ar.go

Documentation: cmd/link/internal/ld

     1  // Inferno utils/include/ar.h
     2  // https://bitbucket.org/inferno-os/inferno-os/src/master/utils/include/ar.h
     3  //
     4  //	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
     5  //	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
     6  //	Portions Copyright © 1997-1999 Vita Nuova Limited
     7  //	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
     8  //	Portions Copyright © 2004,2006 Bruce Ellis
     9  //	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
    10  //	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
    11  //	Portions Copyright © 2009 The Go Authors. All rights reserved.
    12  //
    13  // Permission is hereby granted, free of charge, to any person obtaining a copy
    14  // of this software and associated documentation files (the "Software"), to deal
    15  // in the Software without restriction, including without limitation the rights
    16  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    17  // copies of the Software, and to permit persons to whom the Software is
    18  // furnished to do so, subject to the following conditions:
    19  //
    20  // The above copyright notice and this permission notice shall be included in
    21  // all copies or substantial portions of the Software.
    22  //
    23  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    24  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    25  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
    26  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    27  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    28  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    29  // THE SOFTWARE.
    30  
    31  package ld
    32  
    33  import (
    34  	"cmd/internal/bio"
    35  	"cmd/link/internal/loader"
    36  	"cmd/link/internal/sym"
    37  	"encoding/binary"
    38  	"fmt"
    39  	"internal/buildcfg"
    40  	"io"
    41  	"os"
    42  	"path/filepath"
    43  	"strings"
    44  )
    45  
    46  const (
    47  	SARMAG  = 8
    48  	SAR_HDR = 16 + 44
    49  )
    50  
    51  const (
    52  	ARMAG = "!<arch>\n"
    53  )
    54  
    55  type ArHdr struct {
    56  	name string
    57  	date string
    58  	uid  string
    59  	gid  string
    60  	mode string
    61  	size string
    62  	fmag string
    63  }
    64  
    65  // pruneUndefsForWindows trims the list "undefs" of currently
    66  // outstanding unresolved symbols to remove references to DLL import
    67  // symbols (e.g. "__imp_XXX"). In older versions of the linker, we
    68  // would just immediately forward references from the import sym
    69  // (__imp_XXX) to the DLL sym (XXX), but with newer compilers this
    70  // strategy falls down in certain cases. We instead now do this
    71  // forwarding later on as a post-processing step, and meaning that
    72  // during the middle part of host object loading we can see a lot of
    73  // unresolved (SXREF) import symbols. We do not, however, want to
    74  // trigger the inclusion of an object from a host archive if the
    75  // reference is going to be eventually forwarded to the corresponding
    76  // SDYNIMPORT symbol, so here we strip out such refs from the undefs
    77  // list.
    78  func pruneUndefsForWindows(ldr *loader.Loader, undefs, froms []loader.Sym) ([]loader.Sym, []loader.Sym) {
    79  	var newundefs []loader.Sym
    80  	var newfroms []loader.Sym
    81  	for _, s := range undefs {
    82  		sname := ldr.SymName(s)
    83  		if strings.HasPrefix(sname, "__imp_") {
    84  			dname := sname[len("__imp_"):]
    85  			ds := ldr.Lookup(dname, 0)
    86  			if ds != 0 && ldr.SymType(ds) == sym.SDYNIMPORT {
    87  				// Don't try to pull things out of a host archive to
    88  				// satisfy this symbol.
    89  				continue
    90  			}
    91  		}
    92  		newundefs = append(newundefs, s)
    93  		newfroms = append(newfroms, s)
    94  	}
    95  	return newundefs, newfroms
    96  }
    97  
    98  // hostArchive reads an archive file holding host objects and links in
    99  // required objects. The general format is the same as a Go archive
   100  // file, but it has an armap listing symbols and the objects that
   101  // define them. This is used for the compiler support library
   102  // libgcc.a.
   103  func hostArchive(ctxt *Link, name string) {
   104  	if ctxt.Debugvlog > 1 {
   105  		ctxt.Logf("hostArchive(%s)\n", name)
   106  	}
   107  	f, err := bio.Open(name)
   108  	if err != nil {
   109  		if os.IsNotExist(err) {
   110  			// It's OK if we don't have a libgcc file at all.
   111  			if ctxt.Debugvlog != 0 {
   112  				ctxt.Logf("skipping libgcc file: %v\n", err)
   113  			}
   114  			return
   115  		}
   116  		Exitf("cannot open file %s: %v", name, err)
   117  	}
   118  	defer f.Close()
   119  
   120  	var magbuf [len(ARMAG)]byte
   121  	if _, err := io.ReadFull(f, magbuf[:]); err != nil {
   122  		Exitf("file %s too short", name)
   123  	}
   124  
   125  	if string(magbuf[:]) != ARMAG {
   126  		Exitf("%s is not an archive file", name)
   127  	}
   128  
   129  	var arhdr ArHdr
   130  	l := nextar(f, f.Offset(), &arhdr)
   131  	if l <= 0 {
   132  		Exitf("%s missing armap", name)
   133  	}
   134  
   135  	var armap archiveMap
   136  	if arhdr.name == "/" || arhdr.name == "/SYM64/" {
   137  		armap = readArmap(name, f, arhdr)
   138  	} else {
   139  		Exitf("%s missing armap", name)
   140  	}
   141  
   142  	loaded := make(map[uint64]bool)
   143  	any := true
   144  	for any {
   145  		var load []uint64
   146  		returnAllUndefs := -1
   147  		undefs, froms := ctxt.loader.UndefinedRelocTargets(returnAllUndefs)
   148  		if buildcfg.GOOS == "windows" {
   149  			undefs, froms = pruneUndefsForWindows(ctxt.loader, undefs, froms)
   150  		}
   151  		for k, symIdx := range undefs {
   152  			sname := ctxt.loader.SymName(symIdx)
   153  			if off := armap[sname]; off != 0 && !loaded[off] {
   154  				load = append(load, off)
   155  				loaded[off] = true
   156  				if ctxt.Debugvlog > 1 {
   157  					ctxt.Logf("hostArchive(%s): selecting object at offset %x to resolve %s [%d] reference from %s [%d]\n", name, off, sname, symIdx, ctxt.loader.SymName(froms[k]), froms[k])
   158  				}
   159  			}
   160  		}
   161  
   162  		for _, off := range load {
   163  			l := nextar(f, int64(off), &arhdr)
   164  			if l <= 0 {
   165  				Exitf("%s missing archive entry at offset %d", name, off)
   166  			}
   167  			pname := fmt.Sprintf("%s(%s)", name, arhdr.name)
   168  			l = atolwhex(arhdr.size)
   169  
   170  			pkname := filepath.Base(name)
   171  			if i := strings.LastIndex(pkname, ".a"); i >= 0 {
   172  				pkname = pkname[:i]
   173  			}
   174  			libar := sym.Library{Pkg: pkname}
   175  			h := ldobj(ctxt, f, &libar, l, pname, name)
   176  			if h.ld == nil {
   177  				Errorf(nil, "%s unrecognized object file at offset %d", name, off)
   178  				continue
   179  			}
   180  			f.MustSeek(h.off, 0)
   181  			h.ld(ctxt, f, h.pkg, h.length, h.pn)
   182  			if *flagCaptureHostObjs != "" {
   183  				captureHostObj(h)
   184  			}
   185  		}
   186  
   187  		any = len(load) > 0
   188  	}
   189  }
   190  
   191  // archiveMap is an archive symbol map: a mapping from symbol name to
   192  // offset within the archive file.
   193  type archiveMap map[string]uint64
   194  
   195  // readArmap reads the archive symbol map.
   196  func readArmap(filename string, f *bio.Reader, arhdr ArHdr) archiveMap {
   197  	is64 := arhdr.name == "/SYM64/"
   198  	wordSize := 4
   199  	if is64 {
   200  		wordSize = 8
   201  	}
   202  
   203  	contents := make([]byte, atolwhex(arhdr.size))
   204  	if _, err := io.ReadFull(f, contents); err != nil {
   205  		Exitf("short read from %s", filename)
   206  	}
   207  
   208  	var c uint64
   209  	if is64 {
   210  		c = binary.BigEndian.Uint64(contents)
   211  	} else {
   212  		c = uint64(binary.BigEndian.Uint32(contents))
   213  	}
   214  	contents = contents[wordSize:]
   215  
   216  	ret := make(archiveMap)
   217  
   218  	names := contents[c*uint64(wordSize):]
   219  	for i := uint64(0); i < c; i++ {
   220  		n := 0
   221  		for names[n] != 0 {
   222  			n++
   223  		}
   224  		name := string(names[:n])
   225  		names = names[n+1:]
   226  
   227  		// For Mach-O and PE/386 files we strip a leading
   228  		// underscore from the symbol name.
   229  		if buildcfg.GOOS == "darwin" || buildcfg.GOOS == "ios" || (buildcfg.GOOS == "windows" && buildcfg.GOARCH == "386") {
   230  			if name[0] == '_' && len(name) > 1 {
   231  				name = name[1:]
   232  			}
   233  		}
   234  
   235  		var off uint64
   236  		if is64 {
   237  			off = binary.BigEndian.Uint64(contents)
   238  		} else {
   239  			off = uint64(binary.BigEndian.Uint32(contents))
   240  		}
   241  		contents = contents[wordSize:]
   242  
   243  		ret[name] = off
   244  	}
   245  
   246  	return ret
   247  }
   248
View as plain text