KDB调试内核代码步骤记录：
一、配置内核，内核版本为Linux4.2.6
Kernel hacking --->
printk and dmesg options --->
[*] Show timing information on printks
(4) Default message log level (1-7)
[ ] Delay each boot printk message by N milliseconds
[*] Enable dynamic printk() support
[*] KGDB: kernel debugger --->
<*> KGDB: use kgdb over the serial console
[*] KGDB_KDB: include kdb frontend for kgdb
(0x1) KDB: Select kdb command functions to be enabled by default
[*] KGDB_KDB: keyboard as input device
(0) KDB: continue after catastrophic errors二、重新编译内核烧写到开发板，并且配置其u-boot参数，在bootargs设置中加上“kgdboc=ttySAC0,115200 kgdbwait kgdbcon”
三、启动系统，最终内核会显示到下面过
[ 0.206841] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
[ 0.208123] 13800000.serial: ttySAC0 at MMIO 0x13800000 (irq = 46, base_baud = 0) is a S3C6400/10
[ 0.834111] console [ttySAC0] enabled
[ 0.838058] 13810000.serial: ttySAC1 at MMIO 0x13810000 (irq = 47, base_baud = 0) is a S3C6400/10
[ 0.846849] 13820000.serial: ttySAC2 at MMIO 0x13820000 (irq = 48, base_baud = 0) is a S3C6400/10
[ 0.855689] 13830000.serial: ttySAC3 at MMIO 0x13830000 (irq = 49, base_baud = 0) is a S3C6400/10
[ 0.864861] KGDB: Registered I/O driver kgdboc
[ 0.906749] KGDB: Waiting for connection from remote gdb...
Entering kdb (current=0xee878000, pid 1) on processor 1 due to Keyboard Entry
[1]kdb>
四、接下来就可以来调试内核了，不过在调试内核之前有两种方式，一种直接使用kdb来调试，一种使用gdb调试vmlinux文件。
第一种方式也就是上面连接成功后直接使用kdb的命令来设置断点，调试。
第二种方式首先也是需要板子启动到KGDB: Waiting for connection from remote gdb...这里来，只不过下面可以使用ubuntu来中来调试。具体步骤如下：
1、首先确认进入到KGDB: Waiting for connection from remote gdb...
2、断开串口，把开发板的串口链接到ubuntu上，链接上来的串口显示/dev/ttyUSB0
（NOTE：也有人直接在ubuntu下开启minicon来显示开发板信息，也一样需要断开，不然会冲突，后面去target remote /dev/ttyUSB0的时候会打印“Ignoring packet error, continuing...”）
3、在Linux源码目录下，先使用arm-linux-gdb vmlinux。接着使用target remote /dev/ttyUSB0
最后就开始各种设置断电，各种单步调试了。如下：
root@ubuntu:/work/a9_board/tiny4412/linux_for_dts/linux-4.2.6# /work/a9_board/tiny4412/buildroot-2015.08/output/host/usr/bin/arm-linux-gdb vmlinux
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Type "show configuration" for configuration details.
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Reading symbols from vmlinux...done.
(gdb) target remote /dev/ttyUSB0
Remote debugging using /dev/ttyUSB0
0xc008fdc0 in arch_kgdb_breakpoint () at ./arch/arm/include/asm/outercache.h:142
142 outer_cache.sync();
(gdb) b usb4604_init
Breakpoint 1 at 0xc0383608: file drivers/usb/host/ehci-exynos.c, line 145.
(gdb) c
Continuing.
[ 38.339126] KGDB: kernel/debug/debug_core.c kgdb_register_io_module 1021...
[ 38.362864] [drm] Initialized drm 1.1.0 20060810
[ 38.386095] brd: module loaded
[ 38.404344] loop: module loaded
[ 38.417272] usbcore: registered new interface driver cdc_ether
[ 38.437386] usbcore: registered new interface driver dm9601
[ 38.458694] usbcore: registered new interface driver cdc_subset
[ 38.480702] usbcore: registered new interface driver zaurus
[ 38.501868] usbcore: registered new interface driver cdc_ncm
[ 38.523123] ehci_hcd: USB 2.0 'Enhanced' Host Controller (EHCI) Driver
[ 38.546737] ehci-exynos: EHCI EXYNOS driver
[ 38.564799] drivers/usb/host/ehci-exynos.c ehci_exynos_init 369
[ 38.586865] drivers/usb/host/ehci-exynos.c exynos_ehci_probe 181
[ 38.607813] drivers/usb/host/ehci-exynos.c exynos_ehci_probe 186
[ 38.631819] drivers/usb/host/ehci-exynos.c exynos_ehci_probe 197
[ 38.653826] drivers/usb/host/ehci-exynos.c exynos_ehci_probe 202
[ 38.676898] drivers/usb/host/ehci-exynos.c exynos_ehci_probe 207
Breakpoint 1, exynos_ehci_probe (pdev=0xee9b9400)
at drivers/usb/host/ehci-exynos.c:208
208 usb4604_init();
(gdb) n
[ 51.127535] usb4604 initialize............
212 exynos_ehci->clk = devm_clk_get(&pdev->dev, "usbhost");
(gdb) s
devm_clk_get (dev=0xee9b9410, id=0xc06ea0c0 "usbhost")
at drivers/clk/clk-devres.c:18
18 {
(gdb)
NOTE: 最不好的是在调试的过程中，时间久了会系统会自动复位，找了好久都不知道为什么。最好发现CPU温度非常高，反正只要CPU温度正常KDB怎么调试都行。一旦温度升高到一定程度就自动复位了，使用的板子是TINY4412的开发板。
离线
没用过这么高级的，感觉多线程情况下不太好调吧
离线