golang/go

cmd/link: -race doesn't work by default on FreeBSD with cgo

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#73788 opened on May 19, 2025

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BugReportNeedsFixOS-FreeBSDcompiler/runtimehelp wanted

Description

On our freebsd-amd64 builders (14.2-RELEASE-p2):

package main

/*
int foo(void) { return 42; }
*/
import "C"
import "fmt"

func main() {
        fmt.Println(C.foo())
}

$ go build cgo.go
$ ./cgo
42
$ go build -race cgo.go
$ ./cgo
This sanitizer is not compatible with enabled ASLR and binaries compiled with PIE
$ go build -race -ldflags=-linkmode=internal cgo.go
$ ./cgo
42

i.e., using cgo defaults to external linking, but it seems that external linking breaks -race mode.

cc @golang/freebsd

Contributor guide

Tech stack
go
Domain
backend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Go programmingcgo basicsunderstanding of linking
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
Investigate the cmd/link package to understand why external linking with race fails on FreeBSD when using cgo. The issue shows that using ldflags= linkmode=internal works. Look at the linker's handling of race detection on FreeBSD, possibly in src/cmd/link/internal/ld or specific platform files. Check if there is a missing compatibility check for ASLR/PIE when external linking is used with the race detector.