利用GDB工具定位kernel Oops错误

错误log：

[   55.132887] Unable to handle kernel paging request at virtual address 0000676d
[   55.140503] pgd = c0004000
[   55.143278] [0000676d] *pgd=00000000
[   55.147001] Internal error: Oops: 5 [#1] PREEMPT SMP
[   55.152084] Modules linked in: ssd1306 rtk_btusb
[   55.156985] CPU: 1    Tainted: G        W    (3.0.35-gcbc3f7a4c9f-dirty #43)
[   55.164158] PC is at i2c_smbus_xfer+0x8/0x564
[   55.168580] LR is at i2c_smbus_read_byte_data+0x58/0xac
[   55.173922] pc : [<c0413964>]    lr : []    psr: 200f0013
[   55.173927] sp : d4057eac  ip : d4057ee6  fp : 00000089
[   55.185587] r10: c0046840  r9 : 00007069  r8 : c0a04b5c
[   55.190874] r7 : d4725000  r6 : c09b4440  r5 : 00000008  r4 : c0878290
[   55.197517] r3 : 00000001  r2 : 00005f66  r1 : 00007069  r0 : 00006765
[   55.204111] Flags: nzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment kernel
[   55.211536] Control: 10c53c7d  Table: 2082404a  DAC: 00000015

上面红字“PC is at i2c_smbus_xfer+0x8/0x564”说明，PC指针指向出问题函数的地址，出问题的函数是i2c_smbus_xfer，那他的地址是多少呢？

找到System.map所在位置，执行如下命令

root@root:~/android-work/kernel_imx$ grep i2c_smbus_xfer ./System.map

c041395c T i2c_smbus_xfer
c08b18d0 r __ksymtab_i2c_smbus_xfer
c08bc21c r __kcrctab_i2c_smbus_xfer
c08d220d r __kstrtab_i2c_smbus_xfer

这句日志最后[   55.164158] PC is at i2c_smbus_xfer+0x8/0x564, 0x564是i2c_smbus_xfer函数的大小，0x8是i2c_smbus_xfer函数的地址偏移。

结合错误日志c041395c就是i2c_smbus_xfer的地址，i2c_smbus_xfer+0x8即0xc041395c+0x8=0xc0413964，这就对上了这句话：[   55.173922] pc : [<c0413964>]    lr : []    psr: 200f0013

下面用GDB工具具体定位：

root@root:~/android-work/kernel_imx$ gdb ./vmlinux
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Reading symbols from ./vmlinux...done.
(gdb) b *0xc0413964
Breakpoint 1 at 0xc0413964: file drivers/i2c/i2c-core.c, line 2098.
(gdb)