4 files changed, 264 insertions, 0 deletions
diff --git a/src/cmd/internal/bio/buf.go b/src/cmd/internal/bio/buf.go
new file mode 100644
index 0000000..c4c2514
--- /dev/null
+++ b/src/cmd/internal/bio/buf.go
@@ -0,0 +1,148 @@
+// Copyright 2015 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 bio implements common I/O abstractions used within the Go toolchain.
+package bio
+
+import (
+	"bufio"
+	"io"
+	"log"
+	"os"
+)
+
+// Reader implements a seekable buffered io.Reader.
+type Reader struct {
+	f *os.File
+	*bufio.Reader
+}
+
+// Writer implements a seekable buffered io.Writer.
+type Writer struct {
+	f *os.File
+	*bufio.Writer
+}
+
+// Create creates the file named name and returns a Writer
+// for that file.
+func Create(name string) (*Writer, error) {
+	f, err := os.Create(name)
+	if err != nil {
+		return nil, err
+	}
+	return &Writer{f: f, Writer: bufio.NewWriter(f)}, nil
+}
+
+// Open returns a Reader for the file named name.
+func Open(name string) (*Reader, error) {
+	f, err := os.Open(name)
+	if err != nil {
+		return nil, err
+	}
+	return NewReader(f), nil
+}
+
+// NewReader returns a Reader from an open file.
+func NewReader(f *os.File) *Reader {
+	return &Reader{f: f, Reader: bufio.NewReader(f)}
+}
+
+func (r *Reader) MustSeek(offset int64, whence int) int64 {
+	if whence == 1 {
+		offset -= int64(r.Buffered())
+	}
+	off, err := r.f.Seek(offset, whence)
+	if err != nil {
+		log.Fatalf("seeking in output: %v", err)
+	}
+	r.Reset(r.f)
+	return off
+}
+
+func (w *Writer) MustSeek(offset int64, whence int) int64 {
+	if err := w.Flush(); err != nil {
+		log.Fatalf("writing output: %v", err)
+	}
+	off, err := w.f.Seek(offset, whence)
+	if err != nil {
+		log.Fatalf("seeking in output: %v", err)
+	}
+	return off
+}
+
+func (r *Reader) Offset() int64 {
+	off, err := r.f.Seek(0, 1)
+	if err != nil {
+		log.Fatalf("seeking in output [0, 1]: %v", err)
+	}
+	off -= int64(r.Buffered())
+	return off
+}
+
+func (w *Writer) Offset() int64 {
+	if err := w.Flush(); err != nil {
+		log.Fatalf("writing output: %v", err)
+	}
+	off, err := w.f.Seek(0, 1)
+	if err != nil {
+		log.Fatalf("seeking in output [0, 1]: %v", err)
+	}
+	return off
+}
+
+func (r *Reader) Close() error {
+	return r.f.Close()
+}
+
+func (w *Writer) Close() error {
+	err := w.Flush()
+	err1 := w.f.Close()
+	if err == nil {
+		err = err1
+	}
+	return err
+}
+
+func (r *Reader) File() *os.File {
+	return r.f
+}
+
+func (w *Writer) File() *os.File {
+	return w.f
+}
+
+// Slice reads the next length bytes of r into a slice.
+//
+// This slice may be backed by mmap'ed memory. Currently, this memory
+// will never be unmapped. The second result reports whether the
+// backing memory is read-only.
+func (r *Reader) Slice(length uint64) ([]byte, bool, error) {
+	if length == 0 {
+		return []byte{}, false, nil
+	}
+
+	data, ok := r.sliceOS(length)
+	if ok {
+		return data, true, nil
+	}
+
+	data = make([]byte, length)
+	_, err := io.ReadFull(r, data)
+	if err != nil {
+		return nil, false, err
+	}
+	return data, false, nil
+}
+
+// SliceRO returns a slice containing the next length bytes of r
+// backed by a read-only mmap'd data. If the mmap cannot be
+// established (limit exceeded, region too small, etc) a nil slice
+// will be returned. If mmap succeeds, it will never be unmapped.
+func (r *Reader) SliceRO(length uint64) []byte {
+	data, ok := r.sliceOS(length)
+	if ok {
+		return data
+	}
+	return nil
+}
diff --git a/src/cmd/internal/bio/buf_mmap.go b/src/cmd/internal/bio/buf_mmap.go
new file mode 100644
index 0000000..d089efa
--- /dev/null
+++ b/src/cmd/internal/bio/buf_mmap.go
@@ -0,0 +1,62 @@
+// Copyright 2019 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.
+
+//go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || (solaris && go1.20)
+
+package bio
+
+import (
+	"runtime"
+	"sync/atomic"
+	"syscall"
+)
+
+// mmapLimit is the maximum number of mmaped regions to create before
+// falling back to reading into a heap-allocated slice. This exists
+// because some operating systems place a limit on the number of
+// distinct mapped regions per process. As of this writing:
+//
+//	Darwin    unlimited
+//	DragonFly   1000000 (vm.max_proc_mmap)
+//	FreeBSD   unlimited
+//	Linux         65530 (vm.max_map_count) // TODO: query /proc/sys/vm/max_map_count?
+//	NetBSD    unlimited
+//	OpenBSD   unlimited
+var mmapLimit int32 = 1<<31 - 1
+
+func init() {
+	// Linux is the only practically concerning OS.
+	if runtime.GOOS == "linux" {
+		mmapLimit = 30000
+	}
+}
+
+func (r *Reader) sliceOS(length uint64) ([]byte, bool) {
+	// For small slices, don't bother with the overhead of a
+	// mapping, especially since we have no way to unmap it.
+	const threshold = 16 << 10
+	if length < threshold {
+		return nil, false
+	}
+
+	// Have we reached the mmap limit?
+	if atomic.AddInt32(&mmapLimit, -1) < 0 {
+		atomic.AddInt32(&mmapLimit, 1)
+		return nil, false
+	}
+
+	// Page-align the offset.
+	off := r.Offset()
+	align := syscall.Getpagesize()
+	aoff := off &^ int64(align-1)
+
+	data, err := syscall.Mmap(int(r.f.Fd()), aoff, int(length+uint64(off-aoff)), syscall.PROT_READ, syscall.MAP_SHARED|syscall.MAP_FILE)
+	if err != nil {
+		return nil, false
+	}
+
+	data = data[off-aoff:]
+	r.MustSeek(int64(length), 1)
+	return data, true
+}
diff --git a/src/cmd/internal/bio/buf_nommap.go b/src/cmd/internal/bio/buf_nommap.go
new file mode 100644
index 0000000..5ebe906
--- /dev/null
+++ b/src/cmd/internal/bio/buf_nommap.go
@@ -0,0 +1,11 @@
+// Copyright 2019 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.
+
+//go:build !aix && !darwin && !dragonfly && !freebsd && !linux && !netbsd && !openbsd && !(solaris && go1.20)
+
+package bio
+
+func (r *Reader) sliceOS(length uint64) ([]byte, bool) {
+	return nil, false
+}
diff --git a/src/cmd/internal/bio/must.go b/src/cmd/internal/bio/must.go
new file mode 100644
index 0000000..3604b29
--- /dev/null
+++ b/src/cmd/internal/bio/must.go
@@ -0,0 +1,43 @@
+// Copyright 2016 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 bio
+
+import (
+	"io"
+	"log"
+)
+
+// MustClose closes Closer c and calls log.Fatal if it returns a non-nil error.
+func MustClose(c io.Closer) {
+	if err := c.Close(); err != nil {
+		log.Fatal(err)
+	}
+}
+
+// MustWriter returns a Writer that wraps the provided Writer,
+// except that it calls log.Fatal instead of returning a non-nil error.
+func MustWriter(w io.Writer) io.Writer {
+	return mustWriter{w}
+}
+
+type mustWriter struct {
+	w io.Writer
+}
+
+func (w mustWriter) Write(b []byte) (int, error) {
+	n, err := w.w.Write(b)
+	if err != nil {
+		log.Fatal(err)
+	}
+	return n, nil
+}
+
+func (w mustWriter) WriteString(s string) (int, error) {
+	n, err := io.WriteString(w.w, s)
+	if err != nil {
+		log.Fatal(err)
+	}
+	return n, nil
+}