Fangrui Song 1b704e889f [MC,llvm-readobj,yaml2obj] Support CREL relocation format ...

CREL is a compact relocation format for the ELF object file format.

This patch adds integrated assembler support (using the RELA form)
available with `llvm-mc -filetype=obj -crel a.s -o a.o`.
A dependent patch will add `clang -c -Wa,--crel,--allow-experimental-crel`.

Also add llvm-readobj support (for both REL and RELA forms) to
facilitate testing the assembler. Additionally, yaml2obj gains support
for the RELA form to aid testing with llvm-readobj.

We temporarily assign the section type code 0x40000020 from the generic
range to `SHT_CREL`. We avoided using `SHT_LLVM_` or `SHT_GNU_` to
avoid code churn and maintain broader applicability for interested psABIs.
Similarly, `DT_CREL` is temporarily 0x40000026.

LLVM will change the code and break compatibility. This is not an issue
if all relocatable files using CREL are regenerated (aka no prebuilt
relocatable files).

Link: https://discourse.llvm.org/t/rfc-crel-a-compact-relocation-format-for-elf/77600

Pull Request: https://github.com/llvm/llvm-project/pull/91280

2024-07-01 10:32:02 -07:00

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