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update 1.3_linux_basic.md
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@ -12,6 +12,7 @@
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- [核心转储](#核心转储)
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- [调用约定](#调用约定)
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- [环境变量](#环境变量)
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- [/proc/[pid]](#procpid)
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## 常用基础命令
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@ -489,3 +490,198 @@ $ file ~/libc.so.6
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/home/firmy/libc.so.6: ELF 64-bit LSB shared object, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=088a6e00a1814622219f346b41e775b8dd46c518, for GNU/Linux 2.6.32, stripped
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```
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一个在 `interpreter /usr/lib/ld-linux-x86-64.so.2`，而另一个在 `interpreter /lib64/ld-linux-x86-64.so.2`。
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## /proc/[pid]
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proc 文件系统是 Linux 内核提供的，为访问系统内核数据的操作提供接口。在该文件系统下，有一些以数字命名的目录，这些数字是进程的 PID 号，而这些目录是进程目录。
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目录下的所有文件如下，然后会介绍几个比较重要的：
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```
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$ cat - &
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[1] 2865
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$ ls /proc/2865/
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attr cpuset limits ns root statm
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autogroup cwd map_files numa_maps sched status
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auxv environ maps oom_adj schedstat syscall
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cgroup exe mem oom_score setgroups task
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clear_refs fd mountinfo oom_score_adj smaps timers
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cmdline fdinfo mounts pagemap smaps_rollup timerslack_ns
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comm gid_map mountstats personality stack uid_map
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coredump_filter io net projid_map stat wchan
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[1]+ Stopped cat -
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```
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#### /proc/[pid]/maps
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这个文件大概是最常用的，用于显示进程的内存区域映射信息：
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```
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$ cat /proc/2865/maps
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5580631c6000-5580631ce000 r-xp 00000000 08:01 4981196 /usr/bin/cat
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5580633cd000-5580633ce000 r--p 00007000 08:01 4981196 /usr/bin/cat
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5580633ce000-5580633cf000 rw-p 00008000 08:01 4981196 /usr/bin/cat
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558063c7d000-558063c9e000 rw-p 00000000 00:00 0 [heap]
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7f6301cd7000-7f6302027000 r--p 00000000 08:01 4993768 /usr/lib/locale/locale-archive
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7f6302027000-7f63021d5000 r-xp 00000000 08:01 4982395 /usr/lib/libc-2.26.so
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7f63021d5000-7f63023d5000 ---p 001ae000 08:01 4982395 /usr/lib/libc-2.26.so
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7f63023d5000-7f63023d9000 r--p 001ae000 08:01 4982395 /usr/lib/libc-2.26.so
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7f63023d9000-7f63023db000 rw-p 001b2000 08:01 4982395 /usr/lib/libc-2.26.so
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7f63023db000-7f63023df000 rw-p 00000000 00:00 0
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7f63023df000-7f6302404000 r-xp 00000000 08:01 4982398 /usr/lib/ld-2.26.so
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7f63025c1000-7f63025c3000 rw-p 00000000 00:00 0
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7f63025e1000-7f6302603000 rw-p 00000000 00:00 0
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7f6302603000-7f6302604000 r--p 00024000 08:01 4982398 /usr/lib/ld-2.26.so
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7f6302604000-7f6302605000 rw-p 00025000 08:01 4982398 /usr/lib/ld-2.26.so
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7f6302605000-7f6302606000 rw-p 00000000 00:00 0
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7fff2ab81000-7fff2aba2000 rw-p 00000000 00:00 0 [stack]
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7fff2abef000-7fff2abf2000 r--p 00000000 00:00 0 [vvar]
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7fff2abf2000-7fff2abf4000 r-xp 00000000 00:00 0 [vdso]
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ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
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```
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#### /proc/[pid]/stack
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这个文件表示当前进程的内核调用栈信息：
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```
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$ sudo cat /proc/2865/stack
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[<ffffffffa008d05e>] do_signal_stop+0xae/0x1f0
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[<ffffffffa008e50c>] get_signal+0x18c/0x5a0
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[<ffffffffa002ac26>] do_signal+0x36/0x610
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[<ffffffffa0003019>] exit_to_usermode_loop+0x69/0xa0
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[<ffffffffa00038eb>] syscall_return_slowpath+0x9b/0xb0
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[<ffffffffa06926e4>] entry_SYSCALL_64_fastpath+0x7b/0x7d
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[<ffffffffffffffff>] 0xffffffffffffffff
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```
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#### /proc/[pid]/auxv
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该文件包含了传递给进程的解释器信息，即 auxv(AUXiliary Vector)，每一项都是由一个 unsigned long 长度的 ID 加上一个 unsigned long 长度的值构成：
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```
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$ xxd -e -g8 /proc/2865/auxv
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00000000: 0000000000000021 00007fff2abf2000 !........ .*....
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00000010: 0000000000000010 00000000bfebfbff ................
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00000020: 0000000000000006 0000000000001000 ................
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00000030: 0000000000000011 0000000000000064 ........d.......
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00000040: 0000000000000003 00005580631c6040 ........@`.c.U..
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00000050: 0000000000000004 0000000000000038 ........8.......
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00000060: 0000000000000005 0000000000000009 ................
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00000070: 0000000000000007 00007f63023df000 ..........=.c...
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00000080: 0000000000000008 0000000000000000 ................
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00000090: 0000000000000009 00005580631c8290 ...........c.U..
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000000a0: 000000000000000b 00000000000003e8 ................
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000000b0: 000000000000000c 00000000000003e8 ................
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000000c0: 000000000000000d 00000000000003e8 ................
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000000d0: 000000000000000e 00000000000003e8 ................
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000000e0: 0000000000000017 0000000000000000 ................
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000000f0: 0000000000000019 00007fff2ab9ff39 ........9..*....
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00000100: 000000000000001a 0000000000000000 ................
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00000110: 000000000000001f 00007fff2aba1feb ...........*....
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00000120: 000000000000000f 00007fff2ab9ff49 ........I..*....
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00000130: 0000000000000000 0000000000000000 ................
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```
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每个值具体是做什么的，可以用下面的办法显示出来，对比看一看，更详细的可以查看 `/usr/include/elf.h` 和 `man ld.so`：
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```
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$ LD_SHOW_AUXV=1 cat -
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AT_SYSINFO_EHDR: 0x7fff6afb3000
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AT_HWCAP: bfebfbff
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AT_PAGESZ: 4096
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AT_CLKTCK: 100
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AT_PHDR: 0x557b68217040
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AT_PHENT: 56
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AT_PHNUM: 9
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AT_BASE: 0x7f41e5689000
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AT_FLAGS: 0x0
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AT_ENTRY: 0x557b68219290
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AT_UID: 1000
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AT_EUID: 1000
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AT_GID: 1000
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AT_EGID: 1000
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AT_SECURE: 0
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AT_RANDOM: 0x7fff6aedc0a9
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AT_HWCAP2: 0x0
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AT_EXECFN: /usr/bin/cat
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AT_PLATFORM: x86_64
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```
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值得一提的是，`AT_SYSINFO_EHDR` 所对应的值是一个叫做的 VDSO(Virtual Dynamic Shared Object) 的地址。在 ret2vdso 漏洞利用方法中会用到（参考章节6.1.6）。
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#### /proc/[pid]/environ
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该文件包含了进程的环境变量：
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```
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$ strings /proc/2865/environ
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```
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#### /proc/[pid]/fd
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该文件包含了进程打开文件的情况：
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```
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$ ls -al /proc/2865/fd
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total 0
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dr-x------ 2 firmy firmy 0 12月 30 11:13 .
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dr-xr-xr-x 9 firmy firmy 0 12月 30 11:13 ..
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lrwx------ 1 firmy firmy 64 12月 30 12:31 0 -> /dev/pts/2
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lrwx------ 1 firmy firmy 64 12月 30 12:31 1 -> /dev/pts/2
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lrwx------ 1 firmy firmy 64 12月 30 12:31 2 -> /dev/pts/2
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```
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#### /proc/[pid]/status
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该文件包含了进程的状态信息：
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```
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$ cat /proc/2865/status
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Name: cat
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Umask: 0022
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State: T (stopped)
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Tgid: 2865
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Ngid: 0
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Pid: 2865
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PPid: 2059
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TracerPid: 0
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Uid: 1000 1000 1000 1000
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Gid: 1000 1000 1000 1000
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FDSize: 256
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Groups: 3 7 10 56 90 91 93 95 96 98 1000
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NStgid: 2865
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NSpid: 2865
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NSpgid: 2865
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NSsid: 2059
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VmPeak: 7828 kB
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VmSize: 7828 kB
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VmLck: 0 kB
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VmPin: 0 kB
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VmHWM: 788 kB
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VmRSS: 788 kB
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RssAnon: 64 kB
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RssFile: 724 kB
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RssShmem: 0 kB
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VmData: 312 kB
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VmStk: 132 kB
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VmExe: 32 kB
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VmLib: 1876 kB
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VmPTE: 40 kB
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VmPMD: 12 kB
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VmSwap: 0 kB
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HugetlbPages: 0 kB
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Threads: 1
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SigQ: 2/47723
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SigPnd: 0000000000000000
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ShdPnd: 0000000000000000
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SigBlk: 0000000000000000
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SigIgn: 0000000000000000
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SigCgt: 0000000000000000
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CapInh: 0000000000000000
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CapPrm: 0000000000000000
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CapEff: 0000000000000000
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CapBnd: 0000003fffffffff
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CapAmb: 0000000000000000
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NoNewPrivs: 0
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Seccomp: 0
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Cpus_allowed: ff
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Cpus_allowed_list: 0-7
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Mems_allowed: 00000001
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Mems_allowed_list: 0
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voluntary_ctxt_switches: 1
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nonvoluntary_ctxt_switches: 0
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```
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#### /proc/[pid]/syscall
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该文件包含了进程正在执行的系统调用：
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```
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$ sudo cat /proc/2865/syscall
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0 0x0 0x7f63025e2000 0x20000 0x22 0xffffffffffffffff 0x0 0x7fff2ab9f958 0x7f630210ea11
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```
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第一个值是系统调用号，后面跟着是六个参数，最后两个值分别是堆栈指针和指令计数器的值。
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@ -518,7 +518,7 @@ reading from file slip-bad-direction.pcap, link-type SLIP (SLIP)
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```
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具体代码的修改如下所示，文件 `print-sl.c` 用于打印 CSLIP（Compressed Serial Line Internet Protocol），即压缩的 SLIP：
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```C
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```diff
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$ git diff 09b1185 378ac56 print-sl.c
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diff --git a/print-sl.c b/print-sl.c
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index 3fd7e898..a02077b3 100644
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