使用skyeye运行《Linux设备驱动开发详解》的实例（二）

# strace modprobe hello
execve("/sbin/modprobe", ["modprobe", "hello"], [/* 7 vars */]) = 0
uname({sys="Linux", node="lihacker", ...}) = 0
brk(0)                                  = 0x15d000
brk(0x15dd02)                           = 0x15dd02
set_tls(0x15d4a0, 0x1573c0, 0, 0x1, 0x15d4a0) = 0
brk(0x17ed02)                           = 0x17ed02
brk(0x17f000)                           = 0x17f000
getuid32()                              = 0
chdir("/lib/modules")                   = 0
uname({sys="Linux", node="lihacker", ...}) = 0
chdir("2.6.31.6-svn79")                 = 0
open("/proc/modules", O_RDONLY)         = 3
fstat64(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40000000
read(3, ""..., 1024)                    = 0
close(3)                                = 0
munmap(0x40000000, 4096)                = 0
lstat64("/etc/modprobe.conf", 0xbe846880) = -1 ENOENT (No such file or directory)
lstat64("/etc/modprobe.d", 0xbe846880) = -1 ENOENT (No such file or directory)
open("modules.dep", O_RDONLY)           = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=17141, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40001000
read(3, "/lib/modules/2.6.31.6-svn79/kerne"..., 1024) = 1024
read(3, "nel/net/netfilter/x_tables.ko\n/li"..., 1024) = 1024
read(3, "/lib/modules/2.6.31.6-svn79/kerne"..., 1024) = 1024
read(3, "/net/netfilter/xt_esp.ko: /lib/mo"..., 1024) = 1024
read(3, "ables.ko /lib/modules/2.6.31.6-sv"..., 1024) = 1024
read(3, "es/2.6.31.6-svn79/kernel/net/netf"..., 1024) = 1024
read(3, ".6-svn79/kernel/net/netfilter/nf_"..., 1024) = 1024
read(3, "b/modules/2.6.31.6-svn79/kernel/n"..., 1024) = 1024
read(3, "etfilter/nf_conntrack_ipv4.ko /li"..., 1024) = 1024
read(3, ".6.31.6-svn79/kernel/net/netfilte"..., 1024) = 1024
read(3, "defrag_ipv4.ko\n/lib/modules/2.6.3"..., 1024) = 1024
read(3, "tfilter/nf_conntrack_ipv4.ko /lib"..., 1024) = 1024
read(3, ".6-svn79/kernel/net/ipv4/netfilte"..., 1024) = 1024
read(3, "1.6-svn79/kernel/net/netfilter/x_"..., 1024) = 1024
read(3, "ib/modules/2.6.31.6-svn79/kernel/"..., 1024) = 1024
read(3, "ib/modules/2.6.31.6-svn79/kernel/"..., 1024) = 1024
read(3, "o:\n/lib/modules/2.6.31.6-svn79/ke"..., 1024) = 757
close(3)                                = 0
munmap(0x40001000, 4096)                = 0
open("/lib/modules/2.6.31.6-svn79/kernel/drivers/char/driver_examples/hello.ko", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=2425, ...}) = 0
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\1\0(\0\1\0\0\0\0\0\0\0\0\0\0\0\210"..., 3072) = 2425
read(3, ""..., 647)                     = 0
close(3)                                = 0
init_module(0x15e300, 2425, ""Unable to handle kernel paging request at virtual address bf000000
pgd = c0620000
[bf000000] *pgd=00000000
Internal error: Oops: 807 [#1]
Modules linked in:
CPU: 0    Not tainted (2.6.31.6-svn79 #21)
PC is at __memzero+0x24/0x80
LR is at 0x0
pc : [<c0107404>]    lr : [<00000000>]    psr: 20000013
sp : c069ff0c ip : 00000000 fp : 00000005
r10: c2807230 r9 : c2807000 r8 : c2807388
r7 : 00000004 r6 : c2807168 r5 : 00000012 r4 : bf000000
r3 : 00000000 r2 : 00000000 r1 : 00000464 r0 : bf000000
Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
Control: 0000317f Table: c0620000 DAC: 00000015
Process modprobe (pid: 796, stack limit = 0xc069e270)
Stack: (0xc069ff0c to 0xc06a0000)
ff00:                            c005fba0 00000000 00000000 c2807518 c2807608
ff20: c28072dc c1139240 c28078a0 00000010 00000000 c2807388 00000000 c2807630
ff40: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
ff60: 00000000 00000979 0015e2f0 00000000 0015e300 c002bf48 c069e000 00000000
ff80: 00000000 c0060878 be846958 c002dbe0 00000000 00000979 0015e2f0 0015dfa8
ffa0: 00000080 c002bf0c 00000979 0015e2f0 0015e300 00000979 0015e2f0 00000000
ffc0: 00000979 0015e2f0 0015dfa8 00000080 0015e2a0 0015dfbc 00000001 00000000
ffe0: be846958 be846948 000177f8 00009350 20000010 0015e300 ebff1fc9 e3500000
[<c0107404>] (__memzero+0x24/0x80) from [<00000000>] (0x0)
Code: e52de004 e1a0c002 e1a0e002 e2511040 (a8a0500c)
---[ end trace 1e19dcbb1e19dcba ]---
<unfinished ...>
+++ killed by SIGSEGV +++

很明显，死在内核的linux-2.6.31/kernel/module.c的init_module()函数中,加上几个printk:

2453 SYSCALL_DEFINE3(init_module, void __user *, umod,
2454         unsigned long, len, const char __user *, uargs)
2455 {
2456     struct module *mod;
2457     int ret = 0;
2458
2459     printk("%s %d\n", __func__, __LINE__);
2460
2461     /* Must have permission */
2462     if (!capable(CAP_SYS_MODULE) || modules_disabled)
2463         return -EPERM;
2464
2465     +printk("%s %d\n", __func__, __LINE__);
2466
2467     /* Only one module load at a time, please */
2468     if (mutex_lock_interruptible(&module_mutex) != 0)
2469         return -EINTR;
2470
2471     +printk("%s %d\n", __func__, __LINE__);
2472
2473     /* Do all the hard work */
2474     mod = load_module(umod, len, uargs);
2475     if (IS_ERR(mod)) {
2476         mutex_unlock(&module_mutex);
2477         return PTR_ERR(mod);
2478     }
2479
2480     +printk("%s %d\n", __func__, __LINE__);
2481

再次运行:

# modprobe hello
sys_init_module 2459
sys_init_module 2465
sys_init_module 2471
Unable to handle kernel paging request at virtual address bf000000
pgd = c05f0000
[bf000000] *pgd=00000000
Internal error: Oops: 807 [#1]
Modules linked in:

从打印信息可以看出，panic发生在load_module函数，既然"sys_init_module 2471"被打印而"sys_init_module 2480"未打印。继续跟进load_module()，直到最后发现内核崩溃在memset(ptr, 0, mod->core_size);：

static noinline struct module *load_module(void __user *umod,
                   unsigned long len,
                   const char __user *uargs)
{
...
     ptr = module_alloc_update_bounds(mod->core_size);
...
     kmemleak_not_leak(ptr);
...
     memset(ptr, 0, mod->core_size);

一路跟踪源代码，发现ARM的Kernel会将模块的内存申请在3G-16M到3G的区域，而skyeye在内核空间处理3G以下地址的时候，会发生错误:

"Unable to handle kernel paging request at virtual address bf000000"

因此，workaround掉这个bug:

Index: arch/arm/kernel/module.c
===================================================================
--- arch/arm/kernel/module.c    (revision 87)
+++ arch/arm/kernel/module.c    (working copy)
@@ -38,7 +38,7 @@
#ifdef CONFIG_MMU
void *module_alloc(unsigned long size)
{
-       struct vm_struct *area;
+       /*struct vm_struct *area;

        size = PAGE_ALIGN(size);
        if (!size)
@@ -49,6 +49,9 @@
                return NULL;

        return __vmalloc_area(area, GFP_KERNEL, PAGE_KERNEL_EXEC);
+*/
+
+       return size == 0 ? NULL : kmalloc(size, GFP_KERNEL);
}
#else /* CONFIG_MMU */
void *module_alloc(unsigned long size)
@@ -59,7 +62,7 @@

void module_free(struct module *module, void *region)
{
-       vfree(region);
+       kfree(region);
}

int module_frob_arch_sections(Elf_Ehdr *hdr,

由于此workaround使用了kmalloc，如果内核模块很大，kmalloc申请的内存不够存放，则可以修改： include/linux/slab.h中的KMALLOC_SHIFT_HIGH宏定义。另外，此workaround成立的条件是mem=32M或小于32M。现在我们可以自由地加载模块了，看看结果：

加载模块：
# modprobe hello
Hello World enter
# modprobe globalmem globalmem_major=250
# modprobe globalfifo globalfifo_major=251

查看加载的模块:
# lsmod
Not tainted
globalmem 3356 0 - Live 0xc0f66000
hello 1188 0 - Live 0xc1128000
globalfifo 4292 0 - Live 0xc182a000

查看设备：
# cat /proc/devices
Character devices:
1 mem
2 pty
3 ttyp
4 /dev/vc/0
4 tty
4 ttyS
5 /dev/tty
5 /dev/console
5 /dev/ptmx
7 vcs
10 misc
13 input
21 sg
29 fb
128 ptm
136 pts
204 s3c2410_serial
250 globalmem
251 globalfifo

建立结点：
# mknod /dev/globalmem c 250 0
# mknod /dev/globalfifo c 251 0
#
读写设备文件：
# echo "hello, cisco" > /dev/globalmem
written 13 bytes(s) from 0
# cat /dev/globalmem
read 4096 bytes(s) from 0
hello, cisco

# cat /dev/globalfifo &
# echo "hello,Linux, I love you" > /dev/globalfifo
written 24 bytes(s),current_len:24
# read 24 bytes(s),current_len:0
hello,cisco, I love you

已经做好的包位于： http://ldd6410.googlecode.com/files/ldd6410-skyeye-pack-with-module.tar.gz