cmd/go: CGO_CFLAGS variable with spaces is parsed incorrectly on windows

[justinfx]

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

$ go version
go version go1.16.2 windows/amd64

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using?

windows10, amd64, intel

go env Output

$ go env
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\justin\AppData\Local\go-build
set GOENV=C:\Users\justin\AppData\Roaming\go\env
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=C:\Users\justin\go\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\justin\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=C:\Program Files\Go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=C:\Program Files\Go\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=go1.16.2
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=NUL
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\justin\AppData\Local\Temp\go-build995163971=/tmp/go-build -gno-record-gcc-switches

What did you do?

While attempting to build a cgo project on windows, I am finding that the value CGO_CFLAGS is parsed incorrectly if an include path contains spaces.

.
├── go.mod
├── main.c
└── main.go

// main.go
package main

import "C"

func main() {}

// main.c
// <empty>

> set CGO_CFLAGS='-IC:/Program Files/Foo'
> go env CGO_CFLAGS
'-IC:/Program Files/Foo'

> go build -x
WORK=C:\Users\justin\AppData\Local\Temp\go-build1942282733
mkdir -p $WORK\b003\
cd C:\Program Files\Go\src\runtime\cgo
TERM='dumb' CGO_LDFLAGS='"-g" "-O2"' "C:\\Program Files\\Go\\pkg\\tool\\windows_amd64\\cgo.exe" -objdir "$WORK\\b003\\" -importpath runtime/cgo -import_runtime_cgo=false -import_syscall=false -- -I "$WORK\\b003\\" '-IC:/Program Files/Foo' -Wall -Werror "C:\\Program Files\\Go\\src\\runtime\\cgo\\cgo.go"
# runtime/cgo
gcc: error: '-IC:/Program: Invalid argument
gcc: error: Files/Foo': No such file or directory

I've also tried various combinations of quoting and escaping with no change in result:

set CGO_CFLAGS=-I'C:/Program Files/Foo'
set CGO_CFLAGS='-IC:/Program\ Files/Foo'
set CGO_CFLAGS='-IC:/Program\\ Files/Foo'

What did you expect to see?

I would expect the full single string value of "C:/Program Files/Foo" to be passed to the "-I" include flag when compiling.

What did you see instead?

The path is split on spaces, acting like multiple arguments to gcc

# runtime/cgo
gcc: error: '-IC:/Program: Invalid argument
gcc: error: Files/Foo': No such file or directory

[justinfx]

Similar to #41400

[networkimprov]

cc @alexbrainman @mattn @zx2c4

[bminer]

Is this still an issue? When I run go env, I get something like this:

set AR=ar
set CC=gcc
set CGO_CFLAGS="-I'C:/Program" Files (x86)/National "Instruments/Shared/ExternalCompilerSupport/C/include'"
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-O2 -g
set CGO_ENABLED=1
set CGO_FFLAGS=-O2 -g
set CGO_LDFLAGS="-L'C:/Program" Files (x86)/National "Instruments/Shared/ExternalCompilerSupport/C/lib64/msvc'"
set CXX=g++
...

Notice the strange extra double quote between Program and Files: -I'C:/Program" Files (x86)/...

It appears correct from cmd.exe:

echo %CGO_CFLAGS%
-I'C:/Program Files (x86)/National Instruments/Shared/ExternalCompilerSupport/C/include'

Running go version go1.24.0 windows/amd64

Some compilers don't like this very much:

CC=C:/Users/bminer/mingw64/bin/x86_64-w64-mingw32-gcc.exe go build ./cmd/web
# runtime/cgo
x86_64-w64-mingw32-gcc.exe: warning: Files: linker input file unused because linking not done
x86_64-w64-mingw32-gcc.exe: error: Files: linker input file not found: No such file or directory
x86_64-w64-mingw32-gcc.exe: warning: (x86)/National: linker input file unused because linking not done
x86_64-w64-mingw32-gcc.exe: error: (x86)/National: linker input file not found: No such file or directory
x86_64-w64-mingw32-gcc.exe: warning: Instruments/Shared/ExternalCompilerSupport/C/include': linker input file unused because linking not done
x86_64-w64-mingw32-gcc.exe: error: Instruments/Shared/ExternalCompilerSupport/C/include': linker input file not found: No such file or directory

whereas others build okay:

CC=C:/cygwin64/bin/x86_64-w64-mingw32-gcc.exe go build ./cmd/web
# build is okay!

[bminer]

I wonder if the bug is here: https://github.com/golang/go/blob/master/src/cmd/cgo/gcc.go#L140

Or perhaps if the bug is downstream in the GCC compiler. For example, splitQuoted takes the input -I'C:/Program Files (x86)/National Instruments/Shared/ExternalCompilerSupport/C/include' and returns a single element array with the string -IC:/Program Files (x86)/National Instruments/Shared/ExternalCompilerSupport/C/include. I wonder if this is passed down correctly when the compiler is invoked...

[bminer]

Actually, the more I look here, the more I think it's actually a compiler issue, not a Go bug. This issue can probably be closed.

[matloob]

Thanks for looking into this @bminer! It looks like this is working as intended. CGO_CFLAGS is a space separated list. double quotes can be used to quote elements with spaces.