Introduction

Syntastic is a syntax checking plugin for Vim that detects syntax errors using external tools and return them back in Vim. I use it in in C++ development and it works pretty well. But to get started with syntastic in every project, I have to do some setup at first (How to setup syntastic in C++ development). Basically, I have to add a .syntastic_cpp_config file in the root path of the project that contains the include paths, such as -I/usr/include or -I$(project)/include/.

It’s a pretty simple task, but things will get worse when it comes to a huge project with a tree structure Makefiles/CMakeLists distributed in sub directories. Moreover, since all we need are in these Makefiles, why bother to read these files again?

Get Started

Well, I start thinking of a way to automate this. A straightforward idea is to track all subprocesses and analysis the passed-in parameters if it’s gcc. To get started, I tried pstree. It’s easy to get executing parameters using pstree -a, like below:

sshd -D
  ├─sshd
  │   └─sshd
  │       └─bash
  │           └─screen -r blog
  └─sshd

However, it’s hard to to live tracking the process in this way. Then my Linux guru friend suggested me to give a shot with strace. I used strace before to do error debugging and code analysis, but to be honestly, I didn’t think about it in this problem. The truth is, strace provides a very elegant one-liner solution:

strace -eexecve -s 200 -o output -f make
simple output:
1370 execve("/bin/mkdir", ["mkdir", "-p", "x86_64-linux-gcc"], [/* 63 vars */]) = 0
1269 execve("/usr/bin/ld", ["/usr/bin/ld", "--eh-frame-hdr", "--build-id", "-m", "elf_x86_64", "--hash-style=gnu", "-dynamic-linker", "/lib64/ld-linux-x86-64.so.2", "-o", "x86_64-linux-gcc/quotefeed",  "/usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../lib64/crti.o", "/usr/lib/gcc/x86_64-redhat-linux/4.4.7/crtbegin.o", "-L/usr/lib64” /* omit more words by mylsef*/], [/* 69 vars */]) = 0

The syntax is just strace [command args] but a lot additional options are provided:

To know more about strace, just read the man page and “strace Wow Much Syscall “ by Brendan Gregg

With the powerful strace, we could have a two-line solution that meet our basic requirements:

strace -eexecve -s 200 -o output -f make
perl -ne 'while(m/(-I.*?)",/g) {print "$1\n";}' output | sort | uniq > .syntastic_cpp_config

About the regex, here is a explanation example, the key is to use non-greedy match and lookahead assertion.

Improve

One problem is there are sometimes relative path in Makefile in subdirectories. To overcome this, we trace getcwd systemcall as well and map them to execve tracing result based on pid. The final solution is in python and provided here. The usage is pretty simple, instead of running make, run autosyntastic make and a .syntastic_cpp_config will show up in the current directory.

One importatn thing to know is strace will significantly slow down the performance. Therefore, I suggest run autosyntastic only during setup.

Final words

Tracing is very interesting and a lot of fun. I introduced perf and systemtap before, which are also powerful tracking tools. I feel that with learning of different tracking tools, I could gradually understand performance better, understand programming better and even understand kernel better. With the comming of Linux 4.0, more and more tracing tools and apis will be available. Well, more to learn and long way to the top!