Windows 6.2.1 x86_64 toolchain is resulting in exit code -1073741819

[award999]

While debugging a vscode-swift issue swiftlang/vscode-swift#1937 I came to realize something is different with 6.2.1 toolchain on Windows. So we call swift --version and various other SwiftPM commands on extension activation to setup the development environment. With 6.2.1 we get the right STDOUT but exit code -1073741819 which I think indicates STATUS_ACCESS_VIOLATION.

PS > swift --version
Swift version 6.2.1 (swift-6.2.1-RELEASE)
Target: x86_64-unknown-windows-msvc
Build config: +assertions
PS > $LASTEXITCODE
-1073741819

Now I'm reproducing using the x86_64 toolchain on ARM64 Windows because for the longest time ARM64 toolchain did not work on Windows. I tried installing the ARM64 6.2.1 toolchain on Windows and the extension activates fine so I only reproduce with x86_64 toolchain on an ARM64 Windows but that worked as recently as 6.2.0. I downgraded to 6.2.0 and 6.1.3 with no issues, so think legit issue with the x86_64 toolchain for 6.2.1

[award999]

@shahmishal

[shahmishal]

cc: @compnerd

[award999]

Also worth noting this lines up perfectly with our nightly 6.2 Windows job starting to fail https://github.com/swiftlang/vscode-swift/actions/runs/19350317255/job/55360633338. Now IDK if the GitHub actions Windows runner is ARM64 or x86_64 so maybe there is a problem on x86_64 Windows as well

[compnerd]

This isn't an installer issue, moving to swiftlang/swift

[compnerd]

I cannot seem to reproduce this:

Can you verify that this occurs on x64 hardware natively? Can you provide information about the CPU that you are using?

[award999]

I'm using Parallels on macOS, I can try to track down an x86_64 box

[compnerd]

@Steelskin was able to reproduce this under Parallels on ARM64. I think that this is likely a WONTFIX, as we should encourage people to use the ARM64 toolchain on ARM64. My suspicion is that the emulation layer does not support some of the instructions in the toolchain which results in the CPU fault resulting in the access violation.

[Steelskin]

Running swiftc.exe under windbg shows that the access violation is here:

(3f88.3f8c): Access violation - code c0000005 (first chance)
mimalloc!mi_free+0x30:
00007fff`c87d3000 488b11          mov     rdx,qword ptr [rcx] ds:00000000`00000000=????????????????

My guess is that mimalloc does not work properly under the x64 emulation layer scenario.

[award999]

More concerned that vscode CI jobs started to fail with 6.2.1 and that should be x86_64 so I'll see if I can find an x86_64 box to use later in the week to reproduce

[award999]

@compnerd, @matthewbastien has been able to reproduce on an x86_64 windows box