Description

I was using the following command to build a Swift package for fuzzing before:

swift build -c debug -Xswiftc -sanitize=fuzzer,address -Xswiftc -parse-as-library

After updating to Xcode 15 this no longer works with the following error:

Building for debugging...
error: link command failed with exit code 1 (use -v to see invocation)
Undefined symbols for architecture arm64:
  "_Fuzz_main", referenced from:
      _main in command-line-aliases-file
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
[6/8] Linking Fuzz

I've tried 5.10-DEVELOPMENT-SNAPSHOT-2023-12-21-a and 6.0-DEVELOPMENT-SNAPSHOT-2024-08-08-a Swift builds.

If I switch to Xcode 14, which is a bit of a pain, since it's no longer supported on macOS 14, then everything works just fine again:

> swift build -c debug -Xswiftc -sanitize=fuzzer,address -Xswiftc -parse-as-library
Building for debugging...
ld: warning: undefined base symbol '_Fuzz_main' for alias '_main'
/Users/name/Documents/Fuzzing/.build/arm64-apple-macosx/debug/Fuzz: replacing existing signature
[6/6] Applying Fuzz
Build complete! (12.94s)

Reproduction

Download the latest Swift snapshot from https://www.swift.org/download/#snapshots Version 5 or 6, doesn't matter.

Create an empty SPM project with the following Package.swift:

// swift-tools-version: 5.7

import PackageDescription

let package = Package(
    name: "Fuzzer",
    targets: [
        .executableTarget(name: "Fuzz"),
    ]
)

and main.swift:

import Foundation

@_cdecl("LLVMFuzzerTestOneInput") public func fuzz(ptr: UnsafePointer<CChar>, size: CInt) -> CInt {
    return 0
}

Whole package: FuzzingSample.zip

Select the required Swift version using swiftenv, like:

swiftenv local 5.10-DEVELOPMENT-SNAPSHOT-2023-12-21-a

Run:

swift build -c debug -Xswiftc -sanitize=fuzzer,address -Xswiftc -parse-as-library

Expected behavior

An ability to fuzz Swift code using libFuzzer.

Environment

Apple Swift version 5.10-dev (LLVM e8e5be8d5b39f46, Swift 935dc3eae905669)
Target: arm64-apple-macosx14.0

Xcode 15.4 (15F31d)
macOS 14.5 (23F79)

Additional information

No response