Question

I am writing an ELF analyzer, but I’m having some trouble converting endianness properly. I have functions to determine the endianness of the analyzer and the endiannness of the object file.

Basically, there are four possible scenarios:

1. A big endian compiled analyzer run on a big endian object file
   • nothing needs converted
2. A big endian compiled analyzer run on a little endian object file
   • the byte order needs swapped, but ntohs/l() and htons/l() are both null macros on a big endian machine, so they won’t swap the byte order. This is the problem
3. A little endian compiled analyzer run on a big endian object file
   • the byte order needs swapped, so use htons() to swap the byte order
4. A little endian compiled analyzer run on a little endian object file.
   • nothing needs converted

Is there a function I can use to explicitly swap byte order/change endianness, since ntohs/l() and htons/l() take the host’s endianness into account and sometimes don’t convert? Or do I need to find/write my own swap byte order function?

Answer 1

Do I need to find/write my own swap byte order function?

Yes you do. But, to make it easy, I refer you to this question: How do I convert between big-endian and little-endian values in C++? which gives a list of compiler specific byte order swap functions, as well as some implementations of byte order swap functions.