From: Jeff R. Allen <jra@nella.org>
Date: Wed, 8 Nov 2017 08:43:56 +0000 (+0100)
Subject: cmd/compile: do not write slices/strings > 2g
X-Git-Tag: go1.10beta1~338
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=d7ac9bb9927bfdbb1e6aa582d94e10b3374b88ce;p=gostls13.git

cmd/compile: do not write slices/strings > 2g

The linker will refuse to work on objects larger than
2e9 bytes (see issue #9862 for why).

With this change, the compiler gives a useful error
message explaining this, instead of leaving it to the
linker to give a cryptic message later.

Fixes #1700.

Change-Id: I3933ce08ef846721ece7405bdba81dff644cb004
Reviewed-on: https://go-review.googlesource.com/74330
Reviewed-by: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
---

diff --git a/src/cmd/compile/internal/gc/obj.go b/src/cmd/compile/internal/gc/obj.go
index fdde0ce35b..874c59cb44 100644
--- a/src/cmd/compile/internal/gc/obj.go
+++ b/src/cmd/compile/internal/gc/obj.go
@@ -9,6 +9,7 @@ import (
 	"cmd/internal/bio"
 	"cmd/internal/obj"
 	"cmd/internal/objabi"
+	"cmd/internal/src"
 	"crypto/sha256"
 	"fmt"
 	"io"
@@ -330,7 +331,7 @@ func dbvec(s *obj.LSym, off int, bv bvec) int {
 	return off
 }
 
-func stringsym(s string) (data *obj.LSym) {
+func stringsym(pos src.XPos, s string) (data *obj.LSym) {
 	var symname string
 	if len(s) > 100 {
 		// Huge strings are hashed to avoid long names in object files.
@@ -351,7 +352,7 @@ func stringsym(s string) (data *obj.LSym) {
 
 	if !symdata.SeenGlobl() {
 		// string data
-		off := dsname(symdata, 0, s)
+		off := dsname(symdata, 0, s, pos, "string")
 		ggloblsym(symdata, int32(off), obj.DUPOK|obj.RODATA|obj.LOCAL)
 	}
 
@@ -367,7 +368,7 @@ func slicebytes(nam *Node, s string, len int) {
 	sym.Def = asTypesNode(newname(sym))
 
 	lsym := sym.Linksym()
-	off := dsname(lsym, 0, s)
+	off := dsname(lsym, 0, s, nam.Pos, "slice")
 	ggloblsym(lsym, int32(off), obj.NOPTR|obj.LOCAL)
 
 	if nam.Op != ONAME {
@@ -380,7 +381,15 @@ func slicebytes(nam *Node, s string, len int) {
 	duintptr(nsym, off, uint64(len))
 }
 
-func dsname(s *obj.LSym, off int, t string) int {
+func dsname(s *obj.LSym, off int, t string, pos src.XPos, what string) int {
+	// Objects that are too large will cause the data section to overflow right away,
+	// causing a cryptic error message by the linker. Check for oversize objects here
+	// and provide a useful error message instead.
+	if int64(len(t)) > 2e9 {
+		yyerrorl(pos, "%v with length %v is too big", what, len(t))
+		return 0
+	}
+
 	s.WriteString(Ctxt, int64(off), len(t), t)
 	return off + len(t)
 }
@@ -445,7 +454,7 @@ func gdata(nam *Node, nr *Node, wid int) {
 			}
 
 		case string:
-			symdata := stringsym(u)
+			symdata := stringsym(nam.Pos, u)
 			s.WriteAddr(Ctxt, nam.Xoffset, Widthptr, symdata, 0)
 			s.WriteInt(Ctxt, nam.Xoffset+int64(Widthptr), Widthptr, int64(len(u)))
 
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 7780953e90..f30016b8a9 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -5067,7 +5067,7 @@ func (e *ssafn) StringData(s string) interface{} {
 	if e.strings == nil {
 		e.strings = make(map[string]interface{})
 	}
-	data := stringsym(s)
+	data := stringsym(e.curfn.Pos, s)
 	e.strings[s] = data
 	return data
 }
diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go
index 847f6991ee..7e47c286e2 100644
--- a/src/cmd/compile/internal/gc/walk.go
+++ b/src/cmd/compile/internal/gc/walk.go
@@ -1744,7 +1744,7 @@ opswitch:
 		// Emit string symbol now to avoid emitting
 		// any concurrently during the backend.
 		if s, ok := n.Val().U.(string); ok {
-			_ = stringsym(s)
+			_ = stringsym(n.Pos, s)
 		}
 	}
 
diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index a6e03baafa..e8e7a53bdb 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -1008,11 +1008,13 @@ func (d bySizeAndName) Less(i, j int) bool {
 	return s1.name < s2.name
 }
 
-const cutoff int64 = 2e9 // 2 GB (or so; looks better in errors than 2^31)
+// cutoff is the maximum data section size permitted by the linker
+// (see issue #9862).
+const cutoff = 2e9 // 2 GB (or so; looks better in errors than 2^31)
 
 func checkdatsize(ctxt *Link, datsize int64, symn sym.SymKind) {
 	if datsize > cutoff {
-		Errorf(nil, "too much data in section %v (over %d bytes)", symn, cutoff)
+		Errorf(nil, "too much data in section %v (over %v bytes)", symn, cutoff)
 	}
 }