静态分析生成C语言函数调用关系的利器——cflow

cflow的说明和安装

cflow是一款静态分析C语言代码的工具，通过它可以生成函数的调用关系。和calltree不一样，cflow有独立的网页介绍它（https://www.gnu.org/software/cflow/#TOCdocumentation）。而且在Ubuntu系统上，我们可以不用去编译cflow的源码，而直接使用下面命令获取

apt-get install cflow

cflow的使用

安装完毕，我们可以使用下面指令看到cflow的参数说明

cflow --h

Usage: cflow [OPTION...] [FILE]...
generate a program flowgraph

 General options:
  -d, --depth=NUMBER         Set the depth at which the flowgraph is cut off
  -f, --format=NAME          Use given output format NAME. Valid names are
                             `gnu' (default) and `posix'
  -i, --include=CLASSES      Include specified classes of symbols (see below).
                             Prepend CLASSES with ^ or - to exclude them from
                             the output
  -o, --output=FILE          Set output file name (default -, meaning stdout)
  -r, --reverse              * Print reverse call tree
  -x, --xref                 Produce cross-reference listing only

 Symbols classes for --include argument

    _                        symbols whose names begin with an underscore
    s                        static symbols
    t                        typedefs (for cross-references only)
    x                        all data symbols, both external and static

 Parser control:

  -a, --ansi                 * Accept only sources in ANSI C
  -D, --define=NAME[=DEFN]   Predefine NAME as a macro
  -I, --include-dir=DIR      Add the directory DIR to the list of directories
                             to be searched for header files.
  -m, --main=NAME            Assume main function to be called NAME
  -p, --pushdown=NUMBER      Set initial token stack size to NUMBER
      --preprocess[=COMMAND], --cpp[=COMMAND]
                             * Run the specified preprocessor command
  -s, --symbol=SYMBOL:[=]TYPE   Register SYMBOL with given TYPE, or define an
                             alias (if := is used). Valid types are: keyword
                             (or kw), modifier, qualifier, identifier, type,
                             wrapper. Any unambiguous abbreviation of the above
                             is also accepted
  -S, --use-indentation      * Rely on indentation
  -U, --undefine=NAME        Cancel any previous definition of NAME

 Output control:

  -b, --brief                * Brief output
      --emacs                * Additionally format output for use with GNU
                             Emacs
  -l, --print-level          * Print nesting level along with the call tree
      --level-indent=ELEMENT Control graph appearance
  -n, --number               * Print line numbers
      --omit-arguments       * Do not print argument lists in function
                             declarations
      --omit-symbol-names    * Do not print symbol names in declaration strings
                            
  -T, --tree                 * Draw ASCII art tree

 Informational options:

      --debug[=NUMBER]       Set debugging level
  -v, --verbose              * Verbose error diagnostics

  -?, --help                 give this help list
      --usage                give a short usage message
  -V, --version              print program version

Mandatory or optional arguments to long options are also mandatory or optional
for any corresponding short options.

* The effect of each option marked with an asterisk is reversed if the option's
long name is prefixed with `no-'. For example, --no-cpp cancels --cpp.

Report bugs to .

我只列出我觉得有意思的几个参数:

-T输出函数调用树状图

-m指定需要分析的函数名

-n输出函数所在行号

-r输出调用的反向关系图

文本输出

最简单的使用方法是以ASCII文本的方式输出结果，比如

cflow -T -m -n timer.c

+-main() 
  +-ev_timer_init()
  +-timeout_cb() 
  | +-puts()
  | \-ev_break()
  +-ev_timer_start()
  \-ev_run()

然而，对于有一定代码量的项目，我们不会使用ASCII文本的方式去查看函数调用关系，因为调用是相当复杂的，而文本图并不适合人去理解。于是我们希望能cflow能产出一个可供其他软件转换成图片的格式的文件。可惜cflow并不支持，好在网上有开发者做了一个工具，可将其结果转换成dot格式。

转成dot文件

wget -c https://github.com/tinyclub/linux-0.11-lab/raw/master/tools/tree2dotx

cd /usr/bin
ln -s 【Your Path】/tree2dotx tree2dotx

具体的转换方法是

cflow -T -m -n timer.c > main.txt
cat main.txt | tree2dotx > main.dot

dot文件生成图片

我们需要借助graphviz（没有安装的可以使用apt-get install graphviz先安装）生成图片，指令是

dot -Tgif main.dot -o main.gif