This replaces multiple uses of `std::vector::operator[]` where the
parameter is a constant `0` with the use of C++11's `std::vector::data`
method. This fixes the root cause of invalid memory accesses.
`std::vector::operator[]` is an unchecked memory access, and when the
buffers are zero-sized (that is the buffer container is empty) either
due to a 0 padding in the case of elfloader or NULL parameters to
syscalls where permitted, the unchecked access may cause an invalid
memory access. The use of `std::vector::data` is permitted even in such
a case, though the returned memory may not be dereferenced. The general
usage of the returned pointer is to pass to `memif_t`, which is careful
about 0-sized buffer accesses, and so passing the result of
`std::vector::data` is safe. This is theoretically a better access
pattern as it also avoids having the compiler to re-materialize the
pointer from the de-referenced location.
Andrew Waterman
Saleem Abdulrasool