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cmd/cgo: document how to cross-compile from darwin/amd64 to darwin/arm64 with cgo #44112

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briandealwis opened this issue Feb 5, 2021 · 6 comments

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@briandealwis
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@briandealwis briandealwis commented Feb 5, 2021

Attempting to use cgo for cross-compiling a Go app for darwin/arm64 from darwin/amd64 is not entirely straightforward for those not familiar with Apple's toolchain when compiling from macOS 10.15 or earlier.

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

go 1.16rc1

Does this issue reproduce with the latest release?

Yes

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

go env Output
$ go1.16rc1 env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/bdealwis/Library/Caches/go-build"
GOENV="/Users/bdealwis/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/bdealwis/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/bdealwis/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/bdealwis/sdk/go1.16rc1"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/bdealwis/sdk/go1.16rc1/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.16rc1"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/bdealwis/Projects/Skaffold/repo-skaffold/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/jp/fyjblw1x6k71gyjnz3smzbjr00kl65/T/go-build1743423011=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I was trying to build Skaffold for darwin/arm64. We normally build Skaffold with cgo to take advantage of github.com/rjeczalik/notify's bindings to native file-watching APIs like macOS's FSEvents.

I understood that XCode 12.2 and later support cross-compilation between amd64 and arm64, I thought this would be straightforward. But my attempts failed with odd errors:

$ CGO_ENABLED=1 GOOS=darwin GOARCH=arm64 \
    go1.16rc1 build ./cmd/skaffold 
# runtime/cgo
In file included from _cgo_export.c:3:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include/stdlib.h:62:
/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include/sys/cdefs.h:807:2: error: Unsupported architecture
In file included from _cgo_export.c:3:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include/stdlib.h:64:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include/_types.h:27:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include/sys/_types.h:33:
/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include/machine/_types.h:34:2: error: architecture not supported
...

It turns out that cross-compiling for arm64 from amd64 requires using a macOS SDK 11.x. As I was building from a machine running macOS 10.15, the default SDK used for compilation was 10.15. It was not clear how to specify an 11.x SDK. From what I found online, it seemed like I should be able to build by specifying CC='clang --target arm64-apple-macos11, or CC='clang -isysroot to point to a macOS 11.x SDK, but these failed in the similar fashion:

$ CGO_ENABLED=1 GOOS=darwin GOARCH=arm64 \
    CC='clang -isystem /Library/Developer/CommandLineTools/SDKs/MacOSX11.1.sdk` \
    go1.16rc1 build -o out/skaffold-darwin-arm64 ./cmd/skaffold
# runtime/cgo
In file included from _cgo_export.c:3:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include/stdlib.h:62:
/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include/sys/cdefs.h:807:2: error: Unsupported architecture
...

After much more digging, it turns out the best way is to set the SDKROOT environment variable to point to the SDK. And to use xcrun to find the newest SDK installed:

$ CGO_ENABLED=1 GOOS=darwin GOARCH=arm64 \
    SDKROOT=$(xcrun --sdk macosx --show-sdk-path) \
    go1.16rc1 build -o out/skaffold-darwin-arm64 ./cmd/skaffold

The --sdk macosx chooses the MacOSX.sdk, which is normally linked to the latest SDK.

@seankhliao
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@seankhliao seankhliao commented Feb 5, 2021

feel free to add a page to the wiki

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@seankhliao seankhliao changed the title Document how to cross-compile from darwin/amd64 to darwin/arm64 with cgo cmd/cgo: document how to cross-compile from darwin/amd64 to darwin/arm64 with cgo Feb 5, 2021
@bcmills
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@bcmills bcmills commented Feb 5, 2021

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@cherrymui
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@cherrymui cherrymui commented Feb 5, 2021

I think the general question is how to cross compile with cgo, which boils down to how to cross compile C code. It is not specific to darwin. Basically, it needs a C cross compiler, and set CC and/or CGO_CFLAGS/CGO_LDFLAGS accordingly. Sometimes it is relatively easy, and sometimes it requires a nontrivial amount of work.

I don't think we want do document about how to cross compile C. Are there existing documentation about that? Maybe we can link to that, and add the part of setting CC/CGO_CFLAGS/etc.

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@briandealwis
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@briandealwis briandealwis commented Feb 6, 2021

I thought it was worth calling out darwin/arm64 as most build systems do not yet support Apple M1 and are on macOS 10.15 or earlier. One of the wiki pages seems fine? Perhaps https://github.com/golang/go/wiki/Darwin?

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@dmitshur dmitshur added this to the Backlog milestone Feb 8, 2021
bazbremner added a commit to bazbremner/aws-vault that referenced this issue Mar 26, 2021
This is an attempt to fix a lack of keychain support in darwin/arm64
binaries that have been cross-compiled on other platforms as described
in 99designs#758 and hinted at in
the linked
99designs/keyring@756c48d

Given the keychain support from keyring[1] is provided by cgo, and CGO
is disabled by default in cross-compilation, we need to enable that,
and deal with dev tooling/libraries.

I dug this solution from the Go issues, specifically
golang/go#44112

Be warned, I am not familiar with the ins and outs of Go compilation,
especially when it comes to cross-compilation of CGO code, but at
least in this case, this change allows for a functional cross-compiled
binary.

I fully expect that attempting to cross-compile darwin/arm64 on
anything other than darwin/amd64 (or the opposite way around) is going
to end badly.

[1] https://github.com/99designs/keyring
bazbremner added a commit to bazbremner/aws-vault that referenced this issue Mar 26, 2021
This is an attempt to fix a lack of keychain support in darwin/arm64
binaries that have been cross-compiled on other platforms as described
in 99designs#758 and hinted at in
the linked
99designs/keyring@756c48d

Given the keychain support from keyring[1] is provided by cgo, and CGO
is disabled by default in cross-compilation, we need to enable that,
and deal with dev tooling/libraries.

I dug this solution from the Go issues, specifically
golang/go#44112

Be warned, I am not familiar with the ins and outs of Go compilation,
especially when it comes to cross-compilation of CGO code, but at
least in this case, this change allows for a functional cross-compiled
binary.

I fully expect that attempting to cross-compile darwin/arm64 on
anything other than darwin/amd64 (or the opposite way around) is going
to end badly.

[1] https://github.com/99designs/keyring
@MuweiHe
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@MuweiHe MuweiHe commented Oct 8, 2021

I chose MacOSX.sdk but still got unsupported arch errors:

In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/stdlib.h:62:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/cdefs.h:807:2: error: Unsupported architecture

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@rk0cc
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@rk0cc rk0cc commented Nov 1, 2021

Any detailed information that do the same thing in GitHub Action? Since I don't sure the SDK path is the same form the action one.

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