本文共 6097 字，大约阅读时间需要 20 分钟。
先将上节的代码
#if 1 usb_buffer_alloc(usbdev, len, GFP_ATOMIC, &usb_dma_buff_phys_addr); //初开始没有给bus_buff赋值，导致内核引用出现错误 #else usb_buff = usb_buffer_alloc(usbdev, len, GFP_ATOMIC, &usb_dma_buff_phys_addr); //分配缓冲空间，用来返回缓冲地址 #endif
改为1这样就能弹出oops错误，但是还需要汇编代码，要不然弹出的oops错误不知从何处找到错误
现在来先修改一下Makefile，加入下面一句
arm-linux-objdump -D -m arm -S usbmouse_as_key.ko>usbmouse.dis
下面这个模块加载之后，移动鼠标就会弹出以下oops错误，
Unable to handle kernel NULL pointer dereference at virtual address 00000000pgd = c0004000[00000000] *pgd=00000000Internal error: Oops: 17 [#1]Modules linked in: usbmouse_as_keyCPU: 0 Not tainted (2.6.29.4-FriendlyARM #14)PC is at usbmouse_callback+0x1c/0xac [usbmouse_as_key]LR is at usb_hcd_giveback_urb+0x6c/0x108pc : [] lr : [ ] psr: 60000093sp : c035de18 ip : c035de48 fp : c035de44r10: 00000000 r9 : bf0003a0 r8 : 00000000r7 : c38984c0 r6 : bf000c5c r5 : c3898400 r4 : 00000000r3 : 00000000 r2 : 00000003 r1 : 00000204 r0 : c38fdb80Flags: nZCv IRQs off FIQs on Mode SVC_32 ISA ARM Segment kernelControl: c000717f Table: 33954000 DAC: 00000017Process swapper (pid: 0, stack limit = 0xc035c268)Stack: (0xc035de18 to 0xc035e000)de00: 00000000 c38fdb80 de20: c3898400 00000000 c38984c0 00000004 c38984c0 00000000 c035de64 c035de48 de40: c01a2754 bf0002a4 c3898400 c38fdb80 00000000 c38984c0 c035de84 c035de68 de60: c01b1634 c01a26f8 c38d2a60 ffc42040 c38fdb80 00000000 c035dec4 c035de88 de80: c01b2f50 c01b15e4 c0042af0 c3898400 00000002 c4e00000 c03a07c8 c3898400 dea0: 00000093 00000000 0000002a 3001b2e4 41129200 3001b2b0 c035dedc c035dec8 dec0: c01a2448 c01b2be0 c38d2180 00000000 c035defc c035dee0 c005dca8 c01a2414 dee0: c036580c c38d2180 0000002a c03a20d0 c035df1c c035df00 c005efc0 c005dc74 df00: 0000002a c03a4674 00000000 c037e484 c035df3c c035df20 c0026044 c005ef2c df20: ffffffff f4000000 04000000 c037e484 c035df94 c035df40 c0026a44 c0026010 df40: f4100000 00000032 f4100000 60000013 c0027edc c035c000 c0027edc c037e484 df60: 3001b2e4 41129200 3001b2b0 c035df94 c035df98 c035df88 c00284f8 c0027f3c df80: 60000013 ffffffff c035dfb4 c035df98 c00284f8 c0027eec c03a2464 c037e440 dfa0: c001c000 c0360440 c035dfc4 c035dfb8 c02899b4 c00284bc c035dff4 c035dfc8 dfc0: c0008930 c0289968 c0008470 00000000 00000000 c001cd38 00000000 c0007175 dfe0: c037e55c c001cd34 00000000 c035dff8 30008034 c0008740 00000000 00000000 Backtrace: [ ] (usbmouse_callback+0x0/0xac [usbmouse_as_key]) from [ ] (usb_hcd_giveback_urb+0x6c/0x108)[ ] (usb_hcd_giveback_urb+0x0/0x108) from [ ] (finish_urb+0x60/0xa8) r7:c38984c0 r6:00000000 r5:c38fdb80 r4:c3898400[ ] (finish_urb+0x0/0xa8) from [ ] (ohci_irq+0x380/0x44c) r7:00000000 r6:c38fdb80 r5:ffc42040 r4:c38d2a60[ ] (ohci_irq+0x0/0x44c) from [ ] (usb_hcd_irq+0x44/0xac)[ ] (usb_hcd_irq+0x0/0xac) from [ ] (handle_IRQ_event+0x44/0x80) r5:00000000 r4:c38d2180[ ] (handle_IRQ_event+0x0/0x80) from [ ] (handle_edge_irq+0xa4/0x160) r7:c03a20d0 r6:0000002a r5:c38d2180 r4:c036580c[ ] (handle_edge_irq+0x0/0x160) from [ ] (__exception_text_start+0x44/0x70) r7:c037e484 r6:00000000 r5:c03a4674 r4:0000002a[ ] (__exception_text_start+0x0/0x70) from [ ] (__irq_svc+0x24/0xa0)Exception stack(0xc035df40 to 0xc035df88)df40: f4100000 00000032 f4100000 60000013 c0027edc c035c000 c0027edc c037e484 df60: 3001b2e4 41129200 3001b2b0 c035df94 c035df98 c035df88 c00284f8 c0027f3c df80: 60000013 ffffffff r7:c037e484 r6:04000000 r5:f4000000 r4:ffffffff[ ] (default_idle+0x0/0xac) from [ ] (cpu_idle+0x4c/0x68)[ ] (cpu_idle+0x0/0x68) from [ ] (rest_init+0x5c/0x70) r7:c0360440 r6:c001c000 r5:c037e440 r4:c03a2464[ ] (rest_init+0x0/0x70) from [ ] (start_kernel+0x200/0x268)[ ] (start_kernel+0x0/0x268) from [<30008034>] (0x30008034) r6:c001cd34 r5:c037e55c r4:c0007175Code: e59f608c e59f908c e5968008 e3a04000 (e5d8c000) Kernel panic - not syncing: Fatal exception in interrupt
Unable to handle kernel NULL pointer dereference at virtual address 00000000
从这里面我们知道是一个空指针，但是我们并不知道具体在哪里呀，所以我们看下面
PC is at usbmouse_callback+0x1c/0xac [usbmouse_as_key] LR is at usb_hcd_giveback_urb+0x6c/0x108
这里给我了出错的为位置和返回的位置，但这个位置还是比较空泛，根本不知道在哪呀！
再看下trace，从中我们可以理解调用关系，以下是被调用(请参看上面的代码)
usbmouse_callback <- usb_hcd_giveback_urb <- finish_urb <- ohci_irq <- usb_hcd_irq <- handle_IRQ_event <- handle_edge_irq <- __exception_text_start <- __irq_svc
下面我就来看具体的位置
将刚才我们make产生的汇编代码带上来，看看到底是哪里出错了？
由于汇编产生的代码过于庞大，现在只摘取usbmous_callback处的代码