build: cgo assumes mingw, causes failures with clang for windows

[nadiasvertex]

What version of Go are you using (go version)?

go version go1.7 windows/amd64

What operating system and processor architecture are you using (go env)?

Windows Server 2012 R2 / AMD64

What did you do?

I used CGO with Clang for Windows 3.8.1 (http://llvm.org/releases/3.8.1/LLVM-3.8.1-win64.exe) like this:

set CC=clang
set CGO_CFLAGS="-m64 -Ipath/to/my/includes"
set CGO_LDFLAGS = "-v -Xlinker -libpath:path/to/libs -lwldap32 -ladvapi32 -lws2_32 -ldbghelp -luser32"

go build

What did you expect to see?

Expected to see nothing (ie, successful compile)

What did you see instead?

clang version 3.8.1 (branches/release_38)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: D:\llvm\bin
 "C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\bin\\amd64\\link.exe" "-out:C:\\Users\\USAWTB~1\\AppData\\Local\\Temp\\2\\go-build808013706\\editor
\\dom\\_obj\\_all.o" "-libpath:C:\\Program Files (x86)\\Microsoft Visual Studio
14.0\\VC\\lib\\amd64" "-libpath:C:\\Program Files (x86)\\Windows Kits\\10\\Lib\\
10.0.10586.0\\ucrt\\x64" "-libpath:C:\\Program Files (x86)\\Windows Kits\\10\\Li
b\\10.0.10586.0\\um\\x64" -nologo "C:\\Users\\USAWTB~1\\AppData\\Local\\Temp\\2\
\go-build808013706\\editor\\dom\\_obj\\_cgo_export.o" "C:\\Users\\USAWTB~1\\AppD
ata\\Local\\Temp\\2\\go-build808013706\\editor\\dom\\_obj\\binding.cgo2.o" -Xlin
ker -r --start-group mingwex.lib mingw32.lib --end-group
LINK : warning LNK4044: unrecognized option '/Xlinker'; ignored
LINK : warning LNK4044: unrecognized option '/r'; ignored
LINK : warning LNK4044: unrecognized option '/-start-group'; ignored
LINK : warning LNK4044: unrecognized option '/-end-group'; ignored
LINK : fatal error LNK1181: cannot open input file 'mingwex.lib'
clang.exe: error: linker command failed with exit code 1181 (use -v to see invocation)

I believe the basic problem is the -Xlinker -r --start-group mingwex.lib mingw32.lib --end-group at the end. This is added in cmd/go/build.go, line 3427.

Perhaps the go build command could check the version of the compiler, since:

$ clang -v
clang version 3.8.1 (branches/release_38)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: D:\llvm\bin

The "msvc" tag would be a good indication not to use mingw.

[alexbrainman]

I just removed (https://go-review.googlesource.com/#/c/26670/) line 3427 from cmd/go/build.go.

Alex

[nadiasvertex]

I can verify that this fix resolves this error for me.

[luna-duclos]

I have another error using clang for windows: cgo tries to add -lm to the linker flags, which with gcc, includes the math library, however, this library doesn't exist on clang for windows, and the flag shouldn't be there.

Perhaps this should be reopened and fixed under the same issue ? Or should I log a seperate issue ?

[alexbrainman]

cgo tries to add -lm to the linker flags, which with gcc, includes the math library, however, this library doesn't exist on clang for windows, and the flag shouldn't be there.

http://golang.org/cl/31791 to remove -lm flag.

Alex