main.go

     1  // Inferno utils/6l/obj.c
     2  // https://bitbucket.org/inferno-os/inferno-os/src/master/utils/6l/obj.c
     3  //
     4  //	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
     5  //	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
     6  //	Portions Copyright © 1997-1999 Vita Nuova Limited
     7  //	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
     8  //	Portions Copyright © 2004,2006 Bruce Ellis
     9  //	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
    10  //	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
    11  //	Portions Copyright © 2009 The Go Authors. All rights reserved.
    12  //
    13  // Permission is hereby granted, free of charge, to any person obtaining a copy
    14  // of this software and associated documentation files (the "Software"), to deal
    15  // in the Software without restriction, including without limitation the rights
    16  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    17  // copies of the Software, and to permit persons to whom the Software is
    18  // furnished to do so, subject to the following conditions:
    19  //
    20  // The above copyright notice and this permission notice shall be included in
    21  // all copies or substantial portions of the Software.
    22  //
    23  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    24  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    25  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
    26  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    27  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    28  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    29  // THE SOFTWARE.
    30  
    31  package ld
    32  
    33  import (
    34  	"bufio"
    35  	"cmd/internal/goobj"
    36  	"cmd/internal/objabi"
    37  	"cmd/internal/quoted"
    38  	"cmd/internal/sys"
    39  	"cmd/internal/telemetry/counter"
    40  	"cmd/link/internal/benchmark"
    41  	"flag"
    42  	"internal/buildcfg"
    43  	"log"
    44  	"os"
    45  	"runtime"
    46  	"runtime/pprof"
    47  	"strconv"
    48  	"strings"
    49  )
    50  
    51  var (
    52  	pkglistfornote []byte
    53  	windowsgui     bool // writes a "GUI binary" instead of a "console binary"
    54  	ownTmpDir      bool // set to true if tmp dir created by linker (e.g. no -tmpdir)
    55  )
    56  
    57  func init() {
    58  	flag.Var(&flagExtld, "extld", "use `linker` when linking in external mode")
    59  	flag.Var(&flagExtldflags, "extldflags", "pass `flags` to external linker")
    60  	flag.Var(&macOS, "macos", "mac OS version to write in build info (only used in internal linking)")
    61  	flag.Var(&macSDK, "macsdk", "mac SDK version to write in build info (only used in internal linking)")
    62  	flag.Var(&rpath, "r", "set the ELF dynamic linker search `path` to dir1:dir2:...")
    63  	flag.Var(&flagW, "w", "disable DWARF generation")
    64  }
    65  
    66  // Flags used by the linker. The exported flags are used by the architecture-specific packages.
    67  var (
    68  	flagBuildid = flag.String("buildid", "", "record `id` as Go toolchain build id")
    69  	flagBindNow = flag.Bool("bindnow", false, "mark a dynamically linked ELF object for immediate function binding")
    70  
    71  	flagOutfile    = flag.String("o", "", "write output to `file`")
    72  	flagPluginPath = flag.String("pluginpath", "", "full path name for plugin")
    73  	flagFipso      = flag.String("fipso", "", "write fips module to `file`")
    74  
    75  	flagInstallSuffix = flag.String("installsuffix", "", "set package directory `suffix`")
    76  	flagDumpDep       = flag.Bool("dumpdep", false, "dump symbol dependency graph")
    77  	flagRace          = flag.Bool("race", false, "enable race detector")
    78  	flagMsan          = flag.Bool("msan", false, "enable MSan interface")
    79  	flagAsan          = flag.Bool("asan", false, "enable ASan interface")
    80  	flagAslr          = flag.Bool("aslr", true, "enable ASLR for buildmode=c-shared on windows")
    81  
    82  	flagFieldTrack = flag.String("k", "", "set field tracking `symbol`")
    83  	flagLibGCC     = flag.String("libgcc", "", "compiler support lib for internal linking; use \"none\" to disable")
    84  	flagTmpdir     = flag.String("tmpdir", "", "use `directory` for temporary files")
    85  
    86  	flagExtld      quoted.Flag
    87  	flagExtldflags quoted.Flag
    88  	flagExtar      = flag.String("extar", "", "archive program for buildmode=c-archive")
    89  
    90  	flagCaptureHostObjs = flag.String("capturehostobjs", "", "capture host object files loaded during internal linking to specified dir")
    91  
    92  	flagA             = flag.Bool("a", false, "no-op (deprecated)")
    93  	FlagC             = flag.Bool("c", false, "dump call graph")
    94  	FlagD             = flag.Bool("d", false, "disable dynamic executable")
    95  	flagF             = flag.Bool("f", false, "ignore version mismatch")
    96  	flagG             = flag.Bool("g", false, "disable go package data checks")
    97  	flagH             = flag.Bool("h", false, "halt on error")
    98  	flagN             = flag.Bool("n", false, "no-op (deprecated)")
    99  	FlagS             = flag.Bool("s", false, "disable symbol table")
   100  	flag8             bool // use 64-bit addresses in symbol table
   101  	flagHostBuildid   = flag.String("B", "", "set ELF NT_GNU_BUILD_ID `note` or Mach-O UUID; use \"gobuildid\" to generate it from the Go build ID; \"none\" to disable")
   102  	flagInterpreter   = flag.String("I", "", "use `linker` as ELF dynamic linker")
   103  	flagCheckLinkname = flag.Bool("checklinkname", true, "check linkname symbol references")
   104  	FlagDebugTramp    = flag.Int("debugtramp", 0, "debug trampolines")
   105  	FlagDebugTextSize = flag.Int("debugtextsize", 0, "debug text section max size")
   106  	flagDebugNosplit  = flag.Bool("debugnosplit", false, "dump nosplit call graph")
   107  	FlagStrictDups    = flag.Int("strictdups", 0, "sanity check duplicate symbol contents during object file reading (1=warn 2=err).")
   108  	FlagRound         = flag.Int64("R", -1, "set address rounding `quantum`")
   109  	FlagTextAddr      = flag.Int64("T", -1, "set the start address of text symbols")
   110  	FlagDataAddr      = flag.Int64("D", -1, "set the start address of data symbols")
   111  	FlagFuncAlign     = flag.Int("funcalign", 0, "set function align to `N` bytes")
   112  	flagEntrySymbol   = flag.String("E", "", "set `entry` symbol name")
   113  	flagPruneWeakMap  = flag.Bool("pruneweakmap", true, "prune weak mapinit refs")
   114  	flagRandLayout    = flag.Int64("randlayout", 0, "randomize function layout")
   115  	flagAllErrors     = flag.Bool("e", false, "no limit on number of errors reported")
   116  	cpuprofile        = flag.String("cpuprofile", "", "write cpu profile to `file`")
   117  	memprofile        = flag.String("memprofile", "", "write memory profile to `file`")
   118  	memprofilerate    = flag.Int64("memprofilerate", 0, "set runtime.MemProfileRate to `rate`")
   119  	benchmarkFlag     = flag.String("benchmark", "", "set to 'mem' or 'cpu' to enable phase benchmarking")
   120  	benchmarkFileFlag = flag.String("benchmarkprofile", "", "emit phase profiles to `base`_phase.{cpu,mem}prof")
   121  
   122  	flagW ternaryFlag
   123  	FlagW = new(bool) // the -w flag, computed in main from flagW
   124  )
   125  
   126  // ternaryFlag is like a boolean flag, but has a default value that is
   127  // neither true nor false, allowing it to be set from context (e.g. from another
   128  // flag).
   129  // *ternaryFlag implements flag.Value.
   130  type ternaryFlag int
   131  
   132  const (
   133  	ternaryFlagUnset ternaryFlag = iota
   134  	ternaryFlagFalse
   135  	ternaryFlagTrue
   136  )
   137  
   138  func (t *ternaryFlag) Set(s string) error {
   139  	v, err := strconv.ParseBool(s)
   140  	if err != nil {
   141  		return err
   142  	}
   143  	if v {
   144  		*t = ternaryFlagTrue
   145  	} else {
   146  		*t = ternaryFlagFalse
   147  	}
   148  	return nil
   149  }
   150  
   151  func (t *ternaryFlag) String() string {
   152  	switch *t {
   153  	case ternaryFlagFalse:
   154  		return "false"
   155  	case ternaryFlagTrue:
   156  		return "true"
   157  	}
   158  	return "unset"
   159  }
   160  
   161  func (t *ternaryFlag) IsBoolFlag() bool { return true } // parse like a boolean flag
   162  
   163  // Main is the main entry point for the linker code.
   164  func Main(arch *sys.Arch, theArch Arch) {
   165  	log.SetPrefix("link: ")
   166  	log.SetFlags(0)
   167  	counter.Open()
   168  	counter.Inc("link/invocations")
   169  
   170  	thearch = theArch
   171  	ctxt := linknew(arch)
   172  	ctxt.Bso = bufio.NewWriter(os.Stdout)
   173  
   174  	// For testing behavior of go command when tools crash silently.
   175  	// Undocumented, not in standard flag parser to avoid
   176  	// exposing in usage message.
   177  	for _, arg := range os.Args {
   178  		if arg == "-crash_for_testing" {
   179  			os.Exit(2)
   180  		}
   181  	}
   182  
   183  	if buildcfg.GOROOT == "" {
   184  		// cmd/go clears the GOROOT variable when -trimpath is set,
   185  		// so omit it from the binary even if cmd/link itself has an
   186  		// embedded GOROOT value reported by runtime.GOROOT.
   187  	} else {
   188  		addstrdata1(ctxt, "runtime.defaultGOROOT="+buildcfg.GOROOT)
   189  	}
   190  
   191  	buildVersion := buildcfg.Version
   192  	if goexperiment := buildcfg.Experiment.String(); goexperiment != "" {
   193  		sep := " "
   194  		if !strings.Contains(buildVersion, "-") { // See go.dev/issue/75953.
   195  			sep = "-"
   196  		}
   197  		buildVersion += sep + "X:" + goexperiment
   198  	}
   199  	addstrdata1(ctxt, "runtime.buildVersion="+buildVersion)
   200  
   201  	// TODO(matloob): define these above and then check flag values here
   202  	if ctxt.Arch.Family == sys.AMD64 && buildcfg.GOOS == "plan9" {
   203  		flag.BoolVar(&flag8, "8", false, "use 64-bit addresses in symbol table")
   204  	}
   205  	flagHeadType := flag.String("H", "", "set header `type`")
   206  	flag.BoolVar(&ctxt.linkShared, "linkshared", false, "link against installed Go shared libraries")
   207  	flag.Var(&ctxt.LinkMode, "linkmode", "set link `mode`")
   208  	flag.Var(&ctxt.BuildMode, "buildmode", "set build `mode`")
   209  	flag.BoolVar(&ctxt.compressDWARF, "compressdwarf", true, "compress DWARF if possible")
   210  	objabi.Flagfn1("L", "add specified `directory` to library path", func(a string) { Lflag(ctxt, a) })
   211  	objabi.AddVersionFlag() // -V
   212  	objabi.Flagfn1("X", "add string value `definition` of the form importpath.name=value", func(s string) { addstrdata1(ctxt, s) })
   213  	objabi.Flagcount("v", "print link trace", &ctxt.Debugvlog)
   214  	objabi.Flagfn1("importcfg", "read import configuration from `file`", ctxt.readImportCfg)
   215  
   216  	objabi.Flagparse(usage)
   217  	counter.CountFlags("link/flag:", *flag.CommandLine)
   218  
   219  	if ctxt.Debugvlog > 0 {
   220  		// dump symbol info on crash
   221  		defer func() { ctxt.loader.Dump() }()
   222  	}
   223  	if ctxt.Debugvlog > 1 {
   224  		// dump symbol info on error
   225  		AtExit(func() {
   226  			if nerrors > 0 {
   227  				ctxt.loader.Dump()
   228  			}
   229  		})
   230  	}
   231  
   232  	switch *flagHeadType {
   233  	case "":
   234  	case "windowsgui":
   235  		ctxt.HeadType = objabi.Hwindows
   236  		windowsgui = true
   237  	default:
   238  		if err := ctxt.HeadType.Set(*flagHeadType); err != nil {
   239  			Errorf("%v", err)
   240  			usage()
   241  		}
   242  	}
   243  	if ctxt.HeadType == objabi.Hunknown {
   244  		ctxt.HeadType.Set(buildcfg.GOOS)
   245  	}
   246  
   247  	if !*flagAslr && ctxt.BuildMode != BuildModeCShared {
   248  		Errorf("-aslr=false is only allowed for -buildmode=c-shared")
   249  		usage()
   250  	}
   251  
   252  	if *FlagD && ctxt.UsesLibc() {
   253  		Exitf("dynamic linking required on %s; -d flag cannot be used", buildcfg.GOOS)
   254  	}
   255  
   256  	isPowerOfTwo := func(n int64) bool {
   257  		return n > 0 && n&(n-1) == 0
   258  	}
   259  	if *FlagRound != -1 && (*FlagRound < 4096 || !isPowerOfTwo(*FlagRound)) {
   260  		Exitf("invalid -R value 0x%x", *FlagRound)
   261  	}
   262  	if *FlagFuncAlign != 0 && !isPowerOfTwo(int64(*FlagFuncAlign)) {
   263  		Exitf("invalid -funcalign value %d", *FlagFuncAlign)
   264  	}
   265  
   266  	checkStrictDups = *FlagStrictDups
   267  
   268  	switch flagW {
   269  	case ternaryFlagFalse:
   270  		*FlagW = false
   271  	case ternaryFlagTrue:
   272  		*FlagW = true
   273  	case ternaryFlagUnset:
   274  		*FlagW = *FlagS // -s implies -w if not explicitly set
   275  		if ctxt.IsDarwin() && ctxt.BuildMode == BuildModeCShared {
   276  			*FlagW = true // default to -w in c-shared mode on darwin, see #61229
   277  		}
   278  	}
   279  
   280  	if !buildcfg.Experiment.RegabiWrappers {
   281  		abiInternalVer = 0
   282  	}
   283  
   284  	startProfile()
   285  	if ctxt.BuildMode == BuildModeUnset {
   286  		ctxt.BuildMode.Set("exe")
   287  	}
   288  
   289  	if ctxt.BuildMode != BuildModeShared && flag.NArg() != 1 {
   290  		usage()
   291  	}
   292  
   293  	if *flagOutfile == "" {
   294  		*flagOutfile = "a.out"
   295  		if ctxt.HeadType == objabi.Hwindows {
   296  			*flagOutfile += ".exe"
   297  		}
   298  	}
   299  
   300  	interpreter = *flagInterpreter
   301  
   302  	if *flagHostBuildid == "" && *flagBuildid != "" {
   303  		*flagHostBuildid = "gobuildid"
   304  	}
   305  	addbuildinfo(ctxt)
   306  
   307  	// enable benchmarking
   308  	var bench *benchmark.Metrics
   309  	if len(*benchmarkFlag) != 0 {
   310  		if *benchmarkFlag == "mem" {
   311  			bench = benchmark.New(benchmark.GC, *benchmarkFileFlag)
   312  		} else if *benchmarkFlag == "cpu" {
   313  			bench = benchmark.New(benchmark.NoGC, *benchmarkFileFlag)
   314  		} else {
   315  			Errorf("unknown benchmark flag: %q", *benchmarkFlag)
   316  			usage()
   317  		}
   318  	}
   319  
   320  	bench.Start("libinit")
   321  	libinit(ctxt) // creates outfile
   322  	bench.Start("computeTLSOffset")
   323  	ctxt.computeTLSOffset()
   324  	bench.Start("Archinit")
   325  	thearch.Archinit(ctxt)
   326  
   327  	if *FlagDataAddr != -1 && *FlagDataAddr%*FlagRound != 0 {
   328  		Exitf("invalid -D value 0x%x: not aligned to rounding quantum 0x%x", *FlagDataAddr, *FlagRound)
   329  	}
   330  
   331  	if ctxt.linkShared && !ctxt.IsELF {
   332  		Exitf("-linkshared can only be used on elf systems")
   333  	}
   334  
   335  	if ctxt.Debugvlog != 0 {
   336  		onOff := func(b bool) string {
   337  			if b {
   338  				return "on"
   339  			}
   340  			return "off"
   341  		}
   342  		ctxt.Logf("build mode: %s, symbol table: %s, DWARF: %s\n", ctxt.BuildMode, onOff(!*FlagS), onOff(dwarfEnabled(ctxt)))
   343  		ctxt.Logf("HEADER = -H%d -T0x%x -R0x%x\n", ctxt.HeadType, uint64(*FlagTextAddr), uint32(*FlagRound))
   344  	}
   345  
   346  	zerofp := goobj.FingerprintType{}
   347  	switch ctxt.BuildMode {
   348  	case BuildModeShared:
   349  		for i := 0; i < flag.NArg(); i++ {
   350  			arg := flag.Arg(i)
   351  			parts := strings.SplitN(arg, "=", 2)
   352  			var pkgpath, file string
   353  			if len(parts) == 1 {
   354  				pkgpath, file = "main", arg
   355  			} else {
   356  				pkgpath, file = parts[0], parts[1]
   357  			}
   358  			pkglistfornote = append(pkglistfornote, pkgpath...)
   359  			pkglistfornote = append(pkglistfornote, '\n')
   360  			addlibpath(ctxt, "command line", "command line", file, pkgpath, "", zerofp)
   361  		}
   362  	case BuildModePlugin:
   363  		addlibpath(ctxt, "command line", "command line", flag.Arg(0), *flagPluginPath, "", zerofp)
   364  	default:
   365  		addlibpath(ctxt, "command line", "command line", flag.Arg(0), "main", "", zerofp)
   366  	}
   367  	bench.Start("loadlib")
   368  	ctxt.loadlib()
   369  
   370  	bench.Start("inittasks")
   371  	ctxt.inittasks()
   372  
   373  	bench.Start("deadcode")
   374  	deadcode(ctxt)
   375  
   376  	bench.Start("linksetup")
   377  	ctxt.linksetup()
   378  
   379  	bench.Start("dostrdata")
   380  	ctxt.dostrdata()
   381  	if buildcfg.Experiment.FieldTrack {
   382  		bench.Start("fieldtrack")
   383  		fieldtrack(ctxt.Arch, ctxt.loader)
   384  	}
   385  
   386  	bench.Start("dwarfGenerateDebugInfo")
   387  	dwarfGenerateDebugInfo(ctxt)
   388  
   389  	bench.Start("callgraph")
   390  	ctxt.callgraph()
   391  
   392  	bench.Start("doStackCheck")
   393  	ctxt.doStackCheck()
   394  
   395  	bench.Start("mangleTypeSym")
   396  	ctxt.mangleTypeSym()
   397  
   398  	if ctxt.IsELF {
   399  		bench.Start("doelf")
   400  		ctxt.doelf()
   401  	}
   402  	if ctxt.IsDarwin() {
   403  		bench.Start("domacho")
   404  		ctxt.domacho()
   405  	}
   406  	if ctxt.IsWindows() {
   407  		bench.Start("dope")
   408  		ctxt.dope()
   409  		bench.Start("windynrelocsyms")
   410  		ctxt.windynrelocsyms()
   411  	}
   412  	if ctxt.IsAIX() {
   413  		bench.Start("doxcoff")
   414  		ctxt.doxcoff()
   415  	}
   416  
   417  	bench.Start("textbuildid")
   418  	ctxt.textbuildid()
   419  	bench.Start("addexport")
   420  	ctxt.setArchSyms()
   421  	ctxt.addexport()
   422  	bench.Start("Gentext")
   423  	thearch.Gentext(ctxt, ctxt.loader) // trampolines, call stubs, etc.
   424  
   425  	bench.Start("textaddress")
   426  	ctxt.textaddress()
   427  	bench.Start("buildinfo")
   428  	ctxt.buildinfo()
   429  	bench.Start("pclntab")
   430  	containers := ctxt.findContainerSyms()
   431  	pclnState := ctxt.pclntab(containers)
   432  	bench.Start("findfunctab")
   433  	ctxt.findfunctab(pclnState, containers)
   434  	bench.Start("dwarfGenerateDebugSyms")
   435  	dwarfGenerateDebugSyms(ctxt)
   436  	bench.Start("symtab")
   437  	symGroupType := ctxt.symtab(pclnState)
   438  	bench.Start("dodata")
   439  	ctxt.dodata(symGroupType)
   440  	bench.Start("address")
   441  	order := ctxt.address()
   442  	bench.Start("dwarfcompress")
   443  	dwarfcompress(ctxt)
   444  	bench.Start("layout")
   445  	filesize := ctxt.layout(order)
   446  
   447  	// Write out the output file.
   448  	// It is split into two parts (Asmb and Asmb2). The first
   449  	// part writes most of the content (sections and segments),
   450  	// for which we have computed the size and offset, in a
   451  	// mmap'd region. The second part writes more content, for
   452  	// which we don't know the size.
   453  	if ctxt.Arch.Family != sys.Wasm {
   454  		// Don't mmap if we're building for Wasm. Wasm file
   455  		// layout is very different so filesize is meaningless.
   456  		if err := ctxt.Out.Mmap(filesize); err != nil {
   457  			Exitf("mapping output file failed: %v", err)
   458  		}
   459  	}
   460  	// asmb will redirect symbols to the output file mmap, and relocations
   461  	// will be applied directly there.
   462  	bench.Start("Asmb")
   463  	asmb(ctxt)
   464  	exitIfErrors()
   465  
   466  	// Generate additional symbols for the native symbol table just prior
   467  	// to code generation.
   468  	bench.Start("GenSymsLate")
   469  	if thearch.GenSymsLate != nil {
   470  		thearch.GenSymsLate(ctxt, ctxt.loader)
   471  	}
   472  
   473  	asmbfips(ctxt, *flagFipso)
   474  
   475  	bench.Start("Asmb2")
   476  	asmb2(ctxt)
   477  
   478  	bench.Start("Munmap")
   479  	ctxt.Out.Close() // Close handles Munmapping if necessary.
   480  
   481  	bench.Start("hostlink")
   482  	ctxt.hostlink()
   483  	if ctxt.Debugvlog != 0 {
   484  		ctxt.Logf("%s", ctxt.loader.Stat())
   485  		ctxt.Logf("%d liveness data\n", liveness)
   486  	}
   487  	bench.Start("Flush")
   488  	ctxt.Bso.Flush()
   489  	bench.Start("archive")
   490  	ctxt.archive()
   491  	bench.Report(os.Stdout)
   492  
   493  	errorexit()
   494  }
   495  
   496  type Rpath struct {
   497  	set bool
   498  	val string
   499  }
   500  
   501  func (r *Rpath) Set(val string) error {
   502  	r.set = true
   503  	r.val = val
   504  	return nil
   505  }
   506  
   507  func (r *Rpath) String() string {
   508  	return r.val
   509  }
   510  
   511  func startProfile() {
   512  	if *cpuprofile != "" {
   513  		f, err := os.Create(*cpuprofile)
   514  		if err != nil {
   515  			log.Fatalf("%v", err)
   516  		}
   517  		if err := pprof.StartCPUProfile(f); err != nil {
   518  			log.Fatalf("%v", err)
   519  		}
   520  		AtExit(func() {
   521  			pprof.StopCPUProfile()
   522  			if err = f.Close(); err != nil {
   523  				log.Fatalf("error closing cpu profile: %v", err)
   524  			}
   525  		})
   526  	}
   527  	if *memprofile != "" {
   528  		if *memprofilerate != 0 {
   529  			runtime.MemProfileRate = int(*memprofilerate)
   530  		}
   531  		f, err := os.Create(*memprofile)
   532  		if err != nil {
   533  			log.Fatalf("%v", err)
   534  		}
   535  		AtExit(func() {
   536  			// Profile all outstanding allocations.
   537  			runtime.GC()
   538  			// compilebench parses the memory profile to extract memstats,
   539  			// which are only written in the legacy pprof format.
   540  			// See golang.org/issue/18641 and runtime/pprof/pprof.go:writeHeap.
   541  			const writeLegacyFormat = 1
   542  			if err := pprof.Lookup("heap").WriteTo(f, writeLegacyFormat); err != nil {
   543  				log.Fatalf("%v", err)
   544  			}
   545  			// Close the file after writing the profile.
   546  			if err := f.Close(); err != nil {
   547  				log.Fatalf("could not close %v: %v", *memprofile, err)
   548  			}
   549  		})
   550  	}
   551  }
   552
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