decodesym.go

     1  // Copyright 2012 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package ld
     6  
     7  import (
     8  	"cmd/internal/sys"
     9  	"cmd/link/internal/loader"
    10  	"cmd/link/internal/sym"
    11  	"debug/elf"
    12  	"encoding/binary"
    13  	"internal/abi"
    14  	"log"
    15  )
    16  
    17  // Decoding the type.* symbols.	 This has to be in sync with
    18  // ../../runtime/type.go, or more specifically, with what
    19  // cmd/compile/internal/reflectdata/reflect.go stuffs in these.
    20  
    21  func decodeInuxi(arch *sys.Arch, p []byte, sz int) uint64 {
    22  	switch sz {
    23  	case 2:
    24  		return uint64(arch.ByteOrder.Uint16(p))
    25  	case 4:
    26  		return uint64(arch.ByteOrder.Uint32(p))
    27  	case 8:
    28  		return arch.ByteOrder.Uint64(p)
    29  	default:
    30  		Exitf("dwarf: decode inuxi %d", sz)
    31  		panic("unreachable")
    32  	}
    33  }
    34  
    35  func commonsize(arch *sys.Arch) int      { return abi.CommonSize(arch.PtrSize) }      // runtime._type
    36  func structfieldSize(arch *sys.Arch) int { return abi.StructFieldSize(arch.PtrSize) } // runtime.structfield
    37  func uncommonSize(arch *sys.Arch) int    { return int(abi.UncommonSize()) }           // runtime.uncommontype
    38  
    39  // Type.commonType.kind
    40  func decodetypeKind(arch *sys.Arch, p []byte) abi.Kind {
    41  	return abi.Kind(p[2*arch.PtrSize+7]) //  0x13
    42  }
    43  
    44  // Type.commonType.size
    45  func decodetypeSize(arch *sys.Arch, p []byte) int64 {
    46  	return int64(decodeInuxi(arch, p, arch.PtrSize)) // 0x8 / 0x10
    47  }
    48  
    49  // Type.commonType.ptrdata
    50  func decodetypePtrdata(arch *sys.Arch, p []byte) int64 {
    51  	return int64(decodeInuxi(arch, p[arch.PtrSize:], arch.PtrSize)) // 0x8 / 0x10
    52  }
    53  
    54  // Type.commonType.tflag
    55  func decodetypeHasUncommon(arch *sys.Arch, p []byte) bool {
    56  	return abi.TFlag(p[abi.TFlagOff(arch.PtrSize)])&abi.TFlagUncommon != 0
    57  }
    58  
    59  // Type.commonType.tflag
    60  func decodetypeGCMaskOnDemand(arch *sys.Arch, p []byte) bool {
    61  	return abi.TFlag(p[abi.TFlagOff(arch.PtrSize)])&abi.TFlagGCMaskOnDemand != 0
    62  }
    63  
    64  // Type.FuncType.dotdotdot
    65  func decodetypeFuncDotdotdot(arch *sys.Arch, p []byte) bool {
    66  	return uint16(decodeInuxi(arch, p[commonsize(arch)+2:], 2))&(1<<15) != 0
    67  }
    68  
    69  // Type.FuncType.inCount
    70  func decodetypeFuncInCount(arch *sys.Arch, p []byte) int {
    71  	return int(decodeInuxi(arch, p[commonsize(arch):], 2))
    72  }
    73  
    74  func decodetypeFuncOutCount(arch *sys.Arch, p []byte) int {
    75  	return int(uint16(decodeInuxi(arch, p[commonsize(arch)+2:], 2)) & (1<<15 - 1))
    76  }
    77  
    78  // InterfaceType.methods.length
    79  func decodetypeIfaceMethodCount(arch *sys.Arch, p []byte) int64 {
    80  	return int64(decodeInuxi(arch, p[commonsize(arch)+2*arch.PtrSize:], arch.PtrSize))
    81  }
    82  
    83  func decodeReloc(ldr *loader.Loader, symIdx loader.Sym, relocs *loader.Relocs, off int32) loader.Reloc {
    84  	for j := 0; j < relocs.Count(); j++ {
    85  		rel := relocs.At(j)
    86  		if rel.Off() == off {
    87  			return rel
    88  		}
    89  	}
    90  	return loader.Reloc{}
    91  }
    92  
    93  func decodeRelocSym(ldr *loader.Loader, symIdx loader.Sym, relocs *loader.Relocs, off int32) loader.Sym {
    94  	return decodeReloc(ldr, symIdx, relocs, off).Sym()
    95  }
    96  
    97  // decodetypeName decodes the name from a reflect.name.
    98  func decodetypeName(ldr *loader.Loader, symIdx loader.Sym, relocs *loader.Relocs, off int) string {
    99  	r := decodeRelocSym(ldr, symIdx, relocs, int32(off))
   100  	if r == 0 {
   101  		return ""
   102  	}
   103  
   104  	data := ldr.DataString(r)
   105  	n := 1 + binary.MaxVarintLen64
   106  	if len(data) < n {
   107  		n = len(data)
   108  	}
   109  	nameLen, nameLenLen := binary.Uvarint([]byte(data[1:n]))
   110  	return data[1+nameLenLen : 1+nameLenLen+int(nameLen)]
   111  }
   112  
   113  func decodetypeNameEmbedded(ldr *loader.Loader, symIdx loader.Sym, relocs *loader.Relocs, off int) bool {
   114  	r := decodeRelocSym(ldr, symIdx, relocs, int32(off))
   115  	if r == 0 {
   116  		return false
   117  	}
   118  	data := ldr.Data(r)
   119  	return data[0]&(1<<3) != 0
   120  }
   121  
   122  func decodetypeFuncInType(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, relocs *loader.Relocs, i int) loader.Sym {
   123  	uadd := abi.RTypeSize(abi.Func, arch.PtrSize)
   124  	if decodetypeHasUncommon(arch, ldr.Data(symIdx)) {
   125  		uadd += uncommonSize(arch)
   126  	}
   127  	return decodeRelocSym(ldr, symIdx, relocs, int32(uadd+i*arch.PtrSize))
   128  }
   129  
   130  func decodetypeFuncOutType(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, relocs *loader.Relocs, i int) loader.Sym {
   131  	return decodetypeFuncInType(ldr, arch, symIdx, relocs, i+decodetypeFuncInCount(arch, ldr.Data(symIdx)))
   132  }
   133  
   134  func decodetypeArrayElem(ctxt *Link, arch *sys.Arch, symIdx loader.Sym) loader.Sym {
   135  	return decodeTargetSym(ctxt, arch, symIdx, int64(commonsize(arch))) // 0x1c / 0x30
   136  }
   137  
   138  func decodetypeArrayLen(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym) int64 {
   139  	data := ldr.Data(symIdx)
   140  	return int64(decodeInuxi(arch, data[commonsize(arch)+2*arch.PtrSize:], arch.PtrSize))
   141  }
   142  
   143  func decodetypeChanElem(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym) loader.Sym {
   144  	relocs := ldr.Relocs(symIdx)
   145  	return decodeRelocSym(ldr, symIdx, &relocs, int32(commonsize(arch))) // 0x1c / 0x30
   146  }
   147  
   148  func decodetypeMapKey(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym) loader.Sym {
   149  	relocs := ldr.Relocs(symIdx)
   150  	return decodeRelocSym(ldr, symIdx, &relocs, int32(commonsize(arch))) // 0x1c / 0x30
   151  }
   152  
   153  func decodetypeMapValue(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym) loader.Sym {
   154  	relocs := ldr.Relocs(symIdx)
   155  	return decodeRelocSym(ldr, symIdx, &relocs, int32(commonsize(arch))+int32(arch.PtrSize)) // 0x20 / 0x38
   156  }
   157  
   158  func decodetypeMapGroup(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym) loader.Sym {
   159  	relocs := ldr.Relocs(symIdx)
   160  	return decodeRelocSym(ldr, symIdx, &relocs, int32(commonsize(arch))+2*int32(arch.PtrSize)) // 0x24 / 0x40
   161  }
   162  
   163  func decodetypePtrElem(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym) loader.Sym {
   164  	relocs := ldr.Relocs(symIdx)
   165  	return decodeRelocSym(ldr, symIdx, &relocs, int32(commonsize(arch))) // 0x1c / 0x30
   166  }
   167  
   168  func decodetypeStructFieldCount(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym) int {
   169  	data := ldr.Data(symIdx)
   170  	return int(decodeInuxi(arch, data[commonsize(arch)+2*arch.PtrSize:], arch.PtrSize))
   171  }
   172  
   173  func decodetypeStructFieldArrayOff(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, i int) int {
   174  	data := ldr.Data(symIdx)
   175  	off := abi.RTypeSize(abi.Struct, arch.PtrSize)
   176  	if decodetypeHasUncommon(arch, data) {
   177  		off += uncommonSize(arch)
   178  	}
   179  	off += i * structfieldSize(arch)
   180  	return off
   181  }
   182  
   183  func decodetypeStructFieldName(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, i int) string {
   184  	off := decodetypeStructFieldArrayOff(ldr, arch, symIdx, i)
   185  	relocs := ldr.Relocs(symIdx)
   186  	return decodetypeName(ldr, symIdx, &relocs, off)
   187  }
   188  
   189  func decodetypeStructFieldType(ctxt *Link, arch *sys.Arch, symIdx loader.Sym, i int) loader.Sym {
   190  	ldr := ctxt.loader
   191  	off := decodetypeStructFieldArrayOff(ldr, arch, symIdx, i)
   192  	return decodeTargetSym(ctxt, arch, symIdx, int64(off+arch.PtrSize))
   193  }
   194  
   195  func decodetypeStructFieldOffset(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, i int) int64 {
   196  	off := decodetypeStructFieldArrayOff(ldr, arch, symIdx, i)
   197  	data := ldr.Data(symIdx)
   198  	return int64(decodeInuxi(arch, data[off+2*arch.PtrSize:], arch.PtrSize))
   199  }
   200  
   201  func decodetypeStructFieldEmbedded(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, i int) bool {
   202  	off := decodetypeStructFieldArrayOff(ldr, arch, symIdx, i)
   203  	relocs := ldr.Relocs(symIdx)
   204  	return decodetypeNameEmbedded(ldr, symIdx, &relocs, off)
   205  }
   206  
   207  // decodetypeStr returns the contents of an rtype's str field (a nameOff).
   208  func decodetypeStr(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym) string {
   209  	relocs := ldr.Relocs(symIdx)
   210  	str := decodetypeName(ldr, symIdx, &relocs, 4*arch.PtrSize+8)
   211  	data := ldr.Data(symIdx)
   212  	if data[abi.TFlagOff(arch.PtrSize)]&byte(abi.TFlagExtraStar) != 0 {
   213  		return str[1:]
   214  	}
   215  	return str
   216  }
   217  
   218  func decodetypeGcmask(ctxt *Link, s loader.Sym) []byte {
   219  	if ctxt.loader.SymType(s) == sym.SDYNIMPORT {
   220  		symData := ctxt.loader.Data(s)
   221  		addr := decodetypeGcprogShlib(ctxt, symData)
   222  		ptrdata := decodetypePtrdata(ctxt.Arch, symData)
   223  		sect := findShlibSection(ctxt, ctxt.loader.SymPkg(s), addr)
   224  		if sect != nil {
   225  			bits := ptrdata / int64(ctxt.Arch.PtrSize)
   226  			r := make([]byte, (bits+7)/8)
   227  			// ldshlibsyms avoids closing the ELF file so sect.ReadAt works.
   228  			// If we remove this read (and the ones in decodetypeGcprog), we
   229  			// can close the file.
   230  			_, err := sect.ReadAt(r, int64(addr-sect.Addr))
   231  			if err != nil {
   232  				log.Fatal(err)
   233  			}
   234  			return r
   235  		}
   236  		Exitf("cannot find gcmask for %s", ctxt.loader.SymName(s))
   237  		return nil
   238  	}
   239  	relocs := ctxt.loader.Relocs(s)
   240  	mask := decodeRelocSym(ctxt.loader, s, &relocs, 2*int32(ctxt.Arch.PtrSize)+8+1*int32(ctxt.Arch.PtrSize))
   241  	return ctxt.loader.Data(mask)
   242  }
   243  
   244  // Find the elf.Section of a given shared library that contains a given address.
   245  func findShlibSection(ctxt *Link, path string, addr uint64) *elf.Section {
   246  	for _, shlib := range ctxt.Shlibs {
   247  		if shlib.Path == path {
   248  			for _, sect := range shlib.File.Sections[1:] { // skip the NULL section
   249  				if sect.Addr <= addr && addr < sect.Addr+sect.Size {
   250  					return sect
   251  				}
   252  			}
   253  		}
   254  	}
   255  	return nil
   256  }
   257  
   258  func decodetypeGcprogShlib(ctxt *Link, data []byte) uint64 {
   259  	return decodeInuxi(ctxt.Arch, data[2*int32(ctxt.Arch.PtrSize)+8+1*int32(ctxt.Arch.PtrSize):], ctxt.Arch.PtrSize)
   260  }
   261  
   262  // decodeItabType returns the itab.Type field from an itab.
   263  func decodeItabType(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym) loader.Sym {
   264  	relocs := ldr.Relocs(symIdx)
   265  	return decodeRelocSym(ldr, symIdx, &relocs, int32(abi.ITabTypeOff(arch.PtrSize)))
   266  }
   267  
   268  // decodeTargetSym finds the symbol pointed to by the pointer slot at offset off in s.
   269  func decodeTargetSym(ctxt *Link, arch *sys.Arch, s loader.Sym, off int64) loader.Sym {
   270  	ldr := ctxt.loader
   271  	if ldr.SymType(s) == sym.SDYNIMPORT {
   272  		// In this case, relocations are not associated with a
   273  		// particular symbol. Instead, they are all listed together
   274  		// in the containing shared library. Find the relocation
   275  		// in that shared library record.
   276  		name := ldr.SymName(s)
   277  		for _, sh := range ctxt.Shlibs {
   278  			addr, ok := sh.symAddr[name]
   279  			if !ok {
   280  				continue
   281  			}
   282  			addr += uint64(off)
   283  			target := sh.relocTarget[addr]
   284  			if target == "" {
   285  				Exitf("can't find relocation in %s at offset %d", name, off)
   286  			}
   287  			t := ldr.Lookup(target, 0)
   288  			if t == 0 {
   289  				Exitf("can't find target of relocation in %s at offset %d: %s", name, off, target)
   290  			}
   291  			return t
   292  		}
   293  	}
   294  
   295  	// For the normal case, just find the relocation within the symbol that
   296  	// lives at the requested offset.
   297  	relocs := ldr.Relocs(s)
   298  	return decodeRelocSym(ldr, s, &relocs, int32(off))
   299  }
   300
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