Support R_ARM_PREL31 relocation

[dcoles]

Describe the enhancement you're suggesting.

LLVM generates R_ARM_PREL31 relocations for .ARM.exidx.* symbols for section unwinding. This is needed to support features like Rust's panic = "unwind" and C++ exception unwinding.

The workaround is to set panic = "abort" for Rust programs and -fno-exceptions flag for C++, so the program will immediately abort instead of trying to unwind the stack.

This is not a critical issue now that #1850 has been merged, but it would still be nice to support eventually.

Anything else?

I might take a look at implementing this in the future, but since abort and exceptions typically just trigger furi_crash, it's not particularly urgent.

[hedger]

Reference implementation: https://opensource.apple.com/source/gdb/gdb-768/src/bfd/elf32-arm.c.auto.html, look for R_ARM_PREL31.

[DrZlo13]

I don't think it's a thing worth wasting time on. Stack unwinding takes up a lot of valuable memory, which increases load time and makes it impossible to write large programs.

It also requires writing support libraries for stack unwinding, AFAIK.

[skotopes]

Yep, clearly not for embed.

[dcoles]

Thanks for the feedback. I'll keep an eye out if I see anything else that generates R_ARM_PREL31 relocations.