【转】gdb 调试段错误

发布时间:2017-1-22 11:45:54 编辑:www.fx114.net 分享查询网我要评论
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【转】gdb 调试段错误

转自:blog.csdn.net/yangzhu1982/article/details/6318600

开发嵌入式Linux的时候经常会遇到segmentation fault,也就是段异常错误,一般是使用错误的指针访问内存导致。这种错误可以通过打开内核的异常信息输出,再用gdb对发生段异常的地址进行定位。

1.打开内核的异常信息输出:

mips的内核代码关闭了arch/mips/mm/fault.c的do_page_fault():133中的这段代码:

#if 0  printk("do_page_fault() #2: sending SIGSEGV to %s for "         "invalid %s/n%0*lx (epc == %0*lx, ra == %0*lx)/n",         tsk->comm,         write ? "write access to" : "read access from",         field, address,         field, (unsigned long) regs->cp0_epc,         field, (unsigned long) regs->regs[31]);#endif 

在发生段异常的时候会打印当前是哪个进程出错,出错的epc和返回地址ra是多少。打开这段代码,这样可以得到发生段异常时的指令地址。还可以增加打印内核栈和寄存器的函数,例如:

#if 1                printk("do_page_fault() #2: sending SIGSEGV to %s for "                       "invalid %s/n%0*lx (epc == %0*lx, ra == %0*lx)/n",                       tsk->comm,                       write ? "write access to" : "read access from",                       field, address,                       field, (unsigned long) regs->cp0_epc,                       field, (unsigned long) regs->regs[31]);                show_registers(regs);                dump_stack();#endif 

2.定位发生段异常的代码

打印的出错信息:

do_page_fault() #2: sending SIGSEGV to myprog for invalid read access from00000004 (epc == 00479628, ra == 00482228).......     Lo    : 00000001epc   : 00479628 0x479628     Not taintedra    : 00482228 0x482228Status: 0000f413    USER EXL IE Cause : 00800008BadVA : 00000004PrId  : 00019374Modules linked in: pppoe ppp_async ppp_deflate ppp_mppe pppox ppp_generic slhcProcess myprog (pid: 7487, threadinfo=81096000, task=811135b8)Stack : 2ab4f360 00000001 100055a0 004d0000 1000b320 004d0000 100055a0 00482228        10036248 004d0000 2ab4f360 00000001 1000b320 004d0000 004cac44 004825f0        00000000 004ba948 004bebe0 004ccce8 004cac44 000000a8 100055a4 0043886c        1000b320 0040d8d0 00000000 0040d8d0 00000000 10003494 0040ddfc 0040dd18        004b2250 004b2278 004b2284 0040d83c 1000b320 00000000 1000b320 7fcdff80        ...Call Trace:Code: 00000000  1090000a  00000000 <8c820004> 8c830000  8f998078  ac430000  0320f809  ac620004 Call Trace: [<8006dc04>] do_page_fault+0x214/0x430 [<8006dbfc>] do_page_fault+0x20c/0x430 [<800a881c>] handle_IRQ_event+0x70/0xfc [<800a89e4>] __do_IRQ+0x13c/0x158 [<8006e328>] tlb_do_page_fault_0+0xf8/0x100 [<8006130c>] ar7100_interrupt_receive+0xec/0x100Segmentation fault 

可以看到,发生异常的程序地址(epc寄存器)是0x00479628,程序返回地址(ra寄存器)是0x00482228。使用gdb来定位,注意编译myprog程序时要带编译参数-g -ggdb,否则myprog中没有调试信息。

#mipseb-linux-uclibc-gdb myprog(gdb) l *(0x00479628)0x479628 is in DropAll (../../../include/util.h:107).102      *103      * This is only for internal list manipulation where we know104      * the prev/next entries already!105      */106     static inline void __list_del(struct list_head *prev, struct list_head *next)107     {108         next->prev = prev;109          prev->next = next;110     }111(gdb) l *(0x00482228)0x482228 is in FW_CleanEnv (firewall.c:325).320         {321             g _apstFwHashTable[i] = NULL;322         }323324         /* ?3? ¢ */325         DropAll(&g_lLanDev);326          DropAll(&g_lWanDev);

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