swiftlang/swift-package-manager

dsymutil emits warnings with experimental lto mode

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#6890 opened on Sep 12, 2023

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bughelp wanted

Description

When using --experimental-lto-mode=full dsymutil complains about not being able to find (intermediate?) object files created during the LTO process. Example:

$ git clone git@github.com:apple/swift-nio.git
$ cd swift-nio
$ swift build --configuration release --experimental-lto-mode=full --verbose
warning: (arm64) /tmp/lto.o unable to open object file: No such file or directory
warning: (arm64)  could not find object file symbol for symbol _$sSo14_sa_DoubleWordaMa
warning: (arm64)  could not find object file symbol for symbol _$sSo14_sa_DoubleWordaMaTm
...

Contributor guide

Tech stack
swift
Domain
build systemcli
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Swift programmingSwift package manager usageBasic understanding of LTO
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
Investigate how the swift build command handles LTO mode and passes object files to dsymutil. Check the CI logs for similar warnings. Look at the BuildOptions handling in the Swift Package Manager source code to see if there is a missing step to preserve LTO object files.