[release-branch.go1.8] cmd/compile: added special case for reflect header fields...

The uintptr-typed Data field in reflect.SliceHeader and
reflect.StringHeader needs special treatment because it is
really a pointer.  Add the special treatment in walk for
bug #19168 to escape analysis.

Includes extra debugging that was helpful.

Fixes #19743.

Change-Id: I6dab5002f0d436c3b2a7cdc0156e4fc48a43d6fe
Reviewed-on: https://go-review.googlesource.com/39616
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

diff --git a/src/cmd/compile/internal/gc/esc.go b/src/cmd/compile/internal/gc/esc.go
index 4f37ff0e34f49348a2af83b872db146143065186..f4a70c4ac6f3807133877f106de7f54d738bcaf4 100644 (file)
--- a/src/cmd/compile/internal/gc/esc.go
+++ b/src/cmd/compile/internal/gc/esc.go
@@ -477,6 +477,10 @@ func escAnalyze(all []*Node, recursive bool) {
        for _, n := range all {
                if n.Op == ODCLFUNC {
                        n.Esc = EscFuncPlanned
+                       if Debug['m'] > 3 {
+                               Dump("escAnalyze", n)
+                       }
+
                }
        }
 
@@ -1675,7 +1679,10 @@ func (e *EscState) escflows(dst, src *Node, why *EscStep) {
        }
 
        // Don't bother building a graph for scalars.
-       if src.Type != nil && !haspointers(src.Type) {
+       if src.Type != nil && !haspointers(src.Type) && !isReflectHeaderDataField(src) {
+               if Debug['m'] > 3 {
+                       fmt.Printf("%v::NOT flows:: %S <- %S\n", linestr(lineno), dst, src)
+               }
                return
        }
 

diff --git a/test/fixedbugs/issue19743.go b/test/fixedbugs/issue19743.go
new file mode 100644 (file)
index 0000000..e57b19c
--- /dev/null
+++ b/test/fixedbugs/issue19743.go
@@ -0,0 +1,31 @@
+// errorcheck -0 -m -l
+
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package foo
+
+// Escape analysis needs to treat the uintptr-typed reflect.*Header fields as pointers.
+
+import (
+       "reflect"
+       "unsafe"
+)
+
+type immutableBytes []byte
+
+// Bug was failure to leak param b.
+func toString(b immutableBytes) string { // ERROR "leaking param: b$"
+       var s string
+       if len(b) == 0 {
+               return s
+       }
+
+       strHeader := (*reflect.StringHeader)(unsafe.Pointer(&s))         // ERROR "toString &s does not escape$"
+       strHeader.Data = (*reflect.SliceHeader)(unsafe.Pointer(&b)).Data // ERROR "toString &b does not escape$"
+
+       l := len(b)
+       strHeader.Len = l
+       return s
+}