cmd/link: showing many ld warnings of "building for macOS, but linking in object file"

[avence12]

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

$ go version go1.12.7 darwin/amd64

Does this issue reproduce with the latest release?

yes

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

Mac Mojave 10.14.5

Result of go env:

GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/avence12/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/avence12/.gvm/pkgsets/go1.12.7/global:/Users/avence12/devel/go"
GOPROXY=""
GORACE=""
GOROOT="/Users/avence12/.gvm/gos/go1.12.7"
GOTMPDIR=""
GOTOOLDIR="/Users/avence12/.gvm/gos/go1.12.7/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/9n/_tfc4bt12ps45qjyzh40jt1h0000gn/T/go-build525129295=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

1. Install and use go1.12.7 by GVM
2. Get into my project and run go build ./...
3. The build is successful but seeing lots of ld warning. The same situation when I run go test ./...
4. When I setup export CGO_ENABLED=0, the warning is gone. However I would like to know how to resolve the issue.

What did you expect to see?

No ld warnings when CGO_ENABLED=1

What did you see instead?

$ go build ./cmd/...
# github.com/avence12/myproj/cmd/client
ld: warning: building for macOS, but linking in object file (/var/folders/9n/_tfc4bt12ps45qjyzh40jt1h0000gn/T/go-link-703159202/go.o) built for 
# github.com/avence12/myproj/cmd/server
ld: warning: building for macOS, but linking in object file (/var/folders/9n/_tfc4bt12ps45qjyzh40jt1h0000gn/T/go-link-846047020/go.o) built for 

[ianlancetaylor]

CC @randall77 @thanm

[ianlancetaylor]

Which version of XCode do you have installed?

[thanm]

Is that the complete warning (e.g. "built for" and then nothing more)? Wondering if the output got truncated somehow.

[avence12]

@ianlancetaylor:
I did not install XCode when I saw the issue. After I install XCode Version 10.2.1, the issue remains.

@thanm:
I add the result of go env and complete warning to origin message. There is nothing after "built for".

[juev]

The same issue for me.

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/d.evsyukov/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/d.evsyukov/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/Cellar/go/1.12.7/libexec"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.12.7/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/3k/hqxhm_y10vx682dnsbb64l7r0000gp/T/go-build135546081=/tmp/go-build -gno-record-gcc-switches -fno-common"

$ go get -u github.com/saibing/bingo
# github.com/saibing/bingo
ld: warning: building for macOS, but linking in object file (/var/folders/3k/hqxhm_y10vx682dnsbb64l7r0000gp/T/go-link-834839606/go.o) built for

[xuhrc]

ld: warning: building for macOS, but linking in object file (/var/folders/78/6hfbqt9x3z3bvm41rhn81smhx0t1sf/T/go-link-034794354/go.o) built for

go env:
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPROXY="https://goproxy.io"
GORACE=""
GOROOT="/usr/local/Cellar/go/1.12.7/libexec"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.12.7/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/78/6hfbqt9x3z3bvm41rhn81smhx0t1sf/T/go-build817734651=/tmp/go-build -gno-record-gcc-switches -fno-common"

same issue for me

The warning disappeared after i installed command line tools beta 6

[thanm]

I'm not having any luck reproducing this.

I'm working with a MacOS 10.14.5 macbook, Xcode 10.3, installed go 1.12.7 using "gvm", but when I build the projects above I don't see any warnings.

It might help to know what version of the linker you're working with, since it's the linker issuing the warning.

Please try this small experiment: run clang on a tiny C file to invoke the linker, then using the linker path you see in the output, run "ld -v" to see what version it claims to be:

$ echo "int main() { return 0; }" > small.c
$ clang -v small.c 1> transcript.txt 2>&1
$ fgrep /ld transcript
 "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld" -demangle -lto_library /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/libLTO.dylib -no_deduplicate -dynamic -arch x86_64 -macosx_version_min 10.14.0 -syslibroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk -o a.out /var/folders/y1/14s910p95pj3vb71ywd53wk8008r__/T/small-788b80.o -L/usr/local/lib -lSystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/10.0.1/lib/darwin/libclang_rt.osx.a
$ /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld -v

@(#)PROGRAM:ld  PROJECT:ld64-450.3
BUILD 18:16:53 Apr  5 2019
configured to support archs: armv6 armv7 armv7s arm64 arm64e arm64_32 i386 x86_64 x86_64h armv6m armv7k armv7m armv7em
LTO support using: LLVM version 10.0.1, (clang-1001.0.46.4) (static support for 22, runtime is 22)
TAPI support using: Apple TAPI version 10.0.1 (tapi-1001.0.4.1)

[juev]

$ echo "int main() { return 0; }" > small.c
$ clang -v small.c 1> transcript.txt 2>&1
$ ll
total 16K
-rwxr-xr-x 1 d.evsyukov 4.2K Jul 24 19:16 a.out
-rw-r--r-- 1 d.evsyukov   25 Jul 24 19:16 small.c
-rw-r--r-- 1 d.evsyukov 2.5K Jul 24 19:16 transcript.txt

$ grep /ld transcript.txt
 "/Library/Developer/CommandLineTools/usr/bin/ld" -demangle -lto_library /Library/Developer/CommandLineTools/usr/lib/libLTO.dylib -no_deduplicate -dynamic -arch x86_64 -macosx_version_min 10.14.0 -syslibroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk -o a.out /var/folders/ss/g0zcdcj13p54s6fj2353vlxh0000gn/T/small-f8f73a.o -L/usr/local/lib -lSystem /Library/Developer/CommandLineTools/usr/lib/clang/10.0.1/lib/darwin/libclang_rt.osx.a

$ /Library/Developer/CommandLineTools/usr/bin/ld -v
@(#)PROGRAM:ld  PROJECT:ld64-450.3
BUILD 18:45:16 Apr  4 2019
configured to support archs: armv6 armv7 armv7s arm64 arm64e arm64_32 i386 x86_64 x86_64h armv6m armv7k armv7m armv7em
LTO support using: LLVM version 10.0.1, (clang-1001.0.46.4) (static support for 22, runtime is 22)
TAPI support using: Apple TAPI version 10.0.1 (tapi-1001.0.4.1)

[thanm]

Thanks @juev . Looks like your linker is more or less the same vintage as mine, so nothing notable there.

I also tried deleting Xcode from my Mac and to just the downloaded command line tools, but that didn't help.

How about this as another possible experiment to try: redo the link with -tmpdir set, which should capture the object files feeding into the external linker, then run 'file' on one of the ones the linker is complaining about to see what it looks like. Demo:

$ cd $GOPATH/src/github.com/saibing/bingo
$ go clean -cache ; rm -f bingo
$ mkdir /tmp/xxx
$ go build -ldflags=-tmpdir=/tmp/xxx .
$ ls /tmp/xxx
000000.o	000005.o	000010.o	000015.o	go.dwarf
000001.o	000006.o	000011.o	000016.o	go.o
000002.o	000007.o	000012.o	000017.o	trivial.c
000003.o	000008.o	000013.o	000018.o
000004.o	000009.o	000014.o	a.out
$ file /tmp/xxx/go.o
/tmp/xxx/go.o: Mach-O 64-bit object x86_64
$

[avence12]

@thanm My ld is the same as your version.

$ /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld -v
@(#)PROGRAM:ld  PROJECT:ld64-450.3
BUILD 18:16:53 Apr  5 2019
configured to support archs: armv6 armv7 armv7s arm64 arm64e arm64_32 i386 x86_64 x86_64h armv6m armv7k armv7m armv7em
LTO support using: LLVM version 10.0.1, (clang-1001.0.46.4) (static support for 22, runtime is 22)
TAPI support using: Apple TAPI version 10.0.1 (tapi-1001.0.4.1)

Another test:

$ go get  github.com/saibing/bingo
# github.com/saibing/bingo
ld: warning: building for macOS, but linking in object file (/var/folders/9n/_tfc4bt12ps45qjyzh40jt1h0000gn/T/go-link-110299481/go.o) built for

$ cd $GOPATH/src/github.com/saibing/bingo
$ go clean -cache ; rm -f bingo
$ mkdir /tmp/xxx
$ go build -ldflags=-tmpdir=/tmp/xxx .
# github.com/saibing/bingo
ld: warning: building for macOS, but linking in object file (/tmp/xxx/go.o) built for
$ ls /tmp/xxx
000000.o	000005.o	000010.o	000015.o	go.dwarf
000001.o	000006.o	000011.o	000016.o	go.o
000002.o	000007.o	000012.o	000017.o	trivial.c
000003.o	000008.o	000013.o	000018.o
000004.o	000009.o	000014.o	a.out
$ file /tmp/xxx/go.o
/tmp/xxx/go.o: Mach-O 64-bit object x86_64

One thing may be related, the gcc version:

$ gcc -v
Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/4.2.1
Apple clang version 11.0.0 (clang-1100.0.20.17)
Target: x86_64-apple-darwin18.6.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin