Source file src/cmd/link/internal/ld/data.go

Documentation: cmd/link/internal/ld

     1  // Derived from Inferno utils/6l/obj.c and utils/6l/span.c
     2  // https://bitbucket.org/inferno-os/inferno-os/src/default/utils/6l/obj.c
     3  // https://bitbucket.org/inferno-os/inferno-os/src/default/utils/6l/span.c
     4  //
     5  //	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
     6  //	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
     7  //	Portions Copyright © 1997-1999 Vita Nuova Limited
     8  //	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
     9  //	Portions Copyright © 2004,2006 Bruce Ellis
    10  //	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
    11  //	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
    12  //	Portions Copyright © 2009 The Go Authors. All rights reserved.
    13  //
    14  // Permission is hereby granted, free of charge, to any person obtaining a copy
    15  // of this software and associated documentation files (the "Software"), to deal
    16  // in the Software without restriction, including without limitation the rights
    17  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    18  // copies of the Software, and to permit persons to whom the Software is
    19  // furnished to do so, subject to the following conditions:
    20  //
    21  // The above copyright notice and this permission notice shall be included in
    22  // all copies or substantial portions of the Software.
    23  //
    24  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    25  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    26  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
    27  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    28  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    29  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    30  // THE SOFTWARE.
    31  
    32  package ld
    33  
    34  import (
    35  	"bytes"
    36  	"cmd/internal/gcprog"
    37  	"cmd/internal/objabi"
    38  	"cmd/internal/sys"
    39  	"cmd/link/internal/sym"
    40  	"compress/zlib"
    41  	"encoding/binary"
    42  	"fmt"
    43  	"log"
    44  	"os"
    45  	"sort"
    46  	"strconv"
    47  	"strings"
    48  	"sync"
    49  )
    50  
    51  // isRuntimeDepPkg reports whether pkg is the runtime package or its dependency
    52  func isRuntimeDepPkg(pkg string) bool {
    53  	switch pkg {
    54  	case "runtime",
    55  		"sync/atomic",      // runtime may call to sync/atomic, due to go:linkname
    56  		"internal/bytealg", // for IndexByte
    57  		"internal/cpu":     // for cpu features
    58  		return true
    59  	}
    60  	return strings.HasPrefix(pkg, "runtime/internal/") && !strings.HasSuffix(pkg, "_test")
    61  }
    62  
    63  // Estimate the max size needed to hold any new trampolines created for this function. This
    64  // is used to determine when the section can be split if it becomes too large, to ensure that
    65  // the trampolines are in the same section as the function that uses them.
    66  func maxSizeTrampolinesPPC64(s *sym.Symbol, isTramp bool) uint64 {
    67  	// If thearch.Trampoline is nil, then trampoline support is not available on this arch.
    68  	// A trampoline does not need any dependent trampolines.
    69  	if thearch.Trampoline == nil || isTramp {
    70  		return 0
    71  	}
    72  
    73  	n := uint64(0)
    74  	for ri := range s.R {
    75  		r := &s.R[ri]
    76  		if r.Type.IsDirectJump() {
    77  			n++
    78  		}
    79  	}
    80  	// Trampolines in ppc64 are 4 instructions.
    81  	return n * 16
    82  }
    83  
    84  // detect too-far jumps in function s, and add trampolines if necessary
    85  // ARM, PPC64 & PPC64LE support trampoline insertion for internal and external linking
    86  // On PPC64 & PPC64LE the text sections might be split but will still insert trampolines
    87  // where necessary.
    88  func trampoline(ctxt *Link, s *sym.Symbol) {
    89  	if thearch.Trampoline == nil {
    90  		return // no need or no support of trampolines on this arch
    91  	}
    92  
    93  	for ri := range s.R {
    94  		r := &s.R[ri]
    95  		if !r.Type.IsDirectJump() {
    96  			continue
    97  		}
    98  		if Symaddr(r.Sym) == 0 && r.Sym.Type != sym.SDYNIMPORT {
    99  			if r.Sym.File != s.File {
   100  				if !isRuntimeDepPkg(s.File) || !isRuntimeDepPkg(r.Sym.File) {
   101  					ctxt.ErrorUnresolved(s, r)
   102  				}
   103  				// runtime and its dependent packages may call to each other.
   104  				// they are fine, as they will be laid down together.
   105  			}
   106  			continue
   107  		}
   108  
   109  		thearch.Trampoline(ctxt, r, s)
   110  	}
   111  
   112  }
   113  
   114  // relocsym resolve relocations in "s". The main loop walks through
   115  // the list of relocations attached to "s" and resolves them where
   116  // applicable. Relocations are often architecture-specific, requiring
   117  // calls into the 'archreloc' and/or 'archrelocvariant' functions for
   118  // the architecture. When external linking is in effect, it may not be
   119  // possible to completely resolve the address/offset for a symbol, in
   120  // which case the goal is to lay the groundwork for turning a given
   121  // relocation into an external reloc (to be applied by the external
   122  // linker). For more on how relocations work in general, see
   123  //
   124  //  "Linkers and Loaders", by John R. Levine (Morgan Kaufmann, 1999), ch. 7
   125  //
   126  // This is a performance-critical function for the linker; be careful
   127  // to avoid introducing unnecessary allocations in the main loop.
   128  func relocsym(ctxt *Link, s *sym.Symbol) {
   129  	for ri := int32(0); ri < int32(len(s.R)); ri++ {
   130  		r := &s.R[ri]
   131  		if r.Done {
   132  			// Relocation already processed by an earlier phase.
   133  			continue
   134  		}
   135  		r.Done = true
   136  		off := r.Off
   137  		siz := int32(r.Siz)
   138  		if off < 0 || off+siz > int32(len(s.P)) {
   139  			rname := ""
   140  			if r.Sym != nil {
   141  				rname = r.Sym.Name
   142  			}
   143  			Errorf(s, "invalid relocation %s: %d+%d not in [%d,%d)", rname, off, siz, 0, len(s.P))
   144  			continue
   145  		}
   146  
   147  		if r.Sym != nil && ((r.Sym.Type == sym.Sxxx && !r.Sym.Attr.VisibilityHidden()) || r.Sym.Type == sym.SXREF) {
   148  			// When putting the runtime but not main into a shared library
   149  			// these symbols are undefined and that's OK.
   150  			if ctxt.BuildMode == BuildModeShared {
   151  				if r.Sym.Name == "main.main" || r.Sym.Name == "main.init" {
   152  					r.Sym.Type = sym.SDYNIMPORT
   153  				} else if strings.HasPrefix(r.Sym.Name, "go.info.") {
   154  					// Skip go.info symbols. They are only needed to communicate
   155  					// DWARF info between the compiler and linker.
   156  					continue
   157  				}
   158  			} else {
   159  				ctxt.ErrorUnresolved(s, r)
   160  				continue
   161  			}
   162  		}
   163  
   164  		if r.Type >= 256 {
   165  			continue
   166  		}
   167  		if r.Siz == 0 { // informational relocation - no work to do
   168  			continue
   169  		}
   170  		if r.Type == objabi.R_DWARFFILEREF {
   171  			// These should have been processed previously during
   172  			// line table writing.
   173  			Errorf(s, "orphan R_DWARFFILEREF reloc to %v", r.Sym.Name)
   174  			continue
   175  		}
   176  
   177  		// We need to be able to reference dynimport symbols when linking against
   178  		// shared libraries, and Solaris, Darwin and AIX need it always
   179  		if ctxt.HeadType != objabi.Hsolaris && ctxt.HeadType != objabi.Hdarwin && ctxt.HeadType != objabi.Haix && r.Sym != nil && r.Sym.Type == sym.SDYNIMPORT && !ctxt.DynlinkingGo() && !r.Sym.Attr.SubSymbol() {
   180  			if !(ctxt.Arch.Family == sys.PPC64 && ctxt.LinkMode == LinkExternal && r.Sym.Name == ".TOC.") {
   181  				Errorf(s, "unhandled relocation for %s (type %d (%s) rtype %d (%s))", r.Sym.Name, r.Sym.Type, r.Sym.Type, r.Type, sym.RelocName(ctxt.Arch, r.Type))
   182  			}
   183  		}
   184  		if r.Sym != nil && r.Sym.Type != sym.STLSBSS && r.Type != objabi.R_WEAKADDROFF && !r.Sym.Attr.Reachable() {
   185  			Errorf(s, "unreachable sym in relocation: %s", r.Sym.Name)
   186  		}
   187  
   188  		// TODO(mundaym): remove this special case - see issue 14218.
   189  		if ctxt.Arch.Family == sys.S390X {
   190  			switch r.Type {
   191  			case objabi.R_PCRELDBL:
   192  				r.Type = objabi.R_PCREL
   193  				r.Variant = sym.RV_390_DBL
   194  			case objabi.R_CALL:
   195  				r.Variant = sym.RV_390_DBL
   196  			}
   197  		}
   198  
   199  		var o int64
   200  		switch r.Type {
   201  		default:
   202  			switch siz {
   203  			default:
   204  				Errorf(s, "bad reloc size %#x for %s", uint32(siz), r.Sym.Name)
   205  			case 1:
   206  				o = int64(s.P[off])
   207  			case 2:
   208  				o = int64(ctxt.Arch.ByteOrder.Uint16(s.P[off:]))
   209  			case 4:
   210  				o = int64(ctxt.Arch.ByteOrder.Uint32(s.P[off:]))
   211  			case 8:
   212  				o = int64(ctxt.Arch.ByteOrder.Uint64(s.P[off:]))
   213  			}
   214  			if offset, ok := thearch.Archreloc(ctxt, r, s, o); ok {
   215  				o = offset
   216  			} else {
   217  				Errorf(s, "unknown reloc to %v: %d (%s)", r.Sym.Name, r.Type, sym.RelocName(ctxt.Arch, r.Type))
   218  			}
   219  		case objabi.R_TLS_LE:
   220  			isAndroidX86 := objabi.GOOS == "android" && (ctxt.Arch.InFamily(sys.AMD64, sys.I386))
   221  
   222  			if ctxt.LinkMode == LinkExternal && ctxt.IsELF && !isAndroidX86 {
   223  				r.Done = false
   224  				if r.Sym == nil {
   225  					r.Sym = ctxt.Tlsg
   226  				}
   227  				r.Xsym = r.Sym
   228  				r.Xadd = r.Add
   229  				o = 0
   230  				if ctxt.Arch.Family != sys.AMD64 {
   231  					o = r.Add
   232  				}
   233  				break
   234  			}
   235  
   236  			if ctxt.IsELF && ctxt.Arch.Family == sys.ARM {
   237  				// On ELF ARM, the thread pointer is 8 bytes before
   238  				// the start of the thread-local data block, so add 8
   239  				// to the actual TLS offset (r->sym->value).
   240  				// This 8 seems to be a fundamental constant of
   241  				// ELF on ARM (or maybe Glibc on ARM); it is not
   242  				// related to the fact that our own TLS storage happens
   243  				// to take up 8 bytes.
   244  				o = 8 + r.Sym.Value
   245  			} else if ctxt.IsELF || ctxt.HeadType == objabi.Hplan9 || ctxt.HeadType == objabi.Hdarwin || isAndroidX86 {
   246  				o = int64(ctxt.Tlsoffset) + r.Add
   247  			} else if ctxt.HeadType == objabi.Hwindows {
   248  				o = r.Add
   249  			} else {
   250  				log.Fatalf("unexpected R_TLS_LE relocation for %v", ctxt.HeadType)
   251  			}
   252  		case objabi.R_TLS_IE:
   253  			isAndroidX86 := objabi.GOOS == "android" && (ctxt.Arch.InFamily(sys.AMD64, sys.I386))
   254  
   255  			if ctxt.LinkMode == LinkExternal && ctxt.IsELF && !isAndroidX86 {
   256  				r.Done = false
   257  				if r.Sym == nil {
   258  					r.Sym = ctxt.Tlsg
   259  				}
   260  				r.Xsym = r.Sym
   261  				r.Xadd = r.Add
   262  				o = 0
   263  				if ctxt.Arch.Family != sys.AMD64 {
   264  					o = r.Add
   265  				}
   266  				break
   267  			}
   268  			if ctxt.BuildMode == BuildModePIE && ctxt.IsELF {
   269  				// We are linking the final executable, so we
   270  				// can optimize any TLS IE relocation to LE.
   271  				if thearch.TLSIEtoLE == nil {
   272  					log.Fatalf("internal linking of TLS IE not supported on %v", ctxt.Arch.Family)
   273  				}
   274  				thearch.TLSIEtoLE(s, int(off), int(r.Siz))
   275  				o = int64(ctxt.Tlsoffset)
   276  				// TODO: o += r.Add when ctxt.Arch.Family != sys.AMD64?
   277  				// Why do we treat r.Add differently on AMD64?
   278  				// Is the external linker using Xadd at all?
   279  			} else {
   280  				log.Fatalf("cannot handle R_TLS_IE (sym %s) when linking internally", s.Name)
   281  			}
   282  		case objabi.R_ADDR:
   283  			if ctxt.LinkMode == LinkExternal && r.Sym.Type != sym.SCONST {
   284  				r.Done = false
   285  
   286  				// set up addend for eventual relocation via outer symbol.
   287  				rs := r.Sym
   288  
   289  				r.Xadd = r.Add
   290  				for rs.Outer != nil {
   291  					r.Xadd += Symaddr(rs) - Symaddr(rs.Outer)
   292  					rs = rs.Outer
   293  				}
   294  
   295  				if rs.Type != sym.SHOSTOBJ && rs.Type != sym.SDYNIMPORT && rs.Sect == nil {
   296  					Errorf(s, "missing section for relocation target %s", rs.Name)
   297  				}
   298  				r.Xsym = rs
   299  
   300  				o = r.Xadd
   301  				if ctxt.IsELF {
   302  					if ctxt.Arch.Family == sys.AMD64 {
   303  						o = 0
   304  					}
   305  				} else if ctxt.HeadType == objabi.Hdarwin {
   306  					if rs.Type != sym.SHOSTOBJ {
   307  						o += Symaddr(rs)
   308  					}
   309  				} else if ctxt.HeadType == objabi.Hwindows {
   310  					// nothing to do
   311  				} else {
   312  					Errorf(s, "unhandled pcrel relocation to %s on %v", rs.Name, ctxt.HeadType)
   313  				}
   314  
   315  				break
   316  			}
   317  
   318  			// On AIX, a second relocation must be done by the loader,
   319  			// as section addresses can change once loaded.
   320  			// The "default" symbol address is still needed by the loader so
   321  			// the current relocation can't be skipped.
   322  			if ctxt.HeadType == objabi.Haix && r.Sym.Type != sym.SDYNIMPORT {
   323  				// It's not possible to make a loader relocation in a
   324  				// symbol which is not inside .data section.
   325  				// FIXME: It should be forbidden to have R_ADDR from a
   326  				// symbol which isn't in .data. However, as .text has the
   327  				// same address once loaded, this is possible.
   328  				if s.Sect.Seg == &Segdata {
   329  					Xcoffadddynrel(ctxt, s, r)
   330  				}
   331  			}
   332  
   333  			o = Symaddr(r.Sym) + r.Add
   334  
   335  			// On amd64, 4-byte offsets will be sign-extended, so it is impossible to
   336  			// access more than 2GB of static data; fail at link time is better than
   337  			// fail at runtime. See https://golang.org/issue/7980.
   338  			// Instead of special casing only amd64, we treat this as an error on all
   339  			// 64-bit architectures so as to be future-proof.
   340  			if int32(o) < 0 && ctxt.Arch.PtrSize > 4 && siz == 4 {
   341  				Errorf(s, "non-pc-relative relocation address for %s is too big: %#x (%#x + %#x)", r.Sym.Name, uint64(o), Symaddr(r.Sym), r.Add)
   342  				errorexit()
   343  			}
   344  		case objabi.R_DWARFSECREF:
   345  			if r.Sym.Sect == nil {
   346  				Errorf(s, "missing DWARF section for relocation target %s", r.Sym.Name)
   347  			}
   348  
   349  			if ctxt.LinkMode == LinkExternal {
   350  				r.Done = false
   351  
   352  				// On most platforms, the external linker needs to adjust DWARF references
   353  				// as it combines DWARF sections. However, on Darwin, dsymutil does the
   354  				// DWARF linking, and it understands how to follow section offsets.
   355  				// Leaving in the relocation records confuses it (see
   356  				// https://golang.org/issue/22068) so drop them for Darwin.
   357  				if ctxt.HeadType == objabi.Hdarwin {
   358  					r.Done = true
   359  				}
   360  
   361  				// PE code emits IMAGE_REL_I386_SECREL and IMAGE_REL_AMD64_SECREL
   362  				// for R_DWARFSECREF relocations, while R_ADDR is replaced with
   363  				// IMAGE_REL_I386_DIR32, IMAGE_REL_AMD64_ADDR64 and IMAGE_REL_AMD64_ADDR32.
   364  				// Do not replace R_DWARFSECREF with R_ADDR for windows -
   365  				// let PE code emit correct relocations.
   366  				if ctxt.HeadType != objabi.Hwindows {
   367  					r.Type = objabi.R_ADDR
   368  				}
   369  
   370  				r.Xsym = ctxt.Syms.ROLookup(r.Sym.Sect.Name, 0)
   371  				r.Xadd = r.Add + Symaddr(r.Sym) - int64(r.Sym.Sect.Vaddr)
   372  
   373  				o = r.Xadd
   374  				if ctxt.IsELF && ctxt.Arch.Family == sys.AMD64 {
   375  					o = 0
   376  				}
   377  				break
   378  			}
   379  			o = Symaddr(r.Sym) + r.Add - int64(r.Sym.Sect.Vaddr)
   380  		case objabi.R_WEAKADDROFF:
   381  			if !r.Sym.Attr.Reachable() {
   382  				continue
   383  			}
   384  			fallthrough
   385  		case objabi.R_ADDROFF:
   386  			// The method offset tables using this relocation expect the offset to be relative
   387  			// to the start of the first text section, even if there are multiple.
   388  			if r.Sym.Sect.Name == ".text" {
   389  				o = Symaddr(r.Sym) - int64(Segtext.Sections[0].Vaddr) + r.Add
   390  			} else {
   391  				o = Symaddr(r.Sym) - int64(r.Sym.Sect.Vaddr) + r.Add
   392  			}
   393  
   394  		case objabi.R_ADDRCUOFF:
   395  			// debug_range and debug_loc elements use this relocation type to get an
   396  			// offset from the start of the compile unit.
   397  			o = Symaddr(r.Sym) + r.Add - Symaddr(r.Sym.Lib.Textp[0])
   398  
   399  			// r->sym can be null when CALL $(constant) is transformed from absolute PC to relative PC call.
   400  		case objabi.R_GOTPCREL:
   401  			if ctxt.DynlinkingGo() && ctxt.HeadType == objabi.Hdarwin && r.Sym != nil && r.Sym.Type != sym.SCONST {
   402  				r.Done = false
   403  				r.Xadd = r.Add
   404  				r.Xadd -= int64(r.Siz) // relative to address after the relocated chunk
   405  				r.Xsym = r.Sym
   406  
   407  				o = r.Xadd
   408  				o += int64(r.Siz)
   409  				break
   410  			}
   411  			fallthrough
   412  		case objabi.R_CALL, objabi.R_PCREL:
   413  			if ctxt.LinkMode == LinkExternal && r.Sym != nil && r.Sym.Type != sym.SCONST && (r.Sym.Sect != s.Sect || r.Type == objabi.R_GOTPCREL) {
   414  				r.Done = false
   415  
   416  				// set up addend for eventual relocation via outer symbol.
   417  				rs := r.Sym
   418  
   419  				r.Xadd = r.Add
   420  				for rs.Outer != nil {
   421  					r.Xadd += Symaddr(rs) - Symaddr(rs.Outer)
   422  					rs = rs.Outer
   423  				}
   424  
   425  				r.Xadd -= int64(r.Siz) // relative to address after the relocated chunk
   426  				if rs.Type != sym.SHOSTOBJ && rs.Type != sym.SDYNIMPORT && rs.Sect == nil {
   427  					Errorf(s, "missing section for relocation target %s", rs.Name)
   428  				}
   429  				r.Xsym = rs
   430  
   431  				o = r.Xadd
   432  				if ctxt.IsELF {
   433  					if ctxt.Arch.Family == sys.AMD64 {
   434  						o = 0
   435  					}
   436  				} else if ctxt.HeadType == objabi.Hdarwin {
   437  					if r.Type == objabi.R_CALL {
   438  						if ctxt.LinkMode == LinkExternal && rs.Type == sym.SDYNIMPORT {
   439  							switch ctxt.Arch.Family {
   440  							case sys.AMD64:
   441  								// AMD64 dynamic relocations are relative to the end of the relocation.
   442  								o += int64(r.Siz)
   443  							case sys.I386:
   444  								// I386 dynamic relocations are relative to the start of the section.
   445  								o -= int64(r.Off)                         // offset in symbol
   446  								o -= int64(s.Value - int64(s.Sect.Vaddr)) // offset of symbol in section
   447  							}
   448  						} else {
   449  							if rs.Type != sym.SHOSTOBJ {
   450  								o += int64(uint64(Symaddr(rs)) - rs.Sect.Vaddr)
   451  							}
   452  							o -= int64(r.Off) // relative to section offset, not symbol
   453  						}
   454  					} else if ctxt.Arch.Family == sys.ARM {
   455  						// see ../arm/asm.go:/machoreloc1
   456  						o += Symaddr(rs) - s.Value - int64(r.Off)
   457  					} else {
   458  						o += int64(r.Siz)
   459  					}
   460  				} else if ctxt.HeadType == objabi.Hwindows && ctxt.Arch.Family == sys.AMD64 { // only amd64 needs PCREL
   461  					// PE/COFF's PC32 relocation uses the address after the relocated
   462  					// bytes as the base. Compensate by skewing the addend.
   463  					o += int64(r.Siz)
   464  				} else {
   465  					Errorf(s, "unhandled pcrel relocation to %s on %v", rs.Name, ctxt.HeadType)
   466  				}
   467  
   468  				break
   469  			}
   470  
   471  			o = 0
   472  			if r.Sym != nil {
   473  				o += Symaddr(r.Sym)
   474  			}
   475  
   476  			o += r.Add - (s.Value + int64(r.Off) + int64(r.Siz))
   477  		case objabi.R_SIZE:
   478  			o = r.Sym.Size + r.Add
   479  		}
   480  
   481  		if r.Variant != sym.RV_NONE {
   482  			o = thearch.Archrelocvariant(ctxt, r, s, o)
   483  		}
   484  
   485  		if false {
   486  			nam := "<nil>"
   487  			var addr int64
   488  			if r.Sym != nil {
   489  				nam = r.Sym.Name
   490  				addr = Symaddr(r.Sym)
   491  			}
   492  			xnam := "<nil>"
   493  			if r.Xsym != nil {
   494  				xnam = r.Xsym.Name
   495  			}
   496  			fmt.Printf("relocate %s %#x (%#x+%#x, size %d) => %s %#x +%#x (xsym: %s +%#x) [type %d (%s)/%d, %x]\n", s.Name, s.Value+int64(off), s.Value, r.Off, r.Siz, nam, addr, r.Add, xnam, r.Xadd, r.Type, sym.RelocName(ctxt.Arch, r.Type), r.Variant, o)
   497  		}
   498  		switch siz {
   499  		default:
   500  			Errorf(s, "bad reloc size %#x for %s", uint32(siz), r.Sym.Name)
   501  			fallthrough
   502  
   503  			// TODO(rsc): Remove.
   504  		case 1:
   505  			s.P[off] = byte(int8(o))
   506  		case 2:
   507  			if o != int64(int16(o)) {
   508  				Errorf(s, "relocation address for %s is too big: %#x", r.Sym.Name, o)
   509  			}
   510  			i16 := int16(o)
   511  			ctxt.Arch.ByteOrder.PutUint16(s.P[off:], uint16(i16))
   512  		case 4:
   513  			if r.Type == objabi.R_PCREL || r.Type == objabi.R_CALL {
   514  				if o != int64(int32(o)) {
   515  					Errorf(s, "pc-relative relocation address for %s is too big: %#x", r.Sym.Name, o)
   516  				}
   517  			} else {
   518  				if o != int64(int32(o)) && o != int64(uint32(o)) {
   519  					Errorf(s, "non-pc-relative relocation address for %s is too big: %#x", r.Sym.Name, uint64(o))
   520  				}
   521  			}
   522  
   523  			fl := int32(o)
   524  			ctxt.Arch.ByteOrder.PutUint32(s.P[off:], uint32(fl))
   525  		case 8:
   526  			ctxt.Arch.ByteOrder.PutUint64(s.P[off:], uint64(o))
   527  		}
   528  	}
   529  }
   530  
   531  func (ctxt *Link) reloc() {
   532  	if ctxt.Debugvlog != 0 {
   533  		ctxt.Logf("%5.2f reloc\n", Cputime())
   534  	}
   535  
   536  	for _, s := range ctxt.Textp {
   537  		relocsym(ctxt, s)
   538  	}
   539  	for _, s := range datap {
   540  		relocsym(ctxt, s)
   541  	}
   542  	for _, s := range dwarfp {
   543  		relocsym(ctxt, s)
   544  	}
   545  }
   546  
   547  func windynrelocsym(ctxt *Link, rel, s *sym.Symbol) {
   548  	for ri := range s.R {
   549  		r := &s.R[ri]
   550  		targ := r.Sym
   551  		if targ == nil {
   552  			continue
   553  		}
   554  		if !targ.Attr.Reachable() {
   555  			if r.Type == objabi.R_WEAKADDROFF {
   556  				continue
   557  			}
   558  			Errorf(s, "dynamic relocation to unreachable symbol %s", targ.Name)
   559  		}
   560  		if r.Sym.Plt() == -2 && r.Sym.Got() != -2 { // make dynimport JMP table for PE object files.
   561  			targ.SetPlt(int32(rel.Size))
   562  			r.Sym = rel
   563  			r.Add = int64(targ.Plt())
   564  
   565  			// jmp *addr
   566  			switch ctxt.Arch.Family {
   567  			default:
   568  				Errorf(s, "unsupported arch %v", ctxt.Arch.Family)
   569  				return
   570  			case sys.I386:
   571  				rel.AddUint8(0xff)
   572  				rel.AddUint8(0x25)
   573  				rel.AddAddr(ctxt.Arch, targ)
   574  				rel.AddUint8(0x90)
   575  				rel.AddUint8(0x90)
   576  			case sys.AMD64:
   577  				rel.AddUint8(0xff)
   578  				rel.AddUint8(0x24)
   579  				rel.AddUint8(0x25)
   580  				rel.AddAddrPlus4(targ, 0)
   581  				rel.AddUint8(0x90)
   582  			}
   583  		} else if r.Sym.Plt() >= 0 {
   584  			r.Sym = rel
   585  			r.Add = int64(targ.Plt())
   586  		}
   587  	}
   588  }
   589  
   590  // windynrelocsyms generates jump table to C library functions that will be
   591  // added later. windynrelocsyms writes the table into .rel symbol.
   592  func (ctxt *Link) windynrelocsyms() {
   593  	if !(ctxt.HeadType == objabi.Hwindows && iscgo && ctxt.LinkMode == LinkInternal) {
   594  		return
   595  	}
   596  	if ctxt.Debugvlog != 0 {
   597  		ctxt.Logf("%5.2f windynrelocsyms\n", Cputime())
   598  	}
   599  
   600  	/* relocation table */
   601  	rel := ctxt.Syms.Lookup(".rel", 0)
   602  	rel.Attr |= sym.AttrReachable
   603  	rel.Type = sym.STEXT
   604  	ctxt.Textp = append(ctxt.Textp, rel)
   605  
   606  	for _, s := range ctxt.Textp {
   607  		if s == rel {
   608  			continue
   609  		}
   610  		windynrelocsym(ctxt, rel, s)
   611  	}
   612  }
   613  
   614  func dynrelocsym(ctxt *Link, s *sym.Symbol) {
   615  	for ri := range s.R {
   616  		r := &s.R[ri]
   617  		if ctxt.BuildMode == BuildModePIE && ctxt.LinkMode == LinkInternal {
   618  			// It's expected that some relocations will be done
   619  			// later by relocsym (R_TLS_LE, R_ADDROFF), so
   620  			// don't worry if Adddynrel returns false.
   621  			thearch.Adddynrel(ctxt, s, r)
   622  			continue
   623  		}
   624  
   625  		if r.Sym != nil && r.Sym.Type == sym.SDYNIMPORT || r.Type >= 256 {
   626  			if r.Sym != nil && !r.Sym.Attr.Reachable() {
   627  				Errorf(s, "dynamic relocation to unreachable symbol %s", r.Sym.Name)
   628  			}
   629  			if !thearch.Adddynrel(ctxt, s, r) {
   630  				Errorf(s, "unsupported dynamic relocation for symbol %s (type=%d (%s) stype=%d (%s))", r.Sym.Name, r.Type, sym.RelocName(ctxt.Arch, r.Type), r.Sym.Type, r.Sym.Type)
   631  			}
   632  		}
   633  	}
   634  }
   635  
   636  func dynreloc(ctxt *Link, data *[sym.SXREF][]*sym.Symbol) {
   637  	if ctxt.HeadType == objabi.Hwindows {
   638  		return
   639  	}
   640  	// -d suppresses dynamic loader format, so we may as well not
   641  	// compute these sections or mark their symbols as reachable.
   642  	if *FlagD {
   643  		return
   644  	}
   645  	if ctxt.Debugvlog != 0 {
   646  		ctxt.Logf("%5.2f dynreloc\n", Cputime())
   647  	}
   648  
   649  	for _, s := range ctxt.Textp {
   650  		dynrelocsym(ctxt, s)
   651  	}
   652  	for _, syms := range data {
   653  		for _, s := range syms {
   654  			dynrelocsym(ctxt, s)
   655  		}
   656  	}
   657  	if ctxt.IsELF {
   658  		elfdynhash(ctxt)
   659  	}
   660  }
   661  
   662  func Codeblk(ctxt *Link, addr int64, size int64) {
   663  	CodeblkPad(ctxt, addr, size, zeros[:])
   664  }
   665  func CodeblkPad(ctxt *Link, addr int64, size int64, pad []byte) {
   666  	if *flagA {
   667  		ctxt.Logf("codeblk [%#x,%#x) at offset %#x\n", addr, addr+size, ctxt.Out.Offset())
   668  	}
   669  
   670  	blk(ctxt, ctxt.Textp, addr, size, pad)
   671  
   672  	/* again for printing */
   673  	if !*flagA {
   674  		return
   675  	}
   676  
   677  	syms := ctxt.Textp
   678  	for i, s := range syms {
   679  		if !s.Attr.Reachable() {
   680  			continue
   681  		}
   682  		if s.Value >= addr {
   683  			syms = syms[i:]
   684  			break
   685  		}
   686  	}
   687  
   688  	eaddr := addr + size
   689  	for _, s := range syms {
   690  		if !s.Attr.Reachable() {
   691  			continue
   692  		}
   693  		if s.Value >= eaddr {
   694  			break
   695  		}
   696  
   697  		if addr < s.Value {
   698  			ctxt.Logf("%-20s %.8x|", "_", uint64(addr))
   699  			for ; addr < s.Value; addr++ {
   700  				ctxt.Logf(" %.2x", 0)
   701  			}
   702  			ctxt.Logf("\n")
   703  		}
   704  
   705  		ctxt.Logf("%.6x\t%-20s\n", uint64(addr), s.Name)
   706  		q := s.P
   707  
   708  		for len(q) >= 16 {
   709  			ctxt.Logf("%.6x\t% x\n", uint64(addr), q[:16])
   710  			addr += 16
   711  			q = q[16:]
   712  		}
   713  
   714  		if len(q) > 0 {
   715  			ctxt.Logf("%.6x\t% x\n", uint64(addr), q)
   716  			addr += int64(len(q))
   717  		}
   718  	}
   719  
   720  	if addr < eaddr {
   721  		ctxt.Logf("%-20s %.8x|", "_", uint64(addr))
   722  		for ; addr < eaddr; addr++ {
   723  			ctxt.Logf(" %.2x", 0)
   724  		}
   725  	}
   726  }
   727  
   728  func blk(ctxt *Link, syms []*sym.Symbol, addr, size int64, pad []byte) {
   729  	for i, s := range syms {
   730  		if !s.Attr.SubSymbol() && s.Value >= addr {
   731  			syms = syms[i:]
   732  			break
   733  		}
   734  	}
   735  
   736  	// This doesn't distinguish the memory size from the file
   737  	// size, and it lays out the file based on Symbol.Value, which
   738  	// is the virtual address. DWARF compression changes file sizes,
   739  	// so dwarfcompress will fix this up later if necessary.
   740  	eaddr := addr + size
   741  	for _, s := range syms {
   742  		if s.Attr.SubSymbol() {
   743  			continue
   744  		}
   745  		if s.Value >= eaddr {
   746  			break
   747  		}
   748  		if s.Value < addr {
   749  			Errorf(s, "phase error: addr=%#x but sym=%#x type=%d", addr, s.Value, s.Type)
   750  			errorexit()
   751  		}
   752  		if addr < s.Value {
   753  			ctxt.Out.WriteStringPad("", int(s.Value-addr), pad)
   754  			addr = s.Value
   755  		}
   756  		ctxt.Out.Write(s.P)
   757  		addr += int64(len(s.P))
   758  		if addr < s.Value+s.Size {
   759  			ctxt.Out.WriteStringPad("", int(s.Value+s.Size-addr), pad)
   760  			addr = s.Value + s.Size
   761  		}
   762  		if addr != s.Value+s.Size {
   763  			Errorf(s, "phase error: addr=%#x value+size=%#x", addr, s.Value+s.Size)
   764  			errorexit()
   765  		}
   766  		if s.Value+s.Size >= eaddr {
   767  			break
   768  		}
   769  	}
   770  
   771  	if addr < eaddr {
   772  		ctxt.Out.WriteStringPad("", int(eaddr-addr), pad)
   773  	}
   774  	ctxt.Out.Flush()
   775  }
   776  
   777  func Datblk(ctxt *Link, addr int64, size int64) {
   778  	if *flagA {
   779  		ctxt.Logf("datblk [%#x,%#x) at offset %#x\n", addr, addr+size, ctxt.Out.Offset())
   780  	}
   781  
   782  	blk(ctxt, datap, addr, size, zeros[:])
   783  
   784  	/* again for printing */
   785  	if !*flagA {
   786  		return
   787  	}
   788  
   789  	syms := datap
   790  	for i, sym := range syms {
   791  		if sym.Value >= addr {
   792  			syms = syms[i:]
   793  			break
   794  		}
   795  	}
   796  
   797  	eaddr := addr + size
   798  	for _, sym := range syms {
   799  		if sym.Value >= eaddr {
   800  			break
   801  		}
   802  		if addr < sym.Value {
   803  			ctxt.Logf("\t%.8x| 00 ...\n", uint64(addr))
   804  			addr = sym.Value
   805  		}
   806  
   807  		ctxt.Logf("%s\n\t%.8x|", sym.Name, uint64(addr))
   808  		for i, b := range sym.P {
   809  			if i > 0 && i%16 == 0 {
   810  				ctxt.Logf("\n\t%.8x|", uint64(addr)+uint64(i))
   811  			}
   812  			ctxt.Logf(" %.2x", b)
   813  		}
   814  
   815  		addr += int64(len(sym.P))
   816  		for ; addr < sym.Value+sym.Size; addr++ {
   817  			ctxt.Logf(" %.2x", 0)
   818  		}
   819  		ctxt.Logf("\n")
   820  
   821  		if ctxt.LinkMode != LinkExternal {
   822  			continue
   823  		}
   824  		for i := range sym.R {
   825  			r := &sym.R[i] // Copying sym.Reloc has measurable impact on performance
   826  			rsname := ""
   827  			if r.Sym != nil {
   828  				rsname = r.Sym.Name
   829  			}
   830  			typ := "?"
   831  			switch r.Type {
   832  			case objabi.R_ADDR:
   833  				typ = "addr"
   834  			case objabi.R_PCREL:
   835  				typ = "pcrel"
   836  			case objabi.R_CALL:
   837  				typ = "call"
   838  			}
   839  			ctxt.Logf("\treloc %.8x/%d %s %s+%#x [%#x]\n", uint(sym.Value+int64(r.Off)), r.Siz, typ, rsname, r.Add, r.Sym.Value+r.Add)
   840  		}
   841  	}
   842  
   843  	if addr < eaddr {
   844  		ctxt.Logf("\t%.8x| 00 ...\n", uint(addr))
   845  	}
   846  	ctxt.Logf("\t%.8x|\n", uint(eaddr))
   847  }
   848  
   849  func Dwarfblk(ctxt *Link, addr int64, size int64) {
   850  	if *flagA {
   851  		ctxt.Logf("dwarfblk [%#x,%#x) at offset %#x\n", addr, addr+size, ctxt.Out.Offset())
   852  	}
   853  
   854  	blk(ctxt, dwarfp, addr, size, zeros[:])
   855  }
   856  
   857  var zeros [512]byte
   858  
   859  var (
   860  	strdata  = make(map[string]string)
   861  	strnames []string
   862  )
   863  
   864  func addstrdata1(ctxt *Link, arg string) {
   865  	eq := strings.Index(arg, "=")
   866  	dot := strings.LastIndex(arg[:eq+1], ".")
   867  	if eq < 0 || dot < 0 {
   868  		Exitf("-X flag requires argument of the form importpath.name=value")
   869  	}
   870  	pkg := arg[:dot]
   871  	if ctxt.BuildMode == BuildModePlugin && pkg == "main" {
   872  		pkg = *flagPluginPath
   873  	}
   874  	pkg = objabi.PathToPrefix(pkg)
   875  	name := pkg + arg[dot:eq]
   876  	value := arg[eq+1:]
   877  	if _, ok := strdata[name]; !ok {
   878  		strnames = append(strnames, name)
   879  	}
   880  	strdata[name] = value
   881  }
   882  
   883  // addstrdata sets the initial value of the string variable name to value.
   884  func addstrdata(ctxt *Link, name, value string) {
   885  	s := ctxt.Syms.ROLookup(name, 0)
   886  	if s == nil || s.Gotype == nil {
   887  		// Not defined in the loaded packages.
   888  		return
   889  	}
   890  	if s.Gotype.Name != "type.string" {
   891  		Errorf(s, "cannot set with -X: not a var of type string (%s)", s.Gotype.Name)
   892  		return
   893  	}
   894  	if s.Type == sym.SBSS {
   895  		s.Type = sym.SDATA
   896  	}
   897  
   898  	p := fmt.Sprintf("%s.str", s.Name)
   899  	sp := ctxt.Syms.Lookup(p, 0)
   900  
   901  	Addstring(sp, value)
   902  	sp.Type = sym.SRODATA
   903  
   904  	s.Size = 0
   905  	s.P = s.P[:0]
   906  	s.R = s.R[:0]
   907  	reachable := s.Attr.Reachable()
   908  	s.AddAddr(ctxt.Arch, sp)
   909  	s.AddUint(ctxt.Arch, uint64(len(value)))
   910  
   911  	// addstring, addaddr, etc., mark the symbols as reachable.
   912  	// In this case that is not necessarily true, so stick to what
   913  	// we know before entering this function.
   914  	s.Attr.Set(sym.AttrReachable, reachable)
   915  
   916  	sp.Attr.Set(sym.AttrReachable, reachable)
   917  }
   918  
   919  func (ctxt *Link) dostrdata() {
   920  	for _, name := range strnames {
   921  		addstrdata(ctxt, name, strdata[name])
   922  	}
   923  }
   924  
   925  func Addstring(s *sym.Symbol, str string) int64 {
   926  	if s.Type == 0 {
   927  		s.Type = sym.SNOPTRDATA
   928  	}
   929  	s.Attr |= sym.AttrReachable
   930  	r := s.Size
   931  	if s.Name == ".shstrtab" {
   932  		elfsetstring(s, str, int(r))
   933  	}
   934  	s.P = append(s.P, str...)
   935  	s.P = append(s.P, 0)
   936  	s.Size = int64(len(s.P))
   937  	return r
   938  }
   939  
   940  // addgostring adds str, as a Go string value, to s. symname is the name of the
   941  // symbol used to define the string data and must be unique per linked object.
   942  func addgostring(ctxt *Link, s *sym.Symbol, symname, str string) {
   943  	sdata := ctxt.Syms.Lookup(symname, 0)
   944  	if sdata.Type != sym.Sxxx {
   945  		Errorf(s, "duplicate symname in addgostring: %s", symname)
   946  	}
   947  	sdata.Attr |= sym.AttrReachable
   948  	sdata.Attr |= sym.AttrLocal
   949  	sdata.Type = sym.SRODATA
   950  	sdata.Size = int64(len(str))
   951  	sdata.P = []byte(str)
   952  	s.AddAddr(ctxt.Arch, sdata)
   953  	s.AddUint(ctxt.Arch, uint64(len(str)))
   954  }
   955  
   956  func addinitarrdata(ctxt *Link, s *sym.Symbol) {
   957  	p := s.Name + ".ptr"
   958  	sp := ctxt.Syms.Lookup(p, 0)
   959  	sp.Type = sym.SINITARR
   960  	sp.Size = 0
   961  	sp.Attr |= sym.AttrDuplicateOK
   962  	sp.AddAddr(ctxt.Arch, s)
   963  }
   964  
   965  func dosymtype(ctxt *Link) {
   966  	switch ctxt.BuildMode {
   967  	case BuildModeCArchive, BuildModeCShared:
   968  		for _, s := range ctxt.Syms.Allsym {
   969  			// Create a new entry in the .init_array section that points to the
   970  			// library initializer function.
   971  			if s.Name == *flagEntrySymbol {
   972  				addinitarrdata(ctxt, s)
   973  			}
   974  		}
   975  	}
   976  }
   977  
   978  // symalign returns the required alignment for the given symbol s.
   979  func symalign(s *sym.Symbol) int32 {
   980  	min := int32(thearch.Minalign)
   981  	if s.Align >= min {
   982  		return s.Align
   983  	} else if s.Align != 0 {
   984  		return min
   985  	}
   986  	if strings.HasPrefix(s.Name, "go.string.") || strings.HasPrefix(s.Name, "type..namedata.") {
   987  		// String data is just bytes.
   988  		// If we align it, we waste a lot of space to padding.
   989  		return min
   990  	}
   991  	align := int32(thearch.Maxalign)
   992  	for int64(align) > s.Size && align > min {
   993  		align >>= 1
   994  	}
   995  	return align
   996  }
   997  
   998  func aligndatsize(datsize int64, s *sym.Symbol) int64 {
   999  	return Rnd(datsize, int64(symalign(s)))
  1000  }
  1001  
  1002  const debugGCProg = false
  1003  
  1004  type GCProg struct {
  1005  	ctxt *Link
  1006  	sym  *sym.Symbol
  1007  	w    gcprog.Writer
  1008  }
  1009  
  1010  func (p *GCProg) Init(ctxt *Link, name string) {
  1011  	p.ctxt = ctxt
  1012  	p.sym = ctxt.Syms.Lookup(name, 0)
  1013  	p.w.Init(p.writeByte(ctxt))
  1014  	if debugGCProg {
  1015  		fmt.Fprintf(os.Stderr, "ld: start GCProg %s\n", name)
  1016  		p.w.Debug(os.Stderr)
  1017  	}
  1018  }
  1019  
  1020  func (p *GCProg) writeByte(ctxt *Link) func(x byte) {
  1021  	return func(x byte) {
  1022  		p.sym.AddUint8(x)
  1023  	}
  1024  }
  1025  
  1026  func (p *GCProg) End(size int64) {
  1027  	p.w.ZeroUntil(size / int64(p.ctxt.Arch.PtrSize))
  1028  	p.w.End()
  1029  	if debugGCProg {
  1030  		fmt.Fprintf(os.Stderr, "ld: end GCProg\n")
  1031  	}
  1032  }
  1033  
  1034  func (p *GCProg) AddSym(s *sym.Symbol) {
  1035  	typ := s.Gotype
  1036  	// Things without pointers should be in sym.SNOPTRDATA or sym.SNOPTRBSS;
  1037  	// everything we see should have pointers and should therefore have a type.
  1038  	if typ == nil {
  1039  		switch s.Name {
  1040  		case "runtime.data", "runtime.edata", "runtime.bss", "runtime.ebss":
  1041  			// Ignore special symbols that are sometimes laid out
  1042  			// as real symbols. See comment about dyld on darwin in
  1043  			// the address function.
  1044  			return
  1045  		}
  1046  		Errorf(s, "missing Go type information for global symbol: size %d", s.Size)
  1047  		return
  1048  	}
  1049  
  1050  	ptrsize := int64(p.ctxt.Arch.PtrSize)
  1051  	nptr := decodetypePtrdata(p.ctxt.Arch, typ) / ptrsize
  1052  
  1053  	if debugGCProg {
  1054  		fmt.Fprintf(os.Stderr, "gcprog sym: %s at %d (ptr=%d+%d)\n", s.Name, s.Value, s.Value/ptrsize, nptr)
  1055  	}
  1056  
  1057  	if decodetypeUsegcprog(p.ctxt.Arch, typ) == 0 {
  1058  		// Copy pointers from mask into program.
  1059  		mask := decodetypeGcmask(p.ctxt, typ)
  1060  		for i := int64(0); i < nptr; i++ {
  1061  			if (mask[i/8]>>uint(i%8))&1 != 0 {
  1062  				p.w.Ptr(s.Value/ptrsize + i)
  1063  			}
  1064  		}
  1065  		return
  1066  	}
  1067  
  1068  	// Copy program.
  1069  	prog := decodetypeGcprog(p.ctxt, typ)
  1070  	p.w.ZeroUntil(s.Value / ptrsize)
  1071  	p.w.Append(prog[4:], nptr)
  1072  }
  1073  
  1074  // dataSortKey is used to sort a slice of data symbol *sym.Symbol pointers.
  1075  // The sort keys are kept inline to improve cache behavior while sorting.
  1076  type dataSortKey struct {
  1077  	size int64
  1078  	name string
  1079  	sym  *sym.Symbol
  1080  }
  1081  
  1082  type bySizeAndName []dataSortKey
  1083  
  1084  func (d bySizeAndName) Len() int      { return len(d) }
  1085  func (d bySizeAndName) Swap(i, j int) { d[i], d[j] = d[j], d[i] }
  1086  func (d bySizeAndName) Less(i, j int) bool {
  1087  	s1, s2 := d[i], d[j]
  1088  	if s1.size != s2.size {
  1089  		return s1.size < s2.size
  1090  	}
  1091  	return s1.name < s2.name
  1092  }
  1093  
  1094  // cutoff is the maximum data section size permitted by the linker
  1095  // (see issue #9862).
  1096  const cutoff = 2e9 // 2 GB (or so; looks better in errors than 2^31)
  1097  
  1098  func checkdatsize(ctxt *Link, datsize int64, symn sym.SymKind) {
  1099  	if datsize > cutoff {
  1100  		Errorf(nil, "too much data in section %v (over %v bytes)", symn, cutoff)
  1101  	}
  1102  }
  1103  
  1104  // datap is a collection of reachable data symbols in address order.
  1105  // Generated by dodata.
  1106  var datap []*sym.Symbol
  1107  
  1108  func (ctxt *Link) dodata() {
  1109  	if ctxt.Debugvlog != 0 {
  1110  		ctxt.Logf("%5.2f dodata\n", Cputime())
  1111  	}
  1112  
  1113  	if ctxt.DynlinkingGo() && ctxt.HeadType == objabi.Hdarwin {
  1114  		// The values in moduledata are filled out by relocations
  1115  		// pointing to the addresses of these special symbols.
  1116  		// Typically these symbols have no size and are not laid
  1117  		// out with their matching section.
  1118  		//
  1119  		// However on darwin, dyld will find the special symbol
  1120  		// in the first loaded module, even though it is local.
  1121  		//
  1122  		// (An hypothesis, formed without looking in the dyld sources:
  1123  		// these special symbols have no size, so their address
  1124  		// matches a real symbol. The dynamic linker assumes we
  1125  		// want the normal symbol with the same address and finds
  1126  		// it in the other module.)
  1127  		//
  1128  		// To work around this we lay out the symbls whose
  1129  		// addresses are vital for multi-module programs to work
  1130  		// as normal symbols, and give them a little size.
  1131  		bss := ctxt.Syms.Lookup("runtime.bss", 0)
  1132  		bss.Size = 8
  1133  		bss.Attr.Set(sym.AttrSpecial, false)
  1134  
  1135  		ctxt.Syms.Lookup("runtime.ebss", 0).Attr.Set(sym.AttrSpecial, false)
  1136  
  1137  		data := ctxt.Syms.Lookup("runtime.data", 0)
  1138  		data.Size = 8
  1139  		data.Attr.Set(sym.AttrSpecial, false)
  1140  
  1141  		ctxt.Syms.Lookup("runtime.edata", 0).Attr.Set(sym.AttrSpecial, false)
  1142  
  1143  		types := ctxt.Syms.Lookup("runtime.types", 0)
  1144  		types.Type = sym.STYPE
  1145  		types.Size = 8
  1146  		types.Attr.Set(sym.AttrSpecial, false)
  1147  
  1148  		etypes := ctxt.Syms.Lookup("runtime.etypes", 0)
  1149  		etypes.Type = sym.SFUNCTAB
  1150  		etypes.Attr.Set(sym.AttrSpecial, false)
  1151  	}
  1152  
  1153  	// Collect data symbols by type into data.
  1154  	var data [sym.SXREF][]*sym.Symbol
  1155  	for _, s := range ctxt.Syms.Allsym {
  1156  		if !s.Attr.Reachable() || s.Attr.Special() || s.Attr.SubSymbol() {
  1157  			continue
  1158  		}
  1159  		if s.Type <= sym.STEXT || s.Type >= sym.SXREF {
  1160  			continue
  1161  		}
  1162  		data[s.Type] = append(data[s.Type], s)
  1163  	}
  1164  
  1165  	// Now that we have the data symbols, but before we start
  1166  	// to assign addresses, record all the necessary
  1167  	// dynamic relocations. These will grow the relocation
  1168  	// symbol, which is itself data.
  1169  	//
  1170  	// On darwin, we need the symbol table numbers for dynreloc.
  1171  	if ctxt.HeadType == objabi.Hdarwin {
  1172  		machosymorder(ctxt)
  1173  	}
  1174  	dynreloc(ctxt, &data)
  1175  
  1176  	if ctxt.UseRelro() {
  1177  		// "read only" data with relocations needs to go in its own section
  1178  		// when building a shared library. We do this by boosting objects of
  1179  		// type SXXX with relocations to type SXXXRELRO.
  1180  		for _, symnro := range sym.ReadOnly {
  1181  			symnrelro := sym.RelROMap[symnro]
  1182  
  1183  			ro := []*sym.Symbol{}
  1184  			relro := data[symnrelro]
  1185  
  1186  			for _, s := range data[symnro] {
  1187  				isRelro := len(s.R) > 0
  1188  				switch s.Type {
  1189  				case sym.STYPE, sym.STYPERELRO, sym.SGOFUNCRELRO:
  1190  					// Symbols are not sorted yet, so it is possible
  1191  					// that an Outer symbol has been changed to a
  1192  					// relro Type before it reaches here.
  1193  					isRelro = true
  1194  				}
  1195  				if isRelro {
  1196  					s.Type = symnrelro
  1197  					if s.Outer != nil {
  1198  						s.Outer.Type = s.Type
  1199  					}
  1200  					relro = append(relro, s)
  1201  				} else {
  1202  					ro = append(ro, s)
  1203  				}
  1204  			}
  1205  
  1206  			// Check that we haven't made two symbols with the same .Outer into
  1207  			// different types (because references two symbols with non-nil Outer
  1208  			// become references to the outer symbol + offset it's vital that the
  1209  			// symbol and the outer end up in the same section).
  1210  			for _, s := range relro {
  1211  				if s.Outer != nil && s.Outer.Type != s.Type {
  1212  					Errorf(s, "inconsistent types for symbol and its Outer %s (%v != %v)",
  1213  						s.Outer.Name, s.Type, s.Outer.Type)
  1214  				}
  1215  			}
  1216  
  1217  			data[symnro] = ro
  1218  			data[symnrelro] = relro
  1219  		}
  1220  	}
  1221  
  1222  	// Sort symbols.
  1223  	var dataMaxAlign [sym.SXREF]int32
  1224  	var wg sync.WaitGroup
  1225  	for symn := range data {
  1226  		symn := sym.SymKind(symn)
  1227  		wg.Add(1)
  1228  		go func() {
  1229  			data[symn], dataMaxAlign[symn] = dodataSect(ctxt, symn, data[symn])
  1230  			wg.Done()
  1231  		}()
  1232  	}
  1233  	wg.Wait()
  1234  
  1235  	// Allocate sections.
  1236  	// Data is processed before segtext, because we need
  1237  	// to see all symbols in the .data and .bss sections in order
  1238  	// to generate garbage collection information.
  1239  	datsize := int64(0)
  1240  
  1241  	// Writable data sections that do not need any specialized handling.
  1242  	writable := []sym.SymKind{
  1243  		sym.SELFSECT,
  1244  		sym.SMACHO,
  1245  		sym.SMACHOGOT,
  1246  		sym.SWINDOWS,
  1247  	}
  1248  	for _, symn := range writable {
  1249  		for _, s := range data[symn] {
  1250  			sect := addsection(ctxt.Arch, &Segdata, s.Name, 06)
  1251  			sect.Align = symalign(s)
  1252  			datsize = Rnd(datsize, int64(sect.Align))
  1253  			sect.Vaddr = uint64(datsize)
  1254  			s.Sect = sect
  1255  			s.Type = sym.SDATA
  1256  			s.Value = int64(uint64(datsize) - sect.Vaddr)
  1257  			datsize += s.Size
  1258  			sect.Length = uint64(datsize) - sect.Vaddr
  1259  		}
  1260  		checkdatsize(ctxt, datsize, symn)
  1261  	}
  1262  
  1263  	// .got (and .toc on ppc64)
  1264  	if len(data[sym.SELFGOT]) > 0 {
  1265  		sect := addsection(ctxt.Arch, &Segdata, ".got", 06)
  1266  		sect.Align = dataMaxAlign[sym.SELFGOT]
  1267  		datsize = Rnd(datsize, int64(sect.Align))
  1268  		sect.Vaddr = uint64(datsize)
  1269  		for _, s := range data[sym.SELFGOT] {
  1270  			datsize = aligndatsize(datsize, s)
  1271  			s.Sect = sect
  1272  			s.Type = sym.SDATA
  1273  			s.Value = int64(uint64(datsize) - sect.Vaddr)
  1274  
  1275  			// Resolve .TOC. symbol for this object file (ppc64)
  1276  			toc := ctxt.Syms.ROLookup(".TOC.", int(s.Version))
  1277  			if toc != nil {
  1278  				toc.Sect = sect
  1279  				toc.Outer = s
  1280  				toc.Sub = s.Sub
  1281  				s.Sub = toc
  1282  
  1283  				toc.Value = 0x8000
  1284  			}
  1285  
  1286  			datsize += s.Size
  1287  		}
  1288  		checkdatsize(ctxt, datsize, sym.SELFGOT)
  1289  		sect.Length = uint64(datsize) - sect.Vaddr
  1290  	}
  1291  
  1292  	/* pointer-free data */
  1293  	sect := addsection(ctxt.Arch, &Segdata, ".noptrdata", 06)
  1294  	sect.Align = dataMaxAlign[sym.SNOPTRDATA]
  1295  	datsize = Rnd(datsize, int64(sect.Align))
  1296  	sect.Vaddr = uint64(datsize)
  1297  	ctxt.Syms.Lookup("runtime.noptrdata", 0).Sect = sect
  1298  	ctxt.Syms.Lookup("runtime.enoptrdata", 0).Sect = sect
  1299  	for _, s := range data[sym.SNOPTRDATA] {
  1300  		datsize = aligndatsize(datsize, s)
  1301  		s.Sect = sect
  1302  		s.Type = sym.SDATA
  1303  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  1304  		datsize += s.Size
  1305  	}
  1306  	checkdatsize(ctxt, datsize, sym.SNOPTRDATA)
  1307  	sect.Length = uint64(datsize) - sect.Vaddr
  1308  
  1309  	hasinitarr := ctxt.linkShared
  1310  
  1311  	/* shared library initializer */
  1312  	switch ctxt.BuildMode {
  1313  	case BuildModeCArchive, BuildModeCShared, BuildModeShared, BuildModePlugin:
  1314  		hasinitarr = true
  1315  	}
  1316  	if hasinitarr && len(data[sym.SINITARR]) > 0 {
  1317  		sect := addsection(ctxt.Arch, &Segdata, ".init_array", 06)
  1318  		sect.Align = dataMaxAlign[sym.SINITARR]
  1319  		datsize = Rnd(datsize, int64(sect.Align))
  1320  		sect.Vaddr = uint64(datsize)
  1321  		for _, s := range data[sym.SINITARR] {
  1322  			datsize = aligndatsize(datsize, s)
  1323  			s.Sect = sect
  1324  			s.Value = int64(uint64(datsize) - sect.Vaddr)
  1325  			datsize += s.Size
  1326  		}
  1327  		sect.Length = uint64(datsize) - sect.Vaddr
  1328  		checkdatsize(ctxt, datsize, sym.SINITARR)
  1329  	}
  1330  
  1331  	/* data */
  1332  	sect = addsection(ctxt.Arch, &Segdata, ".data", 06)
  1333  	sect.Align = dataMaxAlign[sym.SDATA]
  1334  	datsize = Rnd(datsize, int64(sect.Align))
  1335  	sect.Vaddr = uint64(datsize)
  1336  	ctxt.Syms.Lookup("runtime.data", 0).Sect = sect
  1337  	ctxt.Syms.Lookup("runtime.edata", 0).Sect = sect
  1338  	var gc GCProg
  1339  	gc.Init(ctxt, "runtime.gcdata")
  1340  	for _, s := range data[sym.SDATA] {
  1341  		s.Sect = sect
  1342  		s.Type = sym.SDATA
  1343  		datsize = aligndatsize(datsize, s)
  1344  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  1345  		gc.AddSym(s)
  1346  		datsize += s.Size
  1347  	}
  1348  	// On AIX, TOC entries must be the last of .data
  1349  	for _, s := range data[sym.SXCOFFTOC] {
  1350  		s.Sect = sect
  1351  		s.Type = sym.SDATA
  1352  		datsize = aligndatsize(datsize, s)
  1353  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  1354  		datsize += s.Size
  1355  	}
  1356  	checkdatsize(ctxt, datsize, sym.SDATA)
  1357  	sect.Length = uint64(datsize) - sect.Vaddr
  1358  	gc.End(int64(sect.Length))
  1359  
  1360  	/* bss */
  1361  	sect = addsection(ctxt.Arch, &Segdata, ".bss", 06)
  1362  	sect.Align = dataMaxAlign[sym.SBSS]
  1363  	datsize = Rnd(datsize, int64(sect.Align))
  1364  	sect.Vaddr = uint64(datsize)
  1365  	ctxt.Syms.Lookup("runtime.bss", 0).Sect = sect
  1366  	ctxt.Syms.Lookup("runtime.ebss", 0).Sect = sect
  1367  	gc = GCProg{}
  1368  	gc.Init(ctxt, "runtime.gcbss")
  1369  	for _, s := range data[sym.SBSS] {
  1370  		s.Sect = sect
  1371  		datsize = aligndatsize(datsize, s)
  1372  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  1373  		gc.AddSym(s)
  1374  		datsize += s.Size
  1375  	}
  1376  	checkdatsize(ctxt, datsize, sym.SBSS)
  1377  	sect.Length = uint64(datsize) - sect.Vaddr
  1378  	gc.End(int64(sect.Length))
  1379  
  1380  	/* pointer-free bss */
  1381  	sect = addsection(ctxt.Arch, &Segdata, ".noptrbss", 06)
  1382  	sect.Align = dataMaxAlign[sym.SNOPTRBSS]
  1383  	datsize = Rnd(datsize, int64(sect.Align))
  1384  	sect.Vaddr = uint64(datsize)
  1385  	ctxt.Syms.Lookup("runtime.noptrbss", 0).Sect = sect
  1386  	ctxt.Syms.Lookup("runtime.enoptrbss", 0).Sect = sect
  1387  	for _, s := range data[sym.SNOPTRBSS] {
  1388  		datsize = aligndatsize(datsize, s)
  1389  		s.Sect = sect
  1390  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  1391  		datsize += s.Size
  1392  	}
  1393  
  1394  	sect.Length = uint64(datsize) - sect.Vaddr
  1395  	ctxt.Syms.Lookup("runtime.end", 0).Sect = sect
  1396  	checkdatsize(ctxt, datsize, sym.SNOPTRBSS)
  1397  
  1398  	if len(data[sym.STLSBSS]) > 0 {
  1399  		var sect *sym.Section
  1400  		if ctxt.IsELF && (ctxt.LinkMode == LinkExternal || !*FlagD) {
  1401  			sect = addsection(ctxt.Arch, &Segdata, ".tbss", 06)
  1402  			sect.Align = int32(ctxt.Arch.PtrSize)
  1403  			sect.Vaddr = 0
  1404  		}
  1405  		datsize = 0
  1406  
  1407  		for _, s := range data[sym.STLSBSS] {
  1408  			datsize = aligndatsize(datsize, s)
  1409  			s.Sect = sect
  1410  			s.Value = datsize
  1411  			datsize += s.Size
  1412  		}
  1413  		checkdatsize(ctxt, datsize, sym.STLSBSS)
  1414  
  1415  		if sect != nil {
  1416  			sect.Length = uint64(datsize)
  1417  		}
  1418  	}
  1419  
  1420  	/*
  1421  	 * We finished data, begin read-only data.
  1422  	 * Not all systems support a separate read-only non-executable data section.
  1423  	 * ELF and Windows PE systems do.
  1424  	 * OS X and Plan 9 do not.
  1425  	 * And if we're using external linking mode, the point is moot,
  1426  	 * since it's not our decision; that code expects the sections in
  1427  	 * segtext.
  1428  	 */
  1429  	var segro *sym.Segment
  1430  	if ctxt.IsELF && ctxt.LinkMode == LinkInternal {
  1431  		segro = &Segrodata
  1432  	} else if ctxt.HeadType == objabi.Hwindows {
  1433  		segro = &Segrodata
  1434  	} else {
  1435  		segro = &Segtext
  1436  	}
  1437  
  1438  	datsize = 0
  1439  
  1440  	/* read-only executable ELF, Mach-O sections */
  1441  	if len(data[sym.STEXT]) != 0 {
  1442  		Errorf(nil, "dodata found an sym.STEXT symbol: %s", data[sym.STEXT][0].Name)
  1443  	}
  1444  	for _, s := range data[sym.SELFRXSECT] {
  1445  		sect := addsection(ctxt.Arch, &Segtext, s.Name, 04)
  1446  		sect.Align = symalign(s)
  1447  		datsize = Rnd(datsize, int64(sect.Align))
  1448  		sect.Vaddr = uint64(datsize)
  1449  		s.Sect = sect
  1450  		s.Type = sym.SRODATA
  1451  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  1452  		datsize += s.Size
  1453  		sect.Length = uint64(datsize) - sect.Vaddr
  1454  		checkdatsize(ctxt, datsize, sym.SELFRXSECT)
  1455  	}
  1456  
  1457  	/* read-only data */
  1458  	sect = addsection(ctxt.Arch, segro, ".rodata", 04)
  1459  
  1460  	sect.Vaddr = 0
  1461  	ctxt.Syms.Lookup("runtime.rodata", 0).Sect = sect
  1462  	ctxt.Syms.Lookup("runtime.erodata", 0).Sect = sect
  1463  	if !ctxt.UseRelro() {
  1464  		ctxt.Syms.Lookup("runtime.types", 0).Sect = sect
  1465  		ctxt.Syms.Lookup("runtime.etypes", 0).Sect = sect
  1466  	}
  1467  	for _, symn := range sym.ReadOnly {
  1468  		align := dataMaxAlign[symn]
  1469  		if sect.Align < align {
  1470  			sect.Align = align
  1471  		}
  1472  	}
  1473  	datsize = Rnd(datsize, int64(sect.Align))
  1474  	for _, symn := range sym.ReadOnly {
  1475  		for _, s := range data[symn] {
  1476  			datsize = aligndatsize(datsize, s)
  1477  			s.Sect = sect
  1478  			s.Type = sym.SRODATA
  1479  			s.Value = int64(uint64(datsize) - sect.Vaddr)
  1480  			datsize += s.Size
  1481  		}
  1482  		checkdatsize(ctxt, datsize, symn)
  1483  	}
  1484  	sect.Length = uint64(datsize) - sect.Vaddr
  1485  
  1486  	/* read-only ELF, Mach-O sections */
  1487  	for _, s := range data[sym.SELFROSECT] {
  1488  		sect = addsection(ctxt.Arch, segro, s.Name, 04)
  1489  		sect.Align = symalign(s)
  1490  		datsize = Rnd(datsize, int64(sect.Align))
  1491  		sect.Vaddr = uint64(datsize)
  1492  		s.Sect = sect
  1493  		s.Type = sym.SRODATA
  1494  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  1495  		datsize += s.Size
  1496  		sect.Length = uint64(datsize) - sect.Vaddr
  1497  	}
  1498  	checkdatsize(ctxt, datsize, sym.SELFROSECT)
  1499  
  1500  	for _, s := range data[sym.SMACHOPLT] {
  1501  		sect = addsection(ctxt.Arch, segro, s.Name, 04)
  1502  		sect.Align = symalign(s)
  1503  		datsize = Rnd(datsize, int64(sect.Align))
  1504  		sect.Vaddr = uint64(datsize)
  1505  		s.Sect = sect
  1506  		s.Type = sym.SRODATA
  1507  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  1508  		datsize += s.Size
  1509  		sect.Length = uint64(datsize) - sect.Vaddr
  1510  	}
  1511  	checkdatsize(ctxt, datsize, sym.SMACHOPLT)
  1512  
  1513  	// There is some data that are conceptually read-only but are written to by
  1514  	// relocations. On GNU systems, we can arrange for the dynamic linker to
  1515  	// mprotect sections after relocations are applied by giving them write
  1516  	// permissions in the object file and calling them ".data.rel.ro.FOO". We
  1517  	// divide the .rodata section between actual .rodata and .data.rel.ro.rodata,
  1518  	// but for the other sections that this applies to, we just write a read-only
  1519  	// .FOO section or a read-write .data.rel.ro.FOO section depending on the
  1520  	// situation.
  1521  	// TODO(mwhudson): It would make sense to do this more widely, but it makes
  1522  	// the system linker segfault on darwin.
  1523  	addrelrosection := func(suffix string) *sym.Section {
  1524  		return addsection(ctxt.Arch, segro, suffix, 04)
  1525  	}
  1526  
  1527  	if ctxt.UseRelro() {
  1528  		addrelrosection = func(suffix string) *sym.Section {
  1529  			seg := &Segrelrodata
  1530  			if ctxt.LinkMode == LinkExternal {
  1531  				// Using a separate segment with an external
  1532  				// linker results in some programs moving
  1533  				// their data sections unexpectedly, which
  1534  				// corrupts the moduledata. So we use the
  1535  				// rodata segment and let the external linker
  1536  				// sort out a rel.ro segment.
  1537  				seg = &Segrodata
  1538  			}
  1539  			return addsection(ctxt.Arch, seg, ".data.rel.ro"+suffix, 06)
  1540  		}
  1541  		/* data only written by relocations */
  1542  		sect = addrelrosection("")
  1543  
  1544  		sect.Vaddr = 0
  1545  		ctxt.Syms.Lookup("runtime.types", 0).Sect = sect
  1546  		ctxt.Syms.Lookup("runtime.etypes", 0).Sect = sect
  1547  		for _, symnro := range sym.ReadOnly {
  1548  			symn := sym.RelROMap[symnro]
  1549  			align := dataMaxAlign[symn]
  1550  			if sect.Align < align {
  1551  				sect.Align = align
  1552  			}
  1553  		}
  1554  		datsize = Rnd(datsize, int64(sect.Align))
  1555  		for _, symnro := range sym.ReadOnly {
  1556  			symn := sym.RelROMap[symnro]
  1557  			for _, s := range data[symn] {
  1558  				datsize = aligndatsize(datsize, s)
  1559  				if s.Outer != nil && s.Outer.Sect != nil && s.Outer.Sect != sect {
  1560  					Errorf(s, "s.Outer (%s) in different section from s, %s != %s", s.Outer.Name, s.Outer.Sect.Name, sect.Name)
  1561  				}
  1562  				s.Sect = sect
  1563  				s.Type = sym.SRODATA
  1564  				s.Value = int64(uint64(datsize) - sect.Vaddr)
  1565  				datsize += s.Size
  1566  			}
  1567  			checkdatsize(ctxt, datsize, symn)
  1568  		}
  1569  
  1570  		sect.Length = uint64(datsize) - sect.Vaddr
  1571  	}
  1572  
  1573  	/* typelink */
  1574  	sect = addrelrosection(".typelink")
  1575  	sect.Align = dataMaxAlign[sym.STYPELINK]
  1576  	datsize = Rnd(datsize, int64(sect.Align))
  1577  	sect.Vaddr = uint64(datsize)
  1578  	typelink := ctxt.Syms.Lookup("runtime.typelink", 0)
  1579  	typelink.Sect = sect
  1580  	typelink.Type = sym.SRODATA
  1581  	datsize += typelink.Size
  1582  	checkdatsize(ctxt, datsize, sym.STYPELINK)
  1583  	sect.Length = uint64(datsize) - sect.Vaddr
  1584  
  1585  	/* itablink */
  1586  	sect = addrelrosection(".itablink")
  1587  	sect.Align = dataMaxAlign[sym.SITABLINK]
  1588  	datsize = Rnd(datsize, int64(sect.Align))
  1589  	sect.Vaddr = uint64(datsize)
  1590  	ctxt.Syms.Lookup("runtime.itablink", 0).Sect = sect
  1591  	ctxt.Syms.Lookup("runtime.eitablink", 0).Sect = sect
  1592  	for _, s := range data[sym.SITABLINK] {
  1593  		datsize = aligndatsize(datsize, s)
  1594  		s.Sect = sect
  1595  		s.Type = sym.SRODATA
  1596  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  1597  		datsize += s.Size
  1598  	}
  1599  	checkdatsize(ctxt, datsize, sym.SITABLINK)
  1600  	sect.Length = uint64(datsize) - sect.Vaddr
  1601  
  1602  	/* gosymtab */
  1603  	sect = addrelrosection(".gosymtab")
  1604  	sect.Align = dataMaxAlign[sym.SSYMTAB]
  1605  	datsize = Rnd(datsize, int64(sect.Align))
  1606  	sect.Vaddr = uint64(datsize)
  1607  	ctxt.Syms.Lookup("runtime.symtab", 0).Sect = sect
  1608  	ctxt.Syms.Lookup("runtime.esymtab", 0).Sect = sect
  1609  	for _, s := range data[sym.SSYMTAB] {
  1610  		datsize = aligndatsize(datsize, s)
  1611  		s.Sect = sect
  1612  		s.Type = sym.SRODATA
  1613  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  1614  		datsize += s.Size
  1615  	}
  1616  	checkdatsize(ctxt, datsize, sym.SSYMTAB)
  1617  	sect.Length = uint64(datsize) - sect.Vaddr
  1618  
  1619  	/* gopclntab */
  1620  	sect = addrelrosection(".gopclntab")
  1621  	sect.Align = dataMaxAlign[sym.SPCLNTAB]
  1622  	datsize = Rnd(datsize, int64(sect.Align))
  1623  	sect.Vaddr = uint64(datsize)
  1624  	ctxt.Syms.Lookup("runtime.pclntab", 0).Sect = sect
  1625  	ctxt.Syms.Lookup("runtime.epclntab", 0).Sect = sect
  1626  	for _, s := range data[sym.SPCLNTAB] {
  1627  		datsize = aligndatsize(datsize, s)
  1628  		s.Sect = sect
  1629  		s.Type = sym.SRODATA
  1630  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  1631  		datsize += s.Size
  1632  	}
  1633  	checkdatsize(ctxt, datsize, sym.SRODATA)
  1634  	sect.Length = uint64(datsize) - sect.Vaddr
  1635  
  1636  	// 6g uses 4-byte relocation offsets, so the entire segment must fit in 32 bits.
  1637  	if datsize != int64(uint32(datsize)) {
  1638  		Errorf(nil, "read-only data segment too large: %d", datsize)
  1639  	}
  1640  
  1641  	for symn := sym.SELFRXSECT; symn < sym.SXREF; symn++ {
  1642  		datap = append(datap, data[symn]...)
  1643  	}
  1644  
  1645  	dwarfGenerateDebugSyms(ctxt)
  1646  
  1647  	var i int
  1648  	for ; i < len(dwarfp); i++ {
  1649  		s := dwarfp[i]
  1650  		if s.Type != sym.SDWARFSECT {
  1651  			break
  1652  		}
  1653  
  1654  		sect = addsection(ctxt.Arch, &Segdwarf, s.Name, 04)
  1655  		sect.Align = 1
  1656  		datsize = Rnd(datsize, int64(sect.Align))
  1657  		sect.Vaddr = uint64(datsize)
  1658  		s.Sect = sect
  1659  		s.Type = sym.SRODATA
  1660  		s.Value = int64(uint64(datsize) - sect.Vaddr)
  1661  		datsize += s.Size
  1662  		sect.Length = uint64(datsize) - sect.Vaddr
  1663  	}
  1664  	checkdatsize(ctxt, datsize, sym.SDWARFSECT)
  1665  
  1666  	for i < len(dwarfp) {
  1667  		curType := dwarfp[i].Type
  1668  		var sect *sym.Section
  1669  		switch curType {
  1670  		case sym.SDWARFINFO:
  1671  			sect = addsection(ctxt.Arch, &Segdwarf, ".debug_info", 04)
  1672  		case sym.SDWARFRANGE:
  1673  			sect = addsection(ctxt.Arch, &Segdwarf, ".debug_ranges", 04)
  1674  		case sym.SDWARFLOC:
  1675  			sect = addsection(ctxt.Arch, &Segdwarf, ".debug_loc", 04)
  1676  		default:
  1677  			Errorf(dwarfp[i], "unknown DWARF section %v", curType)
  1678  		}
  1679  
  1680  		sect.Align = 1
  1681  		datsize = Rnd(datsize, int64(sect.Align))
  1682  		sect.Vaddr = uint64(datsize)
  1683  		for ; i < len(dwarfp); i++ {
  1684  			s := dwarfp[i]
  1685  			if s.Type != curType {
  1686  				break
  1687  			}
  1688  			s.Sect = sect
  1689  			s.Type = sym.SRODATA
  1690  			s.Value = int64(uint64(datsize) - sect.Vaddr)
  1691  			s.Attr |= sym.AttrLocal
  1692  			datsize += s.Size
  1693  		}
  1694  		sect.Length = uint64(datsize) - sect.Vaddr
  1695  		checkdatsize(ctxt, datsize, curType)
  1696  	}
  1697  
  1698  	/* number the sections */
  1699  	n := int32(1)
  1700  
  1701  	for _, sect := range Segtext.Sections {
  1702  		sect.Extnum = int16(n)
  1703  		n++
  1704  	}
  1705  	for _, sect := range Segrodata.Sections {
  1706  		sect.Extnum = int16(n)
  1707  		n++
  1708  	}
  1709  	for _, sect := range Segrelrodata.Sections {
  1710  		sect.Extnum = int16(n)
  1711  		n++
  1712  	}
  1713  	for _, sect := range Segdata.Sections {
  1714  		sect.Extnum = int16(n)
  1715  		n++
  1716  	}
  1717  	for _, sect := range Segdwarf.Sections {
  1718  		sect.Extnum = int16(n)
  1719  		n++
  1720  	}
  1721  }
  1722  
  1723  func dodataSect(ctxt *Link, symn sym.SymKind, syms []*sym.Symbol) (result []*sym.Symbol, maxAlign int32) {
  1724  	if ctxt.HeadType == objabi.Hdarwin {
  1725  		// Some symbols may no longer belong in syms
  1726  		// due to movement in machosymorder.
  1727  		newSyms := make([]*sym.Symbol, 0, len(syms))
  1728  		for _, s := range syms {
  1729  			if s.Type == symn {
  1730  				newSyms = append(newSyms, s)
  1731  			}
  1732  		}
  1733  		syms = newSyms
  1734  	}
  1735  
  1736  	var head, tail *sym.Symbol
  1737  	symsSort := make([]dataSortKey, 0, len(syms))
  1738  	for _, s := range syms {
  1739  		if s.Attr.OnList() {
  1740  			log.Fatalf("symbol %s listed multiple times", s.Name)
  1741  		}
  1742  		s.Attr |= sym.AttrOnList
  1743  		switch {
  1744  		case s.Size < int64(len(s.P)):
  1745  			Errorf(s, "initialize bounds (%d < %d)", s.Size, len(s.P))
  1746  		case s.Size < 0:
  1747  			Errorf(s, "negative size (%d bytes)", s.Size)
  1748  		case s.Size > cutoff:
  1749  			Errorf(s, "symbol too large (%d bytes)", s.Size)
  1750  		}
  1751  
  1752  		// If the usually-special section-marker symbols are being laid
  1753  		// out as regular symbols, put them either at the beginning or
  1754  		// end of their section.
  1755  		if ctxt.DynlinkingGo() && ctxt.HeadType == objabi.Hdarwin {
  1756  			switch s.Name {
  1757  			case "runtime.text", "runtime.bss", "runtime.data", "runtime.types":
  1758  				head = s
  1759  				continue
  1760  			case "runtime.etext", "runtime.ebss", "runtime.edata", "runtime.etypes":
  1761  				tail = s
  1762  				continue
  1763  			}
  1764  		}
  1765  
  1766  		key := dataSortKey{
  1767  			size: s.Size,
  1768  			name: s.Name,
  1769  			sym:  s,
  1770  		}
  1771  
  1772  		switch s.Type {
  1773  		case sym.SELFGOT:
  1774  			// For ppc64, we want to interleave the .got and .toc sections
  1775  			// from input files. Both are type sym.SELFGOT, so in that case
  1776  			// we skip size comparison and fall through to the name
  1777  			// comparison (conveniently, .got sorts before .toc).
  1778  			key.size = 0
  1779  		}
  1780  
  1781  		symsSort = append(symsSort, key)
  1782  	}
  1783  
  1784  	sort.Sort(bySizeAndName(symsSort))
  1785  
  1786  	off := 0
  1787  	if head != nil {
  1788  		syms[0] = head
  1789  		off++
  1790  	}
  1791  	for i, symSort := range symsSort {
  1792  		syms[i+off] = symSort.sym
  1793  		align := symalign(symSort.sym)
  1794  		if maxAlign < align {
  1795  			maxAlign = align
  1796  		}
  1797  	}
  1798  	if tail != nil {
  1799  		syms[len(syms)-1] = tail
  1800  	}
  1801  
  1802  	if ctxt.IsELF && symn == sym.SELFROSECT {
  1803  		// Make .rela and .rela.plt contiguous, the ELF ABI requires this
  1804  		// and Solaris actually cares.
  1805  		reli, plti := -1, -1
  1806  		for i, s := range syms {
  1807  			switch s.Name {
  1808  			case ".rel.plt", ".rela.plt":
  1809  				plti = i
  1810  			case ".rel", ".rela":
  1811  				reli = i
  1812  			}
  1813  		}
  1814  		if reli >= 0 && plti >= 0 && plti != reli+1 {
  1815  			var first, second int
  1816  			if plti > reli {
  1817  				first, second = reli, plti
  1818  			} else {
  1819  				first, second = plti, reli
  1820  			}
  1821  			rel, plt := syms[reli], syms[plti]
  1822  			copy(syms[first+2:], syms[first+1:second])
  1823  			syms[first+0] = rel
  1824  			syms[first+1] = plt
  1825  
  1826  			// Make sure alignment doesn't introduce a gap.
  1827  			// Setting the alignment explicitly prevents
  1828  			// symalign from basing it on the size and
  1829  			// getting it wrong.
  1830  			rel.Align = int32(ctxt.Arch.RegSize)
  1831  			plt.Align = int32(ctxt.Arch.RegSize)
  1832  		}
  1833  	}
  1834  
  1835  	return syms, maxAlign
  1836  }
  1837  
  1838  // Add buildid to beginning of text segment, on non-ELF systems.
  1839  // Non-ELF binary formats are not always flexible enough to
  1840  // give us a place to put the Go build ID. On those systems, we put it
  1841  // at the very beginning of the text segment.
  1842  // This ``header'' is read by cmd/go.
  1843  func (ctxt *Link) textbuildid() {
  1844  	if ctxt.IsELF || ctxt.BuildMode == BuildModePlugin || *flagBuildid == "" {
  1845  		return
  1846  	}
  1847  
  1848  	s := ctxt.Syms.Lookup("go.buildid", 0)
  1849  	s.Attr |= sym.AttrReachable
  1850  	// The \xff is invalid UTF-8, meant to make it less likely
  1851  	// to find one of these accidentally.
  1852  	data := "\xff Go build ID: " + strconv.Quote(*flagBuildid) + "\n \xff"
  1853  	s.Type = sym.STEXT
  1854  	s.P = []byte(data)
  1855  	s.Size = int64(len(s.P))
  1856  
  1857  	ctxt.Textp = append(ctxt.Textp, nil)
  1858  	copy(ctxt.Textp[1:], ctxt.Textp)
  1859  	ctxt.Textp[0] = s
  1860  }
  1861  
  1862  // assign addresses to text
  1863  func (ctxt *Link) textaddress() {
  1864  	addsection(ctxt.Arch, &Segtext, ".text", 05)
  1865  
  1866  	// Assign PCs in text segment.
  1867  	// Could parallelize, by assigning to text
  1868  	// and then letting threads copy down, but probably not worth it.
  1869  	sect := Segtext.Sections[0]
  1870  
  1871  	sect.Align = int32(Funcalign)
  1872  
  1873  	text := ctxt.Syms.Lookup("runtime.text", 0)
  1874  	text.Sect = sect
  1875  
  1876  	if ctxt.DynlinkingGo() && ctxt.HeadType == objabi.Hdarwin {
  1877  		etext := ctxt.Syms.Lookup("runtime.etext", 0)
  1878  		etext.Sect = sect
  1879  
  1880  		ctxt.Textp = append(ctxt.Textp, etext, nil)
  1881  		copy(ctxt.Textp[1:], ctxt.Textp)
  1882  		ctxt.Textp[0] = text
  1883  	}
  1884  
  1885  	va := uint64(*FlagTextAddr)
  1886  	n := 1
  1887  	sect.Vaddr = va
  1888  	ntramps := 0
  1889  	for _, s := range ctxt.Textp {
  1890  		sect, n, va = assignAddress(ctxt, sect, n, s, va, false)
  1891  
  1892  		trampoline(ctxt, s) // resolve jumps, may add trampolines if jump too far
  1893  
  1894  		// lay down trampolines after each function
  1895  		for ; ntramps < len(ctxt.tramps); ntramps++ {
  1896  			tramp := ctxt.tramps[ntramps]
  1897  			sect, n, va = assignAddress(ctxt, sect, n, tramp, va, true)
  1898  		}
  1899  	}
  1900  
  1901  	sect.Length = va - sect.Vaddr
  1902  	ctxt.Syms.Lookup("runtime.etext", 0).Sect = sect
  1903  
  1904  	// merge tramps into Textp, keeping Textp in address order
  1905  	if ntramps != 0 {
  1906  		newtextp := make([]*sym.Symbol, 0, len(ctxt.Textp)+ntramps)
  1907  		i := 0
  1908  		for _, s := range ctxt.Textp {
  1909  			for ; i < ntramps && ctxt.tramps[i].Value < s.Value; i++ {
  1910  				newtextp = append(newtextp, ctxt.tramps[i])
  1911  			}
  1912  			newtextp = append(newtextp, s)
  1913  		}
  1914  		newtextp = append(newtextp, ctxt.tramps[i:ntramps]...)
  1915  
  1916  		ctxt.Textp = newtextp
  1917  	}
  1918  }
  1919  
  1920  // assigns address for a text symbol, returns (possibly new) section, its number, and the address
  1921  // Note: once we have trampoline insertion support for external linking, this function
  1922  // will not need to create new text sections, and so no need to return sect and n.
  1923  func assignAddress(ctxt *Link, sect *sym.Section, n int, s *sym.Symbol, va uint64, isTramp bool) (*sym.Section, int, uint64) {
  1924  	if thearch.AssignAddress != nil {
  1925  		return thearch.AssignAddress(ctxt, sect, n, s, va, isTramp)
  1926  	}
  1927  
  1928  	s.Sect = sect
  1929  	if s.Attr.SubSymbol() {
  1930  		return sect, n, va
  1931  	}
  1932  	if s.Align != 0 {
  1933  		va = uint64(Rnd(int64(va), int64(s.Align)))
  1934  	} else {
  1935  		va = uint64(Rnd(int64(va), int64(Funcalign)))
  1936  	}
  1937  	s.Value = 0
  1938  	for sub := s; sub != nil; sub = sub.Sub {
  1939  		sub.Value += int64(va)
  1940  	}
  1941  
  1942  	funcsize := uint64(MINFUNC) // spacing required for findfunctab
  1943  	if s.Size > MINFUNC {
  1944  		funcsize = uint64(s.Size)
  1945  	}
  1946  
  1947  	// On ppc64x a text section should not be larger than 2^26 bytes due to the size of
  1948  	// call target offset field in the bl instruction.  Splitting into smaller text
  1949  	// sections smaller than this limit allows the GNU linker to modify the long calls
  1950  	// appropriately.  The limit allows for the space needed for tables inserted by the linker.
  1951  
  1952  	// If this function doesn't fit in the current text section, then create a new one.
  1953  
  1954  	// Only break at outermost syms.
  1955  
  1956  	if ctxt.Arch.InFamily(sys.PPC64) && s.Outer == nil && ctxt.IsELF && ctxt.LinkMode == LinkExternal && va-sect.Vaddr+funcsize+maxSizeTrampolinesPPC64(s, isTramp) > 0x1c00000 {
  1957  		// Set the length for the previous text section
  1958  		sect.Length = va - sect.Vaddr
  1959  
  1960  		// Create new section, set the starting Vaddr
  1961  		sect = addsection(ctxt.Arch, &Segtext, ".text", 05)
  1962  		sect.Vaddr = va
  1963  		s.Sect = sect
  1964  
  1965  		// Create a symbol for the start of the secondary text sections
  1966  		ctxt.Syms.Lookup(fmt.Sprintf("runtime.text.%d", n), 0).Sect = sect
  1967  		n++
  1968  	}
  1969  	va += funcsize
  1970  
  1971  	return sect, n, va
  1972  }
  1973  
  1974  // address assigns virtual addresses to all segments and sections and
  1975  // returns all segments in file order.
  1976  func (ctxt *Link) address() []*sym.Segment {
  1977  	var order []*sym.Segment // Layout order
  1978  
  1979  	va := uint64(*FlagTextAddr)
  1980  	order = append(order, &Segtext)
  1981  	Segtext.Rwx = 05
  1982  	Segtext.Vaddr = va
  1983  	for _, s := range Segtext.Sections {
  1984  		va = uint64(Rnd(int64(va), int64(s.Align)))
  1985  		s.Vaddr = va
  1986  		va += s.Length
  1987  	}
  1988  
  1989  	Segtext.Length = va - uint64(*FlagTextAddr)
  1990  	if ctxt.HeadType == objabi.Hnacl {
  1991  		va += 32 // room for the "halt sled"
  1992  	}
  1993  
  1994  	if len(Segrodata.Sections) > 0 {
  1995  		// align to page boundary so as not to mix
  1996  		// rodata and executable text.
  1997  		//
  1998  		// Note: gold or GNU ld will reduce the size of the executable
  1999  		// file by arranging for the relro segment to end at a page
  2000  		// boundary, and overlap the end of the text segment with the
  2001  		// start of the relro segment in the file.  The PT_LOAD segments
  2002  		// will be such that the last page of the text segment will be
  2003  		// mapped twice, once r-x and once starting out rw- and, after
  2004  		// relocation processing, changed to r--.
  2005  		//
  2006  		// Ideally the last page of the text segment would not be
  2007  		// writable even for this short period.
  2008  		va = uint64(Rnd(int64(va), int64(*FlagRound)))
  2009  
  2010  		order = append(order, &Segrodata)
  2011  		Segrodata.Rwx = 04
  2012  		Segrodata.Vaddr = va
  2013  		for _, s := range Segrodata.Sections {
  2014  			va = uint64(Rnd(int64(va), int64(s.Align)))
  2015  			s.Vaddr = va
  2016  			va += s.Length
  2017  		}
  2018  
  2019  		Segrodata.Length = va - Segrodata.Vaddr
  2020  	}
  2021  	if len(Segrelrodata.Sections) > 0 {
  2022  		// align to page boundary so as not to mix
  2023  		// rodata, rel-ro data, and executable text.
  2024  		va = uint64(Rnd(int64(va), int64(*FlagRound)))
  2025  
  2026  		order = append(order, &Segrelrodata)
  2027  		Segrelrodata.Rwx = 06
  2028  		Segrelrodata.Vaddr = va
  2029  		for _, s := range Segrelrodata.Sections {
  2030  			va = uint64(Rnd(int64(va), int64(s.Align)))
  2031  			s.Vaddr = va
  2032  			va += s.Length
  2033  		}
  2034  
  2035  		Segrelrodata.Length = va - Segrelrodata.Vaddr
  2036  	}
  2037  
  2038  	va = uint64(Rnd(int64(va), int64(*FlagRound)))
  2039  	if ctxt.HeadType == objabi.Haix {
  2040  		// Data sections are moved to an unreachable segment
  2041  		// to ensure that they are position-independent.
  2042  		va += uint64(XCOFFDATABASE) - uint64(XCOFFTEXTBASE)
  2043  	}
  2044  	order = append(order, &Segdata)
  2045  	Segdata.Rwx = 06
  2046  	Segdata.Vaddr = va
  2047  	var data *sym.Section
  2048  	var noptr *sym.Section
  2049  	var bss *sym.Section
  2050  	var noptrbss *sym.Section
  2051  	for i, s := range Segdata.Sections {
  2052  		if ctxt.IsELF && s.Name == ".tbss" {
  2053  			continue
  2054  		}
  2055  		vlen := int64(s.Length)
  2056  		if i+1 < len(Segdata.Sections) && !(ctxt.IsELF && Segdata.Sections[i+1].Name == ".tbss") {
  2057  			vlen = int64(Segdata.Sections[i+1].Vaddr - s.Vaddr)
  2058  		}
  2059  		s.Vaddr = va
  2060  		va += uint64(vlen)
  2061  		Segdata.Length = va - Segdata.Vaddr
  2062  		if s.Name == ".data" {
  2063  			data = s
  2064  		}
  2065  		if s.Name == ".noptrdata" {
  2066  			noptr = s
  2067  		}
  2068  		if s.Name == ".bss" {
  2069  			bss = s
  2070  		}
  2071  		if s.Name == ".noptrbss" {
  2072  			noptrbss = s
  2073  		}
  2074  	}
  2075  
  2076  	// Assign Segdata's Filelen omitting the BSS. We do this here
  2077  	// simply because right now we know where the BSS starts.
  2078  	Segdata.Filelen = bss.Vaddr - Segdata.Vaddr
  2079  
  2080  	va = uint64(Rnd(int64(va), int64(*FlagRound)))
  2081  	order = append(order, &Segdwarf)
  2082  	Segdwarf.Rwx = 06
  2083  	Segdwarf.Vaddr = va
  2084  	for i, s := range Segdwarf.Sections {
  2085  		vlen := int64(s.Length)
  2086  		if i+1 < len(Segdwarf.Sections) {
  2087  			vlen = int64(Segdwarf.Sections[i+1].Vaddr - s.Vaddr)
  2088  		}
  2089  		s.Vaddr = va
  2090  		va += uint64(vlen)
  2091  		if ctxt.HeadType == objabi.Hwindows {
  2092  			va = uint64(Rnd(int64(va), PEFILEALIGN))
  2093  		}
  2094  		Segdwarf.Length = va - Segdwarf.Vaddr
  2095  	}
  2096  
  2097  	var (
  2098  		text     = Segtext.Sections[0]
  2099  		rodata   = ctxt.Syms.Lookup("runtime.rodata", 0).Sect
  2100  		itablink = ctxt.Syms.Lookup("runtime.itablink", 0).Sect
  2101  		symtab   = ctxt.Syms.Lookup("runtime.symtab", 0).Sect
  2102  		pclntab  = ctxt.Syms.Lookup("runtime.pclntab", 0).Sect
  2103  		types    = ctxt.Syms.Lookup("runtime.types", 0).Sect
  2104  	)
  2105  	lasttext := text
  2106  	// Could be multiple .text sections
  2107  	for _, sect := range Segtext.Sections {
  2108  		if sect.Name == ".text" {
  2109  			lasttext = sect
  2110  		}
  2111  	}
  2112  
  2113  	for _, s := range datap {
  2114  		if s.Sect != nil {
  2115  			s.Value += int64(s.Sect.Vaddr)
  2116  		}
  2117  		for sub := s.Sub; sub != nil; sub = sub.Sub {
  2118  			sub.Value += s.Value
  2119  		}
  2120  	}
  2121  
  2122  	for _, s := range dwarfp {
  2123  		if s.Sect != nil {
  2124  			s.Value += int64(s.Sect.Vaddr)
  2125  		}
  2126  		for sub := s.Sub; sub != nil; sub = sub.Sub {
  2127  			sub.Value += s.Value
  2128  		}
  2129  	}
  2130  
  2131  	if ctxt.BuildMode == BuildModeShared {
  2132  		s := ctxt.Syms.Lookup("go.link.abihashbytes", 0)
  2133  		sectSym := ctxt.Syms.Lookup(".note.go.abihash", 0)
  2134  		s.Sect = sectSym.Sect
  2135  		s.Value = int64(sectSym.Sect.Vaddr + 16)
  2136  	}
  2137  
  2138  	ctxt.xdefine("runtime.text", sym.STEXT, int64(text.Vaddr))
  2139  	ctxt.xdefine("runtime.etext", sym.STEXT, int64(lasttext.Vaddr+lasttext.Length))
  2140  
  2141  	// If there are multiple text sections, create runtime.text.n for
  2142  	// their section Vaddr, using n for index
  2143  	n := 1
  2144  	for _, sect := range Segtext.Sections[1:] {
  2145  		if sect.Name != ".text" {
  2146  			break
  2147  		}
  2148  		symname := fmt.Sprintf("runtime.text.%d", n)
  2149  		ctxt.xdefine(symname, sym.STEXT, int64(sect.Vaddr))
  2150  		n++
  2151  	}
  2152  
  2153  	ctxt.xdefine("runtime.rodata", sym.SRODATA, int64(rodata.Vaddr))
  2154  	ctxt.xdefine("runtime.erodata", sym.SRODATA, int64(rodata.Vaddr+rodata.Length))
  2155  	ctxt.xdefine("runtime.types", sym.SRODATA, int64(types.Vaddr))
  2156  	ctxt.xdefine("runtime.etypes", sym.SRODATA, int64(types.Vaddr+types.Length))
  2157  	ctxt.xdefine("runtime.itablink", sym.SRODATA, int64(itablink.Vaddr))
  2158  	ctxt.xdefine("runtime.eitablink", sym.SRODATA, int64(itablink.Vaddr+itablink.Length))
  2159  
  2160  	s := ctxt.Syms.Lookup("runtime.gcdata", 0)
  2161  	s.Attr |= sym.AttrLocal
  2162  	ctxt.xdefine("runtime.egcdata", sym.SRODATA, Symaddr(s)+s.Size)
  2163  	ctxt.Syms.Lookup("runtime.egcdata", 0).Sect = s.Sect
  2164  
  2165  	s = ctxt.Syms.Lookup("runtime.gcbss", 0)
  2166  	s.Attr |= sym.AttrLocal
  2167  	ctxt.xdefine("runtime.egcbss", sym.SRODATA, Symaddr(s)+s.Size)
  2168  	ctxt.Syms.Lookup("runtime.egcbss", 0).Sect = s.Sect
  2169  
  2170  	ctxt.xdefine("runtime.symtab", sym.SRODATA, int64(symtab.Vaddr))
  2171  	ctxt.xdefine("runtime.esymtab", sym.SRODATA, int64(symtab.Vaddr+symtab.Length))
  2172  	ctxt.xdefine("runtime.pclntab", sym.SRODATA, int64(pclntab.Vaddr))
  2173  	ctxt.xdefine("runtime.epclntab", sym.SRODATA, int64(pclntab.Vaddr+pclntab.Length))
  2174  	ctxt.xdefine("runtime.noptrdata", sym.SNOPTRDATA, int64(noptr.Vaddr))
  2175  	ctxt.xdefine("runtime.enoptrdata", sym.SNOPTRDATA, int64(noptr.Vaddr+noptr.Length))
  2176  	ctxt.xdefine("runtime.bss", sym.SBSS, int64(bss.Vaddr))
  2177  	ctxt.xdefine("runtime.ebss", sym.SBSS, int64(bss.Vaddr+bss.Length))
  2178  	ctxt.xdefine("runtime.data", sym.SDATA, int64(data.Vaddr))
  2179  	ctxt.xdefine("runtime.edata", sym.SDATA, int64(data.Vaddr+data.Length))
  2180  	ctxt.xdefine("runtime.noptrbss", sym.SNOPTRBSS, int64(noptrbss.Vaddr))
  2181  	ctxt.xdefine("runtime.enoptrbss", sym.SNOPTRBSS, int64(noptrbss.Vaddr+noptrbss.Length))
  2182  	ctxt.xdefine("runtime.end", sym.SBSS, int64(Segdata.Vaddr+Segdata.Length))
  2183  
  2184  	return order
  2185  }
  2186  
  2187  // layout assigns file offsets and lengths to the segments in order.
  2188  func (ctxt *Link) layout(order []*sym.Segment) {
  2189  	var prev *sym.Segment
  2190  	for _, seg := range order {
  2191  		if prev == nil {
  2192  			seg.Fileoff = uint64(HEADR)
  2193  		} else {
  2194  			switch ctxt.HeadType {
  2195  			default:
  2196  				// Assuming the previous segment was
  2197  				// aligned, the following rounding
  2198  				// should ensure that this segment's
  2199  				// VA ≡ Fileoff mod FlagRound.
  2200  				seg.Fileoff = uint64(Rnd(int64(prev.Fileoff+prev.Filelen), int64(*FlagRound)))
  2201  				if seg.Vaddr%uint64(*FlagRound) != seg.Fileoff%uint64(*FlagRound) {
  2202  					Exitf("bad segment rounding (Vaddr=%#x Fileoff=%#x FlagRound=%#x)", seg.Vaddr, seg.Fileoff, *FlagRound)
  2203  				}
  2204  			case objabi.Hwindows:
  2205  				seg.Fileoff = prev.Fileoff + uint64(Rnd(int64(prev.Filelen), PEFILEALIGN))
  2206  			case objabi.Hplan9:
  2207  				seg.Fileoff = prev.Fileoff + prev.Filelen
  2208  			}
  2209  		}
  2210  		if seg != &Segdata {
  2211  			// Link.address already set Segdata.Filelen to
  2212  			// account for BSS.
  2213  			seg.Filelen = seg.Length
  2214  		}
  2215  		prev = seg
  2216  	}
  2217  
  2218  }
  2219  
  2220  // add a trampoline with symbol s (to be laid down after the current function)
  2221  func (ctxt *Link) AddTramp(s *sym.Symbol) {
  2222  	s.Type = sym.STEXT
  2223  	s.Attr |= sym.AttrReachable
  2224  	s.Attr |= sym.AttrOnList
  2225  	ctxt.tramps = append(ctxt.tramps, s)
  2226  	if *FlagDebugTramp > 0 && ctxt.Debugvlog > 0 {
  2227  		ctxt.Logf("trampoline %s inserted\n", s)
  2228  	}
  2229  }
  2230  
  2231  // compressSyms compresses syms and returns the contents of the
  2232  // compressed section. If the section would get larger, it returns nil.
  2233  func compressSyms(ctxt *Link, syms []*sym.Symbol) []byte {
  2234  	var total int64
  2235  	for _, sym := range syms {
  2236  		total += sym.Size
  2237  	}
  2238  
  2239  	var buf bytes.Buffer
  2240  	buf.Write([]byte("ZLIB"))
  2241  	var sizeBytes [8]byte
  2242  	binary.BigEndian.PutUint64(sizeBytes[:], uint64(total))
  2243  	buf.Write(sizeBytes[:])
  2244  
  2245  	// Using zlib.BestSpeed achieves very nearly the same
  2246  	// compression levels of zlib.DefaultCompression, but takes
  2247  	// substantially less time. This is important because DWARF
  2248  	// compression can be a significant fraction of link time.
  2249  	z, err := zlib.NewWriterLevel(&buf, zlib.BestSpeed)
  2250  	if err != nil {
  2251  		log.Fatalf("NewWriterLevel failed: %s", err)
  2252  	}
  2253  	for _, sym := range syms {
  2254  		if _, err := z.Write(sym.P); err != nil {
  2255  			log.Fatalf("compression failed: %s", err)
  2256  		}
  2257  		for i := sym.Size - int64(len(sym.P)); i > 0; {
  2258  			b := zeros[:]
  2259  			if i < int64(len(b)) {
  2260  				b = b[:i]
  2261  			}
  2262  			n, err := z.Write(b)
  2263  			if err != nil {
  2264  				log.Fatalf("compression failed: %s", err)
  2265  			}
  2266  			i -= int64(n)
  2267  		}
  2268  	}
  2269  	if err := z.Close(); err != nil {
  2270  		log.Fatalf("compression failed: %s", err)
  2271  	}
  2272  	if int64(buf.Len()) >= total {
  2273  		// Compression didn't save any space.
  2274  		return nil
  2275  	}
  2276  	return buf.Bytes()
  2277  }
  2278  

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