am335x gpio_led_probe的调用过程

在 gpio_led_probe()里制造一个段错误，内核启动出错，便可打印Backtrace ，可以清晰的看到函数调用过程，比起源码里分晰来得更快
[    2.494011] Backtrace:
[    2.496585] [] (gpio_led_probe) from [] (platform_drv_probe+0x58/0xb8)
[    2.505246]  r10:00000000 r9:c0b0061c r8:00000000 r7:fffffdfb r6:c0c3e898 r5:ffffffed
[    2.513443]  r4:dc440650
[    2.516098] [] (platform_drv_probe) from [] (driver_probe_device+0x20c/0x2b8)
[    2.525391]  r7:c0c3e898 r6:00000000 r5:dc440650 r4:c0c95230
[    2.531319] [] (driver_probe_device) from [] (__driver_attach+0xc0/0xc4)
[    2.540160]  r9:c0b0061c r8:000000a1 r7:00000000 r6:dc440684 r5:c0c3e898 r4:dc440650
[    2.548284] [] (__driver_attach) from [] (bus_for_each_dev+0x70/0xa4)
[    2.556849]  r7:00000000 r6:c04fbbac r5:c0c3e898 r4:00000000
[    2.562779] [] (bus_for_each_dev) from [] (driver_attach+0x24/0x28)
[    2.571161]  r6:c0c35688 r5:db5f5340 r4:c0c3e898
[    2.575996] [] (driver_attach) from [] (bus_add_driver+0x110/0x21c)
[    2.584380] [] (bus_add_driver) from [] (driver_register+0x80/0xfc)
[    2.592762]  r7:c0b39830 r6:c0b77388 r5:ffffe000 r4:c0c3e898
[    2.598691] [] (driver_register) from [] (__platform_driver_register+0x48/0x50)
[    2.608163]  r5:ffffe000 r4:c0c35688
[    2.611919] [] (__platform_driver_register) from [] (gpio_led_driver_init+0x1c/0x20)
[    2.621845]  r5:ffffe000 r4:c0b2ab5c
[    2.625595] [] (gpio_led_driver_init) from [] (do_one_initcall+0x4c/0x178)
[    2.634627] [] (do_one_initcall) from [] (kernel_init_freeable+0x13c/0x1cc)
[    2.643739]  r10:00000007 r9:c0b0061c r8:000000a1 r7:c0b39830 r6:c0b77388 r5:c0c49740
[    2.651936]  r4:c0c49740
[    2.654601] [] (kernel_init_freeable) from [] (kernel_init+0x10/0x110)
[    2.663259]  r10:00000000 r9:00000000 r8:00000000 r7:00000000 r6:00000000 r5:c0751e04
[    2.671455]  r4:00000000
[    2.674115] [] (kernel_init) from [] (ret_from_fork+0x14/0x2c)
[    2.682041]  r5:c0751e04 r4:00000000
[    2.685787] Code: e30e11c0 e30e01dc e34c2086 e34c109d (e594c000)
[    2.692285] ---[ end trace fbf3b33402cc06c3 ]---
[    2.697154] Kernel panic - not syncing: Fatal exception
[    2.702632] ---[ end Kernel panic - not syncing: Fatal exception