pcln.go

Documentation: cmd/internal/obj

     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 obj
     6  
     7  import (
     8  	"cmd/internal/goobj"
     9  	"cmd/internal/objabi"
    10  	"encoding/binary"
    11  	"fmt"
    12  	"log"
    13  )
    14  
    15  // funcpctab writes to dst a pc-value table mapping the code in func to the values
    16  // returned by valfunc parameterized by arg. The invocation of valfunc to update the
    17  // current value is, for each p,
    18  //
    19  //	sym = valfunc(func, p, 0, arg);
    20  //	record sym.P as value at p->pc;
    21  //	sym = valfunc(func, p, 1, arg);
    22  //
    23  // where func is the function, val is the current value, p is the instruction being
    24  // considered, and arg can be used to further parameterize valfunc.
    25  func funcpctab(ctxt *Link, func_ *LSym, desc string, valfunc func(*Link, *LSym, int32, *Prog, int32, interface{}) int32, arg interface{}) *LSym {
    26  	dbg := desc == ctxt.Debugpcln
    27  	dst := []byte{}
    28  	sym := &LSym{
    29  		Type:      objabi.SRODATA,
    30  		Attribute: AttrContentAddressable | AttrPcdata,
    31  	}
    32  
    33  	if dbg {
    34  		ctxt.Logf("funcpctab %s [valfunc=%s]\n", func_.Name, desc)
    35  	}
    36  
    37  	val := int32(-1)
    38  	oldval := val
    39  	fn := func_.Func()
    40  	if fn.Text == nil {
    41  		// Return the empty symbol we've built so far.
    42  		return sym
    43  	}
    44  
    45  	pc := fn.Text.Pc
    46  
    47  	if dbg {
    48  		ctxt.Logf("%6x %6d %v\n", uint64(pc), val, fn.Text)
    49  	}
    50  
    51  	buf := make([]byte, binary.MaxVarintLen32)
    52  	started := false
    53  	for p := fn.Text; p != nil; p = p.Link {
    54  		// Update val. If it's not changing, keep going.
    55  		val = valfunc(ctxt, func_, val, p, 0, arg)
    56  
    57  		if val == oldval && started {
    58  			val = valfunc(ctxt, func_, val, p, 1, arg)
    59  			if dbg {
    60  				ctxt.Logf("%6x %6s %v\n", uint64(p.Pc), "", p)
    61  			}
    62  			continue
    63  		}
    64  
    65  		// If the pc of the next instruction is the same as the
    66  		// pc of this instruction, this instruction is not a real
    67  		// instruction. Keep going, so that we only emit a delta
    68  		// for a true instruction boundary in the program.
    69  		if p.Link != nil && p.Link.Pc == p.Pc {
    70  			val = valfunc(ctxt, func_, val, p, 1, arg)
    71  			if dbg {
    72  				ctxt.Logf("%6x %6s %v\n", uint64(p.Pc), "", p)
    73  			}
    74  			continue
    75  		}
    76  
    77  		// The table is a sequence of (value, pc) pairs, where each
    78  		// pair states that the given value is in effect from the current position
    79  		// up to the given pc, which becomes the new current position.
    80  		// To generate the table as we scan over the program instructions,
    81  		// we emit a "(value" when pc == func->value, and then
    82  		// each time we observe a change in value we emit ", pc) (value".
    83  		// When the scan is over, we emit the closing ", pc)".
    84  		//
    85  		// The table is delta-encoded. The value deltas are signed and
    86  		// transmitted in zig-zag form, where a complement bit is placed in bit 0,
    87  		// and the pc deltas are unsigned. Both kinds of deltas are sent
    88  		// as variable-length little-endian base-128 integers,
    89  		// where the 0x80 bit indicates that the integer continues.
    90  
    91  		if dbg {
    92  			ctxt.Logf("%6x %6d %v\n", uint64(p.Pc), val, p)
    93  		}
    94  
    95  		if started {
    96  			pcdelta := (p.Pc - pc) / int64(ctxt.Arch.MinLC)
    97  			n := binary.PutUvarint(buf, uint64(pcdelta))
    98  			dst = append(dst, buf[:n]...)
    99  			pc = p.Pc
   100  		}
   101  
   102  		delta := val - oldval
   103  		n := binary.PutVarint(buf, int64(delta))
   104  		dst = append(dst, buf[:n]...)
   105  		oldval = val
   106  		started = true
   107  		val = valfunc(ctxt, func_, val, p, 1, arg)
   108  	}
   109  
   110  	if started {
   111  		if dbg {
   112  			ctxt.Logf("%6x done\n", uint64(fn.Text.Pc+func_.Size))
   113  		}
   114  		v := (func_.Size - pc) / int64(ctxt.Arch.MinLC)
   115  		if v < 0 {
   116  			ctxt.Diag("negative pc offset: %v", v)
   117  		}
   118  		n := binary.PutUvarint(buf, uint64(v))
   119  		dst = append(dst, buf[:n]...)
   120  		// add terminating varint-encoded 0, which is just 0
   121  		dst = append(dst, 0)
   122  	}
   123  
   124  	if dbg {
   125  		ctxt.Logf("wrote %d bytes to %p\n", len(dst), dst)
   126  		for _, p := range dst {
   127  			ctxt.Logf(" %02x", p)
   128  		}
   129  		ctxt.Logf("\n")
   130  	}
   131  
   132  	sym.Size = int64(len(dst))
   133  	sym.P = dst
   134  	return sym
   135  }
   136  
   137  // pctofileline computes either the file number (arg == 0)
   138  // or the line number (arg == 1) to use at p.
   139  // Because p.Pos applies to p, phase == 0 (before p)
   140  // takes care of the update.
   141  func pctofileline(ctxt *Link, sym *LSym, oldval int32, p *Prog, phase int32, arg interface{}) int32 {
   142  	if p.As == ATEXT || p.As == ANOP || p.Pos.Line() == 0 || phase == 1 {
   143  		return oldval
   144  	}
   145  	f, l := ctxt.getFileIndexAndLine(p.Pos)
   146  	if arg == nil {
   147  		return l
   148  	}
   149  	pcln := arg.(*Pcln)
   150  	pcln.UsedFiles[goobj.CUFileIndex(f)] = struct{}{}
   151  	return int32(f)
   152  }
   153  
   154  // pcinlineState holds the state used to create a function's inlining
   155  // tree and the PC-value table that maps PCs to nodes in that tree.
   156  type pcinlineState struct {
   157  	globalToLocal map[int]int
   158  	localTree     InlTree
   159  }
   160  
   161  // addBranch adds a branch from the global inlining tree in ctxt to
   162  // the function's local inlining tree, returning the index in the local tree.
   163  func (s *pcinlineState) addBranch(ctxt *Link, globalIndex int) int {
   164  	if globalIndex < 0 {
   165  		return -1
   166  	}
   167  
   168  	localIndex, ok := s.globalToLocal[globalIndex]
   169  	if ok {
   170  		return localIndex
   171  	}
   172  
   173  	// Since tracebacks don't include column information, we could
   174  	// use one node for multiple calls of the same function on the
   175  	// same line (e.g., f(x) + f(y)). For now, we use one node for
   176  	// each inlined call.
   177  	call := ctxt.InlTree.nodes[globalIndex]
   178  	call.Parent = s.addBranch(ctxt, call.Parent)
   179  	localIndex = len(s.localTree.nodes)
   180  	s.localTree.nodes = append(s.localTree.nodes, call)
   181  	s.globalToLocal[globalIndex] = localIndex
   182  	return localIndex
   183  }
   184  
   185  func (s *pcinlineState) setParentPC(ctxt *Link, globalIndex int, pc int32) {
   186  	localIndex, ok := s.globalToLocal[globalIndex]
   187  	if !ok {
   188  		// We know where to unwind to when we need to unwind a body identified
   189  		// by globalIndex. But there may be no instructions generated by that
   190  		// body (it's empty, or its instructions were CSEd with other things, etc.).
   191  		// In that case, we don't need an unwind entry.
   192  		// TODO: is this really right? Seems to happen a whole lot...
   193  		return
   194  	}
   195  	s.localTree.setParentPC(localIndex, pc)
   196  }
   197  
   198  // pctoinline computes the index into the local inlining tree to use at p.
   199  // If p is not the result of inlining, pctoinline returns -1. Because p.Pos
   200  // applies to p, phase == 0 (before p) takes care of the update.
   201  func (s *pcinlineState) pctoinline(ctxt *Link, sym *LSym, oldval int32, p *Prog, phase int32, arg interface{}) int32 {
   202  	if phase == 1 {
   203  		return oldval
   204  	}
   205  
   206  	posBase := ctxt.PosTable.Pos(p.Pos).Base()
   207  	if posBase == nil {
   208  		return -1
   209  	}
   210  
   211  	globalIndex := posBase.InliningIndex()
   212  	if globalIndex < 0 {
   213  		return -1
   214  	}
   215  
   216  	if s.globalToLocal == nil {
   217  		s.globalToLocal = make(map[int]int)
   218  	}
   219  
   220  	return int32(s.addBranch(ctxt, globalIndex))
   221  }
   222  
   223  // pctospadj computes the sp adjustment in effect.
   224  // It is oldval plus any adjustment made by p itself.
   225  // The adjustment by p takes effect only after p, so we
   226  // apply the change during phase == 1.
   227  func pctospadj(ctxt *Link, sym *LSym, oldval int32, p *Prog, phase int32, arg interface{}) int32 {
   228  	if oldval == -1 { // starting
   229  		oldval = 0
   230  	}
   231  	if phase == 0 {
   232  		return oldval
   233  	}
   234  	if oldval+p.Spadj < -10000 || oldval+p.Spadj > 1100000000 {
   235  		ctxt.Diag("overflow in spadj: %d + %d = %d", oldval, p.Spadj, oldval+p.Spadj)
   236  		ctxt.DiagFlush()
   237  		log.Fatalf("bad code")
   238  	}
   239  
   240  	return oldval + p.Spadj
   241  }
   242  
   243  // pctopcdata computes the pcdata value in effect at p.
   244  // A PCDATA instruction sets the value in effect at future
   245  // non-PCDATA instructions.
   246  // Since PCDATA instructions have no width in the final code,
   247  // it does not matter which phase we use for the update.
   248  func pctopcdata(ctxt *Link, sym *LSym, oldval int32, p *Prog, phase int32, arg interface{}) int32 {
   249  	if phase == 0 || p.As != APCDATA || p.From.Offset != int64(arg.(uint32)) {
   250  		return oldval
   251  	}
   252  	if int64(int32(p.To.Offset)) != p.To.Offset {
   253  		ctxt.Diag("overflow in PCDATA instruction: %v", p)
   254  		ctxt.DiagFlush()
   255  		log.Fatalf("bad code")
   256  	}
   257  
   258  	return int32(p.To.Offset)
   259  }
   260  
   261  func linkpcln(ctxt *Link, cursym *LSym) {
   262  	pcln := &cursym.Func().Pcln
   263  	pcln.UsedFiles = make(map[goobj.CUFileIndex]struct{})
   264  
   265  	npcdata := 0
   266  	nfuncdata := 0
   267  	for p := cursym.Func().Text; p != nil; p = p.Link {
   268  		// Find the highest ID of any used PCDATA table. This ignores PCDATA table
   269  		// that consist entirely of "-1", since that's the assumed default value.
   270  		//   From.Offset is table ID
   271  		//   To.Offset is data
   272  		if p.As == APCDATA && p.From.Offset >= int64(npcdata) && p.To.Offset != -1 { // ignore -1 as we start at -1, if we only see -1, nothing changed
   273  			npcdata = int(p.From.Offset + 1)
   274  		}
   275  		// Find the highest ID of any FUNCDATA table.
   276  		//   From.Offset is table ID
   277  		if p.As == AFUNCDATA && p.From.Offset >= int64(nfuncdata) {
   278  			nfuncdata = int(p.From.Offset + 1)
   279  		}
   280  	}
   281  
   282  	pcln.Pcdata = make([]*LSym, npcdata)
   283  	pcln.Funcdata = make([]*LSym, nfuncdata)
   284  
   285  	pcln.Pcsp = funcpctab(ctxt, cursym, "pctospadj", pctospadj, nil)
   286  	pcln.Pcfile = funcpctab(ctxt, cursym, "pctofile", pctofileline, pcln)
   287  	pcln.Pcline = funcpctab(ctxt, cursym, "pctoline", pctofileline, nil)
   288  
   289  	// Check that all the Progs used as inline markers are still reachable.
   290  	// See issue #40473.
   291  	fn := cursym.Func()
   292  	inlMarkProgs := make(map[*Prog]struct{}, len(fn.InlMarks))
   293  	for _, inlMark := range fn.InlMarks {
   294  		inlMarkProgs[inlMark.p] = struct{}{}
   295  	}
   296  	for p := fn.Text; p != nil; p = p.Link {
   297  		delete(inlMarkProgs, p)
   298  	}
   299  	if len(inlMarkProgs) > 0 {
   300  		ctxt.Diag("one or more instructions used as inline markers are no longer reachable")
   301  	}
   302  
   303  	pcinlineState := new(pcinlineState)
   304  	pcln.Pcinline = funcpctab(ctxt, cursym, "pctoinline", pcinlineState.pctoinline, nil)
   305  	for _, inlMark := range fn.InlMarks {
   306  		pcinlineState.setParentPC(ctxt, int(inlMark.id), int32(inlMark.p.Pc))
   307  	}
   308  	pcln.InlTree = pcinlineState.localTree
   309  	if ctxt.Debugpcln == "pctoinline" && len(pcln.InlTree.nodes) > 0 {
   310  		ctxt.Logf("-- inlining tree for %s:\n", cursym)
   311  		dumpInlTree(ctxt, pcln.InlTree)
   312  		ctxt.Logf("--\n")
   313  	}
   314  
   315  	// tabulate which pc and func data we have.
   316  	havepc := make([]uint32, (npcdata+31)/32)
   317  	havefunc := make([]uint32, (nfuncdata+31)/32)
   318  	for p := fn.Text; p != nil; p = p.Link {
   319  		if p.As == AFUNCDATA {
   320  			if (havefunc[p.From.Offset/32]>>uint64(p.From.Offset%32))&1 != 0 {
   321  				ctxt.Diag("multiple definitions for FUNCDATA $%d", p.From.Offset)
   322  			}
   323  			havefunc[p.From.Offset/32] |= 1 << uint64(p.From.Offset%32)
   324  		}
   325  
   326  		if p.As == APCDATA && p.To.Offset != -1 {
   327  			havepc[p.From.Offset/32] |= 1 << uint64(p.From.Offset%32)
   328  		}
   329  	}
   330  
   331  	// pcdata.
   332  	for i := 0; i < npcdata; i++ {
   333  		if (havepc[i/32]>>uint(i%32))&1 == 0 {
   334  			// use an empty symbol.
   335  			pcln.Pcdata[i] = &LSym{
   336  				Type:      objabi.SRODATA,
   337  				Attribute: AttrContentAddressable | AttrPcdata,
   338  			}
   339  		} else {
   340  			pcln.Pcdata[i] = funcpctab(ctxt, cursym, "pctopcdata", pctopcdata, interface{}(uint32(i)))
   341  		}
   342  	}
   343  
   344  	// funcdata
   345  	if nfuncdata > 0 {
   346  		for p := fn.Text; p != nil; p = p.Link {
   347  			if p.As != AFUNCDATA {
   348  				continue
   349  			}
   350  			i := int(p.From.Offset)
   351  			if p.To.Type != TYPE_MEM || p.To.Offset != 0 {
   352  				panic(fmt.Sprintf("bad funcdata: %v", p))
   353  			}
   354  			pcln.Funcdata[i] = p.To.Sym
   355  		}
   356  	}
   357  }
   358  
   359  // PCIter iterates over encoded pcdata tables.
   360  type PCIter struct {
   361  	p       []byte
   362  	PC      uint32
   363  	NextPC  uint32
   364  	PCScale uint32
   365  	Value   int32
   366  	start   bool
   367  	Done    bool
   368  }
   369  
   370  // NewPCIter creates a PCIter with a scale factor for the PC step size.
   371  func NewPCIter(pcScale uint32) *PCIter {
   372  	it := new(PCIter)
   373  	it.PCScale = pcScale
   374  	return it
   375  }
   376  
   377  // Next advances it to the Next pc.
   378  func (it *PCIter) Next() {
   379  	it.PC = it.NextPC
   380  	if it.Done {
   381  		return
   382  	}
   383  	if len(it.p) == 0 {
   384  		it.Done = true
   385  		return
   386  	}
   387  
   388  	// Value delta
   389  	val, n := binary.Varint(it.p)
   390  	if n <= 0 {
   391  		log.Fatalf("bad Value varint in pciterNext: read %v", n)
   392  	}
   393  	it.p = it.p[n:]
   394  
   395  	if val == 0 && !it.start {
   396  		it.Done = true
   397  		return
   398  	}
   399  
   400  	it.start = false
   401  	it.Value += int32(val)
   402  
   403  	// pc delta
   404  	pc, n := binary.Uvarint(it.p)
   405  	if n <= 0 {
   406  		log.Fatalf("bad pc varint in pciterNext: read %v", n)
   407  	}
   408  	it.p = it.p[n:]
   409  
   410  	it.NextPC = it.PC + uint32(pc)*it.PCScale
   411  }
   412  
   413  // init prepares it to iterate over p,
   414  // and advances it to the first pc.
   415  func (it *PCIter) Init(p []byte) {
   416  	it.p = p
   417  	it.PC = 0
   418  	it.NextPC = 0
   419  	it.Value = -1
   420  	it.start = true
   421  	it.Done = false
   422  	it.Next()
   423  }
   424
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