Add #objectFormat compilation conditional (SE-0492) #80212

kubamracek · 2025-03-21T20:39:32Z

This implements the relevant part of the "Section Placement" proposal (draft: https://github.com/kubamracek/swift-evolution/blob/section-placement-control/proposals/0nnn-section-control.md, forum thread: https://forums.swift.org/t/pitch-3-section-placement-control/77435). Namely the ability to conditionalize on the object file format that the compiler is targeting (MachO, ELF, COFF of Wasm).

Adding with an underscored name (#_objectFileFormat) until the proposal is codified.

rdar://147505228

kubamracek · 2025-03-21T20:40:24Z

@swift-ci please test

compnerd · 2025-03-21T22:10:16Z

lib/Basic/LangOptions.cpp

Can we rewrite this as:

addPlatformConditionValue(PlatformConditionKind::ObjectFileFormat, llvm::StringSwitch<llvm::Triple::ObjectFormatType>(Target.getObjectFormat()) .Case(llvm::Triple::COFF, "COFF") .Case(llvm::Triple::ELF, "ELF") .Case(llvm::Triple::MachO, "MachO") .Case(llvm::Triple::Wasm, "Wasm"));

Hm, not really, because we're not switching over strings here, but over the enum cases... I could do a regular switch, but that reads worse than the chain of ifs:

StringRef FileFormatName; switch (Target.getObjectFormat()) { case llvm::Triple::COFF: FileFormatName = "COFF"; break; case llvm::Triple::ELF: FileFormatName = "ELF"; break; case llvm::Triple::MachO: FileFormatName = "MachO"; break; case llvm::Triple::Wasm: FileFormatName = "Wasm"; break; default: break; } if (!FileFormatName.empty()) { addPlatformConditionValue(PlatformConditionKind::ObjectFileFormat, FileFormatName); }

The covered switch would make it easier to identify new cases though I think. It is more that I am after a switch rather than a series of cascading if conditions.

kateinoigakukun · 2025-03-22T02:17:05Z

Should we consider gating this behind an experimental feature flag?

kubamracek · 2025-03-22T03:08:50Z

I'm happy to do that if we deem that necessary, though all the other existing not-yet-ratified compilation conditions (e.g. pointerBitWidth) don't do that and just use an underscore.

kubamracek · 2025-03-22T20:10:55Z

swiftlang/swift-syntax#3027

@swift-ci please test

grynspan · 2025-03-23T16:09:07Z

Should we consider gating this behind an experimental feature flag?

Swift Testing will need to make use of this to support Embedded Swift, and requiring an experimental flag will make it more difficult to do so. (When it gets formally featurized, we can eagerly adopt the final version.)

grynspan · 2025-03-23T16:06:35Z

lib/Basic/LangOptions.cpp

Can we add an else clause here that diagnoses the target is unknown? That way if we add a new port, we'll know to update this code.

kubamracek · 2025-03-24T17:54:55Z

@swift-ci please test

kubamracek · 2025-03-24T17:55:31Z

swiftlang/swift-syntax#3027

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kubamracek · 2025-03-24T22:07:29Z

swiftlang/swift-syntax#3027

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kubamracek · 2025-03-27T23:09:15Z

@swift-ci please test

kubamracek · 2025-03-29T17:01:10Z

@swift-ci please test

kubamracek · 2025-03-30T04:27:55Z

@swift-ci please test

grynspan · 2025-03-30T13:00:11Z

Are there any other object formats that LLVM supports? Should we add cases for them even if Swift itself hasn't added toolchain support?

Edit: The following are all the cases in the object format enum in the Swift repo:

  enum ObjectFormatType {
    UnknownObjectFormat,

    COFF,
    DXContainer,
    ELF,
    GOFF,
    MachO,
    SPIRV,
    Wasm,
    XCOFF,
  };

So it may make sense to just switch over the whole enum (with getObjectFormat()).

kubamracek · 2025-03-31T16:38:19Z

@swift-ci please test

kubamracek · 2025-03-31T17:03:51Z

Are there any other object formats that LLVM supports? Should we add cases for them even if Swift itself hasn't added toolchain support?

Edit: The following are all the cases in the object format enum in the Swift repo:
  enum ObjectFormatType {
    UnknownObjectFormat,

    COFF,
    DXContainer,
    ELF,
    GOFF,
    MachO,
    SPIRV,
    Wasm,
    XCOFF,
  };
So it may make sense to just switch over the whole enum (with getObjectFormat()).

I think it's probably undesirable to go beyond the 4 object file formats that Swift targets today, because (1) we'd have to lock down the specific spelling of those and (2) it would suggest that the compiler is actually capable of producing valid object files in these formats, but that's almost certainly not true until someone actively builds that support.

kubamracek · 2025-04-01T02:15:05Z

@swift-ci please test

kubamracek · 2025-04-01T13:46:58Z

@swift-ci please test macOS platform

kubamracek · 2025-04-07T17:36:01Z

@swift-ci please test

compnerd · 2025-04-08T23:46:25Z

it would suggest that the compiler is actually capable of producing valid object files in these formats, but that's almost certainly not true until someone actively builds that support.

I don't know if I agree here. However, we do in a number of places currently just abort if you use a different object file format. Some of these are unlikely to ever be supported (e.g. DXContainer and SPIRV), so adding the full coverage really doesn't add much value, but does add noise.

kubamracek · 2025-10-16T22:32:58Z

swiftlang/swift-syntax#3170
@swift-ci please test

DougGregor · 2025-10-16T23:05:54Z

include/swift/AST/PlatformConditionKinds.def

 PLATFORM_CONDITION_(HasAtomicBitWidth, "hasAtomicBitWidth")

+/// The active target's file format (Mach-O, ELF, COFF, WASM)
+PLATFORM_CONDITION_(ObjectFileFormat, "objectFormat")


No need for the underscore here?

mikeash · 2025-10-17T14:09:28Z

test/Parse/ConditionalCompilation/object_file_format.swift

+// RUN: %swift -typecheck %s -verify -target x86_64-unknown-windows-msvc -parse-stdlib
+// RUN: %swift-ide-test -test-input-complete -source-filename=%s -target arm64-apple-macos
+
+#if objectFormat(MachO) || objectFormat(ELF) || objectFormat(Wasm) || objectFormat(COFF)


Would be good to have this check each one separately and somehow have each RUN line check that it selected the right one. This would detect it if someone managed to accidentally make it always be true or always false.

…ecisely

kubamracek · 2025-10-22T17:39:18Z

swiftlang/swift-syntax#3170
@swift-ci please test

kubamracek · 2025-10-23T02:38:57Z

swiftlang/swift-syntax#3170
@swift-ci please test macOS platform

DougGregor · 2025-10-23T03:03:44Z

lib/ASTGen/Sources/ASTGen/CompilerBuildConfiguration.swift

  }

+  func isActiveTargetObjectFormat(name: String) throws -> Bool {
+    try staticBuildConfiguration.isActiveTargetObjectFormat(name: name)


It doesn't really matter, but I would expect this never to throw, because it's just querying the static build configuration

kubamracek · 2025-10-23T14:35:01Z

@swift-ci please test

kubamracek requested review from DougGregor, ahoppen, eeckstein, jckarter, mikeash, phausler and zoecarver March 21, 2025 20:39

kubamracek requested review from CodaFi, bnbarham, hamishknight, hborla, rintaro, slavapestov and xedin as code owners March 21, 2025 20:39

compnerd reviewed Mar 21, 2025

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kubamracek requested review from MaxDesiatov and kateinoigakukun March 22, 2025 01:59

kubamracek mentioned this pull request Mar 22, 2025

[SwiftSyntax] Add #_objectFileFormat compilation conditional swiftlang/swift-syntax#3027

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grynspan reviewed Mar 23, 2025

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kateinoigakukun approved these changes Mar 23, 2025

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kubamracek force-pushed the object-file-format branch from ea66110 to 4b27ab7 Compare March 24, 2025 17:54

kubamracek requested review from artemcm and tshortli as code owners March 24, 2025 17:54

kubamracek force-pushed the object-file-format branch from 4b27ab7 to 7ee3e63 Compare March 24, 2025 22:07

kubamracek force-pushed the object-file-format branch from 7ee3e63 to 5544dc5 Compare March 29, 2025 17:00

kubamracek force-pushed the object-file-format branch from 5544dc5 to 65a496f Compare March 30, 2025 04:27

Add #objectFormat compilation conditional (SE-0492)

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kubamracek force-pushed the object-file-format branch from 65a496f to c3f865b Compare October 16, 2025 22:32

kubamracek changed the title ~~Add #_objectFileFormat compilation conditional~~ Add #objectFormat compilation conditional (SE-0492) Oct 16, 2025

DougGregor approved these changes Oct 16, 2025

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mikeash approved these changes Oct 17, 2025

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Adjust PlatformConditionKinds.def + target #objectFormat test more pr…

4923db8

…ecisely

DougGregor approved these changes Oct 23, 2025

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kubamracek enabled auto-merge October 23, 2025 14:35

kubamracek merged commit 66eef68 into swiftlang:main Oct 23, 2025
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Add #objectFormat compilation conditional (SE-0492) #80212

Add #objectFormat compilation conditional (SE-0492) #80212

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