Any way to use swift-mmio without a dynamic memory allocator?

Development Embedded
,
1

Hello!

I'm trying to use swift-mmio, but I seem to be encountering some issues trying to build it for aarch64-none-none-elf without a memory allocator. I actually want to use Swift to write a memory allocator, so I can't really have one already.

I'm using SwiftPM to create a static library for the part of my project written in Swift, which does build successfully, but then I link that with the ARM cross-compiler to the assembly and C startup code, which... fails since I don't have a memory allocator. So I tried to build my Swift code with the build option -Xswiftc -no-allocations, since it worked with the Swift compiler, but that seems to fail too saying -no-allocations is only applicable with embedded Swift.

So now I don't really know what to do, I don't know if swift-mmio just doesn't work without a memory allocator, if my toolchain is misbehaving (happened before), or if I'm doing something wrong.

I know that in the swift-embedded-examples, the projects get built for *-apple-none-macho triples, so maybe the solution is an arm64-apple-none-macho build?, but for now I'm trying to get this one working.

My Package.swift:

// swift-tools-version: 6.0

import PackageDescription

let package = Package(
    name: "app",
    platforms: [
        .macOS(.v14),
    ],
    products: [
        .library(name: "appSwift", type: .static, targets: ["appSwift"]),
    ],
    dependencies: [
        .package(url: "https://github.com/apple/swift-mmio.git", branch: "swift-embedded-examples"),
    ],
    targets: [
        .target(
            name: "appSwift",
            dependencies: [
                .product(name: "MMIO", package: "swift-mmio"),
            ],
            path: "./src/swift",
            swiftSettings: [
                .enableExperimentalFeature("Embedded"),
                .unsafeFlags(["-wmo", "-no-allocations", "-disable-cmo", "-Xfrontend", "-gnone", "-Xfrontend", "-disable-stack-protector", "-no-allocations"])
            ]
        ),
    ]
)

My build command (working):
swift build --configuration release --verbose --triple aarch64-none-none-elf -Xswiftc -Xfrontend -Xswiftc -disable-stack-protector

Other build command (not working):
swift build --configuration release --verbose --triple aarch64-none-none-elf -Xswiftc -Xfrontend -Xswiftc -disable-stack-protector -Xswiftc -no-allocations

Lastly the file I'm trying to compile:

import MMIO

@_cdecl("asd")
public func asd(x: Int) -> Int {
    return x + 1
}

If I'm overlooking something trivial, I'm really sorry to bother y'all with this. I understand that both Swift Embedded and swift-mmio are in relatively early development, so they might have bugs or might not have certain features yet, which is totally fine, I just want to make sure if I should continue pursuing this at the moment or not.

Thanks for the help!

2

Sorry to hear you're hitting issues building, but the good news is that swift-mmio definitely does not need an allocator!

Could you share the link error you're seeing?

Also note that -Xswiftc passed to swift build affects both the host and target. This is important because the macros that power swift-mmio are built for the host.

3

Hi!
Sorry to have bothered you, I switched to the Swift 6.0.1 release toolchain, and now everything seems to be working fine.

Thanks for the help though! And thanks for your work on Swift!

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