1. `readlink` does not append a null at the end, so strncpy can't be used.

2. The `buf` may not end with a null, so strstr and strcmp also can't be used.

3. Concatenating `cwd` and `path` is incorrect, which get a string like
`/home/xx/proc/778/exe`. The correct approach is to concatenate `cwd` with the
first string in `cmdline`.

4. Support `box64 test_app`, which is actually a relative path but does not
start with a dot in `cmdline`.