go/internal/gccgoimporter: add XCOFF support

This commit adds support to read XCOFF files and AIX big archives in
go/internal/gccgoimporter.

Fixes: #29113

Change-Id: Id84d40358ff98fae5a576d1ebdd65980896365b9
Reviewed-on: https://go-review.googlesource.com/c/152720
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/build/deps_test.go

@@ -230,7 +230,7 @@ var pkgDeps = map[string][]string{
 	"go/constant":               {"L4", "go/token", "math/big"},
 	"go/importer":               {"L4", "go/build", "go/internal/gccgoimporter", "go/internal/gcimporter", "go/internal/srcimporter", "go/token", "go/types"},
 	"go/internal/gcimporter":    {"L4", "OS", "go/build", "go/constant", "go/token", "go/types", "text/scanner"},
-	"go/internal/gccgoimporter": {"L4", "OS", "debug/elf", "go/constant", "go/token", "go/types", "text/scanner"},
+	"go/internal/gccgoimporter": {"L4", "OS", "debug/elf", "go/constant", "go/token", "go/types", "internal/xcoff", "text/scanner"},
 	"go/internal/srcimporter":   {"L4", "OS", "fmt", "go/ast", "go/build", "go/parser", "go/token", "go/types", "path/filepath"},
 	"go/types":                  {"L4", "GOPARSER", "container/heap", "go/constant"},
 

src/go/internal/gccgoimporter/ar.go

@@ -9,6 +9,7 @@ import (
 	"debug/elf"
 	"errors"
 	"fmt"
+	"internal/xcoff"
 	"io"
 	"strconv"
 	"strings"
@@ -65,13 +66,13 @@ func arExportData(archive io.ReadSeeker) (io.ReadSeeker, error) {
 	case armagt:
 		return nil, errors.New("unsupported thin archive")
 	case armagb:
-		return nil, errors.New("unsupported AIX big archive")
+		return aixBigArExportData(archive)
 	default:
 		return nil, fmt.Errorf("unrecognized archive file format %q", buf[:])
 	}
 }
 
-// standardArExportData returns export data form a standard archive.
+// standardArExportData returns export data from a standard archive.
 func standardArExportData(archive io.ReadSeeker) (io.ReadSeeker, error) {
 	off := int64(len(armag))
 	for {
@@ -126,6 +127,28 @@ func elfFromAr(member *io.SectionReader) (io.ReadSeeker, error) {
 	return sec.Open(), nil
 }
 
+// aixBigArExportData returns export data from an AIX big archive.
+func aixBigArExportData(archive io.ReadSeeker) (io.ReadSeeker, error) {
+	archiveAt := readerAtFromSeeker(archive)
+	arch, err := xcoff.NewArchive(archiveAt)
+	if err != nil {
+		return nil, err
+	}
+
+	for _, mem := range arch.Members {
+		f, err := arch.GetFile(mem.Name)
+		if err != nil {
+			return nil, err
+		}
+		sdat := f.CSect(".go_export")
+		if sdat != nil {
+			return bytes.NewReader(sdat), nil
+		}
+	}
+
+	return nil, fmt.Errorf(".go_export not found in this archive")
+}
+
 // readerAtFromSeeker turns an io.ReadSeeker into an io.ReaderAt.
 // This is only safe because there won't be any concurrent seeks
 // while this code is executing.

src/go/internal/gccgoimporter/importer.go

@@ -6,9 +6,11 @@
 package gccgoimporter // import "go/internal/gccgoimporter"
 
 import (
+	"bytes"
 	"debug/elf"
 	"fmt"
 	"go/types"
+	"internal/xcoff"
 	"io"
 	"os"
 	"path/filepath"
@@ -65,6 +67,7 @@ const (
 	gccgov3Magic    = "v3;\n"
 	goimporterMagic = "\n$$ "
 	archiveMagic    = "!<ar"
+	aixbigafMagic   = "<big"
 )
 
 // Opens the export data file at the given path. If this is an ELF file,
@@ -89,36 +92,47 @@ func openExportFile(fpath string) (reader io.ReadSeeker, closer io.Closer, err e
 		return
 	}
 
-	var elfreader io.ReaderAt
+	var objreader io.ReaderAt
 	switch string(magic[:]) {
 	case gccgov1Magic, gccgov2Magic, gccgov3Magic, goimporterMagic:
 		// Raw export data.
 		reader = f
 		return
 
-	case archiveMagic:
+	case archiveMagic, aixbigafMagic:
 		reader, err = arExportData(f)
 		return
 
 	default:
-		elfreader = f
-	}
-
-	ef, err := elf.NewFile(elfreader)
-	if err != nil {
-		return
+		objreader = f
 	}
 
+	ef, err := elf.NewFile(objreader)
+	if err == nil {
 		sec := ef.Section(".go_export")
 		if sec == nil {
 			err = fmt.Errorf("%s: .go_export section not found", fpath)
 			return
 		}
-
 		reader = sec.Open()
 		return
 	}
 
+	xf, err := xcoff.NewFile(objreader)
+	if err == nil {
+		sdat := xf.CSect(".go_export")
+		if sdat == nil {
+			err = fmt.Errorf("%s: .go_export section not found", fpath)
+			return
+		}
+		reader = bytes.NewReader(sdat)
+		return
+	}
+
+	err = fmt.Errorf("%s: unrecognized file format", fpath)
+	return
+}
+
 // An Importer resolves import paths to Packages. The imports map records
 // packages already known, indexed by package path.
 // An importer must determine the canonical package path and check imports