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(&rpath, "r", "set the ELF dynamic linker search `path` to dir1:dir2:...")
    59  	flag.Var(&flagExtld, "extld", "use `linker` when linking in external mode")
    60  	flag.Var(&flagExtldflags, "extldflags", "pass `flags` to external linker")
    61  	flag.Var(&flagW, "w", "disable DWARF generation")
    62  }
    63  
    64  // Flags used by the linker. The exported flags are used by the architecture-specific packages.
    65  var (
    66  	flagBuildid = flag.String("buildid", "", "record `id` as Go toolchain build id")
    67  	flagBindNow = flag.Bool("bindnow", false, "mark a dynamically linked ELF object for immediate function binding")
    68  
    69  	flagOutfile    = flag.String("o", "", "write output to `file`")
    70  	flagPluginPath = flag.String("pluginpath", "", "full path name for plugin")
    71  	flagFipso      = flag.String("fipso", "", "write fips module to `file`")
    72  
    73  	flagInstallSuffix = flag.String("installsuffix", "", "set package directory `suffix`")
    74  	flagDumpDep       = flag.Bool("dumpdep", false, "dump symbol dependency graph")
    75  	flagRace          = flag.Bool("race", false, "enable race detector")
    76  	flagMsan          = flag.Bool("msan", false, "enable MSan interface")
    77  	flagAsan          = flag.Bool("asan", false, "enable ASan interface")
    78  	flagAslr          = flag.Bool("aslr", true, "enable ASLR for buildmode=c-shared on windows")
    79  
    80  	flagFieldTrack = flag.String("k", "", "set field tracking `symbol`")
    81  	flagLibGCC     = flag.String("libgcc", "", "compiler support lib for internal linking; use \"none\" to disable")
    82  	flagTmpdir     = flag.String("tmpdir", "", "use `directory` for temporary files")
    83  
    84  	flagExtld      quoted.Flag
    85  	flagExtldflags quoted.Flag
    86  	flagExtar      = flag.String("extar", "", "archive program for buildmode=c-archive")
    87  
    88  	flagCaptureHostObjs = flag.String("capturehostobjs", "", "capture host object files loaded during internal linking to specified dir")
    89  
    90  	flagA             = flag.Bool("a", false, "no-op (deprecated)")
    91  	FlagC             = flag.Bool("c", false, "dump call graph")
    92  	FlagD             = flag.Bool("d", false, "disable dynamic executable")
    93  	flagF             = flag.Bool("f", false, "ignore version mismatch")
    94  	flagG             = flag.Bool("g", false, "disable go package data checks")
    95  	flagH             = flag.Bool("h", false, "halt on error")
    96  	flagN             = flag.Bool("n", false, "no-op (deprecated)")
    97  	FlagS             = flag.Bool("s", false, "disable symbol table")
    98  	flag8             bool // use 64-bit addresses in symbol table
    99  	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")
   100  	flagInterpreter   = flag.String("I", "", "use `linker` as ELF dynamic linker")
   101  	flagCheckLinkname = flag.Bool("checklinkname", true, "check linkname symbol references")
   102  	FlagDebugTramp    = flag.Int("debugtramp", 0, "debug trampolines")
   103  	FlagDebugTextSize = flag.Int("debugtextsize", 0, "debug text section max size")
   104  	flagDebugNosplit  = flag.Bool("debugnosplit", false, "dump nosplit call graph")
   105  	FlagStrictDups    = flag.Int("strictdups", 0, "sanity check duplicate symbol contents during object file reading (1=warn 2=err).")
   106  	FlagRound         = flag.Int64("R", -1, "set address rounding `quantum`")
   107  	FlagTextAddr      = flag.Int64("T", -1, "set the start address of text symbols")
   108  	FlagFuncAlign     = flag.Int("funcalign", 0, "set function align to `N` bytes")
   109  	flagEntrySymbol   = flag.String("E", "", "set `entry` symbol name")
   110  	flagPruneWeakMap  = flag.Bool("pruneweakmap", true, "prune weak mapinit refs")
   111  	flagRandLayout    = flag.Int64("randlayout", 0, "randomize function layout")
   112  	flagAllErrors     = flag.Bool("e", false, "no limit on number of errors reported")
   113  	cpuprofile        = flag.String("cpuprofile", "", "write cpu profile to `file`")
   114  	memprofile        = flag.String("memprofile", "", "write memory profile to `file`")
   115  	memprofilerate    = flag.Int64("memprofilerate", 0, "set runtime.MemProfileRate to `rate`")
   116  	benchmarkFlag     = flag.String("benchmark", "", "set to 'mem' or 'cpu' to enable phase benchmarking")
   117  	benchmarkFileFlag = flag.String("benchmarkprofile", "", "emit phase profiles to `base`_phase.{cpu,mem}prof")
   118  
   119  	flagW ternaryFlag
   120  	FlagW = new(bool) // the -w flag, computed in main from flagW
   121  )
   122  
   123  // ternaryFlag is like a boolean flag, but has a default value that is
   124  // neither true nor false, allowing it to be set from context (e.g. from another
   125  // flag).
   126  // *ternaryFlag implements flag.Value.
   127  type ternaryFlag int
   128  
   129  const (
   130  	ternaryFlagUnset ternaryFlag = iota
   131  	ternaryFlagFalse
   132  	ternaryFlagTrue
   133  )
   134  
   135  func (t *ternaryFlag) Set(s string) error {
   136  	v, err := strconv.ParseBool(s)
   137  	if err != nil {
   138  		return err
   139  	}
   140  	if v {
   141  		*t = ternaryFlagTrue
   142  	} else {
   143  		*t = ternaryFlagFalse
   144  	}
   145  	return nil
   146  }
   147  
   148  func (t *ternaryFlag) String() string {
   149  	switch *t {
   150  	case ternaryFlagFalse:
   151  		return "false"
   152  	case ternaryFlagTrue:
   153  		return "true"
   154  	}
   155  	return "unset"
   156  }
   157  
   158  func (t *ternaryFlag) IsBoolFlag() bool { return true } // parse like a boolean flag
   159  
   160  // Main is the main entry point for the linker code.
   161  func Main(arch *sys.Arch, theArch Arch) {
   162  	log.SetPrefix("link: ")
   163  	log.SetFlags(0)
   164  	counter.Open()
   165  	counter.Inc("link/invocations")
   166  
   167  	thearch = theArch
   168  	ctxt := linknew(arch)
   169  	ctxt.Bso = bufio.NewWriter(os.Stdout)
   170  
   171  	// For testing behavior of go command when tools crash silently.
   172  	// Undocumented, not in standard flag parser to avoid
   173  	// exposing in usage message.
   174  	for _, arg := range os.Args {
   175  		if arg == "-crash_for_testing" {
   176  			os.Exit(2)
   177  		}
   178  	}
   179  
   180  	if buildcfg.GOROOT == "" {
   181  		// cmd/go clears the GOROOT variable when -trimpath is set,
   182  		// so omit it from the binary even if cmd/link itself has an
   183  		// embedded GOROOT value reported by runtime.GOROOT.
   184  	} else {
   185  		addstrdata1(ctxt, "runtime.defaultGOROOT="+buildcfg.GOROOT)
   186  	}
   187  
   188  	buildVersion := buildcfg.Version
   189  	if goexperiment := buildcfg.Experiment.String(); goexperiment != "" {
   190  		buildVersion += " X:" + goexperiment
   191  	}
   192  	addstrdata1(ctxt, "runtime.buildVersion="+buildVersion)
   193  
   194  	// TODO(matloob): define these above and then check flag values here
   195  	if ctxt.Arch.Family == sys.AMD64 && buildcfg.GOOS == "plan9" {
   196  		flag.BoolVar(&flag8, "8", false, "use 64-bit addresses in symbol table")
   197  	}
   198  	flagHeadType := flag.String("H", "", "set header `type`")
   199  	flag.BoolVar(&ctxt.linkShared, "linkshared", false, "link against installed Go shared libraries")
   200  	flag.Var(&ctxt.LinkMode, "linkmode", "set link `mode`")
   201  	flag.Var(&ctxt.BuildMode, "buildmode", "set build `mode`")
   202  	flag.BoolVar(&ctxt.compressDWARF, "compressdwarf", true, "compress DWARF if possible")
   203  	objabi.Flagfn1("L", "add specified `directory` to library path", func(a string) { Lflag(ctxt, a) })
   204  	objabi.AddVersionFlag() // -V
   205  	objabi.Flagfn1("X", "add string value `definition` of the form importpath.name=value", func(s string) { addstrdata1(ctxt, s) })
   206  	objabi.Flagcount("v", "print link trace", &ctxt.Debugvlog)
   207  	objabi.Flagfn1("importcfg", "read import configuration from `file`", ctxt.readImportCfg)
   208  
   209  	objabi.Flagparse(usage)
   210  	counter.CountFlags("link/flag:", *flag.CommandLine)
   211  
   212  	if ctxt.Debugvlog > 0 {
   213  		// dump symbol info on crash
   214  		defer func() { ctxt.loader.Dump() }()
   215  	}
   216  	if ctxt.Debugvlog > 1 {
   217  		// dump symbol info on error
   218  		AtExit(func() {
   219  			if nerrors > 0 {
   220  				ctxt.loader.Dump()
   221  			}
   222  		})
   223  	}
   224  
   225  	switch *flagHeadType {
   226  	case "":
   227  	case "windowsgui":
   228  		ctxt.HeadType = objabi.Hwindows
   229  		windowsgui = true
   230  	default:
   231  		if err := ctxt.HeadType.Set(*flagHeadType); err != nil {
   232  			Errorf("%v", err)
   233  			usage()
   234  		}
   235  	}
   236  	if ctxt.HeadType == objabi.Hunknown {
   237  		ctxt.HeadType.Set(buildcfg.GOOS)
   238  	}
   239  
   240  	if !*flagAslr && ctxt.BuildMode != BuildModeCShared {
   241  		Errorf("-aslr=false is only allowed for -buildmode=c-shared")
   242  		usage()
   243  	}
   244  
   245  	if *FlagD && ctxt.UsesLibc() {
   246  		Exitf("dynamic linking required on %s; -d flag cannot be used", buildcfg.GOOS)
   247  	}
   248  
   249  	isPowerOfTwo := func(n int64) bool {
   250  		return n > 0 && n&(n-1) == 0
   251  	}
   252  	if *FlagRound != -1 && (*FlagRound < 4096 || !isPowerOfTwo(*FlagRound)) {
   253  		Exitf("invalid -R value 0x%x", *FlagRound)
   254  	}
   255  	if *FlagFuncAlign != 0 && !isPowerOfTwo(int64(*FlagFuncAlign)) {
   256  		Exitf("invalid -funcalign value %d", *FlagFuncAlign)
   257  	}
   258  
   259  	checkStrictDups = *FlagStrictDups
   260  
   261  	switch flagW {
   262  	case ternaryFlagFalse:
   263  		*FlagW = false
   264  	case ternaryFlagTrue:
   265  		*FlagW = true
   266  	case ternaryFlagUnset:
   267  		*FlagW = *FlagS // -s implies -w if not explicitly set
   268  		if ctxt.IsDarwin() && ctxt.BuildMode == BuildModeCShared {
   269  			*FlagW = true // default to -w in c-shared mode on darwin, see #61229
   270  		}
   271  	}
   272  
   273  	if !buildcfg.Experiment.RegabiWrappers {
   274  		abiInternalVer = 0
   275  	}
   276  
   277  	startProfile()
   278  	if ctxt.BuildMode == BuildModeUnset {
   279  		ctxt.BuildMode.Set("exe")
   280  	}
   281  
   282  	if ctxt.BuildMode != BuildModeShared && flag.NArg() != 1 {
   283  		usage()
   284  	}
   285  
   286  	if *flagOutfile == "" {
   287  		*flagOutfile = "a.out"
   288  		if ctxt.HeadType == objabi.Hwindows {
   289  			*flagOutfile += ".exe"
   290  		}
   291  	}
   292  
   293  	interpreter = *flagInterpreter
   294  
   295  	if *flagBuildid == "" && ctxt.Target.IsOpenbsd() {
   296  		// TODO(jsing): Remove once direct syscalls are no longer in use.
   297  		// OpenBSD 6.7 onwards will not permit direct syscalls from a
   298  		// dynamically linked binary unless it identifies the binary
   299  		// contains a .note.go.buildid ELF note. See issue #36435.
   300  		*flagBuildid = "go-openbsd"
   301  	}
   302  
   303  	if *flagHostBuildid == "" && *flagBuildid != "" {
   304  		*flagHostBuildid = "gobuildid"
   305  	}
   306  	addbuildinfo(ctxt)
   307  
   308  	// enable benchmarking
   309  	var bench *benchmark.Metrics
   310  	if len(*benchmarkFlag) != 0 {
   311  		if *benchmarkFlag == "mem" {
   312  			bench = benchmark.New(benchmark.GC, *benchmarkFileFlag)
   313  		} else if *benchmarkFlag == "cpu" {
   314  			bench = benchmark.New(benchmark.NoGC, *benchmarkFileFlag)
   315  		} else {
   316  			Errorf("unknown benchmark flag: %q", *benchmarkFlag)
   317  			usage()
   318  		}
   319  	}
   320  
   321  	bench.Start("libinit")
   322  	libinit(ctxt) // creates outfile
   323  	bench.Start("computeTLSOffset")
   324  	ctxt.computeTLSOffset()
   325  	bench.Start("Archinit")
   326  	thearch.Archinit(ctxt)
   327  
   328  	if ctxt.linkShared && !ctxt.IsELF {
   329  		Exitf("-linkshared can only be used on elf systems")
   330  	}
   331  
   332  	if ctxt.Debugvlog != 0 {
   333  		onOff := func(b bool) string {
   334  			if b {
   335  				return "on"
   336  			}
   337  			return "off"
   338  		}
   339  		ctxt.Logf("build mode: %s, symbol table: %s, DWARF: %s\n", ctxt.BuildMode, onOff(!*FlagS), onOff(dwarfEnabled(ctxt)))
   340  		ctxt.Logf("HEADER = -H%d -T0x%x -R0x%x\n", ctxt.HeadType, uint64(*FlagTextAddr), uint32(*FlagRound))
   341  	}
   342  
   343  	zerofp := goobj.FingerprintType{}
   344  	switch ctxt.BuildMode {
   345  	case BuildModeShared:
   346  		for i := 0; i < flag.NArg(); i++ {
   347  			arg := flag.Arg(i)
   348  			parts := strings.SplitN(arg, "=", 2)
   349  			var pkgpath, file string
   350  			if len(parts) == 1 {
   351  				pkgpath, file = "main", arg
   352  			} else {
   353  				pkgpath, file = parts[0], parts[1]
   354  			}
   355  			pkglistfornote = append(pkglistfornote, pkgpath...)
   356  			pkglistfornote = append(pkglistfornote, '\n')
   357  			addlibpath(ctxt, "command line", "command line", file, pkgpath, "", zerofp)
   358  		}
   359  	case BuildModePlugin:
   360  		addlibpath(ctxt, "command line", "command line", flag.Arg(0), *flagPluginPath, "", zerofp)
   361  	default:
   362  		addlibpath(ctxt, "command line", "command line", flag.Arg(0), "main", "", zerofp)
   363  	}
   364  	bench.Start("loadlib")
   365  	ctxt.loadlib()
   366  
   367  	bench.Start("inittasks")
   368  	ctxt.inittasks()
   369  
   370  	bench.Start("deadcode")
   371  	deadcode(ctxt)
   372  
   373  	bench.Start("linksetup")
   374  	ctxt.linksetup()
   375  
   376  	bench.Start("dostrdata")
   377  	ctxt.dostrdata()
   378  	if buildcfg.Experiment.FieldTrack {
   379  		bench.Start("fieldtrack")
   380  		fieldtrack(ctxt.Arch, ctxt.loader)
   381  	}
   382  
   383  	bench.Start("dwarfGenerateDebugInfo")
   384  	dwarfGenerateDebugInfo(ctxt)
   385  
   386  	bench.Start("callgraph")
   387  	ctxt.callgraph()
   388  
   389  	bench.Start("doStackCheck")
   390  	ctxt.doStackCheck()
   391  
   392  	bench.Start("mangleTypeSym")
   393  	ctxt.mangleTypeSym()
   394  
   395  	if ctxt.IsELF {
   396  		bench.Start("doelf")
   397  		ctxt.doelf()
   398  	}
   399  	if ctxt.IsDarwin() {
   400  		bench.Start("domacho")
   401  		ctxt.domacho()
   402  	}
   403  	if ctxt.IsWindows() {
   404  		bench.Start("dope")
   405  		ctxt.dope()
   406  		bench.Start("windynrelocsyms")
   407  		ctxt.windynrelocsyms()
   408  	}
   409  	if ctxt.IsAIX() {
   410  		bench.Start("doxcoff")
   411  		ctxt.doxcoff()
   412  	}
   413  
   414  	bench.Start("textbuildid")
   415  	ctxt.textbuildid()
   416  	bench.Start("addexport")
   417  	ctxt.setArchSyms()
   418  	ctxt.addexport()
   419  	bench.Start("Gentext")
   420  	thearch.Gentext(ctxt, ctxt.loader) // trampolines, call stubs, etc.
   421  
   422  	bench.Start("textaddress")
   423  	ctxt.textaddress()
   424  	bench.Start("typelink")
   425  	ctxt.typelink()
   426  	bench.Start("buildinfo")
   427  	ctxt.buildinfo()
   428  	bench.Start("pclntab")
   429  	containers := ctxt.findContainerSyms()
   430  	pclnState := ctxt.pclntab(containers)
   431  	bench.Start("findfunctab")
   432  	ctxt.findfunctab(pclnState, containers)
   433  	bench.Start("dwarfGenerateDebugSyms")
   434  	dwarfGenerateDebugSyms(ctxt)
   435  	bench.Start("symtab")
   436  	symGroupType := ctxt.symtab(pclnState)
   437  	bench.Start("dodata")
   438  	ctxt.dodata(symGroupType)
   439  	bench.Start("address")
   440  	order := ctxt.address()
   441  	bench.Start("dwarfcompress")
   442  	dwarfcompress(ctxt)
   443  	bench.Start("layout")
   444  	filesize := ctxt.layout(order)
   445  
   446  	// Write out the output file.
   447  	// It is split into two parts (Asmb and Asmb2). The first
   448  	// part writes most of the content (sections and segments),
   449  	// for which we have computed the size and offset, in a
   450  	// mmap'd region. The second part writes more content, for
   451  	// which we don't know the size.
   452  	if ctxt.Arch.Family != sys.Wasm {
   453  		// Don't mmap if we're building for Wasm. Wasm file
   454  		// layout is very different so filesize is meaningless.
   455  		if err := ctxt.Out.Mmap(filesize); err != nil {
   456  			Exitf("mapping output file failed: %v", err)
   457  		}
   458  	}
   459  	// asmb will redirect symbols to the output file mmap, and relocations
   460  	// will be applied directly there.
   461  	bench.Start("Asmb")
   462  	asmb(ctxt)
   463  	exitIfErrors()
   464  
   465  	// Generate additional symbols for the native symbol table just prior
   466  	// to code generation.
   467  	bench.Start("GenSymsLate")
   468  	if thearch.GenSymsLate != nil {
   469  		thearch.GenSymsLate(ctxt, ctxt.loader)
   470  	}
   471  
   472  	asmbfips(ctxt, *flagFipso)
   473  
   474  	bench.Start("Asmb2")
   475  	asmb2(ctxt)
   476  
   477  	bench.Start("Munmap")
   478  	ctxt.Out.Close() // Close handles Munmapping if necessary.
   479  
   480  	bench.Start("hostlink")
   481  	ctxt.hostlink()
   482  	if ctxt.Debugvlog != 0 {
   483  		ctxt.Logf("%s", ctxt.loader.Stat())
   484  		ctxt.Logf("%d liveness data\n", liveness)
   485  	}
   486  	bench.Start("Flush")
   487  	ctxt.Bso.Flush()
   488  	bench.Start("archive")
   489  	ctxt.archive()
   490  	bench.Report(os.Stdout)
   491  
   492  	errorexit()
   493  }
   494  
   495  type Rpath struct {
   496  	set bool
   497  	val string
   498  }
   499  
   500  func (r *Rpath) Set(val string) error {
   501  	r.set = true
   502  	r.val = val
   503  	return nil
   504  }
   505  
   506  func (r *Rpath) String() string {
   507  	return r.val
   508  }
   509  
   510  func startProfile() {
   511  	if *cpuprofile != "" {
   512  		f, err := os.Create(*cpuprofile)
   513  		if err != nil {
   514  			log.Fatalf("%v", err)
   515  		}
   516  		if err := pprof.StartCPUProfile(f); err != nil {
   517  			log.Fatalf("%v", err)
   518  		}
   519  		AtExit(func() {
   520  			pprof.StopCPUProfile()
   521  			if err = f.Close(); err != nil {
   522  				log.Fatalf("error closing cpu profile: %v", err)
   523  			}
   524  		})
   525  	}
   526  	if *memprofile != "" {
   527  		if *memprofilerate != 0 {
   528  			runtime.MemProfileRate = int(*memprofilerate)
   529  		}
   530  		f, err := os.Create(*memprofile)
   531  		if err != nil {
   532  			log.Fatalf("%v", err)
   533  		}
   534  		AtExit(func() {
   535  			// Profile all outstanding allocations.
   536  			runtime.GC()
   537  			// compilebench parses the memory profile to extract memstats,
   538  			// which are only written in the legacy pprof format.
   539  			// See golang.org/issue/18641 and runtime/pprof/pprof.go:writeHeap.
   540  			const writeLegacyFormat = 1
   541  			if err := pprof.Lookup("heap").WriteTo(f, writeLegacyFormat); err != nil {
   542  				log.Fatalf("%v", err)
   543  			}
   544  			// Close the file after writing the profile.
   545  			if err := f.Close(); err != nil {
   546  				log.Fatalf("could not close %v: %v", *memprofile, err)
   547  			}
   548  		})
   549  	}
   550  }
   551
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