Stream: git-wasmtime

Topic: wasmtime / PR #14985 cranelift-object: share Mach-O secti...

Wasmtime GitHub notifications bot (Oct 25 2026 at 09:45):

faysou opened PR #14985 from faysou:cranelift-object-macho-shared-custom-sections to bytecodealliance:main:

Problem

ObjectModule::define_data calls add_section for every data object that has a custom section. A Mach-O object holds at most 255 sections, so ObjectProduct::emit fails with Too many sections: 0x12d once a module defines more data objects than that.

This happens in practice with rustc_codegen_cranelift on aarch64 macOS: every inventory::submit! static goes into __DATA,__mod_init_func, and building nautilus-model hits the limit.

Change

On Mach-O, reuse an existing section when segment, name, SectionKind, and Mach-O flags all match, as LLVM does when it merges sections with the same name. ELF and COFF output is unchanged.

Testing

• New macho_data_objects_share_custom_section in cranelift/object/tests/basic.rs: defines 300 objects in __DATA,__mod_init_func,mod_init_funcs plus one in a second custom section, then checks there is exactly one section of each with the expected size and section type. It fails without the fix (Too many sections: 0x12d) and passes with it.
• cargo test -p cranelift-object, cargo fmt --check, and cargo clippy -p cranelift-object --all-targets pass.
  

Wasmtime GitHub notifications bot (Oct 25 2026 at 09:45):

faysou removed the review request for wasmtime-compiler-reviewers from PR #14985.

Wasmtime GitHub notifications bot (Oct 25 2026 at 09:45):

faysou requested fitzgen for a review on PR #14985.

Wasmtime GitHub notifications bot (Oct 25 2026 at 09:45):

faysou requested wasmtime-compiler-reviewers for a review on PR #14985.

Wasmtime GitHub notifications bot (Oct 25 2026 at 11:44):

github-actions[bot] added the label cranelift on PR #14985.

Wasmtime GitHub notifications bot (Oct 25 2026 at 11:44):

github-actions[bot] added the label cranelift:module on PR #14985.

Wasmtime GitHub notifications bot (Oct 26 2026 at 13:15):

:memo: bjorn3 submitted PR review.

Wasmtime GitHub notifications bot (Oct 26 2026 at 13:15):

:speech_balloon: bjorn3 created PR review comment:

            if self.object.format() == BinaryFormat::MachO
                && let Some(&section) = self.macho_custom_sections.get(&(segment.clone(), section.clone(), kind, macho_flags.0))

Wasmtime GitHub notifications bot (Oct 26 2026 at 13:15):

:memo: bjorn3 submitted PR review.

Wasmtime GitHub notifications bot (Oct 26 2026 at 13:15):

:speech_balloon: bjorn3 created PR review comment:

LLVM emits an error when a section is defined twice with different flags.

Wasmtime GitHub notifications bot (Oct 26 2026 at 13:16):

:speech_balloon: bjorn3 deleted PR review comment.

Wasmtime GitHub notifications bot (Oct 26 2026 at 14:00):

faysou updated PR #14985.

Wasmtime GitHub notifications bot (Oct 26 2026 at 14:01):

:memo: faysou submitted PR review.

Wasmtime GitHub notifications bot (Oct 26 2026 at 14:01):

:speech_balloon: faysou created PR review comment:

Thanks, switched to a let-chain. The insert below now checks the format directly too, since there's no optional key anymore.

Wasmtime GitHub notifications bot (Oct 26 2026 at 14:03):

:memo: bjorn3 submitted PR review.

Wasmtime GitHub notifications bot (Oct 26 2026 at 14:03):

:speech_balloon: bjorn3 created PR review comment:

Can you inline this to avoid the clones outside Mach-O?

Wasmtime GitHub notifications bot (Oct 26 2026 at 14:43):

faysou updated PR #14985.

Wasmtime GitHub notifications bot (Oct 26 2026 at 14:43):

:memo: faysou submitted PR review.

Wasmtime GitHub notifications bot (Oct 26 2026 at 14:43):

:speech_balloon: faysou created PR review comment:

Done. The lookup key is now built inside the let-chain, and the insert key is built only for Mach-O before add_section takes ownership of the names.

Last updated: Oct 31 2026 at 23:03 UTC