cmd/compile,reflect: allow longer type names

Encode the length of type names and tags in a varint encoding
instead of a fixed 2-byte encoding. This allows lengths longer
than 65535 (which can happen for large unnamed structs).

Removed the alignment check for #14962, it isn't relevant any more
since we're no longer reading pointers directly out of this data
(it is encoded as an offset which is copied out bytewise).

Fixes #44155
Update #14962

Change-Id: I6084f6027e5955dc16777c87b0dd5ea2baa49629
Reviewed-on: https://go-review.googlesource.com/c/go/+/318249
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 16 insertions, 13 deletions

diff --git a/src/cmd/compile/internal/reflectdata/reflect.go b/src/cmd/compile/internal/reflectdata/reflect.go
index 01eaf26a0a..8c0e33f6df 100644
--- a/src/cmd/compile/internal/reflectdata/reflect.go
+++ b/src/cmd/compile/internal/reflectdata/reflect.go
@@ -5,6 +5,7 @@
 package reflectdata
 
 import (
+	"encoding/binary"
 	"fmt"
 	"internal/buildcfg"
 	"os"
@@ -473,21 +474,25 @@ func dnameField(lsym *obj.LSym, ot int, spkg *types.Pkg, ft *types.Field) int {
 
 // dnameData writes the contents of a reflect.name into s at offset ot.
 func dnameData(s *obj.LSym, ot int, name, tag string, pkg *types.Pkg, exported bool) int {
-	if len(name) > 1<<16-1 {
-		base.Fatalf("name too long: %s", name)
+	if len(name) >= 1<<29 {
+		base.Fatalf("name too long: %d %s...", len(name), name[:1024])
 	}
-	if len(tag) > 1<<16-1 {
-		base.Fatalf("tag too long: %s", tag)
+	if len(tag) >= 1<<29 {
+		base.Fatalf("tag too long: %d %s...", len(tag), tag[:1024])
 	}
+	var nameLen [binary.MaxVarintLen64]byte
+	nameLenLen := binary.PutUvarint(nameLen[:], uint64(len(name)))
+	var tagLen [binary.MaxVarintLen64]byte
+	tagLenLen := binary.PutUvarint(tagLen[:], uint64(len(tag)))
 
 	// Encode name and tag. See reflect/type.go for details.
 	var bits byte
-	l := 1 + 2 + len(name)
+	l := 1 + nameLenLen + len(name)
 	if exported {
 		bits |= 1 << 0
 	}
 	if len(tag) > 0 {
-		l += 2 + len(tag)
+		l += tagLenLen + len(tag)
 		bits |= 1 << 1
 	}
 	if pkg != nil {
@@ -495,14 +500,12 @@ func dnameData(s *obj.LSym, ot int, name, tag string, pkg *types.Pkg, exported b
 	}
 	b := make([]byte, l)
 	b[0] = bits
-	b[1] = uint8(len(name) >> 8)
-	b[2] = uint8(len(name))
-	copy(b[3:], name)
+	copy(b[1:], nameLen[:nameLenLen])
+	copy(b[1+nameLenLen:], name)
 	if len(tag) > 0 {
-		tb := b[3+len(name):]
-		tb[0] = uint8(len(tag) >> 8)
-		tb[1] = uint8(len(tag))
-		copy(tb[2:], tag)
+		tb := b[1+nameLenLen+len(name):]
+		copy(tb, tagLen[:tagLenLen])
+		copy(tb[tagLenLen:], tag)
 	}
 
 	ot = int(s.WriteBytes(base.Ctxt, int64(ot), b))