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stap 命令

SystemTap accepts script as command line option or external file, for example:

  • Command-line script is passed with -e option
    # stap -e 'probe syscall.write { printf("%d\n", $fd); }' [arguments]
  • External file as first argument:
    # stap syscalls. [arguments]

SystemTap command line arguments may be passed to a script, but it distingushes their types: numerical arguments are accessible with $ prefix: $1, $2 ... $n while string arguments have @ prefix: @1, @2 ... @n

Here are some useful stap(1) options:

  • -l PROBESPEC accepts probe specifier without probe keyword (but with wildcards) and prints all matching probe names (more on wildcards in [Probes][lang/probes]). -L will also print probe arguments and their types. For example:
    # stap -l 'scsi.*'
  • -v -- increases verbosity of SystemTap. The more letters you passed, the more diagnostic information will be printed. If only one -v was passed, stap will report only finishing of each stage.
  • -p STAGE -- ends stap process after STAGE, represented with a number starting with 1 (parse).
  • -k -- stap tool won't delete SystemTap temporary files created during compilation (sources and kernel modules kept in /tmp/stapXXXX directory),
  • -g -- enables Guru-mode, that allows to bind to blacklisted probes and write into kernel memory along with using Embedded C in your scripts. Generally speaking, it allows dangerous actions.
  • -c COMMAND and -x PID -- like those in DTrace, they allow to bind SystemTap to a specific process
  • -o FILE -- redirects output to a file. If it already exists, SystemTap rewrites it.
  • -m NAME -- when compiling a module, give it meaningful name instead of stap_<gibberish>.

When SystemTap needs to resolve address into a symbol (for example, instruction pointer to a corresponding function name), it doesn't look into libraries or kernel modules.

Here are some useful command-line options that enable that:

  • -d MODULEPATH -- enables symbol resolving for a specific library or kernel module. Note that in case it is not provided, stap will print a warning with corresponding -d option.
  • --ldd -- for tracing process -- use ldd to add all linked libraries for a resolving.
  • --all-modules -- enable resolving for all kernel modules

SystemTap example

Here is sample SystemTap script:

#!/usr/sbin/stap

probe syscall.write { if(pid() target())

printf("Written %d bytes", $count); }

Save it to test.stp and run like this:

root@host# stap /root/test.stp -c "dd if=/dev/zero of=/dev/null count=1"

_Q__: Run SystemTap with following options: # stap -vv -k -p4 /root/test.stp, find generated directory in /tmp and look into created C source.

Q: Calculate number of probes in a syscall provider and number of variables provided by syscall.write probe:

stap -l 'syscall.*' | wc -l

stap -L 'syscall.write'

运行SystemTap。

运行SystemTap首先需要root权限。

运行SystemTap有三种形式:

1. 从文档(通常以.stp作为文档名后缀)中读入并运行脚本:stap [选项] 文档名。

2. 从标准输入中读入并运行脚本: stap [选项]。

3. 运行命令行中的脚本:stap [选项] -e 脚本。

4. 直接运行脚本文档(需要可执行属性并且第一行加上#!/usr/bin/stap):./脚本文档名用"Ctrl C"中止SystemTap的运行。

systemtap的选项还在不断的扩展和更新中,其中最常用的选项包括:

-v -- 打印中间信息;

-p NUM -- 运行完Pass Num后停止(缺省是运行到Pass 5);

-k -- 运行结束后保留临时文档不删除;

-b -- 使用RelayFS文档系统来将数据从内核空间传输到用户空间;

-M -- 仅当使用-b选项时有效,运行结束时不合并每个CPU的单独数据文档;

-o FILE -- 输出到文档,而不是输出到标准输出;

-c CMD -- 启动探测后,运行CMD命令,直到命令结束后退出;

-g -- 采用guru模式,允许脚本中嵌入C语句;

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