Differences between dcc/objdump and nios2-elf-gcc/nios2-elf-objdump?

As I asked earlier, what are you actually trying to do?

Various commands will give some of that information.

Maybe you don't actually need other parts.

I've never really worried about structure member offsets - even though I often look at hexdumps of structures.

If you are putting code through several compilers, it can be worth doing a compile-time check of the sizes of shared structures - but the numbers are usually irrelevant.

If you are feeling adventurous look into the gcc/gdb code/docs and work out the format of the debug sections.