x/sys/unix: Connectx is broken on darwin/amd64

[database64128]

Go version

go version go1.23.5 darwin/arm64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/database64128/Library/Caches/go-build'
GOENV='/Users/database64128/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/database64128/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/database64128/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/homebrew/Cellar/go/1.23.5/libexec'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/opt/homebrew/Cellar/go/1.23.5/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.23.5'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/database64128/Library/Application Support/go/telemetry'
GCCGO='gccgo'
GOARM64='v8.0'
AR='ar'
CC='cc'
CXX='c++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/xd/v25clzgj08d6_cbbp7lwszfr0000gn/T/go-build880517508=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

@wwqgtxx reports that x/sys/unix.Connectx is broken on darwin/amd64. The call succeeds, but does not return the correct number of bytes sent, and may cause memory corruption (fatal error: stack not a power of 2).

They were able to work around the issue by making the following minimal change:

diff --git a/sys/unix/zsyscall_darwin_amd64.go b/sys/unix/zsyscall_darwin_amd64.go
index 24b346e..f8cc117 100644
--- a/sys/unix/zsyscall_darwin_amd64.go
+++ b/sys/unix/zsyscall_darwin_amd64.go
@@ -848,7 +848,7 @@ func connectx(fd int, endpoints *SaEndpoints, associd SaeAssocID, flags uint32,
 	} else {
 		_p0 = unsafe.Pointer(&_zero)
 	}
-	_, _, e1 := syscall_syscall9(libc_connectx_trampoline_addr, uintptr(fd), uintptr(unsafe.Pointer(endpoints)), uintptr(associd), uintptr(flags), uintptr(_p0), uintptr(len(iov)), uintptr(unsafe.Pointer(n)), uintptr(unsafe.Pointer(connid)), 0)
+	_, _, e1 := Syscall9(SYS_CONNECTX, uintptr(fd), uintptr(unsafe.Pointer(endpoints)), uintptr(associd), uintptr(flags), uintptr(_p0), uintptr(len(iov)), uintptr(unsafe.Pointer(n)), uintptr(unsafe.Pointer(connid)), 0)
 	if e1 != 0 {
 		err = errnoErr(e1)
 	}

Connectx was added by me in golang/sys@59665e5 (CL 606155). It does not have any issues on darwin/arm64. We spent hours on this and were not able to pinpoint the exact cause.

What did you see happen?

Connectx is broken on darwin/amd64.

What did you expect to see?

Connectx works on darwin/amd64.

[gabyhelp]

Related Issues

• cmd/link: Link bug on darwin arm64 #53495 (closed)
• x/sys: gomobile build failed for x/crypto/ssh/terminal #22727 (closed)
• cmd/link: Incorrect symbol linked in darwin/arm64 #58935 (closed)
• x/sys/unix: go:linkname must refer to declared function or variable #51091 (closed)
• cmd/go/internal/list: segmentation fault on darwin #67113 (closed)
• x/sys: some trampolines on darwin/amd64 still causing "unexpected return pc for runtime.sigpanic" #45939 (closed)
• x/sys/unix: add TCP_CONNECTION_INFO #53330 (closed)
• os/user: Lookup fails to find users when running as root on darwin-arm64 cross compiled from darwin-amd64 #43543
• clear #57553 (closed)
• Update #70550 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[mknyszek]

CC @golang/runtime

[mknyszek]

Switching to the underlying syscall instead of libc suggests we're probably holding Darwin's libc wrong? Michael P notes maybe stack corruption from a mistake in how it's called? macOS requires us to call through libc for everything, so I'm not sure we should switch to making the underlying syscall directly.

[randall77]

I think syscall9 is incorrect. The return values might not be plumbed back correctly. Try this patch:

diff --git a/src/runtime/sys_darwin.go b/src/runtime/sys_darwin.go
index 5c769a71ea..af10c53659 100644
--- a/src/runtime/sys_darwin.go
+++ b/src/runtime/sys_darwin.go
@@ -72,10 +72,11 @@ func syscall6()
 //go:nosplit
 //go:cgo_unsafe_args
 func syscall_syscall9(fn, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2, err uintptr) {
+       args := struct{ fn, a1, a2, a3, a4, a5, a6, a7, a8, a9, r1, r2, err uintptr }{fn, a1, a2, a3, a4, a5, a6, a7, a8, a9, 0, 0, 0}
        entersyscall()
-       libcCall(unsafe.Pointer(abi.FuncPCABI0(syscall9)), unsafe.Pointer(&fn))
+       libcCall(unsafe.Pointer(abi.FuncPCABI0(syscall9)), unsafe.Pointer(&args))
        exitsyscall()
-       return
+       return args.r1, args.r2, args.err
 }
 func syscall9()