reflect: make unsafe use of SliceHeader gc-friendly
Revert workaround in compiler and
revert test for compiler workaround.
Tested that the 386 build continues to fail if
the gc change is made without the reflect change.
R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5312041
diff --git a/src/pkg/reflect/value.go b/src/pkg/reflect/value.go
index 056704f..9ddbee0 100644
--- a/src/pkg/reflect/value.go
+++ b/src/pkg/reflect/value.go
@@ -1424,11 +1424,17 @@
typ = iv.typ.toType()
base = (*SliceHeader)(iv.addr).Data
}
- s := new(SliceHeader)
+
+ // Declare slice so that gc can see the base pointer in it.
+ var x []byte
+
+ // Reinterpret as *SliceHeader to edit.
+ s := (*SliceHeader)(unsafe.Pointer(&x))
s.Data = base + uintptr(beg)*typ.Elem().Size()
s.Len = end - beg
- s.Cap = cap - beg
- return valueFromAddr(iv.flag&flagRO, typ, unsafe.Pointer(s))
+ s.Cap = end - beg
+
+ return valueFromAddr(iv.flag&flagRO, typ, unsafe.Pointer(&x))
}
// String returns the string v's underlying value, as a string.
@@ -1654,12 +1660,17 @@
if typ.Kind() != Slice {
panic("reflect: MakeSlice of non-slice type")
}
- s := &SliceHeader{
- Data: uintptr(unsafe.NewArray(typ.Elem(), cap)),
- Len: len,
- Cap: cap,
- }
- return valueFromAddr(0, typ, unsafe.Pointer(s))
+
+ // Declare slice so that gc can see the base pointer in it.
+ var x []byte
+
+ // Reinterpret as *SliceHeader to edit.
+ s := (*SliceHeader)(unsafe.Pointer(&x))
+ s.Data = uintptr(unsafe.NewArray(typ.Elem(), cap))
+ s.Len = len
+ s.Cap = cap
+
+ return valueFromAddr(0, typ, unsafe.Pointer(&x))
}
// MakeChan creates a new channel with the specified type and buffer size.
