swiftlang/swift

Build Debug versions of `swiftrt.o` (`swiftrtd.o`)

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#87468 opened on Feb 24, 2026

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Windowsgood first issueruntime

Description

Windows does not provide a stable ABI between debug and release mode. This requires that we provide a debug build of swiftrt.obj and adjust the driver to select the proper version of swiftrt.obj when linking. This should allow us to build in Debug configurations without running into _ITERATOR_DEBUG_LEVEL mismatches.

Contributor guide

Tech stack
swift
Domain
build systeminfrastructure
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
5
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Swift compiler build system knowledgeWindows ABI debuggingCMake build systemC++ runtime internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
15
Research direction
Investigate the current build of swiftrt.obj for Windows in the Swift repository. Look at the CMake files to understand how the runtime object is built and how the driver selects the version. Check for any existing debug configuration settings. The goal is to create a debug variant (swiftrtd.o) and modify the driver to link the appropriate version based on build configuration.