MIPS32路由器:内核模块未调用module_init [英] MIPS32 router: module_init not called for kernel module
问题描述
我正在开发要在路由器上运行的内核模块.路由器型号为Netgear的DGN2200v2.它在MIPS上运行Linux 2.6.30.我的问题是，当我加载模块时，似乎没有调用module_init.我试图通过修改module_init使其返回-3(指示错误?)来缩小范围，并且insmod仍然报告成功.我可以在lsmod的输出中看到我的模块，但没有看到使用dmesg的printk输出.
I'm developing a kernel module that I want to run on my router. The router model is DGN2200v2 by Netgear. It's running Linux 2.6.30 on MIPS. My problem is that when I load my module it seems that my module_init isn't getting called. I tried to narrow it down by modifying my module_init to return -3 (which indicates an error?) and insmod still reports success. I can see my module in the output of lsmod, but I don't see my printk output using dmesg.
对于初学者来说，我想创建尽可能简单的模块:
For starters, I wanted to create the simplest possible module:
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
static int my_init(void)
{
printk(KERN_EMERG "init_module() called\n");
return -3;
}
static void my_cleanup(void)
{
printk(KERN_EMERG "cleanup_module() called\n");
}
module_init(my_init);
module_exit(my_cleanup);
这是我正在使用的Makefile:
This is the Makefile I'm using:
TOOLCHAIN=/home/user/buildroot-2016.08/output/host/usr/bin/mips-buildroot-linux-uclibc-
ARCH=mips
CC = $(TOOLCHAIN)gcc
KBUILD_CFLAGS:=.
EXTRA_CFLAGS := -I/home/user/buildroot-2016.08/output/build/linux-headers-2.6.30/include\
-I/home/user/buildroot-2016.08/output/build/linux-headers-2.6.30/arch/mips/include/asm/mach-mipssim\
-I/home/user/buildroot-2016.08/output/build/linux-headers-2.6.30/arch/mips/include/asm/mach-generic\
-fno-pic -mno-abicalls -O2
obj-m := module.o
KDIR := /home/user/buildroot-2016.08/output/build/linux-headers-2.6.30
PWD := $(shell pwd)
default:
$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
我正在像这样运行make:
make ARCH=mips CROSS_COMPILE=/home/user/buildroot-2016.08/output/host/usr/bin/mips-buildroot-linux-uclibc-
成功通过.
如您所见，我正在使用Buildroot(我希望它已正确配置).我可以根据需要粘贴.config.
As you can see, I'm using Buildroot which I (hopefully) configured correctly. I can paste my .config if needed.
我在模块上运行了objdump，但没有发现问题.特别是，module_init符号似乎指向与my_init函数相同的位置，并且似乎具有我期望它的代码:
I ran objdump on my module and didn't find a problem. In particular, the module_init symbol seems to point to the same place as my my_init function, and it seems to have the code I expect it to:
module.ko: file format elf32-tradbigmips
module.ko
architecture: mips:isa32, flags 0x00000011:
HAS_RELOC, HAS_SYMS
start address 0x00000000
private flags = 50001001: [abi=O32] [mips32] [not 32bitmode] [noreorder]
MIPS ABI Flags Version: 0
ISA: MIPS32
GPR size: 32
CPR1 size: 0
CPR2 size: 0
FP ABI: Soft float
ISA Extension: None
ASEs:
None
FLAGS 1: 00000001
FLAGS 2: 00000000
Sections:
Idx Name Size VMA LMA File off Algn
0 .MIPS.abiflags 00000018 00000000 00000000 00000038 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA, LINK_ONCE_SAME_SIZE
1 .reginfo 00000018 00000000 00000000 00000050 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA, LINK_ONCE_SAME_SIZE
2 .note.gnu.build-id 00000024 00000018 00000018 00000068 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
3 .text 00000040 00000000 00000000 00000090 2**4
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
4 .rodata.str1.4 00000038 00000000 00000000 000000d0 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
5 .modinfo 0000005c 00000000 00000000 00000108 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
6 .data 00000000 00000000 00000000 00000170 2**4
CONTENTS, ALLOC, LOAD, DATA
7 .gnu.linkonce.this_module 0000014c 00000000 00000000 00000170 2**2
CONTENTS, ALLOC, LOAD, RELOC, DATA, LINK_ONCE_DISCARD
8 .bss 00000000 00000000 00000000 000002c0 2**4
ALLOC
9 .comment 00000040 00000000 00000000 000002c0 2**0
CONTENTS, READONLY
10 .pdr 00000040 00000000 00000000 00000300 2**2
CONTENTS, RELOC, READONLY
11 .gnu.attributes 00000010 00000000 00000000 00000340 2**0
CONTENTS, READONLY
12 .mdebug.abi32 00000000 00000000 00000000 00000350 2**0
CONTENTS, READONLY
SYMBOL TABLE:
00000000 l d .MIPS.abiflags 00000000 .MIPS.abiflags
00000000 l d .reginfo 00000000 .reginfo
00000018 l d .note.gnu.build-id 00000000 .note.gnu.build-id
00000000 l d .text 00000000 .text
00000000 l d .rodata.str1.4 00000000 .rodata.str1.4
00000000 l d .modinfo 00000000 .modinfo
00000000 l d .data 00000000 .data
00000000 l d .gnu.linkonce.this_module 00000000 .gnu.linkonce.this_module
00000000 l d .bss 00000000 .bss
00000000 l d .comment 00000000 .comment
00000000 l d .pdr 00000000 .pdr
00000000 l d .gnu.attributes 00000000 .gnu.attributes
00000000 l d .mdebug.abi32 00000000 .mdebug.abi32
00000000 l df *ABS* 00000000 module.c
00000000 l F .text 0000002c my_init
0000002c l F .text 00000014 my_cleanup
00000000 l .rodata.str1.4 00000000 $LC0
0000001c l .rodata.str1.4 00000000 $LC1
00000000 l df *ABS* 00000000 module.mod.c
00000000 l O .modinfo 00000023 __mod_srcversion23
00000024 l O .modinfo 00000009 __module_depends
00000030 l O .modinfo 0000002c __mod_vermagic5
00000000 g O .gnu.linkonce.this_module 0000014c __this_module
0000002c g F .text 00000014 cleanup_module
00000000 g F .text 0000002c init_module
00000000 *UND* 00000000 printk
Disassembly of section .MIPS.abiflags:
00000000 <.MIPS.abiflags>:
0: 00002001 movf a0,zero,$fcc0
4: 01000003 0x1000003
...
10: 00000001 movf zero,zero,$fcc0
14: 00000000 nop
Disassembly of section .reginfo:
00000000 <.reginfo>:
0: a2000014 sb zero,20(s0)
...
14: 00007fef 0x7fef
Disassembly of section .note.gnu.build-id:
00000018 <.note.gnu.build-id>:
18: 00000004 sllv zero,zero,zero
1c: 00000014 0x14
20: 00000003 sra zero,zero,0x0
24: 474e5500 c1 0x14e5500
28: c8e5d654 lwc2 $5,-10668(a3)
2c: cb477d3d lwc2 $7,32061(k0)
30: dfa48d71 ldc3 $4,-29327(sp)
34: c2ea16da ll t2,5850(s7)
38: f6bcae7d sdc1 $f28,-20867(s5)
Disassembly of section .text:
00000000 <init_module>:
0: 27bdffe8 addiu sp,sp,-24
4: 3c040000 lui a0,0x0
4: R_MIPS_HI16 $LC0
8: 3c020000 lui v0,0x0
8: R_MIPS_HI16 printk
c: afbf0014 sw ra,20(sp)
10: 24420000 addiu v0,v0,0
10: R_MIPS_LO16 printk
14: 0040f809 jalr v0
18: 24840000 addiu a0,a0,0
18: R_MIPS_LO16 $LC0
1c: 8fbf0014 lw ra,20(sp)
20: 2402fffd li v0,-3
24: 03e00008 jr ra
28: 27bd0018 addiu sp,sp,24
modinfo的输出也符合我的期望(与modinfo的输出相同，与在路由器上找到的另一个.ko相同，除了我的模块具有的srcversion，但路由器上的另一个模块没有) :
modinfo output also matches what I expect (same modinfo output as for another .ko that's found on the router, except for the srcversion which my module has but the other module on the router doesn't):
filename: /home/user/module/module.ko
srcversion: B0BADBA395A121CF49B74DC
depends:
vermagic: 2.6.30 mod_unload MIPS32_R1 32BIT
我完全有可能在Buildroot配置中弄乱了某些东西，或者某些东西与路由器的CPU类型不完全匹配，但是我的初始化代码太少了，以至于我对可能出了什么问题的想法一无所知
It's entirely possible that I messed something up in my Buildroot configuration, or something doesn't quite match the CPU type of the router, but my init code is so minimal that I'm out of ideas as to what could be wrong.
推荐答案
事实证明，问题与我的开发环境和路由器之间的内核配置不同有关.具体来说，我的内核使用的是CONFIG_UNUSED_SYMBOLS，而路由器的则不是.
It turns out that the problem was related to a different kernel configuration between my development environment and the router. Specifically, my kernel was using CONFIG_UNUSED_SYMBOLS whereas the router's was not.
即使在琐碎的模块中也引起问题的原因是，当内核加载模块时，它不仅在模块的符号表中查找module_init符号.而是从模块(从.gnu.linkonce.this_module部分)读取module结构，然后通过该结构调用init模块.
The reason this caused a problem even in a trivial module is that when the kernel loads a module it doesn't only look up the module_init symbol in the module's symbol table. Rather, it reads the module struct from the module (from the .gnu.linkonce.this_module section), and then calls the init module through that struct.
module结构中的init函数指针的偏移量取决于内核配置，这解释了为什么在配置不同的情况下内核找不到init函数的原因.
The offset of the init function pointer inside the module struct depends on the kernel configuration, which explains why the kernel can't find the init function if the configuration is different.
感谢萨姆·普罗岑科(Sam Protsenko)花了很多时间来帮助我解决这个问题！
Thanks to Sam Protsenko for investing a lot of time in helping me crack this!
这篇关于MIPS32路由器:内核模块未调用module_init的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
