cmd/link: don't reset variable size when handling -X flag

The linker's -X flag allows setting/changing a string variable's
content at link time. Currently it resets its size then write a
new string header pointing to the new content. This mostly works.
But under ASAN build the string variable can have larger size
than the usual 2 words, due to the red zone. Resetting the size
can cause the variable to "overlap" (in ASAN's view) with other
variables. Don't reset the size.

Fixes #56175.

Change-Id: Ib364208201a7a2fd7f44f9b1797834198736a405
Reviewed-on: https://go-review.googlesource.com/c/go/+/442635
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>

misc/cgo/testsanitizers/asan_test.go

@@ -5,6 +5,7 @@
 package sanitizers_test
 
 import (
+	"fmt"
 	"strings"
 	"testing"
 )
@@ -97,3 +98,44 @@ func TestASAN(t *testing.T) {
 		})
 	}
 }
+
+func TestASANLinkerX(t *testing.T) {
+	// Test ASAN with linker's -X flag (see issue 56175).
+	goos, err := goEnv("GOOS")
+	if err != nil {
+		t.Fatal(err)
+	}
+	goarch, err := goEnv("GOARCH")
+	if err != nil {
+		t.Fatal(err)
+	}
+	// The asan tests require support for the -asan option.
+	if !aSanSupported(goos, goarch) {
+		t.Skipf("skipping on %s/%s; -asan option is not supported.", goos, goarch)
+	}
+	if !compilerRequiredAsanVersion(goos, goarch) {
+		t.Skipf("skipping on %s/%s: too old version of compiler", goos, goarch)
+	}
+
+	t.Parallel()
+	requireOvercommit(t)
+	config := configure("address")
+	config.skipIfCSanitizerBroken(t)
+
+	dir := newTempDir(t)
+	defer dir.RemoveAll(t)
+
+	var ldflags string
+	for i := 1; i <= 10; i++ {
+		ldflags += fmt.Sprintf("-X=main.S%d=%d -X=misc/cgo/testsanitizers/testdata/asan_linkerx/p.S%d=%d ", i, i, i, i)
+	}
+
+	// build the binary
+	outPath := dir.Join("main.exe")
+	cmd := config.goCmd("build", "-ldflags="+ldflags, "-o", outPath)
+	cmd.Dir = srcPath("asan_linkerx")
+	mustRun(t, cmd)
+
+	// run the binary
+	mustRun(t, hangProneCmd(outPath))
+}

misc/cgo/testsanitizers/testdata/asan_linkerx/main.go

@@ -0,0 +1,28 @@
+package main
+
+import "misc/cgo/testsanitizers/testdata/asan_linkerx/p"
+
+func pstring(s *string) {
+	println(*s)
+}
+
+func main() {
+	all := []*string{
+		&S1, &S2, &S3, &S4, &S5, &S6, &S7, &S8, &S9, &S10,
+		&p.S1, &p.S2, &p.S3, &p.S4, &p.S5, &p.S6, &p.S7, &p.S8, &p.S9, &p.S10,
+	}
+	for _, ps := range all {
+		pstring(ps)
+	}
+}
+
+var S1 string
+var S2 string
+var S3 string
+var S4 string
+var S5 string
+var S6 string
+var S7 string
+var S8 string
+var S9 string
+var S10 string

misc/cgo/testsanitizers/testdata/asan_linkerx/p/p.go

@@ -0,0 +1,12 @@
+package p
+
+var S1 string
+var S2 string
+var S3 string
+var S4 string
+var S5 string
+var S6 string
+var S7 string
+var S8 string
+var S9 string
+var S10 string

src/cmd/link/internal/ld/data.go

@@ -1127,12 +1127,14 @@ func addstrdata(arch *sys.Arch, l *loader.Loader, name, value string) {
 	sbld.Addstring(value)
 	sbld.SetType(sym.SRODATA)
 
-	bld.SetSize(0)
+	// Don't reset the variable's size. String variable usually has size of
-	bld.SetData(make([]byte, 0, arch.PtrSize*2))
+	// 2*PtrSize, but in ASAN build it can be larger due to red zone.
+	// (See issue 56175.)
+	bld.SetData(make([]byte, arch.PtrSize*2))
 	bld.SetReadOnly(false)
 	bld.ResetRelocs()
-	bld.AddAddrPlus(arch, sbld.Sym(), 0)
+	bld.SetAddrPlus(arch, 0, sbld.Sym(), 0)
-	bld.AddUint(arch, uint64(len(value)))
+	bld.SetUint(arch, int64(arch.PtrSize), uint64(len(value)))
 }
 
 func (ctxt *Link) dostrdata() {