Re: building C++ wrapper for mabain lib with go1.13

[Mohamed Mahmoud]

On Tuesday, March 17, 2020 at 12:04:34 PM UTC-4, Mohamed Mahmoud wrote:

I have created swigcxx file , since swig now is natively integrated in go tools

I ran the following to build a test program that interact with the mabain wrapper go package to test the APIs

go install -x -i -ldflags '-w -extldflags "-lmabain"'

However I ran into linker errors that I am not able to resolve

# mabain

/tmp/go-build378478658/b001/_x003.o: In function `mbOpen':

./mabain_c_interface.cpp:10: undefined reference to `mabain::CONSTS::ReaderOptions()'

./mabain_c_interface.cpp:12: undefined reference to `mabain::DB::DB(char const*, int, unsigned long, unsigned long, unsigned int)'

./mabain_c_interface.cpp:13: undefined reference to `mabain::DB::is_open() const'

./mabain_c_interface.cpp:14: undefined reference to `mabain::DB::StatusStr() const'

./mabain_c_interface.cpp:11: undefined reference to `mabain::CONSTS::WriterOptions()'

/tmp/go-build378478658/b001/_x003.o: In function `mbFind':

./mabain_c_interface.cpp:44: undefined reference to `mabain::MBData::MBData()'

./mabain_c_interface.cpp:45: undefined reference to `mabain::DB::Find(char const*, int, mabain::MBData&) const'

./mabain_c_interface.cpp:44: undefined reference to `mabain::MBData::~MBData()'

./mabain_c_interface.cpp:44: undefined reference to `mabain::MBData::~MBData()'

/tmp/go-build378478658/b001/_x003.o: In function `mbClose':

./mabain_c_interface.cpp:23: undefined reference to `mabain::DB::Close()'

/tmp/go-build378478658/b001/_x003.o: In function `mbAdd':

./mabain_c_interface.cpp:30: undefined reference to `mabain::DB::Add(char const*, int, char const*, int, bool)'

/tmp/go-build378478658/b001/_x003.o: In function `mbRemove':

./mabain_c_interface.cpp:37: undefined reference to `mabain::DB::Remove(char const*, int)'

collect2: error: ld returned 1 exit status

root@e75d907ebd87:/usr/local/lib# ls -ltr

total 1844

-rwxr-xr-x 1 root root 1887608 Mar 17 11:42 libmabain.so

root@e75d907ebd87:/usr/local/lib# 

root@e75d907ebd87:/usr/local/lib# objdump -t libmabain.so | grep ReaderOption

0000000000022b60 g     F .text 0000000000000003              _ZN6mabain6CONSTS13ReaderOptionsEv

Any suggestions on how to fix this linker error ?

I have added the changes and steps to build here https://github.com/msherif4/mabain/tree/gointerface/swig/golang

 

Thanks!!

[Ian Lance Taylor]

I don't see anything obviously wrong. Add -v to -ldflags to see
exactly how the external linker is being invoked. Make sure that
-lmabain appears at the right point in the link line.

Ian

[Mohamed Mahmoud]

On Tuesday, March 17, 2020 at 5:01:43 PM UTC-4, Mohamed Mahmoud wrote:

I don't see anything obviously wrong.  Add -v to -ldflags to see 

exactly how the external linker is being invoked.  Make sure that
-lmabain appears at the right point in the link line.

Ian

I added -v its not showing libmabain , I am not sure what exactly you mean by having -lmabain at the right point , below is my command line let me know what it should be ?

 Step 25/26 : RUN cd ${MABAIN_SRC}/; go install -x -i -ldflags '-w -extldflags "-lmabain" -v'

 ---> Running in fd8ed360602a

WORK=/tmp/go-build682038651

mkdir -p $WORK/b001/

swig -version

cd $WORK

/usr/local/go/pkg/tool/linux_amd64/compile -o ./b001/_go_.o -trimpath "$WORK/b001=>" -p main -complete -goversion go1.13 -D _$WORK -c=4 ./swig_intsize.go

cd /mabain_src

swig -go -cgo -intgosize 64 -module mabain -o $WORK/b001/mabain_wrap.cxx -outdir $WORK/b001/ -c++ mabain.swigcxx

CGO_LDFLAGS='"-g" "-O2"' /usr/local/go/pkg/tool/linux_amd64/cgo -objdir $WORK/b001/ -importpath _/mabain_src -- -I $WORK/b001/ -g -O2 $WORK/b001/_mabain_swig.go

cd $WORK

gcc -fno-caret-diagnostics -c -x c - -o /dev/null || true

gcc -Qunused-arguments -c -x c - -o /dev/null || true

gcc -fdebug-prefix-map=a=b -c -x c - -o /dev/null || true

gcc -gno-record-gcc-switches -c -x c - -o /dev/null || true

cd $WORK/b001

TERM='dumb' gcc -I /mabain_src -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -o ./_x001.o -c _cgo_export.c

TERM='dumb' gcc -I /mabain_src -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -o ./_x002.o -c _mabain_swig.cgo2.c

cd $WORK

g++ -fno-caret-diagnostics -c -x c - -o /dev/null || true

g++ -Qunused-arguments -c -x c - -o /dev/null || true

g++ -fdebug-prefix-map=a=b -c -x c - -o /dev/null || true

g++ -gno-record-gcc-switches -c -x c - -o /dev/null || true

cd /mabain_src

TERM='dumb' g++ -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches -I $WORK/b001/ -g -O2 -o $WORK/b001/_x003.o -c mabain_c_interface.cpp

cd $WORK/b001

TERM='dumb' g++ -I /mabain_src -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -o ./_x004.o -c mabain_wrap.cxx

TERM='dumb' gcc -I /mabain_src -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -o ./_cgo_main.o -c _cgo_main.c

cd /mabain_src

TERM='dumb' g++ -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches -o $WORK/b001/_cgo_.o $WORK/b001/_cgo_main.o $WORK/b001/_x001.o $WORK/b001/_x002.o $WORK/b001/_x003.o $WORK/b001/_x004.o -g -O2

# _/mabain_src

/tmp/go-build682038651/b001/_x003.o: In function `mbOpen':

./mabain_c_interface.cpp:10: undefined reference to `mabain::CONSTS::ReaderOptions()'

./mabain_c_interface.cpp:12: undefined reference to `mabain::DB::DB(char const*, int, unsigned long, unsigned long, unsigned int)'

./mabain_c_interface.cpp:13: undefined reference to `mabain::DB::is_open() const'

./mabain_c_interface.cpp:14: undefined reference to `mabain::DB::StatusStr() const'

./mabain_c_interface.cpp:11: undefined reference to `mabain::CONSTS::WriterOptions()'

/tmp/go-build682038651/b001/_x003.o: In function `mbFind':

./mabain_c_interface.cpp:44: undefined reference to `mabain::MBData::MBData()'

./mabain_c_interface.cpp:45: undefined reference to `mabain::DB::Find(char const*, int, mabain::MBData&) const'

./mabain_c_interface.cpp:44: undefined reference to `mabain::MBData::~MBData()'

./mabain_c_interface.cpp:44: undefined reference to `mabain::MBData::~MBData()'

/tmp/go-build682038651/b001/_x003.o: In function `mbClose':

./mabain_c_interface.cpp:23: undefined reference to `mabain::DB::Close()'

/tmp/go-build682038651/b001/_x003.o: In function `mbAdd':

./mabain_c_interface.cpp:30: undefined reference to `mabain::DB::Add(char const*, int, char const*, int, bool)'

/tmp/go-build682038651/b001/_x003.o: In function `mbRemove':

./mabain_c_interface.cpp:37: undefined reference to `mabain::DB::Remove(char const*, int)'

collect2: error: ld returned 1 exit status

The command '/bin/sh -c cd ${MABAIN_SRC}/; go install -x -i -ldflags '-w -extldflags "-lmabain" -v'' returned a non-zero code: 2

[Ian Lance Taylor]

It doesn't look like the -ldflags option is getting through to the linker. Try
go build "-ldflags=all=-w -extldflags=-lmabain -v"

Ian

[Mohamed Mahmoud]

It doesn't look like the -ldflags option is getting through to the linker.  Try
    go build "-ldflags=all=-w -extldflags=-lmabain -v"

Ian

I tried the new format however it still can't link mabain lib and I get the same errors

Step 25/26 : RUN cd ${MABAIN_SRC}/; go build -x -i "-ldflags=all=-w -extldflags=-lmabain -v"

 ---> Running in 90e992e27f6b

WORK=/tmp/go-build678792509

/tmp/go-build678792509/b001/_x003.o: In function `mbOpen':

[Mohamed Mahmoud]

root@70c73d4a4f01:/# go version

go version go1.13 linux/amd64

root@70c73d4a4f01:/# swig -version

SWIG Version 3.0.12

Compiled with g++ [x86_64-pc-linux-gnu]

Configured options: +pcre

Please see http://www.swig.org for reporting bugs and further information 

[Ian Lance Taylor]

Oh, sorry, I see now that this is failing in the cgo step, not the link step.

Try adding this to your Go file:

// #cgo LDFLAGS: -lmabain
import "C"

Ian

[Mohamed Mahmoud]

Step 25/26 : RUN cd ${MABAIN_SRC}/; go build -x "-ldflags=all=-w -extldflags=-lmabain -v"

 ---> Running in e570e7fe65fa

WORK=/tmp/go-build247647361

can't load package: package .: use of cgo in test /mabain_src/mabain_test.go not supported

The command '/bin/sh -c cd ${MABAIN_SRC}/; go build -x "-ldflags=all=-w -extldflags=-lmabain -v"' returned a non-zero code: 1

MMAHMOUD-M-45WX:golang mohamedmahmoud$ git diff mabain_test.go 

diff --git a/swig/golang/mabain_test.go b/swig/golang/mabain_test.go

index 3b5be36..d2bc605 100644

--- a/swig/golang/mabain_test.go

+++ b/swig/golang/mabain_test.go

@@ -1,14 +1,16 @@

 package mabain

 

+// #cgo LDFLAGS: -lmabain

 import (

+       "C"

        "fmt"

-       "testing"

        "os"

+       "testing"

 )

 

 const (

        MABAIN_PATH = "/var/tmp/mabain_test"

-       COUNT = 100

+       COUNT       = 100

 )

 I thought we can use either SWIG or CGO but not both ?

[Ian Lance Taylor]

You can use both. It's the only way to let the package define CFLAGS
and LDFLAGS that you want to use for SWIG.

But you can't put the import "C" in a _test.go file. It has to be in
a regular .go file.

Ian