backport for fix of CVE-2023-39323 to Go1.15

https://go-review.googlesource.com/c/go/+/533215

misc/cgo/errors/errors_test.go

@@ -107,6 +107,7 @@ func TestReportsTypeErrors(t *testing.T) {
 	for _, file := range []string{
 		"err1.go",
 		"err2.go",
+		"err5.go",
 		"issue11097a.go",
 		"issue11097b.go",
 		"issue18452.go",

misc/cgo/errors/testdata/err5.go

@@ -0,0 +1,7 @@
+// Copyright 2023 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 main
+//line /tmp/_cgo_.go:1
+//go:cgo_dynamic_linker "/elf/interp" // ERROR HERE: only allowed in cgo-generated code
+func main() {}

src/cmd/compile/internal/gc/noder.go

@@ -1612,14 +1612,33 @@ func (p *noder) pragma(pos syntax.Pos, blankLine bool, text string, old syntax.P
 	return pragma
 }
 
+// trimFilename returns the "trimmed" filename of b, which is the
+// absolute filename after applying -trimpath processing. This
+// filename form is suitable for use in object files and export data.
+//
+// If b's filename has already been trimmed (i.e., because it was read
+// in from an imported package's export data), then the filename is
+// returned unchanged.
+func trimFilename(b *syntax.PosBase) string {
+        filename := b.Filename()
+        if !b.Trimmed() {
+                dir := ""
+                if b.IsFileBase() {
+                        dir = Ctxt.Pathname
+                }
+                filename = objabi.AbsFile(dir, filename, pathPrefix)
+        }
+        return filename
+}
+
 // isCgoGeneratedFile reports whether pos is in a file
 // generated by cgo, which is to say a file with name
 // beginning with "_cgo_". Such files are allowed to
 // contain cgo directives, and for security reasons
 // (primarily misuse of linker flags), other files are not.
 // See golang.org/issue/23672.
 func isCgoGeneratedFile(pos syntax.Pos) bool {
-	return strings.HasPrefix(filepath.Base(filepath.Clean(fileh(pos.Base().Filename()))), "_cgo_")
+	return strings.HasPrefix(filepath.Base(trimFilename(pos.Base().Pos().Base())), "_cgo_")
 }
 
 // safeArg reports whether arg is a "safe" command-line argument,

src/cmd/compile/internal/syntax/parser.go

@@ -146,11 +146,14 @@ func (p *parser) updateBase(pos Pos, tline, tcol uint, text string) {
 	// If we have a column (//line filename:line:col form),
 	// an empty filename means to use the previous filename.
 	filename := text[:i-1] // lop off ":line"
+	trimmed := false
 	if filename == "" && ok2 {
 		filename = p.base.Filename()
+		trimmed = p.base.Trimmed()
 	}
 
-	p.base = NewLineBase(pos, filename, line, col)
+	p.base = NewLineBase(pos, filename, trimmed, line, col)
+
 }
 
 func commentText(s string) string {

src/cmd/compile/internal/syntax/pos.go

@@ -93,24 +93,30 @@ type PosBase struct {
 	pos       Pos
 	filename  string
 	line, col uint32
+	trimmed bool // whether -trimpath has been applied
 }
 
 // NewFileBase returns a new PosBase for the given filename.
 // A file PosBase's position is relative to itself, with the
 // position being filename:1:1.
 func NewFileBase(filename string) *PosBase {
-	base := &PosBase{MakePos(nil, linebase, colbase), filename, linebase, colbase}
-	base.pos.base = base
-	return base
+        return NewTrimmedFileBase(filename, false)
+}
+
+// NewTrimmedFileBase is like NewFileBase, but allows specifying Trimmed.
+func NewTrimmedFileBase(filename string, trimmed bool) *PosBase {
+        base := &PosBase{MakePos(nil, linebase, colbase), filename, linebase, colbase, trimmed}
+        base.pos.base = base
+        return base
 }
 
 // NewLineBase returns a new PosBase for a line directive "line filename:line:col"
 // relative to pos, which is the position of the character immediately following
 // the comment containing the line directive. For a directive in a line comment,
 // that position is the beginning of the next line (i.e., the newline character
 // belongs to the line comment).
-func NewLineBase(pos Pos, filename string, line, col uint) *PosBase {
-	return &PosBase{pos, filename, sat32(line), sat32(col)}
+func NewLineBase(pos Pos, filename string, trimmed bool, line, col uint) *PosBase {
+        return &PosBase{pos, filename, sat32(line), sat32(col), trimmed}
 }
 
 func (base *PosBase) IsFileBase() bool {
@@ -148,6 +154,13 @@ func (base *PosBase) Col() uint {
 	return uint(base.col)
 }
 
+func (base *PosBase) Trimmed() bool {
+        if base == nil {
+                return false
+        }
+        return base.trimmed
+}
+
 func sat32(x uint) uint32 {
 	if x > PosMax {
 		return PosMax