purego: SyscallN r2 return float (#67)

* purego: SyscallN r2 return float

We originally discussed this change and decided against doing it because r2 usually returns the upper 64bits on 32bit platforms. However, on Windows amd64 r2 is actually the float return value.

https://github.com/golang/go/blob/7717ac151ae1556541dddc6a817ac04733f1af44/src/runtime/sys_windows_amd64.s#L66

And there is a TODO for arm64 as well.

https://github.com/golang/go/blob/2cea6cdb6016708e89c9472cdb0504731699681d/src/runtime/sys_windows_arm64.s#L91

Doing this makes supporting float returns easier without having to implement a full C calling convention for RegisterFunc

* Add comment describing when r2 is a float

commit: c2f2945fb3c5d7013c1f9bb4fde65685a24eafab
author: TotallyGamerJet · 3y ago · 2022-11-10 19:08 UTC
committer: GitHub · 3y ago · 2022-11-10 19:08 UTC
parent: 54b6cdc
signature: GPG Unverified4AEE18F83AFDEB23 The key is unknown

3 files · +11 -6

M func_darwin.go +6 -1


@@ -4,6 +4,7 @@
4	4		package purego
5	5
6	6		import (
	7	+	"math"
7	8		"reflect"
8	9		"runtime"
9	10		"unsafe"

@@ -110,7 +111,7 @@ func RegisterFunc(fptr interface{}, cfn uintptr) {
110	111		panic("purego: unsupported kind: " + v.Kind().String())
111	112		}
112	113		}
113		-	r1, _, _ := SyscallN(cfn, sysargs...) //TODO: handle float32/64 and struct types
	114	+	r1, r2, _ := SyscallN(cfn, sysargs...) //TODO: handle float32/64 and struct types
114	115		if ty.NumOut() == 0 {
115	116		return nil
116	117		}

@@ -134,6 +135,10 @@ func RegisterFunc(fptr interface{}, cfn uintptr) {
134	135		RegisterFunc(v.Interface(), r1)
135	136		case reflect.String:
136	137		v.SetString(strings.GoString(r1))
	138	+	case reflect.Float32, reflect.Float64:
	139	+	// NOTE: r2 is only the floating return value on 64bit platforms.
	140	+	// On 32bit platforms r2 is the upper part of a 64bit return.
	141	+	v.SetFloat(math.Float64frombits(uint64(r2)))
137	142		default:
138	143		panic("purego: unsupported return kind: " + outType.Kind().String())
139	144		}

 package purego
 import (
+	"math"
 	"reflect"
 	"runtime"
 	"unsafe"
 				panic("purego: unsupported kind: " + v.Kind().String())
 			}
 		}
-		r1, _, _ := SyscallN(cfn, sysargs...) //TODO: handle float32/64 and struct types
+		r1, r2, _ := SyscallN(cfn, sysargs...) //TODO: handle float32/64 and struct types
 		if ty.NumOut() == 0 {
 			return nil
 		}
 			RegisterFunc(v.Interface(), r1)
 		case reflect.String:
 			v.SetString(strings.GoString(r1))
+		case reflect.Float32, reflect.Float64:
+			// NOTE: r2 is only the floating return value on 64bit platforms.
+			// On 32bit platforms r2 is the upper part of a 64bit return.
+			v.SetFloat(math.Float64frombits(uint64(r2)))
 		default:
 			panic("purego: unsupported return kind: " + outType.Kind().String())
 		}

M sys_darwin_amd64.s +1 -1


@@ -64,7 +64,7 @@ TEXT syscall9X(SB), NOSPLIT, $0
64	64
65	65		MOVQ 24(BP), DI // get the pointer back
66	66		MOVQ AX, syscall9Args_r1(DI) // r1
67		-	MOVQ DX, syscall9Args_r2(DI) // r2
	67	+	MOVQ X0, syscall9Args_r2(DI) // r2
68	68
69	69		XORL AX, AX // no error (it's ignored anyway)
70	70		ADDQ $32, SP


@@ -64,7 +64,7 @@ TEXT syscall9X(SB), NOSPLIT, $0
64			64
65		MOVQ 24(BP), DI // get the pointer back	65		MOVQ 24(BP), DI // get the pointer back
66		MOVQ AX, syscall9Args_r1(DI) // r1	66		MOVQ AX, syscall9Args_r1(DI) // r1
67	-	MOVQ DX, syscall9Args_r2(DI) // r2	67	+	MOVQ X0, syscall9Args_r2(DI) // r2
68			68
69		XORL AX, AX // no error (it's ignored anyway)	69		XORL AX, AX // no error (it's ignored anyway)
70		ADDQ $32, SP	70		ADDQ $32, SP

M sys_darwin_arm64.s +4 -4


@@ -57,10 +57,10 @@ TEXT syscall9X(SB), NOSPLIT, $0
57	57
58	58		BL (R12)
59	59
60		-	MOVD 8(RSP), R2 // pop structure pointer
61		-	ADD $16, RSP
62		-	MOVD R0, syscall9Args_r1(R2) // save r1
63		-	MOVD R1, syscall9Args_r2(R2) // save r2
	60	+	MOVD 8(RSP), R2 // pop structure pointer
	61	+	ADD $16, RSP
	62	+	MOVD R0, syscall9Args_r1(R2) // save r1
	63	+	FMOVD F0, syscall9Args_r2(R2) // save r2
64	64		RET
65	65
66	66		// runtime·cgocallback expects a call to the ABIInternal function


@@ -57,10 +57,10 @@ TEXT syscall9X(SB), NOSPLIT, $0
57			57
58		BL (R12)	58		BL (R12)
59			59
60	-	MOVD 8(RSP), R2 // pop structure pointer	60	+	MOVD 8(RSP), R2 // pop structure pointer
61	-	ADD $16, RSP	61	+	ADD $16, RSP
62	-	MOVD R0, syscall9Args_r1(R2) // save r1	62	+	MOVD R0, syscall9Args_r1(R2) // save r1
63	-	MOVD R1, syscall9Args_r2(R2) // save r2	63	+	FMOVD F0, syscall9Args_r2(R2) // save r2
64		RET	64		RET
65			65
66		// runtime·cgocallback expects a call to the ABIInternal function	66		// runtime·cgocallback expects a call to the ABIInternal function