reflect, cmd/internal/gc: look for pointer types by string before synthesizing

The ptrto field of the type data cannot be relied on when dynamic linking: a
type T may be defined in a module that makes no use of pointers to that type,
but another module can contain a package that imports the first one and does use
*T pointers.  The second module will end up defining type data for *T and a
type.*T symbol pointing at it. It's important that calling .PtrTo() on the
refect.Type for T returns this type data and not some synthesized object, so we
need reflect to be able to find it!

Fortunately, the reflect package already has a mechanism for doing this sort of
thing: ChanOf/MapOf/etc look for pre-existing type data by name.  So this change
just extends PtrTo() to consult this too, and changes the compiler to include
pointer types in the data consulted when compiling for dynamic linking.

Change-Id: I3773c066fd0679a62e9fc52a84bf64f1d67662b7
Reviewed-on: https://go-review.googlesource.com/8232
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>

diff --git a/src/cmd/internal/gc/reflect.go b/src/cmd/internal/gc/reflect.go
index dd751d40170c57942acf993ebd6f8c78169479ba..ef3ebe353788683c5a6c77ad64b59fe353176d63 100644 (file)
--- a/src/cmd/internal/gc/reflect.go
+++ b/src/cmd/internal/gc/reflect.go
@@ -1213,6 +1213,20 @@ ok:
        // we want be able to find.
        if t.Sym == nil {
                switch t.Etype {
+               case TPTR32, TPTR64:
+                       // The ptrto field of the type data cannot be relied on when
+                       // dynamic linking: a type T may be defined in a module that makes
+                       // no use of pointers to that type, but another module can contain
+                       // a package that imports the first one and does use *T pointers.
+                       // The second module will end up defining type data for *T and a
+                       // type.*T symbol pointing at it. It's important that calling
+                       // .PtrTo() on the refect.Type for T returns this type data and
+                       // not some synthesized object, so we need reflect to be able to
+                       // find it!
+                       if !Ctxt.Flag_dynlink {
+                               break
+                       }
+                       fallthrough
                case TARRAY, TCHAN, TFUNC, TMAP:
                        slink := typelinksym(t)
                        dsymptr(slink, 0, s, 0)

diff --git a/src/reflect/type.go b/src/reflect/type.go
index e51b2e7bc7df906941ba6e97acd95beabf7a068a..ef4e548d5c9bac3cc45bcdfd17fba16aab0c1579 100644 (file)
--- a/src/reflect/type.go
+++ b/src/reflect/type.go
@@ -1057,6 +1057,17 @@ func (t *rtype) ptrTo() *rtype {
                return &p.rtype
        }
 
+       // Look in known types.
+       s := "*" + *t.string
+       for _, tt := range typesByString(s) {
+               p = (*ptrType)(unsafe.Pointer(tt))
+               if p.elem == t {
+                       ptrMap.m[t] = p
+                       ptrMap.Unlock()
+                       return &p.rtype
+               }
+       }
+
        // Create a new ptrType starting with the description
        // of an *unsafe.Pointer.
        p = new(ptrType)
@@ -1064,7 +1075,6 @@ func (t *rtype) ptrTo() *rtype {
        prototype := *(**ptrType)(unsafe.Pointer(&iptr))
        *p = *prototype
 
-       s := "*" + *t.string
        p.string = &s
 
        // For the type structures linked into the binary, the