debug/buildinfo: implement for Plan 9 a.out

Plan 9 a.out was not implemented for debug/buildinfo, which
was causing test failures on Plan 9. This adds an implementation,
and causes the tests to pass.

Fixes #53949

Change-Id: I90a307ef9babf8cf381f8746d731cac2206b234a
Reviewed-on: https://go-review.googlesource.com/c/go/+/418014
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

diff --git a/src/debug/buildinfo/buildinfo.go b/src/debug/buildinfo/buildinfo.go
index d1f489275196132c828d1c73ea46e8df51cd05aa..3dbe3fe41def289c3d7ee7b65332c9d226e325ed 100644 (file)
--- a/src/debug/buildinfo/buildinfo.go
+++ b/src/debug/buildinfo/buildinfo.go
@@ -15,6 +15,7 @@ import (
        "debug/elf"
        "debug/macho"
        "debug/pe"
+       "debug/plan9obj"
        "encoding/binary"
        "errors"
        "fmt"
@@ -130,6 +131,12 @@ func readRawBuildInfo(r io.ReaderAt) (vers, mod string, err error) {
                        return "", "", errUnrecognizedFormat
                }
                x = &xcoffExe{f}
+       case hasPlan9Magic(ident):
+               f, err := plan9obj.NewFile(r)
+               if err != nil {
+                       return "", "", errUnrecognizedFormat
+               }
+               x = &plan9objExe{f}
        default:
                return "", "", errUnrecognizedFormat
        }
@@ -205,6 +212,17 @@ func readRawBuildInfo(r io.ReaderAt) (vers, mod string, err error) {
        return vers, mod, nil
 }
 
+func hasPlan9Magic(magic []byte) bool {
+       if len(magic) >= 4 {
+               m := binary.BigEndian.Uint32(magic)
+               switch m {
+               case plan9obj.Magic386, plan9obj.MagicAMD64, plan9obj.MagicARM:
+                       return true
+               }
+       }
+       return false
+}
+
 func decodeString(data []byte) (s string, rest []byte) {
        u, n := binary.Uvarint(data)
        if n <= 0 || u >= uint64(len(data)-n) {
@@ -389,7 +407,7 @@ func (x *xcoffExe) ReadData(addr, size uint64) ([]byte, error) {
                        return data, nil
                }
        }
-       return nil, fmt.Errorf("address not mapped")
+       return nil, errors.New("address not mapped")
 }
 
 func (x *xcoffExe) DataStart() uint64 {
@@ -398,3 +416,34 @@ func (x *xcoffExe) DataStart() uint64 {
        }
        return 0
 }
+
+// plan9objExe is the Plan 9 a.out implementation of the exe interface.
+type plan9objExe struct {
+       f *plan9obj.File
+}
+
+func (x *plan9objExe) DataStart() uint64 {
+       if s := x.f.Section("data"); s != nil {
+               return uint64(s.Offset)
+       }
+       return 0
+}
+
+func (x *plan9objExe) ReadData(addr, size uint64) ([]byte, error) {
+       for _, sect := range x.f.Sections {
+               if uint64(sect.Offset) <= addr && addr <= uint64(sect.Offset+sect.Size-1) {
+                       n := uint64(sect.Offset+sect.Size) - addr
+                       if n > size {
+                               n = size
+                       }
+                       data := make([]byte, n)
+                       _, err := sect.ReadAt(data, int64(addr-uint64(sect.Offset)))
+                       if err != nil {
+                               return nil, err
+                       }
+                       return data, nil
+               }
+       }
+       return nil, errors.New("address not mapped")
+
+}