ci: Compile capnproto with GCC in gnu32 job #383

pull xyzconstant wants to merge 1 commits into bitcoin-core:master from xyzconstant:2026-10-26-fix-gnu32-job-abi-mismatch changing 1 files +6 −1

xyzconstant commented at 11:18 PM on October 27, 2026: contributor

The gnu32 job segfaulted in #382 because of an i686 ABI mismatch between Clang-compiled libkj (the nixpkgs default for capnproto) and GCC-compiled libmultiprocess.

Clang and GCC handle empty struct arguments differently on i686: Clang omits them, while GCC reserves a stack slot.

When the fn.invoke() call in the PassField overload for Proxy.Context fails with an uncaught exception, kj::str(exception) calls kj::operator*(kj::_::Stringifier, const kj::Exception&) with Stringifier as an empty struct. As a result, the Clang-compiled callee reads Exception& from the stack slot reserved by the GCC-compiled caller for Stringifier, thereby causing an invalid read.

This PR builds capnproto with GCC in the gnu32 job, so both sides agree on the layout.

The same crash happened in #218, where it was worked around with getDescription().

ci: Compile capnproto with GCC in gnu32 job

In the gnu32 job, capnproto (libkj) is compiled with Clang while
libmultiprocess is compiled with GCC, but they handle empty structs
differently on i686. Clang omits them, while GCC reserves a stack slot
for them.

This causes a segfault in calls to functions like
`kj::str(kj::Exception)`, which internally pass an empty `Stringifier`
object.

This commit fixes the issue by compiling capnproto with the same
toolchain as libmultiprocess (GCC) when i686 is detected in shell.nix.

04a0465d67

DrahtBot commented at 11:18 PM on October 27, 2026: none



The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.



Reviews

See the guideline and AI policy for information on the review process.

Type Reviewers

ACK Sjors

If your review is incorrectly listed, please copy-paste <code></code> into the comment that the bot should ignore.
Sjors commented at 2:33 AM on October 28, 2026: member

Using consistent toolchains makes sense in general.

ACK 04a0465d67a58040013c74dbb92e0f7a0572cc0e

Type	Reviewers
ACK	Sjors

Contributors

xyzconstant

DrahtBot

Sjors

Linked (view graph)

#218 Better error and log messages #382 proxy-server: Reject `destroy()` during active calls and calls after `destroy()`

ci: Compile capnproto with GCC in gnu32 job #383

Reviews