all: use io.{SeekStart, SeekCurrent, SeekEnd}

Currently we include these symbols in bootstrap code.

Change-Id: I19b504237b0344f0e87cda0fbe651811c72daba1
GitHub-Last-Rev: 5134baec387659c5e2ca8c4fc65a5e73c07f00ce
GitHub-Pull-Request: golang/go#62368
Reviewed-on: https://go-review.googlesource.com/c/go/+/524258
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: qiulaidongfeng <2645477756@qq.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

6 files changed, 13 insertions, 27 deletions

diff --git a/src/debug/elf/file.go b/src/debug/elf/file.go
index 87773541f0..4765c468d8 100644
--- a/src/debug/elf/file.go
+++ b/src/debug/elf/file.go
@@ -29,17 +29,6 @@ import (
 	"strings"
 )
 
-// seekStart, seekCurrent, seekEnd are copies of
-// io.SeekStart, io.SeekCurrent, and io.SeekEnd.
-// We can't use the ones from package io because
-// we want this code to build with Go 1.4 during
-// cmd/dist bootstrap.
-const (
-	seekStart   int = 0
-	seekCurrent int = 1
-	seekEnd     int = 2
-)
-
 // TODO: error reporting detail
 
 /*
@@ -332,7 +321,7 @@ func NewFile(r io.ReaderAt) (*File, error) {
 	switch f.Class {
 	case ELFCLASS32:
 		hdr := new(Header32)
-		sr.Seek(0, seekStart)
+		sr.Seek(0, io.SeekStart)
 		if err := binary.Read(sr, f.ByteOrder, hdr); err != nil {
 			return nil, err
 		}
@@ -351,7 +340,7 @@ func NewFile(r io.ReaderAt) (*File, error) {
 		shstrndx = int(hdr.Shstrndx)
 	case ELFCLASS64:
 		hdr := new(Header64)
-		sr.Seek(0, seekStart)
+		sr.Seek(0, io.SeekStart)
 		if err := binary.Read(sr, f.ByteOrder, hdr); err != nil {
 			return nil, err
 		}
@@ -402,7 +391,7 @@ func NewFile(r io.ReaderAt) (*File, error) {
 	f.Progs = make([]*Prog, phnum)
 	for i := 0; i < phnum; i++ {
 		off := phoff + int64(i)*int64(phentsize)
-		sr.Seek(off, seekStart)
+		sr.Seek(off, io.SeekStart)
 		p := new(Prog)
 		switch f.Class {
 		case ELFCLASS32:
@@ -453,7 +442,7 @@ func NewFile(r io.ReaderAt) (*File, error) {
 	// header at index 0.
 	if shoff > 0 && shnum == 0 {
 		var typ, link uint32
-		sr.Seek(shoff, seekStart)
+		sr.Seek(shoff, io.SeekStart)
 		switch f.Class {
 		case ELFCLASS32:
 			sh := new(Section32)
@@ -506,7 +495,7 @@ func NewFile(r io.ReaderAt) (*File, error) {
 	names := make([]uint32, 0, c)
 	for i := 0; i < shnum; i++ {
 		off := shoff + int64(i)*int64(shentsize)
-		sr.Seek(off, seekStart)
+		sr.Seek(off, io.SeekStart)
 		s := new(Section)
 		switch f.Class {
 		case ELFCLASS32:
diff --git a/src/debug/elf/reader.go b/src/debug/elf/reader.go
index a45843619e..eab437318d 100644
--- a/src/debug/elf/reader.go
+++ b/src/debug/elf/reader.go
@@ -63,11 +63,11 @@ func (r *readSeekerFromReader) Read(p []byte) (n int, err error) {
 func (r *readSeekerFromReader) Seek(offset int64, whence int) (int64, error) {
 	var newOffset int64
 	switch whence {
-	case seekStart:
+	case io.SeekStart:
 		newOffset = offset
-	case seekCurrent:
+	case io.SeekCurrent:
 		newOffset = r.offset + offset
-	case seekEnd:
+	case io.SeekEnd:
 		newOffset = r.size + offset
 	default:
 		return 0, os.ErrInvalid
diff --git a/src/debug/pe/file.go b/src/debug/pe/file.go
index 06c160105f..e7be4ef1a0 100644
--- a/src/debug/pe/file.go
+++ b/src/debug/pe/file.go
@@ -27,9 +27,6 @@ import (
 	"strings"
 )
 
-// Avoid use of post-Go 1.4 io features, to make safe for toolchain bootstrap.
-const seekStart = 0
-
 // A File represents an open PE file.
 type File struct {
 	FileHeader
@@ -92,7 +89,7 @@ func NewFile(r io.ReaderAt) (*File, error) {
 	} else {
 		base = int64(0)
 	}
-	sr.Seek(base, seekStart)
+	sr.Seek(base, io.SeekStart)
 	if err := binary.Read(sr, binary.LittleEndian, &f.FileHeader); err != nil {
 		return nil, err
 	}
@@ -129,7 +126,7 @@ func NewFile(r io.ReaderAt) (*File, error) {
 	}
 
 	// Seek past file header.
-	_, err = sr.Seek(base+int64(binary.Size(f.FileHeader)), seekStart)
+	_, err = sr.Seek(base+int64(binary.Size(f.FileHeader)), io.SeekStart)
 	if err != nil {
 		return nil, err
 	}
diff --git a/src/debug/pe/section.go b/src/debug/pe/section.go
index 70d0c220ce..bab067e06b 100644
--- a/src/debug/pe/section.go
+++ b/src/debug/pe/section.go
@@ -54,7 +54,7 @@ func readRelocs(sh *SectionHeader, r io.ReadSeeker) ([]Reloc, error) {
 	if sh.NumberOfRelocations <= 0 {
 		return nil, nil
 	}
-	_, err := r.Seek(int64(sh.PointerToRelocations), seekStart)
+	_, err := r.Seek(int64(sh.PointerToRelocations), io.SeekStart)
 	if err != nil {
 		return nil, fmt.Errorf("fail to seek to %q section relocations: %v", sh.Name, err)
 	}
diff --git a/src/debug/pe/string.go b/src/debug/pe/string.go
index a156bbef05..6cd08aed71 100644
--- a/src/debug/pe/string.go
+++ b/src/debug/pe/string.go
@@ -31,7 +31,7 @@ func readStringTable(fh *FileHeader, r io.ReadSeeker) (StringTable, error) {
 		return nil, nil
 	}
 	offset := fh.PointerToSymbolTable + COFFSymbolSize*fh.NumberOfSymbols
-	_, err := r.Seek(int64(offset), seekStart)
+	_, err := r.Seek(int64(offset), io.SeekStart)
 	if err != nil {
 		return nil, fmt.Errorf("fail to seek to string table: %v", err)
 	}
diff --git a/src/debug/pe/symbol.go b/src/debug/pe/symbol.go
index 2e03af76bd..02f24ec29d 100644
--- a/src/debug/pe/symbol.go
+++ b/src/debug/pe/symbol.go
@@ -55,7 +55,7 @@ func readCOFFSymbols(fh *FileHeader, r io.ReadSeeker) ([]COFFSymbol, error) {
 	if fh.NumberOfSymbols <= 0 {
 		return nil, nil
 	}
-	_, err := r.Seek(int64(fh.PointerToSymbolTable), seekStart)
+	_, err := r.Seek(int64(fh.PointerToSymbolTable), io.SeekStart)
 	if err != nil {
 		return nil, fmt.Errorf("fail to seek to symbol table: %v", err)
 	}