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Merged
merged 7 commits into from
Sep 26, 2023
Merged

[embedded] Add a simple Swift runtime, written in embedded Swift #68735

merged 7 commits into from
Sep 26, 2023

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kubamracek
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This PR adds a mini Swift runtime to be used in embedded Swift to support heap allocations and deallocations of reference types (classes), reference counting of those, and lazy initialization of global and static variables (swift_once). The runtime is an alternative implementation, separate from the main Swift runtime, and it's entirely written in embedded Swift (!). The initial version is only suitable for strictly single-threaded use (plan is to fix that soon).

The PR also introduces a slightly different model of distribution and use of this runtime (compared to libswiftCore.a/libswiftCore.dylib on mainstream OS's) -- it's bundled into the embedded standard library module, with the expectation that dead-code elimination is going to take care of any unused runtime functionality. To make this work, SILLinker needs to explicitly bring the runtime functions in when building client code (otherwise the functions appear unused at the SIL level). The result is that a single WMO compiler invocation of an embedded Swift app/firmware is going to produce a standalone binary with the necessary runtime support already included, no need to link any extra libraries:

$ swiftc my_firmware.swift -enable-experimental-feature Embedded -wmo -c -o my_firmware.o
$ nm -m my_firmware.o | grep undefined
... no external dependencies beyond basic C functions like malloc/free/memset/etc. ...

The added embedded/runtime.swift test demonstrates that.

@kubamracek kubamracek changed the title [embedded] Add a simple Swift runtime, written is embedded Swift [embedded] Add a simple Swift runtime, written in embedded Swift Sep 24, 2023
@kubamracek kubamracek requested a review from phausler September 24, 2023 19:36
@kubamracek kubamracek added the embedded Embedded Swift label Sep 24, 2023
eeckstein
eeckstein reviewed Sep 25, 2023
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nice!

al45tair
al45tair approved these changes Sep 25, 2023
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:-) Very nice. Looking forward to the day when we can migrate the main runtime to Swift too.

@kubamracek kubamracek requested a review from etcwilde September 25, 2023 17:33
@kubamracek kubamracek force-pushed the embedded-runtime branch 2 times, most recently from 4f414f6 to 5865fd8 Compare September 26, 2023 02:50
@kubamracek
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@swift-ci please test

@kubamracek
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@swift-ci please test

eeckstein
eeckstein reviewed Sep 26, 2023
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stdlib/public/core/EmbeddedRuntime.swift
}

@_cdecl("swift_slowDealloc")
public func swift_slowDealloc(_ ptr: UnsafeMutableRawPointer?, _ size: Int, _ alignMask: Int) {
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Are you going to add the DO_NOT_FREE_BIT here, too?

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I don't think it should go here...? I thought swift_slowDealloc is not used on refcounted objects, and only used to implement things like UnsafePointer.deallocate(). This matches how swift_slowDealloc is implemented in the main runtime (no checking of anything, just a direct call to free).

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Ah sorry, I meant to add this comment for swift_deallocClassInstance

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Aha, then yes -- let me do that as a follow-up in https://github.com/apple/swift/pull/68754/files, I'll rebase it on top of this Swift runtime.

mikeash
mikeash approved these changes Sep 26, 2023
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Very cool!

zoecarver
zoecarver reviewed Sep 26, 2023
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stdlib/public/core/EmbeddedRuntime.swift
@@ -0,0 +1,132 @@
//===----------------------------------------------------------------------===//
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Super cool that you can just put this into the stdlib!

zoecarver
zoecarver approved these changes Sep 26, 2023
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This is super awesome to see!

@kubamracek kubamracek merged commit 125343d into swiftlang:main Sep 26, 2023
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@al45tair al45tair al45tair approved these changes

@eeckstein eeckstein eeckstein left review comments

@mikeash mikeash mikeash approved these changes

@zoecarver zoecarver zoecarver approved these changes

@phausler phausler Awaiting requested review from phausler

@etcwilde etcwilde Awaiting requested review from etcwilde

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5 participants
@kubamracek @mikeash @al45tair @zoecarver @eeckstein