1、引言
Linux内核是一个很大的模块，如果只是看源码有时会难以理解Linux内核的一些代码设计情况，如果可以结合Linux内核运行同时阅读源码再好不过，本文大致介绍Linux内核追踪方式，采用工具为qemu模拟器和gdb工具完成。
2、先决条件
（1）工具：需要使用qemu模拟器和gdb，在默认的Linux发行版中基本都有gdb工具；而对于qemu模拟器则需要自己下载安装，可以使用qemu源码安装，比较麻烦，不建议使用，可以使用Linux发行版中的包管理器进行下载安装，对于ubuntu和debian使用apt-get install命令，而对于centos和federa使用yum包管理器安装；在ubuntu下安装qemu模拟器，对应的包的名字可以在http://packages.ubuntu.com/搜索
（2）Linux内核源码：为了追踪Linux内核，你需要自己编译一个新的Linux内核，Linux内核下载网站https://www.kernel.org/,内核的具体编译方式在Linux内核源码压缩包中README文件有介绍
（3）镜像文件：下载一个ubuntu的iso文件（或者其它Linux发行版的iso文件），使用qemu创建一个ubuntu镜像，创建过程为
a）qemu-img create -f qcow2 ubuntu.img 10G （详细各个参数的含义见qemu-img的手册）
b）qemu-i386 -hda ubuntu.img -cdrom ~/Documents/ubuntu-14.10-desktop-i386.iso
- #include <stdio.h>
- #include <string.h>
- int main()
- {
- int i;
- printf("TK------>>>sizeof i is %d ",sizeof i);
- char *p = NULL;
- strcpy(p,"tankai");
- printf("p is %s ",p);
- return 0;
- }
2.编译
gcc -g -o 1 1.c
3.运行
./1
- TK------>>>sizeof i is 4
- 段错误
二、运行跟踪
1.strace
strace ./1
- execve("./1", ["./1"], [/* 45 vars */]) = 0
- brk(0) = 0x94b000
- access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
- mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f5f5e285000
- access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
- open("tls/x86_64/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory)
- open("tls/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory)
- open("x86_64/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory)
- open("libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory)
- open("/home/lianxi/share/static/tls/x86_64/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory)
- stat("/home/lianxi/share/static/tls/x86_64", 0x7fff7bbb1770) = -1 ENOENT (No such file or directory)
- open("/home/lianxi/share/static/tls/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory)
- stat("/home/lianxi/share/static/tls", 0x7fff7bbb1770) = -1 ENOENT (No such file or directory)
- open("/home/lianxi/share/static/x86_64/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory)
- stat("/home/lianxi/share/static/x86_64", 0x7fff7bbb1770) = -1 ENOENT (No such file or directory)
- open("/home/lianxi/share/static/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory)
- stat("/home/lianxi/share/static", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
- open("/usr/lib/libpython2.6.so.1.0/tls/x86_64/libc.so.6", O_RDONLY) = -1 ENOTDIR (Not a directory)
- stat("/usr/lib/libpython2.6.so.1.0/tls/x86_64", 0x7fff7bbb1770) = -1 ENOTDIR (Not a directory)
- open("/usr/lib/libpython2.6.so.1.0/tls/libc.so.6", O_RDONLY) = -1 ENOTDIR (Not a directory)
- stat("/usr/lib/libpython2.6.so.1.0/tls", 0x7fff7bbb1770) = -1 ENOTDIR (Not a directory)
- open("/usr/lib/libpython2.6.so.1.0/x86_64/libc.so.6", O_RDONLY) = -1 ENOTDIR (Not a directory)
- stat("/usr/lib/libpython2.6.so.1.0/x86_64", 0x7fff7bbb1770) = -1 ENOTDIR (Not a directory)
- open("/usr/lib/libpython2.6.so.1.0/libc.so.6", O_RDONLY) = -1 ENOTDIR (Not a directory)
- stat("/usr/lib/libpython2.6.so.1.0", {st_mode=S_IFREG|0555, st_size=5255963, ...}) = 0
- open("/etc/ld.so.cache", O_RDONLY) = 3
- fstat(3, {st_mode=S_IFREG|0644, st_size=148114, ...}) = 0
- mmap(NULL, 148114, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f5f5e260000
- close(3) = 0
- access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
- open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY) = 3
- read(3, "177ELF211 3 > 1 242 "..., 832) = 832
- fstat(3, {st_mode=S_IFREG|0755, st_size=1694008, ...}) = 0
- mmap(NULL, 3810152, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f5f5dcc4000
- mprotect(0x7f5f5de5d000, 2093056, PROT_NONE) = 0
- mmap(0x7f5f5e05c000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x198000) = 0x7f5f5e05c000
- mmap(0x7f5f5e061000, 21352, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f5f5e061000
- close(3) = 0
- mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f5f5e25f000
- mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f5f5e25d000
- arch_prctl(ARCH_SET_FS, 0x7f5f5e25d720) = 0
- mprotect(0x7f5f5e05c000, 16384, PROT_READ) = 0
- mprotect(0x600000, 4096, PROT_READ) = 0
- mprotect(0x7f5f5e287000, 4096, PROT_READ) = 0
- munmap(0x7f5f5e260000, 148114) = 0
- fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0
- mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f5f5e284000
- write(1, "TK------>>>sizeof i is 4 ", 25TK------>>>sizeof i is 4
- ) = 25
- --- SIGSEGV (Segmentation fault) @ 0 (0) ---
- +++ killed by SIGSEGV +++
- 段错误
2.ltrace
ltrace ./1
- __libc_start_main(0x400544, 1, 0x7fff5acc0c88, 0x4005b0, 0x400640 <unfinished ...>
- printf("TK------>>>sizeof i is %d ", 4TK------>>>sizeof i is 4
- ) = 25
- memcpy(NULL, "tankai", 7 <unfinished ...>
- --- SIGSEGV (Segmentation fault) ---
- +++ killed by SIGSEGV +++
3.gdb
gdb 1
list
b 5
r
n
- (gdb) list
- 1 #include <stdio.h>
- 2 #include <string.h>
- 3
- 4 int main()
- 5 {
- 6 int i;
- 7 printf("TK------>>>sizeof i is %d ",sizeof i);
- 8 char *p = NULL;
- 9 strcpy(p,"tankai");
- 10 printf("p is %s ",p);
- (gdb) b 5
- Breakpoint 1 at 0x40054c: file 1.c, line 5.
- (gdb) r
- Starting program: /home/lianxi/extern/ok/1
- Breakpoint 1, main () at 1.c:7
- 7 printf("TK------>>>sizeof i is %d ",sizeof i);
- (gdb) n
- TK------>>>sizeof i is 4
- 8 char *p = NULL;
- (gdb) n
- 9 strcpy(p,"tankai");
- (gdb) n
- Program received signal SIGSEGV, Segmentation fault.
- 0x00007ffff7b6dec6 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
3、启动qemu追踪内核
（1）启动qemu模拟器：qemu-system-i386 -kernel linux-build/arch/i386/boot/bzImage -hda ubuntu.img -append "root=/dev/sda1" -S
（2）启动gdbserver：切换到qemu模拟器，alt+ctrl+2， 启动gdbserver，侦听端口1234（gdbserver tcp::1234）
（3）启动gdb：gdb ./vmlinux ,然后在gdb命令条件下链接上gdbserver， target remote localhost:1234
4、开始追踪内核
使用gdb的基本常用命令，step， break等（其他具体的命令可以参考gdb手册）。这时你可以查看系统运行的一些内核参数及系统状态信息，结合源码，查看系统的运行状态