compiler, runtime: support unsafe.Add and unsafe.Slice

For golang/go#19367
For golang/go#40481

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/338949

1 files changed, 29 insertions, 0 deletions

diff --git a/libgo/go/runtime/slice.go b/libgo/go/runtime/slice.go
index 27a9777..d4c0e90 100644
--- a/libgo/go/runtime/slice.go
+++ b/libgo/go/runtime/slice.go
@@ -18,6 +18,8 @@ import (
 //go:linkname checkMakeSlice
 //go:linkname makeslice64
 //go:linkname growslice
+//go:linkname unsafeslice
+//go:linkname unsafeslice64
 
 type slice struct {
 	array unsafe.Pointer
@@ -127,6 +129,33 @@ func makeslice64(et *_type, len64, cap64 int64) unsafe.Pointer {
 	return makeslice(et, len, cap)
 }
 
+func unsafeslice(et *_type, ptr unsafe.Pointer, len int) {
+	if len == 0 {
+		return
+	}
+
+	if ptr == nil {
+		panic(errorString("unsafe.Slice: ptr is nil and len is not zero"))
+	}
+
+	mem, overflow := math.MulUintptr(et.size, uintptr(len))
+	if overflow || mem > maxAlloc || len < 0 {
+		panicunsafeslicelen()
+	}
+}
+
+func unsafeslice64(et *_type, ptr unsafe.Pointer, len64 int64) {
+	len := int(len64)
+	if int64(len) != len64 {
+		panicunsafeslicelen()
+	}
+	unsafeslice(et, ptr, len)
+}
+
+func panicunsafeslicelen() {
+	panic(errorString("unsafe.Slice: len out of range"))
+}
+
 // growslice handles slice growth during append.
 // It is passed the slice element type, the old slice, and the desired new minimum capacity,
 // and it returns a new slice with at least that capacity, with the old data