cmd/link: mmap output file
Use mmap for writing most of the output file content,
specifically, the sections and segments. After layout, we
already know the sizes and file offsets for the sections and
segments. So we can just write the bytes by copying to a mmap'd
backing store.
The writing of the output file is split into two parts. The first
part writes the sections and segments to the mmap'd region. The
second part writes some extra content, for which we don't know
the size, so we use direct file IO.
This is in preparation for mmap'ing input files read-only.
Change-Id: I9f3b4616a9f96bfd5c940d74c50aacd6d330f7d2
Reviewed-on: https://go-review.googlesource.com/c/go/+/170738
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
diff --git a/src/cmd/link/internal/amd64/asm.go b/src/cmd/link/internal/amd64/asm.go
index fca4877..7dbe99c 100644
--- a/src/cmd/link/internal/amd64/asm.go
+++ b/src/cmd/link/internal/amd64/asm.go
@@ -704,7 +704,9 @@
ctxt.Out.SeekSet(int64(ld.Segdwarf.Fileoff))
ld.Dwarfblk(ctxt, int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
+}
+func asmb2(ctxt *ld.Link) {
machlink := int64(0)
if ctxt.HeadType == objabi.Hdarwin {
machlink = ld.Domacholink(ctxt)
diff --git a/src/cmd/link/internal/amd64/obj.go b/src/cmd/link/internal/amd64/obj.go
index eeeed1a..23741eb 100644
--- a/src/cmd/link/internal/amd64/obj.go
+++ b/src/cmd/link/internal/amd64/obj.go
@@ -54,6 +54,7 @@
Archreloc: archreloc,
Archrelocvariant: archrelocvariant,
Asmb: asmb,
+ Asmb2: asmb2,
Elfreloc1: elfreloc1,
Elfsetupplt: elfsetupplt,
Gentext: gentext,
diff --git a/src/cmd/link/internal/arm/asm.go b/src/cmd/link/internal/arm/asm.go
index 7ea1fe5..43d387c 100644
--- a/src/cmd/link/internal/arm/asm.go
+++ b/src/cmd/link/internal/arm/asm.go
@@ -800,7 +800,9 @@
ctxt.Out.SeekSet(int64(ld.Segdwarf.Fileoff))
ld.Dwarfblk(ctxt, int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
+}
+func asmb2(ctxt *ld.Link) {
machlink := uint32(0)
if ctxt.HeadType == objabi.Hdarwin {
machlink = uint32(ld.Domacholink(ctxt))
diff --git a/src/cmd/link/internal/arm/obj.go b/src/cmd/link/internal/arm/obj.go
index ea91711..45a406e 100644
--- a/src/cmd/link/internal/arm/obj.go
+++ b/src/cmd/link/internal/arm/obj.go
@@ -52,6 +52,7 @@
Archrelocvariant: archrelocvariant,
Trampoline: trampoline,
Asmb: asmb,
+ Asmb2: asmb2,
Elfreloc1: elfreloc1,
Elfsetupplt: elfsetupplt,
Gentext: gentext,
diff --git a/src/cmd/link/internal/arm64/asm.go b/src/cmd/link/internal/arm64/asm.go
index 5ba038d..c832099 100644
--- a/src/cmd/link/internal/arm64/asm.go
+++ b/src/cmd/link/internal/arm64/asm.go
@@ -426,7 +426,9 @@
ctxt.Out.SeekSet(int64(ld.Segdwarf.Fileoff))
ld.Dwarfblk(ctxt, int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
+}
+func asmb2(ctxt *ld.Link) {
machlink := uint32(0)
if ctxt.HeadType == objabi.Hdarwin {
machlink = uint32(ld.Domacholink(ctxt))
diff --git a/src/cmd/link/internal/arm64/obj.go b/src/cmd/link/internal/arm64/obj.go
index 0420201..2f8a141 100644
--- a/src/cmd/link/internal/arm64/obj.go
+++ b/src/cmd/link/internal/arm64/obj.go
@@ -51,6 +51,7 @@
Archreloc: archreloc,
Archrelocvariant: archrelocvariant,
Asmb: asmb,
+ Asmb2: asmb2,
Elfreloc1: elfreloc1,
Elfsetupplt: elfsetupplt,
Gentext: gentext,
diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index cb74b9a..a6f75b7 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -792,6 +792,7 @@
writeDatblkToOutBuf(ctxt, ctxt.Out, addr, size)
}
+// Used only on Wasm for now.
func DatblkBytes(ctxt *Link, addr int64, size int64) []byte {
buf := bytes.NewBuffer(make([]byte, 0, size))
out := &OutBuf{w: bufio.NewWriter(buf)}
@@ -2319,7 +2320,8 @@
}
// layout assigns file offsets and lengths to the segments in order.
-func (ctxt *Link) layout(order []*sym.Segment) {
+// Returns the file size containing all the segments.
+func (ctxt *Link) layout(order []*sym.Segment) uint64 {
var prev *sym.Segment
for _, seg := range order {
if prev == nil {
@@ -2348,7 +2350,7 @@
}
prev = seg
}
-
+ return prev.Fileoff + prev.Filelen
}
// add a trampoline with symbol s (to be laid down after the current function)
diff --git a/src/cmd/link/internal/ld/lib.go b/src/cmd/link/internal/ld/lib.go
index 62f2453..c4748781 100644
--- a/src/cmd/link/internal/ld/lib.go
+++ b/src/cmd/link/internal/ld/lib.go
@@ -127,8 +127,15 @@
// offset value.
Archrelocvariant func(link *Link, rel *sym.Reloc, sym *sym.Symbol,
offset int64) (relocatedOffset int64)
- Trampoline func(*Link, *sym.Reloc, *sym.Symbol)
- Asmb func(*Link)
+ Trampoline func(*Link, *sym.Reloc, *sym.Symbol)
+
+ // Asmb and Asmb2 are arch-specific routines that write the output
+ // file. Typically, Asmb writes most of the content (sections and
+ // segments), for which we have computed the size and offset. Asmb2
+ // writes the rest.
+ Asmb func(*Link)
+ Asmb2 func(*Link)
+
Elfreloc1 func(*Link, *sym.Reloc, int64) bool
Elfsetupplt func(*Link)
Gentext func(*Link)
@@ -261,7 +268,7 @@
Lflag(ctxt, filepath.Join(objabi.GOROOT, "pkg", fmt.Sprintf("%s_%s%s%s", objabi.GOOS, objabi.GOARCH, suffixsep, suffix)))
mayberemoveoutfile()
- f, err := os.OpenFile(*flagOutfile, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0775)
+ f, err := os.OpenFile(*flagOutfile, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0775)
if err != nil {
Exitf("cannot create %s: %v", *flagOutfile, err)
}
@@ -1014,7 +1021,7 @@
p := filepath.Join(*flagTmpdir, "go.o")
var err error
- f, err := os.OpenFile(p, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0775)
+ f, err := os.OpenFile(p, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0775)
if err != nil {
Exitf("cannot create %s: %v", p, err)
}
diff --git a/src/cmd/link/internal/ld/main.go b/src/cmd/link/internal/ld/main.go
index 48a9953..1b2d376 100644
--- a/src/cmd/link/internal/ld/main.go
+++ b/src/cmd/link/internal/ld/main.go
@@ -241,8 +241,29 @@
order := ctxt.address()
ctxt.reloc()
dwarfcompress(ctxt)
- ctxt.layout(order)
- thearch.Asmb(ctxt)
+ filesize := ctxt.layout(order)
+
+ // Write out the output file.
+ // It is split into two parts (Asmb and Asmb2). The first
+ // part writes most of the content (sections and segments),
+ // for which we have computed the size and offset, in a
+ // mmap'd region. The second part writes more content, for
+ // which we don't know the size.
+ var outputMmapped bool
+ if ctxt.Arch.Family != sys.Wasm {
+ // Don't mmap if we're building for Wasm. Wasm file
+ // layout is very different so filesize is meaningless.
+ err := ctxt.Out.Mmap(filesize)
+ outputMmapped = err == nil
+ }
+ if outputMmapped {
+ thearch.Asmb(ctxt)
+ ctxt.Out.Munmap()
+ } else {
+ thearch.Asmb(ctxt)
+ }
+ thearch.Asmb2(ctxt)
+
ctxt.undef()
ctxt.hostlink()
ctxt.archive()
diff --git a/src/cmd/link/internal/ld/outbuf.go b/src/cmd/link/internal/ld/outbuf.go
index 5df2be4..f1b5d74 100644
--- a/src/cmd/link/internal/ld/outbuf.go
+++ b/src/cmd/link/internal/ld/outbuf.go
@@ -8,6 +8,7 @@
"bufio"
"cmd/internal/sys"
"encoding/binary"
+ "log"
"os"
)
@@ -20,10 +21,18 @@
//
// Second, it provides a very cheap offset counter that doesn't require
// any system calls to read the value.
+//
+// It also mmaps the output file (if available). The intended usage is:
+// - Mmap the output file
+// - Write the content
+// - possibly apply any edits in the output buffer
+// - Munmap the output file
+// - possibly write more content to the file, which will not be edited later.
type OutBuf struct {
arch *sys.Arch
off int64
w *bufio.Writer
+ buf []byte // backing store of mmap'd output file
f *os.File
encbuf [8]byte // temp buffer used by WriteN methods
}
@@ -32,9 +41,11 @@
if p == out.off {
return
}
- out.Flush()
- if _, err := out.f.Seek(p, 0); err != nil {
- Exitf("seeking to %d in %s: %v", p, out.f.Name(), err)
+ if out.buf == nil {
+ out.Flush()
+ if _, err := out.f.Seek(p, 0); err != nil {
+ Exitf("seeking to %d in %s: %v", p, out.f.Name(), err)
+ }
}
out.off = p
}
@@ -49,12 +60,22 @@
// to explicitly handle the returned error as long as Flush is
// eventually called.
func (out *OutBuf) Write(v []byte) (int, error) {
+ if out.buf != nil {
+ n := copy(out.buf[out.off:], v)
+ out.off += int64(n)
+ return n, nil
+ }
n, err := out.w.Write(v)
out.off += int64(n)
return n, err
}
func (out *OutBuf) Write8(v uint8) {
+ if out.buf != nil {
+ out.buf[out.off] = v
+ out.off++
+ return
+ }
if err := out.w.WriteByte(v); err == nil {
out.off++
}
@@ -92,6 +113,14 @@
}
func (out *OutBuf) WriteString(s string) {
+ if out.buf != nil {
+ n := copy(out.buf[out.off:], s)
+ if n != len(s) {
+ log.Fatalf("WriteString truncated. buffer size: %d, offset: %d, len(s)=%d", len(out.buf), out.off, len(s))
+ }
+ out.off += int64(n)
+ return
+ }
n, _ := out.w.WriteString(s)
out.off += int64(n)
}
@@ -120,7 +149,13 @@
}
func (out *OutBuf) Flush() {
- if err := out.w.Flush(); err != nil {
+ var err error
+ if out.buf != nil {
+ err = out.Msync()
+ } else {
+ err = out.w.Flush()
+ }
+ if err != nil {
Exitf("flushing %s: %v", out.f.Name(), err)
}
}
diff --git a/src/cmd/link/internal/ld/outbuf_mmap.go b/src/cmd/link/internal/ld/outbuf_mmap.go
new file mode 100644
index 0000000..4075141
--- /dev/null
+++ b/src/cmd/link/internal/ld/outbuf_mmap.go
@@ -0,0 +1,44 @@
+// 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.
+
+// +build darwin dragonfly freebsd linux openbsd
+
+package ld
+
+import (
+ "syscall"
+ "unsafe"
+)
+
+func (out *OutBuf) Mmap(filesize uint64) error {
+ err := out.f.Truncate(int64(filesize))
+ if err != nil {
+ Exitf("resize output file failed: %v", err)
+ }
+ out.buf, err = syscall.Mmap(int(out.f.Fd()), 0, int(filesize), syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED|syscall.MAP_FILE)
+ return err
+}
+
+func (out *OutBuf) Munmap() {
+ err := out.Msync()
+ if err != nil {
+ Exitf("msync output file failed: %v", err)
+ }
+ syscall.Munmap(out.buf)
+ out.buf = nil
+ _, err = out.f.Seek(out.off, 0)
+ if err != nil {
+ Exitf("seek output file failed: %v", err)
+ }
+}
+
+func (out *OutBuf) Msync() error {
+ // TODO: netbsd supports mmap and msync, but the syscall package doesn't define MSYNC.
+ // It is excluded from the build tag for now.
+ _, _, errno := syscall.Syscall(syscall.SYS_MSYNC, uintptr(unsafe.Pointer(&out.buf[0])), uintptr(len(out.buf)), syscall.MS_SYNC)
+ if errno != 0 {
+ return errno
+ }
+ return nil
+}
diff --git a/src/cmd/link/internal/ld/outbuf_nommap.go b/src/cmd/link/internal/ld/outbuf_nommap.go
new file mode 100644
index 0000000..36a3286
--- /dev/null
+++ b/src/cmd/link/internal/ld/outbuf_nommap.go
@@ -0,0 +1,15 @@
+// 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.
+
+// +build !darwin,!dragonfly,!freebsd,!linux,!openbsd
+
+package ld
+
+import "errors"
+
+var errNotSupported = errors.New("mmap not supported")
+
+func (out *OutBuf) Mmap(filesize uint64) error { return errNotSupported }
+func (out *OutBuf) Munmap() { panic("unreachable") }
+func (out *OutBuf) Msync() error { panic("unreachable") }
diff --git a/src/cmd/link/internal/mips/asm.go b/src/cmd/link/internal/mips/asm.go
index 8409e43..f05455e 100644
--- a/src/cmd/link/internal/mips/asm.go
+++ b/src/cmd/link/internal/mips/asm.go
@@ -197,7 +197,9 @@
ctxt.Out.SeekSet(int64(ld.Segdwarf.Fileoff))
ld.Dwarfblk(ctxt, int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
+}
+func asmb2(ctxt *ld.Link) {
/* output symbol table */
ld.Symsize = 0
diff --git a/src/cmd/link/internal/mips/obj.go b/src/cmd/link/internal/mips/obj.go
index 3c71e23..231e1ff 100644
--- a/src/cmd/link/internal/mips/obj.go
+++ b/src/cmd/link/internal/mips/obj.go
@@ -54,6 +54,7 @@
Archreloc: archreloc,
Archrelocvariant: archrelocvariant,
Asmb: asmb,
+ Asmb2: asmb2,
Elfreloc1: elfreloc1,
Elfsetupplt: elfsetupplt,
Gentext: gentext,
diff --git a/src/cmd/link/internal/mips64/asm.go b/src/cmd/link/internal/mips64/asm.go
index 51eba59..25a1d94 100644
--- a/src/cmd/link/internal/mips64/asm.go
+++ b/src/cmd/link/internal/mips64/asm.go
@@ -209,7 +209,9 @@
ctxt.Out.SeekSet(int64(ld.Segdwarf.Fileoff))
ld.Dwarfblk(ctxt, int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
+}
+func asmb2(ctxt *ld.Link) {
/* output symbol table */
ld.Symsize = 0
diff --git a/src/cmd/link/internal/mips64/obj.go b/src/cmd/link/internal/mips64/obj.go
index b01746e..9604208 100644
--- a/src/cmd/link/internal/mips64/obj.go
+++ b/src/cmd/link/internal/mips64/obj.go
@@ -53,6 +53,7 @@
Archreloc: archreloc,
Archrelocvariant: archrelocvariant,
Asmb: asmb,
+ Asmb2: asmb2,
Elfreloc1: elfreloc1,
Elfsetupplt: elfsetupplt,
Gentext: gentext,
diff --git a/src/cmd/link/internal/ppc64/asm.go b/src/cmd/link/internal/ppc64/asm.go
index d376c4d..365a45e 100644
--- a/src/cmd/link/internal/ppc64/asm.go
+++ b/src/cmd/link/internal/ppc64/asm.go
@@ -1103,7 +1103,9 @@
ctxt.Out.SeekSet(int64(ld.Segdwarf.Fileoff))
ld.Dwarfblk(ctxt, int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
+}
+func asmb2(ctxt *ld.Link) {
/* output symbol table */
ld.Symsize = 0
diff --git a/src/cmd/link/internal/ppc64/obj.go b/src/cmd/link/internal/ppc64/obj.go
index bd85856..51d1791 100644
--- a/src/cmd/link/internal/ppc64/obj.go
+++ b/src/cmd/link/internal/ppc64/obj.go
@@ -54,6 +54,7 @@
Archreloc: archreloc,
Archrelocvariant: archrelocvariant,
Asmb: asmb,
+ Asmb2: asmb2,
Elfreloc1: elfreloc1,
Elfsetupplt: elfsetupplt,
Gentext: gentext,
diff --git a/src/cmd/link/internal/s390x/asm.go b/src/cmd/link/internal/s390x/asm.go
index 46a6ffe..8540377 100644
--- a/src/cmd/link/internal/s390x/asm.go
+++ b/src/cmd/link/internal/s390x/asm.go
@@ -540,7 +540,9 @@
ctxt.Out.SeekSet(int64(ld.Segdwarf.Fileoff))
ld.Dwarfblk(ctxt, int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
+}
+func asmb2(ctxt *ld.Link) {
/* output symbol table */
ld.Symsize = 0
diff --git a/src/cmd/link/internal/s390x/obj.go b/src/cmd/link/internal/s390x/obj.go
index a7e30e2..3454476 100644
--- a/src/cmd/link/internal/s390x/obj.go
+++ b/src/cmd/link/internal/s390x/obj.go
@@ -50,7 +50,8 @@
Archinit: archinit,
Archreloc: archreloc,
Archrelocvariant: archrelocvariant,
- Asmb: asmb, // in asm.go
+ Asmb: asmb, // in asm.go
+ Asmb2: asmb2, // in asm.go
Elfreloc1: elfreloc1,
Elfsetupplt: elfsetupplt,
Gentext: gentext,
diff --git a/src/cmd/link/internal/wasm/asm.go b/src/cmd/link/internal/wasm/asm.go
index ea6b406..8ab58b2 100644
--- a/src/cmd/link/internal/wasm/asm.go
+++ b/src/cmd/link/internal/wasm/asm.go
@@ -92,9 +92,11 @@
return sect, n, va
}
+func asmb(ctxt *ld.Link) {} // dummy
+
// asmb writes the final WebAssembly module binary.
// Spec: https://webassembly.github.io/spec/core/binary/modules.html
-func asmb(ctxt *ld.Link) {
+func asmb2(ctxt *ld.Link) {
if ctxt.Debugvlog != 0 {
ctxt.Logf("%5.2f asmb\n", ld.Cputime())
}
diff --git a/src/cmd/link/internal/wasm/obj.go b/src/cmd/link/internal/wasm/obj.go
index 55f34e3..f8090a3 100644
--- a/src/cmd/link/internal/wasm/obj.go
+++ b/src/cmd/link/internal/wasm/obj.go
@@ -18,6 +18,7 @@
Archinit: archinit,
AssignAddress: assignAddress,
Asmb: asmb,
+ Asmb2: asmb2,
Gentext: gentext,
}
diff --git a/src/cmd/link/internal/x86/asm.go b/src/cmd/link/internal/x86/asm.go
index 9472f55..427ccaf 100644
--- a/src/cmd/link/internal/x86/asm.go
+++ b/src/cmd/link/internal/x86/asm.go
@@ -662,7 +662,9 @@
ctxt.Out.SeekSet(int64(ld.Segdwarf.Fileoff))
ld.Dwarfblk(ctxt, int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
+}
+func asmb2(ctxt *ld.Link) {
machlink := uint32(0)
if ctxt.HeadType == objabi.Hdarwin {
machlink = uint32(ld.Domacholink(ctxt))
diff --git a/src/cmd/link/internal/x86/obj.go b/src/cmd/link/internal/x86/obj.go
index dbb3126..f1fad20 100644
--- a/src/cmd/link/internal/x86/obj.go
+++ b/src/cmd/link/internal/x86/obj.go
@@ -51,6 +51,7 @@
Archreloc: archreloc,
Archrelocvariant: archrelocvariant,
Asmb: asmb,
+ Asmb2: asmb2,
Elfreloc1: elfreloc1,
Elfsetupplt: elfsetupplt,
Gentext: gentext,
