Fix: Start Wasm table for the RTS at offset >= 1

[luc-blaeser]

Rust requires a table offset of at least 1 as the element index 0 is considered invalid and causes a debug null check to panic when called. On the other hand, elem[0] can be used by the Motoko backend code, as correct Rust-generated Wasm code does not call elem[0].

This bug is independent of wasm32 and wasm64.

This issue has been observed in https://github.com/dfinity/motoko/actions/runs/10703077671/job/29672766216?pr=4683 and happened only on Linux and only under nix-build (not nix-shell).

[github-actions]

Comparing from 5b36b8b to 6080b3f:
In terms of gas, no changes are observed in 5 tests.
In terms of size, no changes are observed in 5 tests.

[ggreif]

Why didn't the bytecode-verifier in the replica catch this? Do we have Motoko-compiled canisters out there with this bug baked-in?

[luc-blaeser]

Why didn't the bytecode-verifier in the replica catch this? Do we have Motoko-compiled canisters out there with this bug baked-in?

It is actually only a requirement by Rust, not Wasm. It only affects debug Rust compilation AFAIK. I believe people probably do not release debug Motoko code. So, probably it is okay.

[crusso]

LGTM

[ggreif]

Fine by me!

[luc-blaeser]

Thank you for the review, Claudio and Gabor!