return errno value on darwin amd64/arm64 (#416)

It adds support to return the errno value on Darwin amd64/arm64. I don't recall why I removed it and it is needed if we want to ever return it as an error type from RegisterFunc calls. This also brings it back in line with he function doc for SyscallN that says it returns the errno but right now it doesn't.

Updates #244
Updates #390

commit: d8dcb88add90fa48b3fe17d8f9c861514a9b8f77
author: TotallyGamerJet · 8mo ago · 2026-02-14 14:10 UTC
committer: GitHub · 8mo ago · 2026-02-14 14:10 UTC
parent: 587d406
signature: GPG UnverifiedB5690EEEBB952194 The key is unknown

5 files · +47 -2

M dlfcn_darwin.go +1 -0


@@ -17,3 +17,4 @@ const (
17	17		//go:cgo_import_dynamic purego_dlsym dlsym "/usr/lib/libSystem.B.dylib"
18	18		//go:cgo_import_dynamic purego_dlerror dlerror "/usr/lib/libSystem.B.dylib"
19	19		//go:cgo_import_dynamic purego_dlclose dlclose "/usr/lib/libSystem.B.dylib"
	20	+	//go:cgo_import_dynamic purego_error __error "/usr/lib/libSystem.B.dylib"


@@ -17,3 +17,4 @@ const (
17	//go:cgo_import_dynamic purego_dlsym dlsym "/usr/lib/libSystem.B.dylib"	17		//go:cgo_import_dynamic purego_dlsym dlsym "/usr/lib/libSystem.B.dylib"
18	//go:cgo_import_dynamic purego_dlerror dlerror "/usr/lib/libSystem.B.dylib"	18		//go:cgo_import_dynamic purego_dlerror dlerror "/usr/lib/libSystem.B.dylib"
19	//go:cgo_import_dynamic purego_dlclose dlclose "/usr/lib/libSystem.B.dylib"	19		//go:cgo_import_dynamic purego_dlclose dlclose "/usr/lib/libSystem.B.dylib"
		20	+	//go:cgo_import_dynamic purego_error __error "/usr/lib/libSystem.B.dylib"

M sys_amd64.s +6 -0


@@ -91,6 +91,12 @@ TEXT syscall15X(SB), NOSPLIT\|NOFRAME, $0
91	91		MOVQ X0, syscall15Args_f1(DI) // f1
92	92		MOVQ X1, syscall15Args_f2(DI) // f2
93	93
	94	+	#ifdef GOOS_darwin
	95	+	CALL purego_error(SB)
	96	+	MOVD (AX), AX
	97	+	MOVD AX, syscall15Args_a3(DI) // save errno
	98	+	#endif
	99	+
94	100		XORL AX, AX // no error (it's ignored anyway)
95	101		ADDQ $STACK_SIZE, SP
96	102		MOVQ BP, SP


@@ -91,6 +91,12 @@ TEXT syscall15X(SB), NOSPLIT\|NOFRAME, $0
91	MOVQ X0, syscall15Args_f1(DI) // f1	91		MOVQ X0, syscall15Args_f1(DI) // f1
92	MOVQ X1, syscall15Args_f2(DI) // f2	92		MOVQ X1, syscall15Args_f2(DI) // f2
93		93
		94	+	#ifdef GOOS_darwin
		95	+	CALL purego_error(SB)
		96	+	MOVD (AX), AX
		97	+	MOVD AX, syscall15Args_a3(DI) // save errno
		98	+	#endif
		99	+
94	XORL AX, AX // no error (it's ignored anyway)	100		XORL AX, AX // no error (it's ignored anyway)
95	ADDQ $STACK_SIZE, SP	101		ADDQ $STACK_SIZE, SP
96	MOVQ BP, SP	102		MOVQ BP, SP

M sys_arm64.s +5 -0


@@ -89,4 +89,9 @@ TEXT syscall15X(SB), NOSPLIT, $0
89	89		FMOVD F2, syscall15Args_f3(R2) // save f2
90	90		FMOVD F3, syscall15Args_f4(R2) // save f3
91	91
	92	+	#ifdef GOOS_darwin
	93	+	BL purego_error(SB)
	94	+	MOVD (R0), R0
	95	+	MOVD R0, syscall15Args_a3(R2) // save errno
	96	+	#endif
92	97		RET


@@ -89,4 +89,9 @@ TEXT syscall15X(SB), NOSPLIT, $0
89	FMOVD F2, syscall15Args_f3(R2) // save f2	89		FMOVD F2, syscall15Args_f3(R2) // save f2
90	FMOVD F3, syscall15Args_f4(R2) // save f3	90		FMOVD F3, syscall15Args_f4(R2) // save f3
91		91
		92	+	#ifdef GOOS_darwin
		93	+	BL purego_error(SB)
		94	+	MOVD (R0), R0
		95	+	MOVD R0, syscall15Args_a3(R2) // save errno
		96	+	#endif
92	RET	97		RET

M syscall_sysv.go +1 -1


@@ -26,7 +26,7 @@ func syscall_syscall15X(fn, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a
26	26		}
27	27
28	28		runtime_cgocall(syscall15XABI0, unsafe.Pointer(args))
29		-	return args.a1, args.a2, 0
	29	+	return args.a1, args.a2, args.a3
30	30		}
31	31
32	32		// NewCallback converts a Go function to a function pointer conforming to the C calling convention.


@@ -26,7 +26,7 @@ func syscall_syscall15X(fn, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a
26		}	26		}
27			27
28		runtime_cgocall(syscall15XABI0, unsafe.Pointer(args))	28		runtime_cgocall(syscall15XABI0, unsafe.Pointer(args))
29	-	return args.a1, args.a2, 0	29	+	return args.a1, args.a2, args.a3
30		}	30		}
31			31
32		// NewCallback converts a Go function to a function pointer conforming to the C calling convention.	32		// NewCallback converts a Go function to a function pointer conforming to the C calling convention.

M syscall_test.go +34 -1


@@ -5,9 +5,12 @@ package purego_test
5	5
6	6		import (
7	7		"os"
	8	+	"runtime"
8	9		"testing"
	10	+	"unsafe"
9	11
10		-	_ "github.com/ebitengine/purego"
	12	+	"github.com/ebitengine/purego"
	13	+	"github.com/ebitengine/purego/internal/load"
11	14		)
12	15
13	16		func TestOS(t *testing.T) {

@@ -21,3 +24,33 @@ func TestOS(t *testing.T) {
21	24		t.Errorf("failed to Unsetenv: %s", err)
22	25		}
23	26		}
	27	+
	28	+	func TestErrno(t *testing.T) {
	29	+	if runtime.GOOS != "darwin" {
	30	+	t.Skip("platform does not support returning errno from syscall")
	31	+	}
	32	+
	33	+	libc, err := load.OpenLibrary("/usr/lib/libSystem.B.dylib")
	34	+	if err != nil {
	35	+	t.Fatal(err)
	36	+	}
	37	+
	38	+	openSym, err := load.OpenSymbol(libc, "open")
	39	+	if err != nil {
	40	+	t.Fatal(err)
	41	+	}
	42	+
	43	+	r1, _, errno := purego.SyscallN(openSym, uintptr(unsafe.Pointer(&[]byte("_file_that_does_not_exist_\x00")[0])), uintptr(os.O_RDWR))
	44	+	if int32(r1) != -1 {
	45	+	t.Errorf("open returned %d, wanted -1", r1)
	46	+	}
	47	+
	48	+	var strerror func(int32) string
	49	+	purego.RegisterLibFunc(&strerror, libc, "strerror")
	50	+
	51	+	const expected = "No such file or directory"
	52	+	got := strerror(int32(errno))
	53	+	if got != expected {
	54	+	t.Errorf("strerror returned %q, wanted \"%s\"", got, expected)
	55	+	}
	56	+	}


@@ -5,9 +5,12 @@ package purego_test
5			5
6		import (	6		import (
7		"os"	7		"os"
			8	+	"runtime"
8		"testing"	9		"testing"
			10	+	"unsafe"
9			11
10	-	_ "github.com/ebitengine/purego"	12	+	"github.com/ebitengine/purego"
			13	+	"github.com/ebitengine/purego/internal/load"
11		)	14		)
12			15
13		func TestOS(t *testing.T) {	16		func TestOS(t *testing.T) {

@@ -21,3 +24,33 @@ func TestOS(t *testing.T) {
21		t.Errorf("failed to Unsetenv: %s", err)	24		t.Errorf("failed to Unsetenv: %s", err)
22		}	25		}
23		}	26		}
			27	+
			28	+	func TestErrno(t *testing.T) {
			29	+	if runtime.GOOS != "darwin" {
			30	+	t.Skip("platform does not support returning errno from syscall")
			31	+	}
			32	+
			33	+	libc, err := load.OpenLibrary("/usr/lib/libSystem.B.dylib")
			34	+	if err != nil {
			35	+	t.Fatal(err)
			36	+	}
			37	+
			38	+	openSym, err := load.OpenSymbol(libc, "open")
			39	+	if err != nil {
			40	+	t.Fatal(err)
			41	+	}
			42	+
			43	+	r1, _, errno := purego.SyscallN(openSym, uintptr(unsafe.Pointer(&[]byte("_file_that_does_not_exist_\x00")[0])), uintptr(os.O_RDWR))
			44	+	if int32(r1) != -1 {
			45	+	t.Errorf("open returned %d, wanted -1", r1)
			46	+	}
			47	+
			48	+	var strerror func(int32) string
			49	+	purego.RegisterLibFunc(&strerror, libc, "strerror")
			50	+
			51	+	const expected = "No such file or directory"
			52	+	got := strerror(int32(errno))
			53	+	if got != expected {
			54	+	t.Errorf("strerror returned %q, wanted \"%s\"", got, expected)
			55	+	}
			56	+	}