cmd/cgo: "'_check_for_64_bit_pointer_matching_GoInt' declared as an array with a negative size" on darwin/arm64

[Hywan]

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

$ go version
go version go1.16beta1 darwin/arm64

Does this issue reproduce with the latest release?

Yup. The beta.

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

go env Output

$ go env
GO111MODULE=""
GOARCH="arm64"
GOBIN=""
GOCACHE="/Users/hwhost/Library/Caches/go-build"
GOENV="/Users/hwhost/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/hwhost/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/hwhost/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.16beta1"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="[hidden]"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/vh/wyys3cl57jz0qp5t79vhrd200000gn/T/go-build952033984=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I tried to compile the following file with go build main.go:

package foo

import "C"

func main() { }

What did you expect to see?

A successful built.

What did you see instead?

In file included from _cgo_export.c:4:
cgo-gcc-export-header-prolog:25:55: error: '_check_for_64_bit_pointer_matching_GoInt' declared as an array with a negative size

Extra

It could be related to #38693.
The GOARCH and GOOS are OK in this case.

[Hywan]

_check_for_64_bit_pointer_matchin_GoInt is defined as:

typedef char _check_for_64_bit_pointer_matching_GoInt[sizeof(void*)==64/8 ? 1:-1];

Let's evaluate this super quickly in C:

int main() {
  printf(">> %lu\n", sizeof(void*));
  printf(">> %d\n", 64/8);
}

Execute it:

$ clang a.c -o a && ./a
>> 8
>> 8

I don't know how cgo calls clang, but it seems something is wrong in how it invokes it.

[bcmills]

CC @cherrymui @ianlancetaylor

[bcmills]

Depending on how you were invoking go build, this looks like it may be a duplicate of #43692.

[cherrymui]

Weird. What is the output for go build -x? That should include how C compiler is invoked to compile C code.

it may be a duplicate of #43692.

Could be. Does setting CGO_CFLAGS="-arch arm64" CGO_LDFLAGS="-arch arm64" help?

It is still weird in that even if it defaults to x86_64, it is still 64-bit and the pointer size should still be 8.

[bcmills]

Is it possible that the user's shell is a 32-bit binary, causing clang to default to some 32-bit arch?

[cherrymui]

I don't think ARM64 Mac supports 32-bit binary.

[Hywan]

Running CGO_CFLAGS="-arch arm64" CGO_LDFLAGS="-arch arm64" go build main.go solves the problem. That's weird.

clang and the shell, everything is 64-bit.

[Hywan]

Thanks :-)