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今天很郁闷的遇到了一个oops，以前碰到这类事情我就会退缩的，今天刚好没有任务，就想要不就分析一下，这个还是很重要的，我不能总是逃避这类问题啊，果断开始分析了。
先把oops亮出来给大伙看看，
[ 230.893864] Unable to handle kernel paging request at virtual address
9c0d5030
[ 230.959592] pgd = 9aaf8000
[ 230.962313] [9c0d5030] *pgd=aa003011, *pte=00000000, *ppte=00000000
[ 231.001197] Internal error: Oops: 7 [#1] PREEMPT
[ 231.005821] last sysfs file:
/sys/devices/platform/wakeup_event-driver/wakeup_source
[ 231.013571] Modules linked in: dhd(-)
[ 231.017270] CPU: 0 Not tainted (2.6.35.3 #1)
[ 231.022037] PC is at dhdsdio_htclk+0x28/0x438 [dhd]
[ 231.026977] LR is at dhdsdio_clkctl+0x5c/0x108 [dhd]
[ 231.031950] pc : [<7f012d84>] lr : [<7f013490>] psr: 20000013
[ 231.031956] sp : 9ae41e30 ip : 00000000 fp : 2b3408f0
[ 231.043450] r10: 35c61ef0 r9 : 9ae40000 r8 : 00000001
[ 231.048681] r7 : 00000000 r6 : 00000000 r5 : 9c096000 r4 : 9c09f000
[ 231.055217] r3 : 00000000 r2 : 9c0d5000 r1 : 00004329 r0 : 9c09f000
[ 231.061754] Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
[ 231.068898] Control: 10c5387d Table: aaaf8019 DAC: 00000015
[ 231.074652] Process WifiService (pid: 2580, stack limit = 0x9ae402e8)
[ 231.081100] Stack: (0x9ae41e30 to 0x9ae42000)
[ 231.085468] 1e20: 9ae41eb4 803f17d0 20000093 80814e28
[ 231.093659] 1e40: 94073900 80814e28 00000001 20000013 9c1dc714
9c09f000 00000003 00000000
[ 231.101850] 1e60: 9c1dc03c 00000001 9ae40000 35c61ef0 2b3408f0
7f013490 9c09f000 00000000
[ 231.110042] 1e80: 9ae636c0 7f0155b0 9c09f000 00000001 9ae41e68
00000000 9c1dc000 9c1dc0a8
[ 231.118234] 1ea0: 9c1df000 9c1dc03c 8004c0c4 7f00142c 9c1dc000
7f00159c 9c09f000 9ae636c0
[ 231.126426] 1ec0: 7f025240 67e04660 8004c0c4 7f014638 7f025228
9c093000 7f025240 7f01b24c
[ 231.134617] 1ee0: 922df400 7f02337c 922df43c 802ebcd0 922df408
7f02337c 922df43c 802178b0
[ 231.142809] 1f00: 922df408 7f02337c 922df43c 80217980 7f02337c
00000000 80846374 80216c24
[ 231.151000] 1f20: 7f0233b0 00000000 9ae41f44 7f01b3d0 7f0233b0
7f01b5b0 7f0233b0 8009b1d4
[ 231.159191] 1f40: 00000000 00646864 00000000 9ad9f8dc 00000001
39c2a6d3 00015e23 00000000
[ 231.167382] 1f60: ffffffff 00000000 00000000 39dd6b48 00000003
00000003 39dd6c10 00000107
[ 231.175573] 1f80: 7f0233b0 00000880 9ae41f8c 00000000 39dd6b48
ffffffff 67e04544 00000009
[ 231.183764] 1fa0: 00000081 8004bf40 ffffffff 67e04544 67e04660
00000880 35c61f34 33d63f1c
[ 231.191955] 1fc0: ffffffff 67e04544 00000009 00000081 39dd6b68
35c61f04 35c61ef0 2b3408f0
[ 231.200147] 1fe0: 67e06288 39dd6b30 67e03f01 6fd0c44c 20000010
67e04660 7fff6d67 fdf7f39f
[ 231.208458] [<7f012d84>] (dhdsdio_htclk+0x28/0x438 [dhd]) from
[<7f013490>] (dhdsdio_clkctl+0x5c/0x108 [dhd])
[ 231.218497] [<7f013490>] (dhdsdio_clkctl+0x5c/0x108 [dhd]) from
[<7f0155b0>] (dhd_bus_stop+0x48/0x2ac [dhd])
[ 231.228426] [<7f0155b0>] (dhd_bus_stop+0x48/0x2ac [dhd]) from
[<7f00142c>] (dhd_bus_detach+0x2c/0x44 [dhd])
[ 231.238242] [<7f00142c>] (dhd_bus_detach+0x2c/0x44 [dhd]) from
[<7f00159c>] (dhd_detach+0x158/0x1c0 [dhd])
[ 231.247993] [<7f00159c>] (dhd_detach+0x158/0x1c0 [dhd]) from
[<7f014638>] (dhdsdio_release+0x40/0xcc [dhd])
[ 231.257861] [<7f014638>] (dhdsdio_release+0x40/0xcc [dhd]) from
[<7f01b24c>] (bcmsdh_remove+0x1c/0x8c [dhd])
[ 231.267779] [<7f01b24c>] (bcmsdh_remove+0x1c/0x8c [dhd]) from
[<802ebcd0>] (sdio_bus_remove+0x18/0x54)
[ 231.277116] [<802ebcd0>] (sdio_bus_remove+0x18/0x54) from [<802178b0>]
(__device_release_driver+0x84/0xd0)
[ 231.286790] [<802178b0>] (__device_release_driver+0x84/0xd0) from
[<80217980>] (driver_detach+0x84/0xac)
[ 231.296287] [<80217980>] (driver_detach+0x84/0xac) from [<80216c24>]
(bus_remove_driver+0x90/0xb8)
[ 231.305324] [<80216c24>] (bus_remove_driver+0x90/0xb8) from
[<7f01b3d0>] (sdio_function_cleanup+0xc/0x2c [dhd])
[ 231.315522] [<7f01b3d0>] (sdio_function_cleanup+0xc/0x2c [dhd]) from
[<7f01b5b0>] (dhd_module_cleanup+0x8/0x14 [dhd])
[ 231.326140] unwind: Index not found 7f01b5b0
[ 231.330421] Code: 0a0000d5 e5902008 e3041329 e5d031d8 (e5920030)
[ 232.176926] ---[ end trace 23c706acef457857 ]--- 从上面很明显的可以看出是一个dhd模块出错了，在我的这个板子上是一个wifi的驱动，
这么一大串，吓到了。。。。
乍看是在dhdsdio_htclk这个函数中出错了，因为有这么一个片段的log啊
PC is at dhdsdio_htclk+0x28/0x438 [dhd]此是pc的值是在dhdsdio_htclk这个函数的范围内(啥，，你不知道pc是啥玩意，，那这个就靠你自己去google一下啦)
下面我要做的事情就是要将这个函数所对应的c文件产生的.o文件反汇编一下，如下：
./prebuilt/linux-x86/toolchain/arm-eabi-4.4.3/bin/arm-eabi-objdump -D external/linux-bcm4329-wifi/src/dhd/linux/dhd-cdc-sdmmc-gpl-2.6.35/dhd_sdio.o > dhd_dump.text00000124 <dhdsdio_htclk>:
124: e3510000 cmp r1, #0 ; 0x0 ;r1=on
128: e92d4ff0 push {r4, r5, r6, r7, r8, r9, sl, fp, lr}
12c: e1a04000 mov r4, r0 ;r4=r0=bus
130: e24dd024 sub sp, sp, #36 ; 0x24
134: e1a07002 mov r7, r2
138: e5905004 ldr r5, [r0, #4] ; sdh = bus->sdh; r5=sdh ;ok
13c: 0a0000d5 beq 498 <dhdsdio_htclk+0x374>
140: e5902008 ldr r2, [r0, #8] ; r0+8=bus->sih ; r2=bus->sih ;ok sih's real address
144: e3041329 movw r1, #17193 ; 0x4329 ;ok
148: e5d031d8 ldrb r3, [r0, #472] ;r3=r0+472=bus->alp_only ; r3 = clkreq = bus->alp_only = 0;
14c: e5920030 ldr r0, [r2, #48] ;r0=r2+48=bus->sih->chip ;XXXXXXX NO
150: e3530000 cmp r3, #0 ; 0x0 ;clkreq = bus->alp_only ? SBSDIO_ALP_AVAIL_REQ : SBSDIO_HT_AVAIL_REQ;
154: 13a03008 movne r3, #8 ; 0x8
158: 03a03010 moveq r3, #16 ; 0x10
15c: e1500001 cmp r0, r1
160: 1a000002 bne 170 <dhdsdio_htclk+0x4c>
164: e5922034 ldr r2, [r2, #52] ;;r2+52=bus->sih->chiprev
168: e3520000 cmp r2, #0 ; 0x0
16c: 03833001 orreq r3, r3, #1 ; 0x1 ;clkreq |= SBSDIO_FORCE_ALP; r3=clkreq
170: e1a00005 mov r0, r5
174: e3a01001 mov r1, #1 ; 0x1
178: e59f23a8 ldr r2, [pc, #936] ; 528 <dhdsdio_htclk+0x404>
17c: e28dc01c add ip, sp, #28 ; 0x1c
180: e58dc000 str ip, [sp]
184: ebfffffe bl 0 <bcmsdh_cfg_write>
......(后面省略一大段)static int
dhdsdio_htclk(dhd_bus_t *bus, bool on, bool pendok)
{
int err;
uint8 clkctl, clkreq, devctl;
bcmsdh_info_t *sdh;
DHD_TRACE(("%s: Enter\n", __FUNCTION__));
#if defined(OOB_INTR_ONLY)
pendok = FALSE;
#endif
clkctl = 0;
sdh = bus->sdh;
if (on) {
/* Request HT Avail */
clkreq = bus->alp_only ? SBSDIO_ALP_AVAIL_REQ : SBSDIO_HT_AVAIL_REQ;
if ((bus->sih->chip == BCM4329_CHIP_ID) && (bus->sih->chiprev == 0))
clkreq |= SBSDIO_FORCE_ALP;
bcmsdh_cfg_write(sdh, SDIO_FUNC_1, SBSDIO_FUNC1_CHIPCLKCSR, clkreq, &err);
if (err) {
DHD_ERROR(("%s: HT Avail request error: %d\n", __FUNCTION__, err));
return BCME_ERROR;
}
........(下面省略一大段)由
PC is at dhdsdio_htclk+0x28/0x438 [dhd] 14c: e5920030 ldr r0, [r2, #48] ;r0=r2+48=bus->sih->chip ;XXXXXXX NO
对于这段汇编代码，我在上面已经大概做出注释了，
140: e5902008 ldr r2, [r0, #8] ; r0+8=bus->sih ; r2=bus->sih ;ok sih's real address
typedef struct dhd_bus {
dhd_pub_t *dhd;
bcmsdh_info_t *sdh; /* Handle for BCMSDH calls */
si_t *sih; /* Handle for SI calls */
char *vars; /* Variables (from CIS and/or other) */
...... dhd_bus的定义，下面省略，只需关注sih这个成员变量struct si_pub {
uint socitype;
uint bustype;
uint buscoretype;
uint buscorerev;
uint buscoreidx;
int ccrev;
uint32 cccaps;
int pmurev;
uint32 pmucaps;
uint boardtype;
uint boardvendor;
uint boardflags;
uint chip;
uint chiprev;
uint chippkg;
uint32 chipst;
bool issim;
uint socirev;
bool pci_pr32414;
};
#if defined(WLC_HIGH) && !defined(WLC_LOW)
typedef struct si_pub si_t;
#else
typedef const struct si_pub si_t;
#endif这样就方便看汇编啦，
从上面的分析可知，我们的代码是在读取r2+48(即r2+0x30)这个地址所对应的值，然后保存到r0中的时候出错的，
下面来验证我上面的分析。
-------------------------------------------------------验证---------------------------------------------------------
[ 231.043450] r10: 35c61ef0 r9 : 9ae40000 r8 : 00000001
[ 231.048681] r7 : 00000000 r6 : 00000000 r5 : 9c096000 r4 : 9c09f000
[ 231.055217] r3 : 00000000 r2 : 9c0d5000 r1 : 00004329 r0 : 9c09f000
那么r2+0x30=0x9c0d5030
好了，我们知道是在读取0x9c0d5030这个地址处的值,然后保存到r0的时候出现oops的，那么到底是读取的时候出错了，还是保存的时候出错了呢，
下面我们再来看一句可以验证我们想法的log信息，那就是oops的第一句，如下
Unable to handle kernel paging request at virtual address 9c0d5030
------------------------------------------------------后续--------------------------------------------------------
上面好像一片和谐的景象啊，，结果有了，哈哈哈，可是不要高兴的太早喔，，结果是有了，可是该怎么解决呢，，毕竟我们分析问题的目的就是为了解决问题啊。。
单从该问题来说，我觉得可能是因为sih这个变量已经被deatch了，但是还没有验证，问题比较偶现，，唉，，最烦偶现的bug了，，
其实写这篇文章的目的也主要是为了讲述怎么从oops信息中去查找对应c代码中的错误行的，在linux内核调试中还是很有用的。
Unable to handle kernel paging request at virtual address <pre name="code" class="cpp">9c0d5030其实对于这句话我还是没有能够理解到底是怎么了，怎么会出现这种错误，
如果哪位朋友对这个比较了解的话，希望能不吝赐教，多多回帖帮我解惑，再此先感谢了。
ps: 解答上面的问题
不能访问的内核虚地址为45685516，内核中一般可访问的地址都是以0xCXXXXXXX开头的地址。
//---------------------------------------------------------------------------------------------------------------------------------------------------------------------
Oops: 0002 [#1]
这里面，0002表示Oops的错误代码（写错误，发生在内核空间），#1表示这个错误发生一次。
Oops的错误代码根据错误的原因会有不同的定义，本文中的例子可以参考下面的定义（如果发现自己遇到的Oops和下面无法对应的话，最好去内核代码里查找）：
* error_code:
* bit 0 == 0 means no page found, 1 means protection fault
* bit 1 == 0 means read, 1 means write
* bit 2 == 0 means kernel, 1 means user-mode
* bit 3 == 0 means data, 1 means instruction
1万+
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