Android NDK r23 build problem

ref. Android NDK r22 build problem - #4 by tomasz86

I’ve set up test branch with NDK r23 but I’m running into the compile error @tomasz86 mentionend in the other thread as well.

ld: error: cannot open output file $WORK\b083\_cgo_.o: Function not implemented
clang: error: linker command failed with exit code 1 (use -v to see invocation)
exit status 2
exit status 1

Also tried to changed the CC_FLAGS environment variable but I didn’t find a working solution to compile it.

Branch: https://github.com/Catfriend1/syncthing-android/tree/android-ndk-r23

I hope anyone knows anything on how to fix or workaround this CGO problem. I’m not so into it, so I lack understanding why we need cgo. Turned it off for one try, Syncthing compiled well but I didn’t get the linker to output the libsyncthingnative.so executable file.

Adding CC_FLAGS="-v" outputs more info, but nothing that helped me when Googl’ing it.

NDK r23 ChangeLog from NDK Revision History  |  Android NDK  |  Android Developers

* GNU binutils, excluding the GNU Assembler (GAS), has been removed. GAS will be removed in the next release. If you are building with `-fno-integrated-as`, file bugs if anything is preventing you from removing that flag.
* Support for GDB has ended. GDB will be removed from the next release. Use LLDB instead. Note that `ndk-gdb` uses LLDB by default.
* NDK r23 is the last release that will support non-Neon. Beginning with NDK r24, the armeabi-v7a libraries in the sysroot will be built with Neon. A very small number of very old devices do not support Neon so most apps will not notice aside from the performance improvement.
* Jelly Bean (APIs 16, 17, and 18) will not be supported in the next NDK release. The minimum OS supported by the NDK for r24 will be KitKat (API level 19).

How can we build without GNU binutils? Or is there a replacement we could drop in?

Here’s another project struggling with the removed GNU binutils on Android NDK r23: https://github.com/sqlcipher/android-database-sqlcipher/pull/564

And this one has migrated to LLVM. Can we do this, too? (How?)

The change is documented here: Build System Maintainers Guide

Binutils
LLVM's binutils tools are installed to the NDK at <NDK>/toolchains/llvm/prebuilt/<host-tag>/bin/llvm-<tool>. These include but are not limited to:

llvm-ar
llvm-objcopy
llvm-objdump
llvm-readelf
llvm-strip
Note that llvm-as is not an equivalent of GNU as, but rather a tool for assembling LLVM IR. If you are currently using as directly, you will need to migrate to using clang as a driver for building assembly. See Clang Migration Notes for advice on fixing assembly to be LLVM compatible.

GNU Binutils remains available up to and including r23, but has been removed in r24. In r23 or earlier, GNU binutils tools are installed to <NDK>/toolchains/llvm/prebuilt/<host-tag>/bin/<triple>-<tool> and <NDK>/toolchains/llvm/prebuilt/<host-tag>/<triple>/bin/<tool>.

Note that by default /usr/bin/as is used by Clang if the -fno-integrated-as argument is used, which is almost certainly not what you want!

I still don’t understand what I’ve got to do :-(.

Sounds like binutils are still there and you could adjust the PATH to have them at the front.

1 Like

It’s interesting I can put “CGO_ENABLED=0” and then only build the arm64 variant successfully. x86 and armeabi-v7a won’t build without cgo. Why is 32-Bit Syncthing dependent of CGO - for my deeper understanding.

[INFO] Checking prerequisites ...
[INFO] Performing cleanup ...
[INFO] Building submodule syncthing_v1.18.2 ...
git_bin='C:\Program Files\GitHubDesktop\app-2.5.3\resources\app\git\cmd\git.exe'
Warning: go is not available on the PATH.
Downloaded prebuilt-go to: C:\Temp\git\syncthing-android\syncthing\..\..\syncthing-android-prereq\go_1.17.1.zip
SHA-256: C:\Temp\git\syncthing-android\syncthing\..\..\syncthing-android-prereq\go_1.17.1.zip 2f2d0a5d7c59fb38fcacaf1e272cf701bb8c050300ba8b609fc30d2c5800f02e
[ok] Checksum of C:\Temp\git\syncthing-android\syncthing\..\..\syncthing-android-prereq\go_1.17.1.zip matches expected value.
Adding to PATH: C:\Temp\git\syncthing-android\syncthing\..\..\syncthing-android-prereq\go_1.17.1\bin
go_bin='C:\Temp\git\syncthing-android\syncthing\..\..\syncthing-android-prereq\go_1.17.1\bin\go.exe'
Warning: ANDROID_NDK_HOME environment variable not defined.
Downloaded NDK to: C:\Temp\git\syncthing-android\syncthing\..\..\syncthing-android-prereq\ndk_r23.zip
SHA-1: C:\Temp\git\syncthing-android\syncthing\..\..\syncthing-android-prereq\ndk_r23.zip 14af52e23af9f7a9e7576a17e1814701192745be
[ok] Checksum of C:\Temp\git\syncthing-android\syncthing\..\..\syncthing-android-prereq\ndk_r23.zip matches expected value.
Adding ANDROID_NDK_HOME='C:\Temp\git\syncthing-android\syncthing\..\..\syncthing-android-prereq\android-ndk-r23'
ANDROID_NDK_HOME='C:\Temp\git\syncthing-android\syncthing\..\..\syncthing-android-prereq\android-ndk-r23'
Invoking git fetch ...
Invoking git describe ...
Cleaning go-build cache
Building syncthing version v1.18.2

*** Building for arm64
Notice: Next generation GUI will not be built; see --with-next-gen-gui.
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github.com/sasha-s/go-deadlock
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github.com/syncthing/syncthing/lib/dialer
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github.com/calmh/xdr
github.com/syncthing/syncthing/lib/pmp
github.com/syncthing/syncthing/lib/stats
github.com/syncthing/syncthing/lib/relay/protocol
github.com/ccding/go-stun/stun
github.com/syncthing/syncthing/lib/upnp
github.com/syncthing/syncthing/lib/relay/client
golang.org/x/time/rate
database/sql/driver
github.com/kballard/go-shellquote
github.com/syncthing/syncthing/lib/watchaggregator
github.com/syncthing/syncthing/lib/ur/contract
github.com/syncthing/syncthing/lib/versioner
github.com/chmduquesne/rollinghash
github.com/syncthing/syncthing/lib/tlsutil
github.com/chmduquesne/rollinghash/adler32
github.com/vitrun/qart/gf256
github.com/syncthing/syncthing/lib/weakhash
image
github.com/vitrun/qart/coding
golang.org/x/crypto/blowfish
github.com/lucas-clemente/quic-go/internal/qtls
golang.org/x/crypto/bcrypt
golang.org/x/text/runes
github.com/lucas-clemente/quic-go/internal/qerr
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github.com/vitrun/qart/qr
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github.com/lucas-clemente/quic-go/internal/congestion
github.com/lucas-clemente/quic-go/internal/handshake
github.com/lucas-clemente/quic-go/internal/ackhandler
github.com/lucas-clemente/quic-go
github.com/AudriusButkevicius/pfilter
github.com/syncthing/syncthing/lib/stun
github.com/syncthing/syncthing/lib/connections
github.com/syncthing/syncthing/lib/ur
github.com/syncthing/syncthing/lib/model
github.com/syncthing/syncthing/lib/api
github.com/syncthing/syncthing/lib/syncthing
github.com/syncthing/syncthing/cmd/syncthing
*** Finished build for arm64
All builds finished
[INFO] Reverting "go.mod", "go.sum" to checkout state ...
[INFO] Checking if SyncthingNative was built successfully ...

@calmh I’ve compared Android NDK r22 vs. Android NDK r23. They “just” have removed the GNU binutils, only LLVM is left. I can see this when comparing the directory structures and searching for the removed files.

image

image

It sounds like they should still be there under the llvm dir somewhere:

I have no idea why the arm64 build passes; maybe it uses a different linking mechanism or something.

1 Like

With cgo_enabled=0, it doesn’t need a linker. It ends up a standard go binary I guess. I know you used to need to build with cgo before to have dns working, but perhaps that is no longer the case.

Never the less, we should still built with cgo and the ndk.

1 Like

Can we switch to lld?

Looks like the linker can be changed:

export CC="/path/to/clang"
export GO_LDFLAGS="-extld ${CC}"
1 Like

Thanks @bt90 . Syncthing’s build.go contains:

func ldflags(tags []string) string {
	b := new(strings.Builder)
	b.WriteString("-w")
	fmt.Fprintf(b, " -X github.com/syncthing/syncthing/lib/build.Version=%s", version)
	fmt.Fprintf(b, " -X github.com/syncthing/syncthing/lib/build.Stamp=%d", buildStamp())
	fmt.Fprintf(b, " -X github.com/syncthing/syncthing/lib/build.User=%s", buildUser())
	fmt.Fprintf(b, " -X github.com/syncthing/syncthing/lib/build.Host=%s", buildHost())
	fmt.Fprintf(b, " -X github.com/syncthing/syncthing/lib/build.Tags=%s", strings.Join(tags, ","))
	if v := os.Getenv("EXTRA_LDFLAGS"); v != "" {
		fmt.Fprintf(b, " %s", v)
	}
	return b.String()
}

I assume I need to put EXTRA_LDFLAGS env var to Android workspace’s /syncthing/build-syncthing.py so it says:

environ = os.environ.copy()
environ.update({
    'GOPATH': module_dir,
    'GO111MODULE': 'on',
    'CGO_ENABLED': '1',
    'EXTRA_LDFLAGS': '-extld ' + target['clang'],
})

Is that correct?

@bt90

  • EXTRA_LDFLAGS: It seems the build process doesn’t respect this flag.
  • GO_LDFLAGS: It seems the build process doesn’t respect this flag.
  • CGO_LDFLAGS: Is respected.
'CGO_LDFLAGS': '-extld ' + ndk_clang_fullfn,

lead me to another error:

# runtime/cgo
ld: error: C:\Temp\git\syncthing-android\syncthing\..\..\syncthing-android-prereq\android-ndk-r23\toolchains\llvm\prebuilt\windows-x86_64\bin\armv7a-linux-androideabi16-clang:2: unknown directive: if
>>> if [ "$1" != "-cc1" ]; then
>>> ^
clang: error: linker command failed with exit code 1 (use -v to see invocation)

2nd try:

'CGO_LDFLAGS': '-extld C:\\Temp\\git\\syncthing-android-prereq\\android-ndk-r23\\toolchains\\llvm\\prebuilt\\windows-x86_64\\bin\\clang.exe',
# runtime/cgo
ld: error: C:\Temp\git\syncthing-android-prereq\android-ndk-r23\toolchains\llvm\prebuilt\windows-x86_64\bin\clang.exe: unknown file type
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I think clang is the compiler, not the linker.

1 Like

The llvm dir looks like this.

image

I’ve tried ld.exe and ld.lld.exe but the error is still the same:

# runtime/cgo
ld: error: C:\Temp\git\syncthing-android-prereq\android-ndk-r23\toolchains\llvm\prebuilt\windows-x86_64\bin\ld.lld.exe: unknown file type
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Sorry, I’m trying EVERYTHING but I’m unable to build with CGO.

You should set CC_FLAGS to have -v to see how it invokes the linker.

1 Like

Also you can set BUILDDEBUG=1 to see what the build script does, and hack it to add -x to the go build command line to get extensive output from go itself about what it invokes.

1 Like