Add (draft) ELF128 definitions

[michaeljclark]

ELF128

There needs to be some discussion around how ELF is mapped to 128-bit, given that there may be ABI variants, and there is a distinction between 128-bit integrals vs 128-bit pointers. i.e. An ELF128 ABI could potentially have an 'offset' concept that is a compact memory representation of a 'pointer' relative to some base pointer.

e.g. define Elf128_Off as u64 as this represents an offset within the ELF image, and likewise define Elf128_Xword and Elf128_Sxword as u64 and s64 respectively, as these are used for segment sizes.

This proposed typing based on ELF64 only promotes the Addr type to 128. Linkers and link loaders may store 'offsets' relative to some reference address. e.g. start of segment.

Draft Elf128 types

• typedef u128 Elf128_Addr;
• typedef u16 Elf128_Half;
• typedef u64 Elf128_Off;
• typedef s32 Elf128_Sword;
• typedef u32 Elf128_Word;
• typedef u64 Elf128_Xword;
• typedef s64 Elf128_Sxword;
• typedef u8 Elf128_Byte;

[michaeljclark]

Added ELFCLASS128 = 3 however the types and structures have not yet been defined.