fix(cgo): add unsafe.Pointer intermediary in halPortWrite/halPortPeek casts

[Copilot]

CGO does not allow direct conversion from *byte to *C.char; the cast must go through unsafe.Pointer. This caused a build failure in the passthrough example.

Changes

• src/hal/hal-go/cgo.go: Wrap unsafe.SliceData(...) in unsafe.Pointer(...) before casting to *C.char in both halPortWrite and halPortPeek.

// Before (broken)
ret := C.go_hal_port_write(portPtr, (*C.char)(unsafe.SliceData(data)), C.uint(len(data)))

// After (fixed)
ret := C.go_hal_port_write(portPtr, (*C.char)(unsafe.Pointer(unsafe.SliceData(data))), C.uint(len(data)))

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• linuxcnc.org
  • Triggering command: /usr/bin/go go mod tidy -e (dns block)
  • Triggering command: /usr/bin/go go get -v ./... -O2 -g -Wall -Werror -fno-stack-protector -Wdeclaration-after-statement -ffile-prefix-map=/opt/hostedtoolcache/go/1.24.13/x64=/_/GOROOT -frandom-seed=mCpk0xsceg30uswMFUbN (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

Build failure: CGO type conversion error in cgo.go

When building the passthrough example, the Go compiler fails with:

# linuxcnc.org/hal
../../cgo.go:193:48: cannot convert unsafe.SliceData(data) (value of type *byte) to type *_Ctype_char
../../cgo.go:204:47: cannot convert unsafe.SliceData(buf) (value of type *byte) to type *_Ctype_char

Root cause

In src/hal/hal-go/cgo.go, the halPortWrite and halPortPeek functions pass unsafe.SliceData(data) directly to C functions that expect *C.char. The Go compiler doesn't allow a direct conversion from *byte to *C.char — it must go through unsafe.Pointer first.

Fix

In src/hal/hal-go/cgo.go, change the two affected lines:

Line ~193 in halPortWrite:

// BEFORE (broken):
ret := C.go_hal_port_write(portPtr, (*C.char)(unsafe.SliceData(data)), C.uint(len(data)))

// AFTER (fixed):
ret := C.go_hal_port_write(portPtr, (*C.char)(unsafe.Pointer(unsafe.SliceData(data))), C.uint(len(data)))

Line ~204 in halPortPeek:

// BEFORE (broken):
ret := C.go_hal_port_peek(portPtr, (*C.char)(unsafe.SliceData(buf)), C.uint(count))

// AFTER (fixed):
ret := C.go_hal_port_peek(portPtr, (*C.char)(unsafe.Pointer(unsafe.SliceData(buf))), C.uint(count))

The fix wraps unsafe.SliceData(...) in unsafe.Pointer(...) before casting to *C.char, which is the standard CGO pattern for pointer type conversions.

This pull request was created from Copilot chat.

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