cmd/link: cgo build failed

[chai2010]

https://github.com/chai2010/cgo-bug-20160727

C:\go\gopkg\src\github.com\chai2010\cgo-bug-20160727>go version
go version go1.7rc3 windows/amd64

C:\go\gopkg\src\github.com\chai2010\cgo-bug-20160727>go build ./a

C:\go\gopkg\src\github.com\chai2010\cgo-bug-20160727>go build ./b

C:\go\gopkg\src\github.com\chai2010\cgo-bug-20160727>go build
# github.com/chai2010/cgo-bug-20160727
C:\go\go1.7rc3.windows-amd64\pkg\tool\windows_amd64\link.exe: running g++ failed: exit status 1
C:\Users\chai\AppData\Local\Temp\go-link-802100695\000001.o: In function `mingw_onexit':
C:/crossdev/src/mingw-w64-v4-git/mingw-w64-crt/crt/atonexit.c:34: multiple definition of `mingw_onexit'
C:\Users\chai\AppData\Local\Temp\go-link-802100695\000000.o:C:/crossdev/src/mingw-w64-v4-git/mingw-w64-crt/crt/atonexit.c:34: first defined here
C:\Users\chai\AppData\Local\Temp\go-link-802100695\000001.o: In function `atexit':
C:/crossdev/src/mingw-w64-v4-git/mingw-w64-crt/crt/atonexit.c:57: multiple definition of `atexit'
C:\Users\chai\AppData\Local\Temp\go-link-802100695\000000.o:C:/crossdev/src/mingw-w64-v4-git/mingw-w64-crt/crt/atonexit.c:57: first defined here
C:\Users\chai\AppData\Local\Temp\go-link-802100695\000001.o: In function `_decode_pointer':
C:/crossdev/src/mingw-w64-v4-git/mingw-w64-crt/crt/mingw_helpers.c:20: multiple definition of `_decode_pointer'
C:\Users\chai\AppData\Local\Temp\go-link-802100695\000000.o:C:/crossdev/src/mingw-w64-v4-git/mingw-w64-crt/crt/mingw_helpers.c:20: first defined here
C:\Users\chai\AppData\Local\Temp\go-link-802100695\000001.o: In function `_encode_pointer':
C:/crossdev/src/mingw-w64-v4-git/mingw-w64-crt/crt/mingw_helpers.c:26: multiple definition of `_encode_pointer'
C:\Users\chai\AppData\Local\Temp\go-link-802100695\000000.o:C:/crossdev/src/mingw-w64-v4-git/mingw-w64-crt/crt/mingw_helpers.c:26: first defined here
C:\Users\chai\AppData\Local\Temp\go-link-802100695\000001.o: In function `__gnu_cxx::new_allocator<char>::deallocate(char*, unsigned long long)':
C:/TDM-GCC-64/lib/gcc/x86_64-w64-mingw32/5.1.0/include/c++/ext/new_allocator.h:110: multiple definition of `mingw_app_type'
C:\Users\chai\AppData\Local\Temp\go-link-802100695\000000.o:C:/TDM-GCC-64/lib/gcc/x86_64-w64-mingw32/5.1.0/include/c++/ext/new_allocator.h:110: first defined here
collect2.exe: error: ld returned 1 exit status

C:\go\gopkg\src\github.com\chai2010\cgo-bug-20160727>gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=C:/TDM-GCC-64/bin/../libexec/gcc/x86_64-w64-mingw32/5.1.0/lto-wrapper.exe
Target: x86_64-w64-mingw32
Configured with: ../../../src/gcc-5.1.0/configure --build=x86_64-w64-mingw32 --enable-targets=all --enable-languages=ada,c,c++,fortran,lto,objc,obj-c++ --enable-libgomp --enable-lto --enable-graphite --enable-cxx-flags=-DWINPTHREAD_STATIC --disable-build-with-cxx --disable-build-poststage1-with-cxx --enable-libstdcxx-debug --enable-threads=posix --enable-version-specific-runtime-libs --enable-fully-dynamic-string --enable-libstdcxx-threads --enable-libstdcxx-time --with-gnu-ld --disable-werror --disable-nls --disable-win32-registry --prefix=/mingw64tdm --with-local-prefix=/mingw64tdm --with-pkgversion=tdm64-1 --with-bugurl=http://tdm-gcc.tdragon.net/bugs
Thread model: posix
gcc version 5.1.0 (tdm64-1)

[chai2010]

go env:

set GOARCH=amd64
set GOBIN=
set GOEXE=.exe
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GOPATH=C:\go\gopkg
set GORACE=
set GOROOT=C:\go\go1.7rc3.windows-amd64
set GOTOOLDIR=C:\go\go1.7rc3.windows-amd64\pkg\tool\windows_amd64
set CC=gcc
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\chai\AppData\Local\Temp\go-build756535646=/tmp/go-build -gno-record-gcc-switches
set CXX=g++
set CGO_ENABLED=1

[chai2010]

//#cgo LDFLAGS: -Wl,--allow-multiple-definition
import "C"

LDFLAGS use -Wl,--allow-multiple-definition can avoid the error.

[alexbrainman]

Thanks for report @chai2010 . I can see that this is closed now. But I will try to improve this anyway. I have some plans for issue #8756. Perhaps these two issues are related.

Alex