Having trouble building with Android NDK

[anderspitman]

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

$ go version
go version go1.15.5 linux/amd64

Does this issue reproduce with the latest release?

I don't have the latest release.

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/anders/.cache/go-build"
GOENV="/home/anders/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/anders/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/anders/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build950721048=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I am attempting to build a go CLI program which I will then exec from an Android app and communicate with over HTTP.

Following the instructions here: https://github.com/golang/go/tree/master/misc/android

I tried to build the following go program

package main
import (
	"net/http"
)
func main() {
}

With this command:

GOOS=android GOARCH=arm64 CGO_ENABLED=1 CC_FOR_TARGET=$NDK_ROOT/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android30-clang go build

What did you expect to see?

I would expect to see a go error that net/http is not used, which I could fix by using it...

What did you see instead?

# runtime/cgo
gcc_android.c:6:10: fatal error: android/log.h: No such file or directory
    6 | #include <android/log.h>
      |          ^~~~~~~~~~~~~~~
compilation terminated.

[ericlagergren]

You’ll need to properly set your include paths. This isn’t a problem on Go’s end—clang is complaining.

[anderspitman]

Hey @ericlagergren, thanks for the reply.

When building the following C program with the same compiler:

#include <android/log.h>

int main() {
}

Like this:

$NDK_ROOT/22.0.6917172/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android30-clang main.c

It builds no problem. I verified that it's picking up the file $NDK_ROOT/22.0.6917172/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/include/android/log.h (if I move that file it fails).

So it appears the interaction with Go is somehow involved. Maybe the Go compiler is changing the sysroot when invoking the C compiler, which I'm not sure how to override. Any other ideas?

[anderspitman]

Ok I believe this is sysroot related. If I run this command:

GOOS=android GOARCH=arm64 CGO_ENABLED=1 CC_FOR_TARGET=$NDK_ROOT/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android30-clang CGO_CFLAGS="--sysroot=$NDK_ROOT/toolchains/llvm/prebuilt/linux-x86_64/sysroot" go build

I get new errors:

# runtime/cgo
In file included from /home/anders/Android/Sdk/ndk/22.0.6917172/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/include/sys/types.h:36,
                 from /home/anders/Android/Sdk/ndk/22.0.6917172/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/include/stdio.h:42,
                 from /home/anders/Android/Sdk/ndk/22.0.6917172/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/include/malloc.h:30,
                 from /home/anders/Android/Sdk/ndk/22.0.6917172/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/include/stdlib.h:34,
                 from /home/anders/Android/Sdk/ndk/22.0.6917172/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/local/include/stdlib.h:31,
                 from _cgo_export.c:3:
/home/anders/Android/Sdk/ndk/22.0.6917172/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/include/linux/types.h:21:10: fatal error: asm/types.h: No such file or directory
   21 | #include <asm/types.h>
      |          ^~~~~~~~~~~~~
compilation terminated.

And sure enough that file doesn't exist in the NDK sysroot. I'm still missing something. If I change the simple C program in also include asm/types.h it works fine, so Go is doing something to break the default configuration of the compiler.

[AlexRouSg]

What happens if you set CC instead of CC_FOR_TARGET?

CC_FOR_TARGET is only meant for building Go itself.
i.e. running ./all.bash

[anderspitman]

Different error:

# runtime/cgo
ld: error: duplicate symbol: x_cgo_inittls
>>> defined at gcc_android.c:90
>>>            $WORK/b078/_x003.o:(x_cgo_inittls)
>>> defined at gcc_linux_arm64.c:15
>>>            $WORK/b078/_x006.o:(.bss+0x8)
clang: error: linker command failed with exit code 1 (use -v to see invocation)

CC_FOR_TARGET is only meant for building Go itself

Are you sure? I see it used in lots of cross compiling examples, and the docs mention it explicitly:

When cross-compiling, you must specify a C cross-compiler for cgo to use. You can do this by setting the generic CC_FOR_TARGET

[AlexRouSg]

You didn't read the whole thing ...

When cross-compiling, you must specify a C cross-compiler for cgo to use. You can do this by setting the generic CC_FOR_TARGET or the more specific CC_FOR_${GOOS}_${GOARCH} (for example, CC_FOR_linux_arm) environment variable when building the toolchain using make.bash or you can set the CC environment variable any time you run the go tool.

The new errors are a dupe of #42655 which is NDK version related.

[anderspitman]

Thank you. I've been beating my head against this for 2 days. I'll read more carefully next time.

I can confirm that downgrading to NDK version 21 and using the following command (note NDK version 21 and CC instead of CC_FOR_TARGET) works for me:

GOOS=android GOARCH=arm64 CGO_ENABLED=1 CC=$NDK_ROOT/21.3.6528147/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android30-clang go build