Mark start/stop sections as SHF_GNU_RETAIN

[keith]

Fixes swiftlang/swift-package-manager#5698
Fixes #60406

[keith]

@swift-ci Please test Linux platform

[MaxDesiatov]

@swift-ci build toolchain

[keith]

we might have to test with swiftlang/swift-driver#1402 to be 100% sure this is working

[keith]

Please test with following pull request:
swiftlang/swift-driver#1402

@swift-ci Please test Linux platform

[keith]

Hrm our jobs failed but I don't think it's related to this, but the issues from this in the past were subtle so it could be

[keith]

swiftlang/swift-driver#1402

@swift-ci Please test Linux platform

[keith]

I believe this is the relevant part of the log:

---
4.	While evaluating request ExecuteSILPipelineRequest(Run pipelines { PrepareOptimizationPasses, EarlyModulePasses, HighLevel,Function+EarlyLoopOpt, HighLevel,Module+StackPromote, MidLevel,Function, ClosureSpecialize, LowLevel,Function, LateLoopOpt, SIL Debug Info Generator } on SIL for Swift)
5.	While running pass #38079 SILFunctionTransform "ComputeSideEffects" on SILFunction "@$sSNsSxRzSZ6StrideRpzrlE10startIndexSNsSxRzSZABRQrlE0C0Oyx_Gvg".
 for getter for startIndex (at /home/build-user/swift/stdlib/public/core/ClosedRange.swift:209:14)
Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
/home/build-user/build/buildbot_linux/swift-linux-x86_64/bootstrapping1/bin/swift-frontend[0x6da26d3]

[finagolfin]

This is failing when bootstrapping: my guess is that something about this attribute is making the bootstrap1 compiler crash, as the bootstrap0 compiler works fine on the linux CI. The difference is that the bootstrap1 compiler links against the Swift stdlib that you're modifying here, while the bootstrap0 compiler doesn't.

Is this working for you locally?

[keith]

It works for me locally but I'm not bootstrapping, I'll try that flow!

[keith]

Doesn't fail for me with this command either:

./swift/utils/build-script --release-debuginfo --skip-early-swift-driver --skip-early-swiftsyntax --sccache --build-subdir raw-cmd --extra-cmake-options="-DLLVM_USE_LINKER=/home/ksmiley/.bin/ld.lld,-DSWIFT_ENABLE_EXPERIMENTAL_CXX_INTEROP=NO,-DSWIFT_USE_LINKER=lld"

[keith]

trying with the command from CI:

./swift/utils/build-script --assertions --swift-enable-ast-verifier=0 --no-swift-stdlib-assertions '--swift-install-components=autolink-driver;compiler;clang-resource-dir-symlink;stdlib;swift-remote-mirror;sdk-overlay;static-mirror-lib;toolchain-tools;license;sourcekit-inproc' '--llvm-install-components=llvm-ar;llvm-cov;llvm-profdata;IndexStore;clang;clang-resource-headers;compiler-rt;clangd;lld;LTO;clang-features-file' --llbuild --swiftpm --swift-driver --xctest --libicu --swiftdocc --build-ninja --install-llvm --install-swift --install-lldb --install-llbuild --install-swiftpm --install-swift-driver --install-swiftsyntax --install-xctest --install-libicu --install-prefix=/usr --install-sourcekit-lsp --install-swiftformat --install-swiftdocc --build-swift-static-stdlib --build-swift-static-sdk-overlay --build-swift-stdlib-unittest-extra --test-installable-package --toolchain-benchmarks --install-destdir=/home/build-user/swift-nightly-install --installable-package=/home/build-user/PR-ubuntu2004.tar.gz --relocate-xdg-cache-home-under-build-subdir --skip-early-swift-driver --skip-early-swiftsyntax --build-subdir=buildbot_linux --lldb --release --test --validation-test --long-test --stress-test --test-optimized --foundation --libdispatch --indexstore-db --sourcekit-lsp --swiftdocc '--lit-args=-v --time-tests' --lldb-test-swift-only --install-foundation --install-libdispatch --reconfigure

[finagolfin]

Does adding -DSWIFT_ENABLE_EXPERIMENTAL_CXX_INTEROP=NO disable bootstrapping, because the bootstrap relies on C++ Interop? That may be why that command works for you.

[keith]

🙃 I can try without that, I added that to avoid a different issue originally:

<unknown>:0: warning: the '-enable-experimental-cxx-interop' flag is deprecated; please pass '-cxx-interoperability-mode=' instead
<unknown>:0: note: Swift will maintain source compatibility for imported APIs based on the selected compatibility mode, so updating the Swift compiler will not change how APIs are imported
=== /home/ksmiley/dev/oss-swift/swift/stdlib/public/Cxx/std/std.swift:13:19 ===
12 |
13 | @_exported import CxxStdlib // Clang module
   |                   ^ error: underlying Objective-C module 'CxxStdlib' not found
14 | @_exported import Cxx // Swift module

[keith]

I don't think it disables bootstrapping because I see this in the output:

-- Building host Swift tools for LINUX x86_64
--   Build type:     RelWithDebInfo
--   Assertions:     TRUE
--   LTO:
--   Bootstrapping:  BOOTSTRAPPING

but I will try without it anyways

[finagolfin]

error: underlying Objective-C module 'CxxStdlib' not found

This should be fixed by #65534, if you update to latest trunk or apply that patch to your checkout.

[finagolfin]

I don't think it disables bootstrapping

You can check by running something like this on your build:

> readelf -d build/Ninja-Release/swift-linux-x86_64/bootstrapping1/bin/swift-frontend | grep libswiftCore

[keith]

Locally this one still passes (even without that patch):

./swift/utils/build-script --release-debuginfo --skip-early-swift-driver --skip-early-swiftsyntax --sccache --build-subdir raw-cmd2 --extra-cmake-options="-DLLVM_USE_LINKER=/home/ksmiley/.bin/ld.lld,-DSWIFT_USE_LINKER=lld"

The CI command is still running

[keith]

You can check by running something like this on your build:

I'm not sure exactly what you see as the difference here but I see:

% readelf -d build/raw-cmd2/swift-linux-x86_64/bootstrapping1/bin/swift-frontend| grep -i core
 0x0000000000000001 (NEEDED)             Shared library: [libswiftCore.so]

In this case

[keith]

Interestingly the CI command fails with:

ld.lld: error: relocation R_X86_64_PC32 cannot be used against symbol stderr; recompile with -fPIC
>>> defined in /lib/x86_64-linux-gnu/libc.so.6
>>> referenced by stdio2.h:100 (/usr/include/x86_64-linux-gnu/bits/stdio2.h:100)
>>>               object.o:(_PyObject_AssertFailed) in archive /home/ksmiley/.pyenv/versions/3.10.4/lib/libpython3.10.a

But maybe that's because i'm using not the system python in this case so I'll try to remove that and build again

[finagolfin]

Are you doing clean rebuilds locally? The final thing to try would be to remove your --extra-cmake-options changing the linker to lld, as the linux CI uses gold.

[keith]

Yea I guess the reason I'm using lld is because the bug only surfaces with that, so if it does end up passing with gold (after that crash is resolved) I'm not sure we'd be validating the change actually works

[keith]

In this case my builds were clean yes (I passed a new build-subdir) (although I am using sccache)

[finagolfin]

I guess the reason I'm using lld is because the bug only surfaces with that, so if it does end up passing with gold (after that crash is resolved) I'm not sure we'd be validating the change actually works

The problem is that this pull is currently crashing the linux CI with gold, so you'll have to fix that first to ever have a hope of getting this in.

[kateinoigakukun]

Please test with following pull request:
swiftlang/swift-driver#1402

@swift-ci Please test Linux platform

[finagolfin]

Anything change recently that should make this work?

[kateinoigakukun]

I don't know but I'm going to work on a similar issue for wasm, so I'd like to know the latest status of the fix.

[keith]

I believe the current issue is that there is some other place not covered by this change where these sections are created as well, and we need to flip this option in that place as well. That's just an assumption but the current result is ld.gold crashes I assume because of that mismatch

[keith]

@etcwilde you might be interested in this, I feel like it's close but haven't had the time to dig into it more

[kateinoigakukun]

Just FYI: I'm doing some experiments on #71373

[keith]

#72061