Visual Studio 2022 lld-link: warning/error: ignoring unknown debug$S subsection kind 0xFF in file libucrt.lib

[FrancescElies]

Related to actions/runner-images#5813

Problem

We started seeing lld-link: warning/error: ignoring unknown debug$S subsection kind 0xFF in file libucrt.lib with newer windows-sdks in visual studio 2022 (this does not happen with vs2019)

Is the following a problem in windows-sdks with vs2022 or in lld-link?

example.c

int main(int argc, char **argv) {
  return 0;
}

Invoke-CmdScript (click me)

# https://stackoverflow.com/questions/41399692/running-a-build-script-after-calling-vcvarsall-bat-from-powershell
function Invoke-CmdScript {
  param(
    [String] $scriptName
  )
  $cmdLine = """$scriptName"" $args && set"
  & $Env:SystemRoot\system32\cmd.exe /c $cmdLine |
  select-string '^([^=]*)=(.*)$' | foreach-object {
    $varName = $_.Matches[0].Groups[1].Value
    $varValue = $_.Matches[0].Groups[2].Value
    set-item Env:$varName $varValue
  }
}

With a previous win-sdk version: 10.0.19041.0

Invoke-CmdScript "c:/Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" x64 10.0.19041.0
clang -std=c99 --target=x86_64-pc-windows-msvc -fuse-ld=lld -O1 -g "-Wl,/WX,/errorlimit:5" example.c

# No link warnings or errors

With newer win-sdk version (WX made warnings errors)

Invoke-CmdScript "c:/Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" x64 10.0.22621.0
clang -std=c99 --target=x86_64-pc-windows-msvc -fuse-ld=lld -O1 -g "-Wl,/WX,/errorlimit:5" example.c

lld-link: error: ignoring unknown debug$S subsection kind 0xFF in file libucrt.lib(initialization.obj)
lld-link: error: ignoring unknown debug$S subsection kind 0xFF in file libucrt.lib(argv_data.obj)
lld-link: error: ignoring unknown debug$S subsection kind 0xFF in file libucrt.lib(ncommode.obj)
lld-link: error: ignoring unknown debug$S subsection kind 0xFF in file libucrt.lib(matherr.obj)
lld-link: error: ignoring unknown debug$S subsection kind 0xFF in file libucrt.lib(matherr.obj)
lld-link: error: too many errors emitted, stopping now (use /errorlimit:0 to see all errors)
clang: error: linker command failed with exit code 1 (use -v to see invocation)```

llvm version

❯ clang -v
clang version 14.0.6
Target: x86_64-pc-windows-msvc
Thread model: posix

[llvmbot]

@llvm/issue-subscribers-lld-coff

[rnk]

This suggests that Microsoft has added additional subsection kinds:
https://github.com/microsoft/microsoft-pdb/blob/master/include/cvinfo.h#L4579
The warning exists to detect if and when this happens, so it's working as intended. Ideally, we should try to loop in someone from Microsoft to advise on what to do with the new subsection.

+various others @zmodem @ZequanWu @alanzhao1

[aganea]

Can @StephanTLavavej @gratianlup help here?

[StephanTLavavej]

@aganea I'm very unfamiliar with this area (as I work on the STL), but @rnk's link helped me find the latest enumerators in the internal repo. DEBUG_S_XFGHASH_TYPE is the 0xFF and it's followed by DEBUG_S_XFGHASH_VIRTUAL with the next value 0x100. This was added by internal MSVC-PR-354509 (obviously this link is of no use to you, but it might save an MSVC back-end dev from having to look it up).

I know less about XFG than I do about quantum mechanics, so that's all the info I can provide - but I'll mail the backend devs and ask if someone can comment here. Hope this helps!

[rnk]

Thanks! XFG appears to be for Xtended Flow Guard, so another security hardening technology similar to Control Flow Guard (CFG), which LLD does not yet implement. I think we should:

• add these enums
• add them to the switch
• ignore them until there is interest in XFG

It would be nice if LLD had a warning suppression infrastructure to allow users to suppress individual warnings if this comes up again in the future, but to date the whole idea has been that it's a linker, it shouldn't have warnings, only errors, so there is no infrastructure to leverage for that purpose.

In the absence of such functionality, I'm glad we have the warning, so I'd like to keep it so we find out about future debug subsection additions.

[tru]

Posted a diff here: https://reviews.llvm.org/D129378

I know it needs a test as well - but I couldn't find where other flags that are ignored was tested, so any pointers on how to test it similar to other things that are ignored it would be great.

[tru]

/cherry-pick 576375a

[llvmbot]

/branch llvm/llvm-project-release-prs/issue56285

[llvmbot]

/pull-request llvm/llvm-project-release-prs#73

[kuzminrobin]

I got an impression that linker (lld-link) warnings result in non-zero error code returned by the linker console application. This breaks some of our CI builds.
If that's the case then consider returning zero in case of warnings (as opposed to errors).

[rnk]

@kuzminrobin The user has control of whether warnings should be errors via the /WX flag, which should do what you need.

[kuzminrobin]

Looks like I was wrong. The exit code of lld-link corresponds to my expectations.
The exit code of lld-link is 0 in case of warnings (including with the flag /WX:no and without any flag).
The exit code of lld-link is 1 in case of errors (the warnings treated as errors with the /WX flag).
Sorry for troubling.

---

Looks like the problem with our CI build is related to the output to the stderr. If there is any output to stderr in lld-link (including warnings) then the CI build script treats that as failure. Investigating.