Driver: prevent C++ runtime linkage #26110

compnerd · 2019-07-12T15:51:57Z

Replace this paragraph with a description of your changes and rationale. Provide links to external references/discussions if appropriate.

Resolves SR-NNNN.

compnerd · 2019-07-12T15:52:04Z

CC: @jrose-apple

compnerd · 2019-07-12T15:52:11Z

@swift-ci please test

jrose-apple · 2019-07-12T15:54:48Z

lib/Driver/UnixToolChains.cpp

+  // `--as-needed` however that breaks other Unix semantics of linking where
+  // the dependency on the library is not visible to the linker should still be
+  // linked upon request).
+  Arguments.push_back("-nostdlib++");


Where does the C++ runtime get linked, then?

Why would you need the C++ runtime? Swift doesn't yet allow importing C++, so there is no dependency from any Swift code on the C++ runtime. If you are worried about the standard library, that explicitly links in C++ mode using clang++ rather than the swift driver (separate issue). If you have dependencies which rely on C++, they will be linked against the C++ runtime.

On android you should be linking against stl_port (or if you are targeting something in the future, libc++). On Linux, you should be linking against libstdc++ unless you are running a custom closed environment that is libc++ based. On Windows, you should be linking against msvcprt unless you are using libc++ across your application. On Darwin, you should link against libc++. Because you have multiple options based on the target, we need to either make this explicit from the user at some point. But, given that we currently do not support importing C++ code, I think that we can deal with that issue when the time comes.

Just chiming in here- I don't know enough about this to have a strong opinion either way, but I did notice I have to add -Xclang-linker -nostdlib++ to swiftc invocations to prevent libc++ being linked for Swift(-only) binaries on Android with recent compiler versions.

Adding the flag doesn't seem to have any negative effect, but again, I'm far from an expert at this. There's a reason for everything :)

I was thinking about static linking, but I think that's already covered with an explicit -lc++ and I just forgot. Sorry for the distraction!

swift-ci · 2019-07-12T16:31:09Z

Build failed
Swift Test Linux Platform
Git Sha - 38afc15ee79cfabeb6d08d2c21caf65d9278f9a7

compnerd · 2019-07-13T03:43:00Z

Hmm, I think that it is falling back to the system clang which may be older than 7.0 which introduced the flag. I'm not sure what the best way to handle this is. I guess I can restrict this to just android for the time being, though this should apply equally to all Unices.

compnerd · 2019-07-13T03:53:06Z

@swift-ci please test

swift-ci · 2019-07-13T03:55:49Z

Build failed
Swift Test OS X Platform
Git Sha - a4336f8e6847682cd10b25f579e81fc4a5ea26f5

swift-ci · 2019-07-13T04:17:55Z

Build failed
Swift Test Linux Platform
Git Sha - a4336f8e6847682cd10b25f579e81fc4a5ea26f5

compnerd · 2019-07-13T04:23:27Z

@swift-ci please test

swift-ci · 2019-07-13T04:23:43Z

Build failed
Swift Test Linux Platform
Git Sha - a4336f8e6847682cd10b25f579e81fc4a5ea26f5

swift-ci · 2019-07-13T04:23:57Z

Build failed
Swift Test OS X Platform
Git Sha - a4336f8e6847682cd10b25f579e81fc4a5ea26f5

gwynne · 2019-07-14T22:55:21Z

My take is to merge this as is for now, with the caveat that it absolutely shouldn't be left this way any longer than it needs to be. The stopgap is, I think, worth it.

jrose-apple · 2019-07-15T16:13:29Z

Another option: go down to clang instead of clang++ to link. https://reviews.llvm.org/D35780

compnerd · 2019-07-15T16:23:50Z

@jrose-apple - yeah, I did consider that, but that means that we also loose out on -lm. Its unclear whether that is worth the effort of trying to make the clang++ driver work right now. Going to update the patch to do that instead.

compnerd · 2019-07-15T16:29:55Z

@swift-ci please test

jrose-apple · 2019-07-15T16:40:21Z

lib/Driver/UnixToolChains.cpp

@@ -153,14 +159,13 @@ toolchains::GenericUnix::constructInvocation(const DynamicLinkJobAction &job,

  // Configure the toolchain.
  // By default, use the system clang++ to link.


Comment needs correction (and would probably be a good place to explain why someone shouldn't just change it back to clang++).

sigh that is what happens when you try to be quick. Thanks for pointing that out. (I'll wait until the tests complete to update the diff).

swift-ci · 2019-07-15T17:17:37Z

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Swift Test OS X Platform
Git Sha - dc597fd2bf3be1fa263ed0c7c662581f9ff11045

swift-ci · 2019-07-15T17:27:31Z

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Git Sha - dc597fd2bf3be1fa263ed0c7c662581f9ff11045

compnerd · 2019-07-16T16:36:04Z

@swift-ci please test

compnerd · 2019-07-16T16:36:23Z

@swift-ci please test Windows platform

swift-ci · 2019-07-16T17:33:18Z

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Swift Test Linux Platform
Git Sha - e22137b50b78bf783105cbadd46c490d60f8cdcc

swift-ci · 2019-07-16T17:35:47Z

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Git Sha - e22137b50b78bf783105cbadd46c490d60f8cdcc

compnerd · 2019-07-18T03:42:33Z

@swift-ci please test macOS platform

swift-ci · 2019-07-18T04:37:40Z

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Git Sha - e22137b50b78bf783105cbadd46c490d60f8cdcc

compnerd · 2019-07-24T02:25:12Z

@swift-ci please test

swift-ci · 2019-07-24T02:25:49Z

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Git Sha - e22137b50b78bf783105cbadd46c490d60f8cdcc

swift-ci · 2019-07-24T02:27:25Z

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compnerd · 2019-07-24T04:04:12Z

@swift-ci please test

swift-ci · 2019-07-24T04:04:32Z

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Git Sha - 4fa9fe44263b5f9bcd12d97ad926f76fadabe0a3

swift-ci · 2019-07-24T04:08:05Z

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drodriguez

The "fake" clang++ that was renamed to clang in test/Driver/Inputs/fake-toolchain/ has lost the executable bits, and so it is not found by the UnixToolChains.cpp and making the tools_directory.swift test fail.

utils/static-executable-args.lnk

compnerd · 2019-07-24T22:48:57Z

@swift-ci please test

swift-ci · 2019-07-24T23:47:49Z

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Swift Test Linux Platform
Git Sha - 32e1342b3a87ab376567be65bf7823bdcbf4f56d

compnerd · 2019-07-25T00:45:58Z

@swift-ci please test

swift-ci · 2019-07-25T00:48:08Z

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Swift Test Linux Platform
Git Sha - 32e1342b3a87ab376567be65bf7823bdcbf4f56d

swift-ci · 2019-07-25T00:49:59Z

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Swift Test OS X Platform
Git Sha - 32e1342b3a87ab376567be65bf7823bdcbf4f56d

Use `clang` rather than `clang++` as the linker driver. This ensures that we do not force a C++ runtime on the general code. This is fine for now as C++ interop is not yet available for Swift. This prevents the accidental mix-and-match of various C++ runtimes. This can cause problems on platforms like android where `libstdc++` is an unsupported runtime but is generally the default for Linux platforms.

compnerd · 2019-07-25T02:52:41Z

@swift-ci please test

swift-ci · 2019-07-25T02:53:08Z

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Swift Test OS X Platform
Git Sha - 3a32c2f37c15afc8b602aaf6bb25e5ce1845223d

swift-ci · 2019-07-25T02:54:55Z

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Git Sha - 3a32c2f37c15afc8b602aaf6bb25e5ce1845223d

jrose-apple reviewed Jul 12, 2019

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compnerd changed the title ~~Minus minus is double plus good~~ Driver: prevent C++ runtime linkage Jul 12, 2019

compnerd force-pushed the minus-minus-is-double-plus-good branch from 38afc15 to a4336f8 Compare July 13, 2019 03:52

compnerd force-pushed the minus-minus-is-double-plus-good branch from a4336f8 to 13f41f2 Compare July 13, 2019 04:23

compnerd force-pushed the minus-minus-is-double-plus-good branch from 13f41f2 to dc597fd Compare July 15, 2019 16:29

jrose-apple reviewed Jul 15, 2019

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compnerd force-pushed the minus-minus-is-double-plus-good branch from dc597fd to e22137b Compare July 16, 2019 16:35

jrose-apple approved these changes Jul 18, 2019

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compnerd force-pushed the minus-minus-is-double-plus-good branch from e22137b to 4fa9fe4 Compare July 23, 2019 23:08

compnerd force-pushed the minus-minus-is-double-plus-good branch from 4fa9fe4 to e8b4ef5 Compare July 24, 2019 04:03

drodriguez requested changes Jul 24, 2019

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drodriguez reviewed Jul 24, 2019

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utils/static-executable-args.lnk Show resolved Hide resolved

compnerd force-pushed the minus-minus-is-double-plus-good branch from e8b4ef5 to 32e1342 Compare July 24, 2019 22:47

compnerd force-pushed the minus-minus-is-double-plus-good branch from 32e1342 to 3a32c2f Compare July 25, 2019 00:45

compnerd force-pushed the minus-minus-is-double-plus-good branch from 3a32c2f to 67475dc Compare July 25, 2019 02:48

compnerd merged commit 123f4b9 into swiftlang:master Jul 25, 2019

compnerd deleted the minus-minus-is-double-plus-good branch July 25, 2019 05:42

martinboehme mentioned this pull request Apr 9, 2020

Link against the C++ standard library when C++ interop is enabled #30914

Merged

finagolfin mentioned this pull request Jun 24, 2020

Driver: update old doc comments from when clang++ was the linker driver #32523

Merged

gribozavr mentioned this pull request May 6, 2020

[SR-12694] Swift does not link in the C++ standard library anymore #54925

Open

		@@ -153,14 +159,13 @@ toolchains::GenericUnix::constructInvocation(const DynamicLinkJobAction &job,

		// Configure the toolchain.
		// By default, use the system clang++ to link.

Driver: prevent C++ runtime linkage #26110

Driver: prevent C++ runtime linkage #26110

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