[Clang] sysroot and /winsysroot doesn't work on cross compilation

[mccakit]

Currently I can't cross compile from WSL to Windows, by passing the Windows SDK dir as --sysroot with clang or passing Windows Build Tools dir as /winsysroot with **clang-cl **.

I face errors such as these
lld-link: error: could not open 'kernel32.lib': No such file or directory

And when I manually provide link directories like this

link_directories(/mnt/c/dev/sysroots/WinSDK/10/Lib/10.0.26100.0/um/x64)
link_directories(/mnt/c/dev/sysroots/WinSDK/10/Lib/10.0.26100.0/spectre/x64)
link_directories(/mnt/c/dev/sysroots/WinSDK/10/Lib/10.0.26100.0/ucrt/x64)
include_directories(/mnt/c/dev/sysroots/WinSDK/10/Include/10.0.26100.0/um)
include_directories(/mnt/c/dev/sysroots/WinSDK/10/Include/10.0.26100.0/ucrt)

I face other sets of errors.

I just want to provide a sdk and optionally manually link libc++ if I build it. That's it, I don't want to do anything else.
Please comfirm if this is an issue, if not please provide me with information what I'm doing wrong, I already checked the clang manual and didn't find a solution.

[llvmbot]

@llvm/issue-subscribers-clang-driver

Author: mccakit (mccakit)

Currently I can't cross compile from WSL to Windows, by passing the Windows SDK dir as --sysroot with **clang** or passing Windows Build Tools dir as /winsysroot with **clang-cl **.

I face errors such as these
lld-link: error: could not open 'kernel32.lib': No such file or directory

And when I manually provide link directories like this

link_directories(/mnt/c/dev/sysroots/WinSDK/10/Lib/10.0.26100.0/um/x64)
link_directories(/mnt/c/dev/sysroots/WinSDK/10/Lib/10.0.26100.0/spectre/x64)
link_directories(/mnt/c/dev/sysroots/WinSDK/10/Lib/10.0.26100.0/ucrt/x64)
include_directories(/mnt/c/dev/sysroots/WinSDK/10/Include/10.0.26100.0/um)
include_directories(/mnt/c/dev/sysroots/WinSDK/10/Include/10.0.26100.0/ucrt)

I face other sets of errors.

I just want to provide a sdk and optionally manually link libc++ if I build it. That's it, I don't want to do anything else.
Please comfirm if this is an issue, if not please provide me with information what I'm doing wrong, I already checked the clang manual and didn't find a solution.

[Andarwinux]

/winsysroot actually works fine in cross-compilation. But I think you can't directly access SDK in NTFS using 9pfs on wsl, which will cause some case conversion problems. I suggest you use msvc-wine to generate winsdk sysroot with a correct layout in wsl's own ext4.

If you use clang instead of clang-cl, the correct /winsysroot equivalent flag is -Xmicrosoft-windows-sys-root.

I must also point out that msvc style toolchains always calls linker directly instead of using the cc driver, and a lot of stupid build systems will do the same for clang --target=*-pc-windows-msvc, so even if you specify -Xmicrosoft-windows-sys-root that's still is not enough. You also need to add /winsysroot: to linker flags (you can do this with _LINK environment variable without having to tell build systems somehow)

[mccakit]

This doesn't work

set(CMAKE_SYSTEM_NAME Windows)
set(CMAKE_SYSTEM_PROCESSOR X86_64)
set(triple x86_64-windows-msvc)

set(CMAKE_C_COMPILER clang)
set(CMAKE_C_COMPILER_TARGET ${triple})
set(CMAKE_CXX_COMPILER clang++)
set(CMAKE_CXX_COMPILER_TARGET ${triple})
set(CMAKE_RC_COMPILER llvm-rc)
set(CMAKE_LINKER_TYPE LLD)
set(CMAKE_AR llvm-ar)
set(CMAKE_RANLIB llvm-ranlib)
set(CMAKE_MT llvm-mt)
set(CMAKE_ASM_COMPILER clang)

add_compile_options(-Xmicrosoft-windows-sys-root /home/mccakit/dev/msvc-wine/Windows Kits)
add_link_options(-Xmicrosoft-windows-sys-root /home/mccakit/dev/msvc-wine/Windows Kits)
set(VULKAN_SDK /mnt/c/VulkanSDK/1.4.313.1)

also this doesn't work

set(CMAKE_SYSTEM_NAME Windows)
set(CMAKE_SYSTEM_PROCESSOR X86_64)
set(triple x86_64-windows-msvc)

set(CMAKE_C_COMPILER clang-cl)
set(CMAKE_C_COMPILER_TARGET ${triple})
set(CMAKE_CXX_COMPILER clang-cl)
set(CMAKE_CXX_COMPILER_TARGET ${triple})
set(CMAKE_RC_COMPILER llvm-rc)
set(CMAKE_LINKER_TYPE LLD)
set(CMAKE_AR llvm-ar)
set(CMAKE_RANLIB llvm-ranlib)
set(CMAKE_MT llvm-mt)
set(CMAKE_ASM_COMPILER clang-cl)

add_compile_options(/winsysroot "/home/mccakit/dev/msvc-wine/Windows Kits")
add_link_options(/winsysroot "/home/mccakit/dev/msvc-wine/Windows Kits")
set(VULKAN_SDK /mnt/c/VulkanSDK/1.4.313.1)

Also this doesn't work

set(CMAKE_SYSTEM_NAME Windows)
set(CMAKE_SYSTEM_PROCESSOR X86_64)
set(triple x86_64-windows-msvc)

set(CMAKE_C_COMPILER clang)
set(CMAKE_C_COMPILER_TARGET ${triple})
set(CMAKE_CXX_COMPILER clang++)
set(CMAKE_CXX_COMPILER_TARGET ${triple})
set(CMAKE_RC_COMPILER llvm-rc)
set(CMAKE_LINKER_TYPE LLD)
set(CMAKE_AR llvm-ar)
set(CMAKE_RANLIB llvm-ranlib)
set(CMAKE_MT llvm-mt)
set(CMAKE_ASM_COMPILER clang)

add_compile_options(--sysroot="/home/mccakit/dev/msvc-wine/Windows Kits")
add_link_options(--sysroot="/home/mccakit/dev/msvc-wine/Windows Kits")
set(VULKAN_SDK /mnt/c/VulkanSDK/1.4.313.1)

Please help, or confirm this is a bug in clang

[Andarwinux]

The correct winsysroot is the parent directory of Windows Kits.

[mccakit]

This works, but msvc-wine needs explicit sdk version to download windows.h, and I need to manually include some stuff

include_directories("/home/mccakit/dev/msvc-wine/Windows Kits/10/Include/10.0.26100.0/um")
include_directories("/home/mccakit/dev/msvc-wine/Windows Kits/10/Include/10.0.26100.0/shared")

You have my utmost gratitude, I will make PR's to do clang manual and msvc-wine so stuff will become easier. It is quite weird that msvc-wine works but normal windows sdk doesn't but I'm not gonna complain.

I will also ask, why doesn't clang automatically include um and shared folders, can we create a PR on that?
I will gladly contribute if I'm able

[Andarwinux]

This works, but msvc-wine needs explicit sdk version to download windows.h, and I need to manually include some stuff

include_directories("/home/mccakit/dev/msvc-wine/Windows Kits/10/Include/10.0.26100.0/um") include_directories("/home/mccakit/dev/msvc-wine/Windows Kits/10/Include/10.0.26100.0/shared")

You have my utmost gratitude, I will make PR's to do clang manual and msvc-wine so stuff will become easier. It is quite weird that msvc-wine works but normal windows sdk doesn't but I'm not gonna complain.

I will also ask, why doesn't clang automatically include um and shared folders, can we create a PR on that? I will gladly contribute if I'm able

That's odd, clang is supposed to include them automatically

[mccakit]

You are using clang 22, I have clang 21.

Let me recompile it again, and see if the issue persists or not

[mccakit]

Issue persists, unfortunately

[Andarwinux]

Maybe open an issue at msvc-wine?

[YexuanXiao]

#96417 is a solution, but it requires reorganizing the libraries and header files from the Windows SDK and MSVC into a new sysroot, which currently relies on manual maintenance.

[mccakit]

That is a completely new feature, though. I'm closing this issue and creating a new issue for fixing -Xmicrosoft-windows-sys-root nto including windows kits include directories