obj.go

Documentation: cmd/compile/internal/gc

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package gc
     6  
     7  import (
     8  	"cmd/compile/internal/base"
     9  	"cmd/compile/internal/ir"
    10  	"cmd/compile/internal/noder"
    11  	"cmd/compile/internal/objw"
    12  	"cmd/compile/internal/pkginit"
    13  	"cmd/compile/internal/reflectdata"
    14  	"cmd/compile/internal/staticdata"
    15  	"cmd/compile/internal/typecheck"
    16  	"cmd/compile/internal/types"
    17  	"cmd/internal/archive"
    18  	"cmd/internal/bio"
    19  	"cmd/internal/obj"
    20  	"cmd/internal/objabi"
    21  	"encoding/json"
    22  	"fmt"
    23  	"strings"
    24  )
    25  
    26  // These modes say which kind of object file to generate.
    27  // The default use of the toolchain is to set both bits,
    28  // generating a combined compiler+linker object, one that
    29  // serves to describe the package to both the compiler and the linker.
    30  // In fact the compiler and linker read nearly disjoint sections of
    31  // that file, though, so in a distributed build setting it can be more
    32  // efficient to split the output into two files, supplying the compiler
    33  // object only to future compilations and the linker object only to
    34  // future links.
    35  //
    36  // By default a combined object is written, but if -linkobj is specified
    37  // on the command line then the default -o output is a compiler object
    38  // and the -linkobj output is a linker object.
    39  const (
    40  	modeCompilerObj = 1 << iota
    41  	modeLinkerObj
    42  )
    43  
    44  func dumpobj() {
    45  	if base.Flag.LinkObj == "" {
    46  		dumpobj1(base.Flag.LowerO, modeCompilerObj|modeLinkerObj)
    47  		return
    48  	}
    49  	dumpobj1(base.Flag.LowerO, modeCompilerObj)
    50  	dumpobj1(base.Flag.LinkObj, modeLinkerObj)
    51  }
    52  
    53  func dumpobj1(outfile string, mode int) {
    54  	bout, err := bio.Create(outfile)
    55  	if err != nil {
    56  		base.FlushErrors()
    57  		fmt.Printf("can't create %s: %v\n", outfile, err)
    58  		base.ErrorExit()
    59  	}
    60  	defer bout.Close()
    61  	bout.WriteString("!<arch>\n")
    62  
    63  	if mode&modeCompilerObj != 0 {
    64  		start := startArchiveEntry(bout)
    65  		dumpCompilerObj(bout)
    66  		finishArchiveEntry(bout, start, "__.PKGDEF")
    67  	}
    68  	if mode&modeLinkerObj != 0 {
    69  		start := startArchiveEntry(bout)
    70  		dumpLinkerObj(bout)
    71  		finishArchiveEntry(bout, start, "_go_.o")
    72  	}
    73  }
    74  
    75  func printObjHeader(bout *bio.Writer) {
    76  	bout.WriteString(objabi.HeaderString())
    77  	if base.Flag.BuildID != "" {
    78  		fmt.Fprintf(bout, "build id %q\n", base.Flag.BuildID)
    79  	}
    80  	if types.LocalPkg.Name == "main" {
    81  		fmt.Fprintf(bout, "main\n")
    82  	}
    83  	fmt.Fprintf(bout, "\n") // header ends with blank line
    84  }
    85  
    86  func startArchiveEntry(bout *bio.Writer) int64 {
    87  	var arhdr [archive.HeaderSize]byte
    88  	bout.Write(arhdr[:])
    89  	return bout.Offset()
    90  }
    91  
    92  func finishArchiveEntry(bout *bio.Writer, start int64, name string) {
    93  	bout.Flush()
    94  	size := bout.Offset() - start
    95  	if size&1 != 0 {
    96  		bout.WriteByte(0)
    97  	}
    98  	bout.MustSeek(start-archive.HeaderSize, 0)
    99  
   100  	var arhdr [archive.HeaderSize]byte
   101  	archive.FormatHeader(arhdr[:], name, size)
   102  	bout.Write(arhdr[:])
   103  	bout.Flush()
   104  	bout.MustSeek(start+size+(size&1), 0)
   105  }
   106  
   107  func dumpCompilerObj(bout *bio.Writer) {
   108  	printObjHeader(bout)
   109  	noder.WriteExports(bout)
   110  }
   111  
   112  func dumpdata() {
   113  	reflectdata.WriteGCSymbols()
   114  	reflectdata.WritePluginTable()
   115  	dumpembeds()
   116  
   117  	if reflectdata.ZeroSize > 0 {
   118  		zero := base.PkgLinksym("go:map", "zero", obj.ABI0)
   119  		objw.Global(zero, int32(reflectdata.ZeroSize), obj.DUPOK|obj.RODATA)
   120  		zero.Set(obj.AttrStatic, true)
   121  	}
   122  
   123  	staticdata.WriteFuncSyms()
   124  	addGCLocals()
   125  }
   126  
   127  func dumpLinkerObj(bout *bio.Writer) {
   128  	printObjHeader(bout)
   129  
   130  	if len(typecheck.Target.CgoPragmas) != 0 {
   131  		// write empty export section; must be before cgo section
   132  		fmt.Fprintf(bout, "\n$$\n\n$$\n\n")
   133  		fmt.Fprintf(bout, "\n$$  // cgo\n")
   134  		if err := json.NewEncoder(bout).Encode(typecheck.Target.CgoPragmas); err != nil {
   135  			base.Fatalf("serializing pragcgobuf: %v", err)
   136  		}
   137  		fmt.Fprintf(bout, "\n$$\n\n")
   138  	}
   139  
   140  	fmt.Fprintf(bout, "\n!\n")
   141  
   142  	obj.WriteObjFile(base.Ctxt, bout)
   143  }
   144  
   145  func dumpGlobal(n *ir.Name) {
   146  	if n.Type() == nil {
   147  		base.Fatalf("external %v nil type\n", n)
   148  	}
   149  	if n.Class == ir.PFUNC {
   150  		return
   151  	}
   152  	if n.Sym().Pkg != types.LocalPkg {
   153  		return
   154  	}
   155  	types.CalcSize(n.Type())
   156  	ggloblnod(n)
   157  	if n.CoverageAuxVar() || n.Linksym().Static() {
   158  		return
   159  	}
   160  	base.Ctxt.DwarfGlobal(types.TypeSymName(n.Type()), n.Linksym())
   161  }
   162  
   163  func dumpGlobalConst(n *ir.Name) {
   164  	// only export typed constants
   165  	t := n.Type()
   166  	if t == nil {
   167  		return
   168  	}
   169  	if n.Sym().Pkg != types.LocalPkg {
   170  		return
   171  	}
   172  	// only export integer constants for now
   173  	if !t.IsInteger() {
   174  		return
   175  	}
   176  	v := n.Val()
   177  	if t.IsUntyped() {
   178  		// Export untyped integers as int (if they fit).
   179  		t = types.Types[types.TINT]
   180  		if ir.ConstOverflow(v, t) {
   181  			return
   182  		}
   183  	} else {
   184  		// If the type of the constant is an instantiated generic, we need to emit
   185  		// that type so the linker knows about it. See issue 51245.
   186  		_ = reflectdata.TypeLinksym(t)
   187  	}
   188  	base.Ctxt.DwarfIntConst(n.Sym().Name, types.TypeSymName(t), ir.IntVal(t, v))
   189  }
   190  
   191  // addGCLocals adds gcargs, gclocals, gcregs, and stack object symbols to Ctxt.Data.
   192  //
   193  // This is done during the sequential phase after compilation, since
   194  // global symbols can't be declared during parallel compilation.
   195  func addGCLocals() {
   196  	for _, s := range base.Ctxt.Text {
   197  		fn := s.Func()
   198  		if fn == nil {
   199  			continue
   200  		}
   201  		for _, gcsym := range []*obj.LSym{fn.GCArgs, fn.GCLocals} {
   202  			if gcsym != nil && !gcsym.OnList() {
   203  				objw.Global(gcsym, int32(len(gcsym.P)), obj.RODATA|obj.DUPOK)
   204  			}
   205  		}
   206  		if x := fn.StackObjects; x != nil {
   207  			objw.Global(x, int32(len(x.P)), obj.RODATA)
   208  			x.Set(obj.AttrStatic, true)
   209  		}
   210  		if x := fn.OpenCodedDeferInfo; x != nil {
   211  			objw.Global(x, int32(len(x.P)), obj.RODATA|obj.DUPOK)
   212  		}
   213  		if x := fn.ArgInfo; x != nil {
   214  			objw.Global(x, int32(len(x.P)), obj.RODATA|obj.DUPOK)
   215  			x.Set(obj.AttrStatic, true)
   216  		}
   217  		if x := fn.ArgLiveInfo; x != nil {
   218  			objw.Global(x, int32(len(x.P)), obj.RODATA|obj.DUPOK)
   219  			x.Set(obj.AttrStatic, true)
   220  		}
   221  		if x := fn.WrapInfo; x != nil && !x.OnList() {
   222  			objw.Global(x, int32(len(x.P)), obj.RODATA|obj.DUPOK)
   223  			x.Set(obj.AttrStatic, true)
   224  		}
   225  		for _, jt := range fn.JumpTables {
   226  			objw.Global(jt.Sym, int32(len(jt.Targets)*base.Ctxt.Arch.PtrSize), obj.RODATA)
   227  		}
   228  	}
   229  }
   230  
   231  func ggloblnod(nam *ir.Name) {
   232  	s := nam.Linksym()
   233  
   234  	// main_inittask and runtime_inittask in package runtime (and in
   235  	// test/initempty.go) aren't real variable declarations, but
   236  	// linknamed variables pointing to the compiler's generated
   237  	// .inittask symbol. The real symbol was already written out in
   238  	// pkginit.Task, so we need to avoid writing them out a second time
   239  	// here, otherwise base.Ctxt.Globl will fail.
   240  	if strings.HasSuffix(s.Name, "..inittask") && s.OnList() {
   241  		return
   242  	}
   243  
   244  	s.Gotype = reflectdata.TypeLinksym(nam.Type())
   245  	flags := 0
   246  	if nam.Readonly() {
   247  		flags = obj.RODATA
   248  	}
   249  	if nam.Type() != nil && !nam.Type().HasPointers() {
   250  		flags |= obj.NOPTR
   251  	}
   252  	size := nam.Type().Size()
   253  	linkname := nam.Sym().Linkname
   254  	name := nam.Sym().Name
   255  
   256  	var saveType objabi.SymKind
   257  	if nam.CoverageAuxVar() {
   258  		saveType = s.Type
   259  	}
   260  
   261  	// We've skipped linkname'd globals's instrument, so we can skip them here as well.
   262  	if base.Flag.ASan && linkname == "" && pkginit.InstrumentGlobalsMap[name] != nil {
   263  		// Write the new size of instrumented global variables that have
   264  		// trailing redzones into object file.
   265  		rzSize := pkginit.GetRedzoneSizeForGlobal(size)
   266  		sizeWithRZ := rzSize + size
   267  		base.Ctxt.Globl(s, sizeWithRZ, flags)
   268  	} else {
   269  		base.Ctxt.Globl(s, size, flags)
   270  	}
   271  	if nam.Libfuzzer8BitCounter() {
   272  		s.Type = objabi.SLIBFUZZER_8BIT_COUNTER
   273  	}
   274  	if nam.CoverageAuxVar() && saveType == objabi.SCOVERAGE_COUNTER {
   275  		// restore specialized counter type (which Globl call above overwrote)
   276  		s.Type = saveType
   277  	}
   278  	if nam.Sym().Linkname != "" {
   279  		// Make sure linkname'd symbol is non-package. When a symbol is
   280  		// both imported and linkname'd, s.Pkg may not set to "_" in
   281  		// types.Sym.Linksym because LSym already exists. Set it here.
   282  		s.Pkg = "_"
   283  	}
   284  }
   285  
   286  func dumpembeds() {
   287  	for _, v := range typecheck.Target.Embeds {
   288  		staticdata.WriteEmbed(v)
   289  	}
   290  }
   291
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