e_flags field for ILP32-on-RV64 about riscv-elf-psabi-doc HOT 2 OPEN

Will a similar flag eventually be needed for ILP64-on-RV128? What would the behavior be if both are set on an RV128 binary? (32-only and 64-only seem self-explanatory, but should both be an error, or use the smaller?)

EDIT: Realized I misparsed the original statement (ILP32-on-RV64 would use ELFCLASS32, and a flag to say "runs on RV64"), so the ILP32-on-RV128 case is actually the interesting one.

In that case, it's a choice between it being an error, and enforcing the larger of the two, as well as specifying what it means if the flag is set on an ELFCLASS128 image, or if the wrong one of the two (presumptive) flags is set on an ELFCLASS64 image.

from riscv-elf-psabi-doc.

One possibility is that RV128 might never use ELF128, i.e., all code and static data for both the program and shared libraries would be in the lower 2^64 bytes, with only parts of the heap above 2^64. So there would be 3 possibilities for an ELF64 binary: RV64-LP64, RV128-LP64, and RV128-LP128.

Anyway, the RV128 ISA isn't even frozen yet :)

from riscv-elf-psabi-doc.