debug/plan9obj: cleanup api

- Don't export Prog structure.
- Remove ProgHeader and ExecTable structures.
- Add Magic, Bss and Entry fields in FileHeader.
- Replace ?_MAGIC variables with constants.
- Ignore final EOF from ReadAt.
- Improve documentation.

Fixes #7989.

LGTM=rsc
R=rsc, bradfitz
CC=golang-codereviews
https://golang.org/cl/91400044

1 files changed, 4 insertions, 59 deletions

diff --git a/src/pkg/debug/plan9obj/plan9obj.go b/src/pkg/debug/plan9obj/plan9obj.go
index 4e3b08f416..af9858562f 100644
--- a/src/pkg/debug/plan9obj/plan9obj.go
+++ b/src/pkg/debug/plan9obj/plan9obj.go
@@ -8,11 +8,6 @@
 
 package plan9obj
 
-import (
-	"bytes"
-	"encoding/binary"
-)
-
 // Plan 9 Program header.
 type prog struct {
 	Magic uint32 /* magic number */
@@ -33,59 +28,9 @@ type sym struct {
 }
 
 const (
-	hsize      = 4 * 8
-	_HDR_MAGIC = 0x00008000 /* header expansion */
-)
-
-func magic(f, b int) string {
-	buf := new(bytes.Buffer)
-	var i uint32 = uint32((f) | ((((4 * (b)) + 0) * (b)) + 7))
-	binary.Write(buf, binary.BigEndian, i)
-	return string(buf.Bytes())
-}
+	Magic64 = 0x8000 // 64-bit expanded header
 
-var (
-	_A_MAGIC = magic(0, 8)           /* 68020 (retired) */
-	_I_MAGIC = magic(0, 11)          /* intel 386 */
-	_J_MAGIC = magic(0, 12)          /* intel 960 (retired) */
-	_K_MAGIC = magic(0, 13)          /* sparc */
-	_V_MAGIC = magic(0, 16)          /* mips 3000 BE */
-	_X_MAGIC = magic(0, 17)          /* att dsp 3210 (retired) */
-	_M_MAGIC = magic(0, 18)          /* mips 4000 BE */
-	_D_MAGIC = magic(0, 19)          /* amd 29000 (retired) */
-	_E_MAGIC = magic(0, 20)          /* arm */
-	_Q_MAGIC = magic(0, 21)          /* powerpc */
-	_N_MAGIC = magic(0, 22)          /* mips 4000 LE */
-	_L_MAGIC = magic(0, 23)          /* dec alpha (retired) */
-	_P_MAGIC = magic(0, 24)          /* mips 3000 LE */
-	_U_MAGIC = magic(0, 25)          /* sparc64 (retired) */
-	_S_MAGIC = magic(_HDR_MAGIC, 26) /* amd64 */
-	_T_MAGIC = magic(_HDR_MAGIC, 27) /* powerpc64 */
-	_R_MAGIC = magic(_HDR_MAGIC, 28) /* arm64 */
+	Magic386   = (4*11+0)*11 + 7
+	MagicAMD64 = (4*26+0)*26 + 7 + Magic64
+	MagicARM   = (4*20+0)*20 + 7
 )
-
-type ExecTable struct {
-	Magic string
-	Ptrsz int
-	Hsize uint32
-}
-
-var exectab = []ExecTable{
-	{_A_MAGIC, 4, hsize},
-	{_I_MAGIC, 4, hsize},
-	{_J_MAGIC, 4, hsize},
-	{_K_MAGIC, 4, hsize},
-	{_V_MAGIC, 4, hsize},
-	{_X_MAGIC, 4, hsize},
-	{_M_MAGIC, 4, hsize},
-	{_D_MAGIC, 4, hsize},
-	{_E_MAGIC, 4, hsize},
-	{_Q_MAGIC, 4, hsize},
-	{_N_MAGIC, 4, hsize},
-	{_L_MAGIC, 4, hsize},
-	{_P_MAGIC, 4, hsize},
-	{_U_MAGIC, 4, hsize},
-	{_S_MAGIC, 8, hsize + 8},
-	{_T_MAGIC, 8, hsize + 8},
-	{_R_MAGIC, 8, hsize + 8},
-}