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；