pcln.go

Documentation: cmd/link/internal/ld

     1  // Copyright 2013 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/goobj"
     9  	"cmd/internal/objabi"
    10  	"cmd/internal/sys"
    11  	"cmd/link/internal/loader"
    12  	"cmd/link/internal/sym"
    13  	"fmt"
    14  	"internal/abi"
    15  	"internal/buildcfg"
    16  	"path/filepath"
    17  	"strings"
    18  )
    19  
    20  const funcSize = 11 * 4 // funcSize is the size of the _func object in runtime/runtime2.go
    21  
    22  // pclntab holds the state needed for pclntab generation.
    23  type pclntab struct {
    24  	// The first and last functions found.
    25  	firstFunc, lastFunc loader.Sym
    26  
    27  	// Running total size of pclntab.
    28  	size int64
    29  
    30  	// runtime.pclntab's symbols
    31  	carrier     loader.Sym
    32  	pclntab     loader.Sym
    33  	pcheader    loader.Sym
    34  	funcnametab loader.Sym
    35  	findfunctab loader.Sym
    36  	cutab       loader.Sym
    37  	filetab     loader.Sym
    38  	pctab       loader.Sym
    39  
    40  	// The number of functions + number of TEXT sections - 1. This is such an
    41  	// unexpected value because platforms that have more than one TEXT section
    42  	// get a dummy function inserted between because the external linker can place
    43  	// functions in those areas. We mark those areas as not covered by the Go
    44  	// runtime.
    45  	//
    46  	// On most platforms this is the number of reachable functions.
    47  	nfunc int32
    48  
    49  	// The number of filenames in runtime.filetab.
    50  	nfiles uint32
    51  }
    52  
    53  // addGeneratedSym adds a generator symbol to pclntab, returning the new Sym.
    54  // It is the caller's responsibility to save the symbol in state.
    55  func (state *pclntab) addGeneratedSym(ctxt *Link, name string, size int64, f generatorFunc) loader.Sym {
    56  	size = Rnd(size, int64(ctxt.Arch.PtrSize))
    57  	state.size += size
    58  	s := ctxt.createGeneratorSymbol(name, 0, sym.SPCLNTAB, size, f)
    59  	ctxt.loader.SetAttrReachable(s, true)
    60  	ctxt.loader.SetCarrierSym(s, state.carrier)
    61  	ctxt.loader.SetAttrNotInSymbolTable(s, true)
    62  	return s
    63  }
    64  
    65  // makePclntab makes a pclntab object, and assembles all the compilation units
    66  // we'll need to write pclntab. Returns the pclntab structure, a slice of the
    67  // CompilationUnits we need, and a slice of the function symbols we need to
    68  // generate pclntab.
    69  func makePclntab(ctxt *Link, container loader.Bitmap) (*pclntab, []*sym.CompilationUnit, []loader.Sym) {
    70  	ldr := ctxt.loader
    71  	state := new(pclntab)
    72  
    73  	// Gather some basic stats and info.
    74  	seenCUs := make(map[*sym.CompilationUnit]struct{})
    75  	compUnits := []*sym.CompilationUnit{}
    76  	funcs := []loader.Sym{}
    77  
    78  	for _, s := range ctxt.Textp {
    79  		if !emitPcln(ctxt, s, container) {
    80  			continue
    81  		}
    82  		funcs = append(funcs, s)
    83  		state.nfunc++
    84  		if state.firstFunc == 0 {
    85  			state.firstFunc = s
    86  		}
    87  		state.lastFunc = s
    88  
    89  		// We need to keep track of all compilation units we see. Some symbols
    90  		// (eg, go.buildid, _cgoexp_, etc) won't have a compilation unit.
    91  		cu := ldr.SymUnit(s)
    92  		if _, ok := seenCUs[cu]; cu != nil && !ok {
    93  			seenCUs[cu] = struct{}{}
    94  			cu.PclnIndex = len(compUnits)
    95  			compUnits = append(compUnits, cu)
    96  		}
    97  	}
    98  	return state, compUnits, funcs
    99  }
   100  
   101  func emitPcln(ctxt *Link, s loader.Sym, container loader.Bitmap) bool {
   102  	if ctxt.Target.IsRISCV64() {
   103  		// Avoid adding local symbols to the pcln table - RISC-V
   104  		// linking generates a very large number of these, particularly
   105  		// for HI20 symbols (which we need to load in order to be able
   106  		// to resolve relocations). Unnecessarily including all of
   107  		// these symbols quickly blows out the size of the pcln table
   108  		// and overflows hash buckets.
   109  		symName := ctxt.loader.SymName(s)
   110  		if symName == "" || strings.HasPrefix(symName, ".L") {
   111  			return false
   112  		}
   113  	}
   114  
   115  	// We want to generate func table entries only for the "lowest
   116  	// level" symbols, not containers of subsymbols.
   117  	return !container.Has(s)
   118  }
   119  
   120  func computeDeferReturn(ctxt *Link, deferReturnSym, s loader.Sym) uint32 {
   121  	ldr := ctxt.loader
   122  	target := ctxt.Target
   123  	deferreturn := uint32(0)
   124  	lastWasmAddr := uint32(0)
   125  
   126  	relocs := ldr.Relocs(s)
   127  	for ri := 0; ri < relocs.Count(); ri++ {
   128  		r := relocs.At(ri)
   129  		if target.IsWasm() && r.Type() == objabi.R_ADDR {
   130  			// wasm/ssa.go generates an ARESUMEPOINT just
   131  			// before the deferreturn call. The "PC" of
   132  			// the deferreturn call is stored in the
   133  			// R_ADDR relocation on the ARESUMEPOINT.
   134  			lastWasmAddr = uint32(r.Add())
   135  		}
   136  		if r.Type().IsDirectCall() && (r.Sym() == deferReturnSym || ldr.IsDeferReturnTramp(r.Sym())) {
   137  			if target.IsWasm() {
   138  				deferreturn = lastWasmAddr - 1
   139  			} else {
   140  				// Note: the relocation target is in the call instruction, but
   141  				// is not necessarily the whole instruction (for instance, on
   142  				// x86 the relocation applies to bytes [1:5] of the 5 byte call
   143  				// instruction).
   144  				deferreturn = uint32(r.Off())
   145  				switch target.Arch.Family {
   146  				case sys.AMD64, sys.I386:
   147  					deferreturn--
   148  				case sys.ARM, sys.ARM64, sys.Loong64, sys.MIPS, sys.MIPS64, sys.PPC64, sys.RISCV64:
   149  					// no change
   150  				case sys.S390X:
   151  					deferreturn -= 2
   152  				default:
   153  					panic(fmt.Sprint("Unhandled architecture:", target.Arch.Family))
   154  				}
   155  			}
   156  			break // only need one
   157  		}
   158  	}
   159  	return deferreturn
   160  }
   161  
   162  // genInlTreeSym generates the InlTree sym for a function with the
   163  // specified FuncInfo.
   164  func genInlTreeSym(ctxt *Link, cu *sym.CompilationUnit, fi loader.FuncInfo, arch *sys.Arch, nameOffsets map[loader.Sym]uint32) loader.Sym {
   165  	ldr := ctxt.loader
   166  	its := ldr.CreateExtSym("", 0)
   167  	inlTreeSym := ldr.MakeSymbolUpdater(its)
   168  	// Note: the generated symbol is given a type of sym.SGOFUNC, as a
   169  	// signal to the symtab() phase that it needs to be grouped in with
   170  	// other similar symbols (gcdata, etc); the dodata() phase will
   171  	// eventually switch the type back to SRODATA.
   172  	inlTreeSym.SetType(sym.SGOFUNC)
   173  	ldr.SetAttrReachable(its, true)
   174  	ldr.SetSymAlign(its, 4) // it has 32-bit fields
   175  	ninl := fi.NumInlTree()
   176  	for i := 0; i < int(ninl); i++ {
   177  		call := fi.InlTree(i)
   178  		nameOff, ok := nameOffsets[call.Func]
   179  		if !ok {
   180  			panic("couldn't find function name offset")
   181  		}
   182  
   183  		inlFunc := ldr.FuncInfo(call.Func)
   184  		var funcID abi.FuncID
   185  		startLine := int32(0)
   186  		if inlFunc.Valid() {
   187  			funcID = inlFunc.FuncID()
   188  			startLine = inlFunc.StartLine()
   189  		} else if !ctxt.linkShared {
   190  			// Inlined functions are always Go functions, and thus
   191  			// must have FuncInfo.
   192  			//
   193  			// Unfortunately, with -linkshared, the inlined
   194  			// function may be external symbols (from another
   195  			// shared library), and we don't load FuncInfo from the
   196  			// shared library. We will report potentially incorrect
   197  			// FuncID in this case. See https://go.dev/issue/55954.
   198  			panic(fmt.Sprintf("inlined function %s missing func info", ldr.SymName(call.Func)))
   199  		}
   200  
   201  		// Construct runtime.inlinedCall value.
   202  		const size = 16
   203  		inlTreeSym.SetUint8(arch, int64(i*size+0), uint8(funcID))
   204  		// Bytes 1-3 are unused.
   205  		inlTreeSym.SetUint32(arch, int64(i*size+4), uint32(nameOff))
   206  		inlTreeSym.SetUint32(arch, int64(i*size+8), uint32(call.ParentPC))
   207  		inlTreeSym.SetUint32(arch, int64(i*size+12), uint32(startLine))
   208  	}
   209  	return its
   210  }
   211  
   212  // makeInlSyms returns a map of loader.Sym that are created inlSyms.
   213  func makeInlSyms(ctxt *Link, funcs []loader.Sym, nameOffsets map[loader.Sym]uint32) map[loader.Sym]loader.Sym {
   214  	ldr := ctxt.loader
   215  	// Create the inline symbols we need.
   216  	inlSyms := make(map[loader.Sym]loader.Sym)
   217  	for _, s := range funcs {
   218  		if fi := ldr.FuncInfo(s); fi.Valid() {
   219  			fi.Preload()
   220  			if fi.NumInlTree() > 0 {
   221  				inlSyms[s] = genInlTreeSym(ctxt, ldr.SymUnit(s), fi, ctxt.Arch, nameOffsets)
   222  			}
   223  		}
   224  	}
   225  	return inlSyms
   226  }
   227  
   228  // generatePCHeader creates the runtime.pcheader symbol, setting it up as a
   229  // generator to fill in its data later.
   230  func (state *pclntab) generatePCHeader(ctxt *Link) {
   231  	ldr := ctxt.loader
   232  	textStartOff := int64(8 + 2*ctxt.Arch.PtrSize)
   233  	size := int64(8 + 8*ctxt.Arch.PtrSize)
   234  	writeHeader := func(ctxt *Link, s loader.Sym) {
   235  		header := ctxt.loader.MakeSymbolUpdater(s)
   236  
   237  		writeSymOffset := func(off int64, ws loader.Sym) int64 {
   238  			diff := ldr.SymValue(ws) - ldr.SymValue(s)
   239  			if diff <= 0 {
   240  				name := ldr.SymName(ws)
   241  				panic(fmt.Sprintf("expected runtime.pcheader(%x) to be placed before %s(%x)", ldr.SymValue(s), name, ldr.SymValue(ws)))
   242  			}
   243  			return header.SetUintptr(ctxt.Arch, off, uintptr(diff))
   244  		}
   245  
   246  		// Write header.
   247  		// Keep in sync with runtime/symtab.go:pcHeader and package debug/gosym.
   248  		header.SetUint32(ctxt.Arch, 0, 0xfffffff1)
   249  		header.SetUint8(ctxt.Arch, 6, uint8(ctxt.Arch.MinLC))
   250  		header.SetUint8(ctxt.Arch, 7, uint8(ctxt.Arch.PtrSize))
   251  		off := header.SetUint(ctxt.Arch, 8, uint64(state.nfunc))
   252  		off = header.SetUint(ctxt.Arch, off, uint64(state.nfiles))
   253  		if off != textStartOff {
   254  			panic(fmt.Sprintf("pcHeader textStartOff: %d != %d", off, textStartOff))
   255  		}
   256  		off += int64(ctxt.Arch.PtrSize) // skip runtimeText relocation
   257  		off = writeSymOffset(off, state.funcnametab)
   258  		off = writeSymOffset(off, state.cutab)
   259  		off = writeSymOffset(off, state.filetab)
   260  		off = writeSymOffset(off, state.pctab)
   261  		off = writeSymOffset(off, state.pclntab)
   262  		if off != size {
   263  			panic(fmt.Sprintf("pcHeader size: %d != %d", off, size))
   264  		}
   265  	}
   266  
   267  	state.pcheader = state.addGeneratedSym(ctxt, "runtime.pcheader", size, writeHeader)
   268  	// Create the runtimeText relocation.
   269  	sb := ldr.MakeSymbolUpdater(state.pcheader)
   270  	sb.SetAddr(ctxt.Arch, textStartOff, ldr.Lookup("runtime.text", 0))
   271  }
   272  
   273  // walkFuncs iterates over the funcs, calling a function for each unique
   274  // function and inlined function.
   275  func walkFuncs(ctxt *Link, funcs []loader.Sym, f func(loader.Sym)) {
   276  	ldr := ctxt.loader
   277  	seen := make(map[loader.Sym]struct{})
   278  	for _, s := range funcs {
   279  		if _, ok := seen[s]; !ok {
   280  			f(s)
   281  			seen[s] = struct{}{}
   282  		}
   283  
   284  		fi := ldr.FuncInfo(s)
   285  		if !fi.Valid() {
   286  			continue
   287  		}
   288  		fi.Preload()
   289  		for i, ni := 0, fi.NumInlTree(); i < int(ni); i++ {
   290  			call := fi.InlTree(i).Func
   291  			if _, ok := seen[call]; !ok {
   292  				f(call)
   293  				seen[call] = struct{}{}
   294  			}
   295  		}
   296  	}
   297  }
   298  
   299  // generateFuncnametab creates the function name table. Returns a map of
   300  // func symbol to the name offset in runtime.funcnamtab.
   301  func (state *pclntab) generateFuncnametab(ctxt *Link, funcs []loader.Sym) map[loader.Sym]uint32 {
   302  	nameOffsets := make(map[loader.Sym]uint32, state.nfunc)
   303  
   304  	// Write the null terminated strings.
   305  	writeFuncNameTab := func(ctxt *Link, s loader.Sym) {
   306  		symtab := ctxt.loader.MakeSymbolUpdater(s)
   307  		for s, off := range nameOffsets {
   308  			symtab.AddCStringAt(int64(off), ctxt.loader.SymName(s))
   309  		}
   310  	}
   311  
   312  	// Loop through the CUs, and calculate the size needed.
   313  	var size int64
   314  	walkFuncs(ctxt, funcs, func(s loader.Sym) {
   315  		nameOffsets[s] = uint32(size)
   316  		size += int64(len(ctxt.loader.SymName(s)) + 1) // NULL terminate
   317  	})
   318  
   319  	state.funcnametab = state.addGeneratedSym(ctxt, "runtime.funcnametab", size, writeFuncNameTab)
   320  	return nameOffsets
   321  }
   322  
   323  // walkFilenames walks funcs, calling a function for each filename used in each
   324  // function's line table.
   325  func walkFilenames(ctxt *Link, funcs []loader.Sym, f func(*sym.CompilationUnit, goobj.CUFileIndex)) {
   326  	ldr := ctxt.loader
   327  
   328  	// Loop through all functions, finding the filenames we need.
   329  	for _, s := range funcs {
   330  		fi := ldr.FuncInfo(s)
   331  		if !fi.Valid() {
   332  			continue
   333  		}
   334  		fi.Preload()
   335  
   336  		cu := ldr.SymUnit(s)
   337  		for i, nf := 0, int(fi.NumFile()); i < nf; i++ {
   338  			f(cu, fi.File(i))
   339  		}
   340  		for i, ninl := 0, int(fi.NumInlTree()); i < ninl; i++ {
   341  			call := fi.InlTree(i)
   342  			f(cu, call.File)
   343  		}
   344  	}
   345  }
   346  
   347  // generateFilenameTabs creates LUTs needed for filename lookup. Returns a slice
   348  // of the index at which each CU begins in runtime.cutab.
   349  //
   350  // Function objects keep track of the files they reference to print the stack.
   351  // This function creates a per-CU list of filenames if CU[M] references
   352  // files[1-N], the following is generated:
   353  //
   354  //	runtime.cutab:
   355  //	  CU[M]
   356  //	   offsetToFilename[0]
   357  //	   offsetToFilename[1]
   358  //	   ..
   359  //
   360  //	runtime.filetab
   361  //	   filename[0]
   362  //	   filename[1]
   363  //
   364  // Looking up a filename then becomes:
   365  //  0. Given a func, and filename index [K]
   366  //  1. Get Func.CUIndex:       M := func.cuOffset
   367  //  2. Find filename offset:   fileOffset := runtime.cutab[M+K]
   368  //  3. Get the filename:       getcstring(runtime.filetab[fileOffset])
   369  func (state *pclntab) generateFilenameTabs(ctxt *Link, compUnits []*sym.CompilationUnit, funcs []loader.Sym) []uint32 {
   370  	// On a per-CU basis, keep track of all the filenames we need.
   371  	//
   372  	// Note, that we store the filenames in a separate section in the object
   373  	// files, and deduplicate based on the actual value. It would be better to
   374  	// store the filenames as symbols, using content addressable symbols (and
   375  	// then not loading extra filenames), and just use the hash value of the
   376  	// symbol name to do this cataloging.
   377  	//
   378  	// TODO: Store filenames as symbols. (Note this would be easiest if you
   379  	// also move strings to ALWAYS using the larger content addressable hash
   380  	// function, and use that hash value for uniqueness testing.)
   381  	cuEntries := make([]goobj.CUFileIndex, len(compUnits))
   382  	fileOffsets := make(map[string]uint32)
   383  
   384  	// Walk the filenames.
   385  	// We store the total filename string length we need to load, and the max
   386  	// file index we've seen per CU so we can calculate how large the
   387  	// CU->global table needs to be.
   388  	var fileSize int64
   389  	walkFilenames(ctxt, funcs, func(cu *sym.CompilationUnit, i goobj.CUFileIndex) {
   390  		// Note we use the raw filename for lookup, but use the expanded filename
   391  		// when we save the size.
   392  		filename := cu.FileTable[i]
   393  		if _, ok := fileOffsets[filename]; !ok {
   394  			fileOffsets[filename] = uint32(fileSize)
   395  			fileSize += int64(len(expandFile(filename)) + 1) // NULL terminate
   396  		}
   397  
   398  		// Find the maximum file index we've seen.
   399  		if cuEntries[cu.PclnIndex] < i+1 {
   400  			cuEntries[cu.PclnIndex] = i + 1 // Store max + 1
   401  		}
   402  	})
   403  
   404  	// Calculate the size of the runtime.cutab variable.
   405  	var totalEntries uint32
   406  	cuOffsets := make([]uint32, len(cuEntries))
   407  	for i, entries := range cuEntries {
   408  		// Note, cutab is a slice of uint32, so an offset to a cu's entry is just the
   409  		// running total of all cu indices we've needed to store so far, not the
   410  		// number of bytes we've stored so far.
   411  		cuOffsets[i] = totalEntries
   412  		totalEntries += uint32(entries)
   413  	}
   414  
   415  	// Write cutab.
   416  	writeCutab := func(ctxt *Link, s loader.Sym) {
   417  		sb := ctxt.loader.MakeSymbolUpdater(s)
   418  
   419  		var off int64
   420  		for i, max := range cuEntries {
   421  			// Write the per CU LUT.
   422  			cu := compUnits[i]
   423  			for j := goobj.CUFileIndex(0); j < max; j++ {
   424  				fileOffset, ok := fileOffsets[cu.FileTable[j]]
   425  				if !ok {
   426  					// We're looping through all possible file indices. It's possible a file's
   427  					// been deadcode eliminated, and although it's a valid file in the CU, it's
   428  					// not needed in this binary. When that happens, use an invalid offset.
   429  					fileOffset = ^uint32(0)
   430  				}
   431  				off = sb.SetUint32(ctxt.Arch, off, fileOffset)
   432  			}
   433  		}
   434  	}
   435  	state.cutab = state.addGeneratedSym(ctxt, "runtime.cutab", int64(totalEntries*4), writeCutab)
   436  
   437  	// Write filetab.
   438  	writeFiletab := func(ctxt *Link, s loader.Sym) {
   439  		sb := ctxt.loader.MakeSymbolUpdater(s)
   440  
   441  		// Write the strings.
   442  		for filename, loc := range fileOffsets {
   443  			sb.AddStringAt(int64(loc), expandFile(filename))
   444  		}
   445  	}
   446  	state.nfiles = uint32(len(fileOffsets))
   447  	state.filetab = state.addGeneratedSym(ctxt, "runtime.filetab", fileSize, writeFiletab)
   448  
   449  	return cuOffsets
   450  }
   451  
   452  // generatePctab creates the runtime.pctab variable, holding all the
   453  // deduplicated pcdata.
   454  func (state *pclntab) generatePctab(ctxt *Link, funcs []loader.Sym) {
   455  	ldr := ctxt.loader
   456  
   457  	// Pctab offsets of 0 are considered invalid in the runtime. We respect
   458  	// that by just padding a single byte at the beginning of runtime.pctab,
   459  	// that way no real offsets can be zero.
   460  	size := int64(1)
   461  
   462  	// Walk the functions, finding offset to store each pcdata.
   463  	seen := make(map[loader.Sym]struct{})
   464  	saveOffset := func(pcSym loader.Sym) {
   465  		if _, ok := seen[pcSym]; !ok {
   466  			datSize := ldr.SymSize(pcSym)
   467  			if datSize != 0 {
   468  				ldr.SetSymValue(pcSym, size)
   469  			} else {
   470  				// Invalid PC data, record as zero.
   471  				ldr.SetSymValue(pcSym, 0)
   472  			}
   473  			size += datSize
   474  			seen[pcSym] = struct{}{}
   475  		}
   476  	}
   477  	var pcsp, pcline, pcfile, pcinline loader.Sym
   478  	var pcdata []loader.Sym
   479  	for _, s := range funcs {
   480  		fi := ldr.FuncInfo(s)
   481  		if !fi.Valid() {
   482  			continue
   483  		}
   484  		fi.Preload()
   485  		pcsp, pcfile, pcline, pcinline, pcdata = ldr.PcdataAuxs(s, pcdata)
   486  
   487  		pcSyms := []loader.Sym{pcsp, pcfile, pcline}
   488  		for _, pcSym := range pcSyms {
   489  			saveOffset(pcSym)
   490  		}
   491  		for _, pcSym := range pcdata {
   492  			saveOffset(pcSym)
   493  		}
   494  		if fi.NumInlTree() > 0 {
   495  			saveOffset(pcinline)
   496  		}
   497  	}
   498  
   499  	// TODO: There is no reason we need a generator for this variable, and it
   500  	// could be moved to a carrier symbol. However, carrier symbols containing
   501  	// carrier symbols don't work yet (as of Aug 2020). Once this is fixed,
   502  	// runtime.pctab could just be a carrier sym.
   503  	writePctab := func(ctxt *Link, s loader.Sym) {
   504  		ldr := ctxt.loader
   505  		sb := ldr.MakeSymbolUpdater(s)
   506  		for sym := range seen {
   507  			sb.SetBytesAt(ldr.SymValue(sym), ldr.Data(sym))
   508  		}
   509  	}
   510  
   511  	state.pctab = state.addGeneratedSym(ctxt, "runtime.pctab", size, writePctab)
   512  }
   513  
   514  // numPCData returns the number of PCData syms for the FuncInfo.
   515  // NB: Preload must be called on valid FuncInfos before calling this function.
   516  func numPCData(ldr *loader.Loader, s loader.Sym, fi loader.FuncInfo) uint32 {
   517  	if !fi.Valid() {
   518  		return 0
   519  	}
   520  	numPCData := uint32(ldr.NumPcdata(s))
   521  	if fi.NumInlTree() > 0 {
   522  		if numPCData < abi.PCDATA_InlTreeIndex+1 {
   523  			numPCData = abi.PCDATA_InlTreeIndex + 1
   524  		}
   525  	}
   526  	return numPCData
   527  }
   528  
   529  // generateFunctab creates the runtime.functab
   530  //
   531  // runtime.functab contains two things:
   532  //
   533  //   - pc->func look up table.
   534  //   - array of func objects, interleaved with pcdata and funcdata
   535  func (state *pclntab) generateFunctab(ctxt *Link, funcs []loader.Sym, inlSyms map[loader.Sym]loader.Sym, cuOffsets []uint32, nameOffsets map[loader.Sym]uint32) {
   536  	// Calculate the size of the table.
   537  	size, startLocations := state.calculateFunctabSize(ctxt, funcs)
   538  	writePcln := func(ctxt *Link, s loader.Sym) {
   539  		ldr := ctxt.loader
   540  		sb := ldr.MakeSymbolUpdater(s)
   541  		// Write the data.
   542  		writePCToFunc(ctxt, sb, funcs, startLocations)
   543  		writeFuncs(ctxt, sb, funcs, inlSyms, startLocations, cuOffsets, nameOffsets)
   544  	}
   545  	state.pclntab = state.addGeneratedSym(ctxt, "runtime.functab", size, writePcln)
   546  }
   547  
   548  // funcData returns the funcdata and offsets for the FuncInfo.
   549  // The funcdata are written into runtime.functab after each func
   550  // object. This is a helper function to make querying the FuncInfo object
   551  // cleaner.
   552  //
   553  // NB: Preload must be called on the FuncInfo before calling.
   554  // NB: fdSyms is used as scratch space.
   555  func funcData(ldr *loader.Loader, s loader.Sym, fi loader.FuncInfo, inlSym loader.Sym, fdSyms []loader.Sym) []loader.Sym {
   556  	fdSyms = fdSyms[:0]
   557  	if fi.Valid() {
   558  		fdSyms = ldr.Funcdata(s, fdSyms)
   559  		if fi.NumInlTree() > 0 {
   560  			if len(fdSyms) < abi.FUNCDATA_InlTree+1 {
   561  				fdSyms = append(fdSyms, make([]loader.Sym, abi.FUNCDATA_InlTree+1-len(fdSyms))...)
   562  			}
   563  			fdSyms[abi.FUNCDATA_InlTree] = inlSym
   564  		}
   565  	}
   566  	return fdSyms
   567  }
   568  
   569  // calculateFunctabSize calculates the size of the pclntab, and the offsets in
   570  // the output buffer for individual func entries.
   571  func (state pclntab) calculateFunctabSize(ctxt *Link, funcs []loader.Sym) (int64, []uint32) {
   572  	ldr := ctxt.loader
   573  	startLocations := make([]uint32, len(funcs))
   574  
   575  	// Allocate space for the pc->func table. This structure consists of a pc offset
   576  	// and an offset to the func structure. After that, we have a single pc
   577  	// value that marks the end of the last function in the binary.
   578  	size := int64(int(state.nfunc)*2*4 + 4)
   579  
   580  	// Now find the space for the func objects. We do this in a running manner,
   581  	// so that we can find individual starting locations.
   582  	for i, s := range funcs {
   583  		size = Rnd(size, int64(ctxt.Arch.PtrSize))
   584  		startLocations[i] = uint32(size)
   585  		fi := ldr.FuncInfo(s)
   586  		size += funcSize
   587  		if fi.Valid() {
   588  			fi.Preload()
   589  			numFuncData := ldr.NumFuncdata(s)
   590  			if fi.NumInlTree() > 0 {
   591  				if numFuncData < abi.FUNCDATA_InlTree+1 {
   592  					numFuncData = abi.FUNCDATA_InlTree + 1
   593  				}
   594  			}
   595  			size += int64(numPCData(ldr, s, fi) * 4)
   596  			size += int64(numFuncData * 4)
   597  		}
   598  	}
   599  
   600  	return size, startLocations
   601  }
   602  
   603  // writePCToFunc writes the PC->func lookup table.
   604  func writePCToFunc(ctxt *Link, sb *loader.SymbolBuilder, funcs []loader.Sym, startLocations []uint32) {
   605  	ldr := ctxt.loader
   606  	textStart := ldr.SymValue(ldr.Lookup("runtime.text", 0))
   607  	pcOff := func(s loader.Sym) uint32 {
   608  		off := ldr.SymValue(s) - textStart
   609  		if off < 0 {
   610  			panic(fmt.Sprintf("expected func %s(%x) to be placed at or after textStart (%x)", ldr.SymName(s), ldr.SymValue(s), textStart))
   611  		}
   612  		return uint32(off)
   613  	}
   614  	for i, s := range funcs {
   615  		sb.SetUint32(ctxt.Arch, int64(i*2*4), pcOff(s))
   616  		sb.SetUint32(ctxt.Arch, int64((i*2+1)*4), startLocations[i])
   617  	}
   618  
   619  	// Final entry of table is just end pc offset.
   620  	lastFunc := funcs[len(funcs)-1]
   621  	sb.SetUint32(ctxt.Arch, int64(len(funcs))*2*4, pcOff(lastFunc)+uint32(ldr.SymSize(lastFunc)))
   622  }
   623  
   624  // writeFuncs writes the func structures and pcdata to runtime.functab.
   625  func writeFuncs(ctxt *Link, sb *loader.SymbolBuilder, funcs []loader.Sym, inlSyms map[loader.Sym]loader.Sym, startLocations, cuOffsets []uint32, nameOffsets map[loader.Sym]uint32) {
   626  	ldr := ctxt.loader
   627  	deferReturnSym := ldr.Lookup("runtime.deferreturn", abiInternalVer)
   628  	gofunc := ldr.Lookup("go:func.*", 0)
   629  	gofuncBase := ldr.SymValue(gofunc)
   630  	textStart := ldr.SymValue(ldr.Lookup("runtime.text", 0))
   631  	funcdata := []loader.Sym{}
   632  	var pcsp, pcfile, pcline, pcinline loader.Sym
   633  	var pcdata []loader.Sym
   634  
   635  	// Write the individual func objects.
   636  	for i, s := range funcs {
   637  		startLine := int32(0)
   638  		fi := ldr.FuncInfo(s)
   639  		if fi.Valid() {
   640  			fi.Preload()
   641  			pcsp, pcfile, pcline, pcinline, pcdata = ldr.PcdataAuxs(s, pcdata)
   642  			startLine = fi.StartLine()
   643  		}
   644  
   645  		off := int64(startLocations[i])
   646  		// entryOff uint32 (offset of func entry PC from textStart)
   647  		entryOff := ldr.SymValue(s) - textStart
   648  		if entryOff < 0 {
   649  			panic(fmt.Sprintf("expected func %s(%x) to be placed before or at textStart (%x)", ldr.SymName(s), ldr.SymValue(s), textStart))
   650  		}
   651  		off = sb.SetUint32(ctxt.Arch, off, uint32(entryOff))
   652  
   653  		// nameOff int32
   654  		nameOff, ok := nameOffsets[s]
   655  		if !ok {
   656  			panic("couldn't find function name offset")
   657  		}
   658  		off = sb.SetUint32(ctxt.Arch, off, uint32(nameOff))
   659  
   660  		// args int32
   661  		// TODO: Move into funcinfo.
   662  		args := uint32(0)
   663  		if fi.Valid() {
   664  			args = uint32(fi.Args())
   665  		}
   666  		off = sb.SetUint32(ctxt.Arch, off, args)
   667  
   668  		// deferreturn
   669  		deferreturn := computeDeferReturn(ctxt, deferReturnSym, s)
   670  		off = sb.SetUint32(ctxt.Arch, off, deferreturn)
   671  
   672  		// pcdata
   673  		if fi.Valid() {
   674  			off = sb.SetUint32(ctxt.Arch, off, uint32(ldr.SymValue(pcsp)))
   675  			off = sb.SetUint32(ctxt.Arch, off, uint32(ldr.SymValue(pcfile)))
   676  			off = sb.SetUint32(ctxt.Arch, off, uint32(ldr.SymValue(pcline)))
   677  		} else {
   678  			off += 12
   679  		}
   680  		off = sb.SetUint32(ctxt.Arch, off, uint32(numPCData(ldr, s, fi)))
   681  
   682  		// Store the offset to compilation unit's file table.
   683  		cuIdx := ^uint32(0)
   684  		if cu := ldr.SymUnit(s); cu != nil {
   685  			cuIdx = cuOffsets[cu.PclnIndex]
   686  		}
   687  		off = sb.SetUint32(ctxt.Arch, off, cuIdx)
   688  
   689  		// startLine int32
   690  		off = sb.SetUint32(ctxt.Arch, off, uint32(startLine))
   691  
   692  		// funcID uint8
   693  		var funcID abi.FuncID
   694  		if fi.Valid() {
   695  			funcID = fi.FuncID()
   696  		}
   697  		off = sb.SetUint8(ctxt.Arch, off, uint8(funcID))
   698  
   699  		// flag uint8
   700  		var flag abi.FuncFlag
   701  		if fi.Valid() {
   702  			flag = fi.FuncFlag()
   703  		}
   704  		off = sb.SetUint8(ctxt.Arch, off, uint8(flag))
   705  
   706  		off += 1 // pad
   707  
   708  		// nfuncdata must be the final entry.
   709  		funcdata = funcData(ldr, s, fi, 0, funcdata)
   710  		off = sb.SetUint8(ctxt.Arch, off, uint8(len(funcdata)))
   711  
   712  		// Output the pcdata.
   713  		if fi.Valid() {
   714  			for j, pcSym := range pcdata {
   715  				sb.SetUint32(ctxt.Arch, off+int64(j*4), uint32(ldr.SymValue(pcSym)))
   716  			}
   717  			if fi.NumInlTree() > 0 {
   718  				sb.SetUint32(ctxt.Arch, off+abi.PCDATA_InlTreeIndex*4, uint32(ldr.SymValue(pcinline)))
   719  			}
   720  		}
   721  
   722  		// Write funcdata refs as offsets from go:func.* and go:funcrel.*.
   723  		funcdata = funcData(ldr, s, fi, inlSyms[s], funcdata)
   724  		// Missing funcdata will be ^0. See runtime/symtab.go:funcdata.
   725  		off = int64(startLocations[i] + funcSize + numPCData(ldr, s, fi)*4)
   726  		for j := range funcdata {
   727  			dataoff := off + int64(4*j)
   728  			fdsym := funcdata[j]
   729  
   730  			// cmd/internal/obj optimistically populates ArgsPointerMaps and
   731  			// ArgInfo for assembly functions, hoping that the compiler will
   732  			// emit appropriate symbols from their Go stub declarations. If
   733  			// it didn't though, just ignore it.
   734  			//
   735  			// TODO(cherryyz): Fix arg map generation (see discussion on CL 523335).
   736  			if fdsym != 0 && (j == abi.FUNCDATA_ArgsPointerMaps || j == abi.FUNCDATA_ArgInfo) && ldr.IsFromAssembly(s) && ldr.Data(fdsym) == nil {
   737  				fdsym = 0
   738  			}
   739  
   740  			if fdsym == 0 {
   741  				sb.SetUint32(ctxt.Arch, dataoff, ^uint32(0)) // ^0 is a sentinel for "no value"
   742  				continue
   743  			}
   744  
   745  			if outer := ldr.OuterSym(fdsym); outer != gofunc {
   746  				panic(fmt.Sprintf("bad carrier sym for symbol %s (funcdata %s#%d), want go:func.* got %s", ldr.SymName(fdsym), ldr.SymName(s), j, ldr.SymName(outer)))
   747  			}
   748  			sb.SetUint32(ctxt.Arch, dataoff, uint32(ldr.SymValue(fdsym)-gofuncBase))
   749  		}
   750  	}
   751  }
   752  
   753  // pclntab initializes the pclntab symbol with
   754  // runtime function and file name information.
   755  
   756  // pclntab generates the pcln table for the link output.
   757  func (ctxt *Link) pclntab(container loader.Bitmap) *pclntab {
   758  	// Go 1.2's symtab layout is documented in golang.org/s/go12symtab, but the
   759  	// layout and data has changed since that time.
   760  	//
   761  	// As of August 2020, here's the layout of pclntab:
   762  	//
   763  	//  .gopclntab/__gopclntab [elf/macho section]
   764  	//    runtime.pclntab
   765  	//      Carrier symbol for the entire pclntab section.
   766  	//
   767  	//      runtime.pcheader  (see: runtime/symtab.go:pcHeader)
   768  	//        8-byte magic
   769  	//        nfunc [thearch.ptrsize bytes]
   770  	//        offset to runtime.funcnametab from the beginning of runtime.pcheader
   771  	//        offset to runtime.pclntab_old from beginning of runtime.pcheader
   772  	//
   773  	//      runtime.funcnametab
   774  	//        []list of null terminated function names
   775  	//
   776  	//      runtime.cutab
   777  	//        for i=0..#CUs
   778  	//          for j=0..#max used file index in CU[i]
   779  	//            uint32 offset into runtime.filetab for the filename[j]
   780  	//
   781  	//      runtime.filetab
   782  	//        []null terminated filename strings
   783  	//
   784  	//      runtime.pctab
   785  	//        []byte of deduplicated pc data.
   786  	//
   787  	//      runtime.functab
   788  	//        function table, alternating PC and offset to func struct [each entry thearch.ptrsize bytes]
   789  	//        end PC [thearch.ptrsize bytes]
   790  	//        func structures, pcdata offsets, func data.
   791  
   792  	state, compUnits, funcs := makePclntab(ctxt, container)
   793  
   794  	ldr := ctxt.loader
   795  	state.carrier = ldr.LookupOrCreateSym("runtime.pclntab", 0)
   796  	ldr.MakeSymbolUpdater(state.carrier).SetType(sym.SPCLNTAB)
   797  	ldr.SetAttrReachable(state.carrier, true)
   798  	setCarrierSym(sym.SPCLNTAB, state.carrier)
   799  
   800  	state.generatePCHeader(ctxt)
   801  	nameOffsets := state.generateFuncnametab(ctxt, funcs)
   802  	cuOffsets := state.generateFilenameTabs(ctxt, compUnits, funcs)
   803  	state.generatePctab(ctxt, funcs)
   804  	inlSyms := makeInlSyms(ctxt, funcs, nameOffsets)
   805  	state.generateFunctab(ctxt, funcs, inlSyms, cuOffsets, nameOffsets)
   806  
   807  	return state
   808  }
   809  
   810  func expandGoroot(s string) string {
   811  	const n = len("$GOROOT")
   812  	if len(s) >= n+1 && s[:n] == "$GOROOT" && (s[n] == '/' || s[n] == '\\') {
   813  		if final := buildcfg.GOROOT; final != "" {
   814  			return filepath.ToSlash(filepath.Join(final, s[n:]))
   815  		}
   816  	}
   817  	return s
   818  }
   819  
   820  const (
   821  	SUBBUCKETS    = 16
   822  	SUBBUCKETSIZE = abi.FuncTabBucketSize / SUBBUCKETS
   823  	NOIDX         = 0x7fffffff
   824  )
   825  
   826  // findfunctab generates a lookup table to quickly find the containing
   827  // function for a pc. See src/runtime/symtab.go:findfunc for details.
   828  func (ctxt *Link) findfunctab(state *pclntab, container loader.Bitmap) {
   829  	ldr := ctxt.loader
   830  
   831  	// find min and max address
   832  	min := ldr.SymValue(ctxt.Textp[0])
   833  	lastp := ctxt.Textp[len(ctxt.Textp)-1]
   834  	max := ldr.SymValue(lastp) + ldr.SymSize(lastp)
   835  
   836  	// for each subbucket, compute the minimum of all symbol indexes
   837  	// that map to that subbucket.
   838  	n := int32((max - min + SUBBUCKETSIZE - 1) / SUBBUCKETSIZE)
   839  
   840  	nbuckets := int32((max - min + abi.FuncTabBucketSize - 1) / abi.FuncTabBucketSize)
   841  
   842  	size := 4*int64(nbuckets) + int64(n)
   843  
   844  	writeFindFuncTab := func(_ *Link, s loader.Sym) {
   845  		t := ldr.MakeSymbolUpdater(s)
   846  
   847  		indexes := make([]int32, n)
   848  		for i := int32(0); i < n; i++ {
   849  			indexes[i] = NOIDX
   850  		}
   851  		idx := int32(0)
   852  		for i, s := range ctxt.Textp {
   853  			if !emitPcln(ctxt, s, container) {
   854  				continue
   855  			}
   856  			p := ldr.SymValue(s)
   857  			var e loader.Sym
   858  			i++
   859  			if i < len(ctxt.Textp) {
   860  				e = ctxt.Textp[i]
   861  			}
   862  			for e != 0 && !emitPcln(ctxt, e, container) && i < len(ctxt.Textp) {
   863  				e = ctxt.Textp[i]
   864  				i++
   865  			}
   866  			q := max
   867  			if e != 0 {
   868  				q = ldr.SymValue(e)
   869  			}
   870  
   871  			//fmt.Printf("%d: [%x %x] %s\n", idx, p, q, ldr.SymName(s))
   872  			for ; p < q; p += SUBBUCKETSIZE {
   873  				i = int((p - min) / SUBBUCKETSIZE)
   874  				if indexes[i] > idx {
   875  					indexes[i] = idx
   876  				}
   877  			}
   878  
   879  			i = int((q - 1 - min) / SUBBUCKETSIZE)
   880  			if indexes[i] > idx {
   881  				indexes[i] = idx
   882  			}
   883  			idx++
   884  		}
   885  
   886  		// fill in table
   887  		for i := int32(0); i < nbuckets; i++ {
   888  			base := indexes[i*SUBBUCKETS]
   889  			if base == NOIDX {
   890  				Errorf(nil, "hole in findfunctab")
   891  			}
   892  			t.SetUint32(ctxt.Arch, int64(i)*(4+SUBBUCKETS), uint32(base))
   893  			for j := int32(0); j < SUBBUCKETS && i*SUBBUCKETS+j < n; j++ {
   894  				idx = indexes[i*SUBBUCKETS+j]
   895  				if idx == NOIDX {
   896  					Errorf(nil, "hole in findfunctab")
   897  				}
   898  				if idx-base >= 256 {
   899  					Errorf(nil, "too many functions in a findfunc bucket! %d/%d %d %d", i, nbuckets, j, idx-base)
   900  				}
   901  
   902  				t.SetUint8(ctxt.Arch, int64(i)*(4+SUBBUCKETS)+4+int64(j), uint8(idx-base))
   903  			}
   904  		}
   905  	}
   906  
   907  	state.findfunctab = ctxt.createGeneratorSymbol("runtime.findfunctab", 0, sym.SRODATA, size, writeFindFuncTab)
   908  	ldr.SetAttrReachable(state.findfunctab, true)
   909  	ldr.SetAttrLocal(state.findfunctab, true)
   910  }
   911  
   912  // findContainerSyms returns a bitmap, indexed by symbol number, where there's
   913  // a 1 for every container symbol.
   914  func (ctxt *Link) findContainerSyms() loader.Bitmap {
   915  	ldr := ctxt.loader
   916  	container := loader.MakeBitmap(ldr.NSym())
   917  	// Find container symbols and mark them as such.
   918  	for _, s := range ctxt.Textp {
   919  		outer := ldr.OuterSym(s)
   920  		if outer != 0 {
   921  			container.Set(outer)
   922  		}
   923  	}
   924  	return container
   925  }
   926
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