[klee-dev] KLEE behaviour with function call to uclibc

[Dan Liew]

On 27 May 2017 at 01:36, Shehbaz Jaffer <shehbaz.jaffer at mail.utoronto.ca> wrote:
> Hello KLEE developers,
>
> I am trying to understand how KLEE emulates environment variables. In particular, how do functions like getopt_long get executed with KLEE, when we give --sym-arg as an argument. getopt_long is found in unistd.h, and is available in uclibc. For a coreutils file like groups.c where the following line is encountered:
>
> while ((optc = getopt_long (argc, argv, "", longopts, NULL)) != -1)
>
> how would KLEE generate different inputs? for simplicity, consider the case where we use --sym-arg 1 10 as a command line argument which leads to argv[1] becoming a symbolic buffer of size 10, if my understanding is correct, when getopt_long is called, one of the two things can happen:
>
> 1) argv[1] is declared as a symbolic buffer, we explore all paths of getopt_long code in uclibc library, so all different if's / elses in getopt_long code will get forked and execute to give different optc values.
> 2) getopt_long is skipped, optc variable is made symbolic, and the main function in groups.c treats optc as symbolic value. on any successive if/else condition in groups.c containing optc, a new state is forked with new value of optc.

Take a look at the `klee_init_env()` function [1]. When KLEE is called
with --posix-runtime the program's `main()` is rewritten to call
`klee_init_env()` at the beginning and change `argc` and `argv`.
The `klee_init_env()` function introduces symbolic arguments if
requested. From that point onwards execution of the program just
proceeds as normal so `getopt_long()` will just be interpreted by KLEE
just like any other function.

[1] https://github.com/klee/klee/blob/bec4ceafe412a08de303678581e07451a1399e1f/runtime/POSIX/klee_init_env.c#L85