff0 in exception_stacks ()
(gdb) break start_kernel
Breakpoint 1 at 0xffffffff82b3caa9: file init/main.c, line 850.
(gdb) continue
Continuing.

Breakpoint 1, start_kernel () at init/main.c:850
850     {
(gdb) list
845     {
846             rest_init();
847     }
848
849     asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
850     {
851             char *command_line;
852             char *after_dashes;
853
854             set_task_stack_end_magic(& init_task);
(gdb)

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