cmd/link: __attribute__((weak_import)) is not honored by the internal linker on Darwin

[qmuntal]

Go version

go version go1.25.3 darwin/arm64

Output of go env in your module/workspace:

AR='ar'
CC='clang'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='clang++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/Users/qmuntaldiaz/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/qmuntaldiaz/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/6_/bk27w0c510ld88800_hfj6j00000gn/T/go-build1729745112=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/Users/qmuntaldiaz/code/gotest/go.mod'
GOMODCACHE='/Users/qmuntaldiaz/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/qmuntaldiaz/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/Users/qmuntaldiaz/sdk/go1.25.3'
GOSUMDB='sum.golang.org'
GOTELEMETRY='on'
GOTELEMETRYDIR='/Users/qmuntaldiaz/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/Users/qmuntaldiaz/sdk/go1.25.3/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.25.3'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

Run the following code with go run -ldflags=-linkmode=internal

package main

/*
#cgo LDFLAGS: -Wl,-undefined,dynamic_lookup

extern void __gotest_cgo_null_api(void) __attribute__((weak_import));

int foo(void) {
    if (__gotest_cgo_null_api) return 1;
    return 0;
}
*/
import "C"

func main() {
	println("foo returned:", C.foo())
}

What did you see happen?

The dynamic loader fails to load the Go binary:

go run -ldflags=-linkmode=internal .
dyld[43497]: symbol not found in flat namespace '___gotest_cgo_null_api'
signal: abort trap

What did you expect to see?

The dynamic loader can load the Go binary, and the binary prints 0.

go run -ldflags=-linkmode=internal .
foo returned: 0

Note that this works when using an external linker, and that GCC and LLVM only support __attribute__((weak_import)) on Darwin.

[gopherbot]

Change https://go.dev/cl/713760 mentions this issue: cmd/link: support weak binding on darwin

[gabyhelp]

Related Issues

• cmd/link: can't dynamically import static CFString constants using the internal linker #71471
• cmd/link: support -linkmode=internal with Cgo #38918
• cmd/link: cgo_import_dynamic with internal linking provides wrong symbol #61220 (closed)
• cmd/link: build fails with: combining dwarf failed #75068 (closed)
• cmd/cgo, cmd/ld: support weak imports on OS X #3141 (closed)
• cmd/go/internal/work/security.go: invalid flag in `#cgo darwin LDFLAGS: -Wl,-rpath -Wl,@loader_path` #70923 (closed)
• cmd/link: cgo fails to link on macos 13 beta (arm64) #53372 (closed)
• cmd/link: internal link issue with outline atomics feature on arm64 #39466 (closed)
• cmd/link: external linking does not link dynamic libraries without cgo #42459 (closed)

Related Code Changes

• cmd/link: support weak binding on darwin

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