bin/59360: ld.elf_so(8): missing RELR support

[campbell+netbsd%mumble.net@localhost]

>Number:         59360
>Category:       bin
>Synopsis:       ld.elf_so(8): missing RELR support
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Apr 26 16:00:00 +0000 2025
>Originator:     Taylor R Campbell
>Release:        current
>Organization:
The PackedBSD Relocation Elves, Inc.
>Environment:
>Description:
The RELR format is a compact format for R_*_RELATIVE-type relocations that dramatically reduces the size of relocation sections, which directly saves disk space and memory, and indirectly saves load time by reducing I/O and memory transactions.

No formal reference in the ELF gABI yet (https://www.sco.com/developers/gabi/latest/ch4.sheader.html) but here's a large dump of information about the background, motivation, and format:

https://maskray.me/blog/2021-10-31-relative-relocations-and-relr

GNU ld supports generating these sections on i386, amd64, amd64-with-ilp32, and powerpc64, with -Wl,-z,pack-relative-relocs.
>How-To-Repeat:
XXX add a simple test case that illustrates ld.elf_so's missing support for RELR
>Fix:
Yes, please!