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Source file src/cmd/internal/obj/pcln.go

Documentation: cmd/internal/obj

  // Copyright 2013 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package obj
  
  import "log"
  
  func addvarint(d *Pcdata, v uint32) {
  	for ; v >= 0x80; v >>= 7 {
  		d.P = append(d.P, uint8(v|0x80))
  	}
  	d.P = append(d.P, uint8(v))
  }
  
  // funcpctab writes to dst a pc-value table mapping the code in func to the values
  // returned by valfunc parameterized by arg. The invocation of valfunc to update the
  // current value is, for each p,
  //
  //	val = valfunc(func, val, p, 0, arg);
  //	record val as value at p->pc;
  //	val = valfunc(func, val, p, 1, arg);
  //
  // where func is the function, val is the current value, p is the instruction being
  // considered, and arg can be used to further parameterize valfunc.
  func funcpctab(ctxt *Link, dst *Pcdata, func_ *LSym, desc string, valfunc func(*Link, *LSym, int32, *Prog, int32, interface{}) int32, arg interface{}) {
  	dbg := desc == ctxt.Debugpcln
  
  	dst.P = dst.P[:0]
  
  	if dbg {
  		ctxt.Logf("funcpctab %s [valfunc=%s]\n", func_.Name, desc)
  	}
  
  	val := int32(-1)
  	oldval := val
  	if func_.Func.Text == nil {
  		return
  	}
  
  	pc := func_.Func.Text.Pc
  
  	if dbg {
  		ctxt.Logf("%6x %6d %v\n", uint64(pc), val, func_.Func.Text)
  	}
  
  	started := false
  	var delta uint32
  	for p := func_.Func.Text; p != nil; p = p.Link {
  		// Update val. If it's not changing, keep going.
  		val = valfunc(ctxt, func_, val, p, 0, arg)
  
  		if val == oldval && started {
  			val = valfunc(ctxt, func_, val, p, 1, arg)
  			if dbg {
  				ctxt.Logf("%6x %6s %v\n", uint64(p.Pc), "", p)
  			}
  			continue
  		}
  
  		// If the pc of the next instruction is the same as the
  		// pc of this instruction, this instruction is not a real
  		// instruction. Keep going, so that we only emit a delta
  		// for a true instruction boundary in the program.
  		if p.Link != nil && p.Link.Pc == p.Pc {
  			val = valfunc(ctxt, func_, val, p, 1, arg)
  			if dbg {
  				ctxt.Logf("%6x %6s %v\n", uint64(p.Pc), "", p)
  			}
  			continue
  		}
  
  		// The table is a sequence of (value, pc) pairs, where each
  		// pair states that the given value is in effect from the current position
  		// up to the given pc, which becomes the new current position.
  		// To generate the table as we scan over the program instructions,
  		// we emit a "(value" when pc == func->value, and then
  		// each time we observe a change in value we emit ", pc) (value".
  		// When the scan is over, we emit the closing ", pc)".
  		//
  		// The table is delta-encoded. The value deltas are signed and
  		// transmitted in zig-zag form, where a complement bit is placed in bit 0,
  		// and the pc deltas are unsigned. Both kinds of deltas are sent
  		// as variable-length little-endian base-128 integers,
  		// where the 0x80 bit indicates that the integer continues.
  
  		if dbg {
  			ctxt.Logf("%6x %6d %v\n", uint64(p.Pc), val, p)
  		}
  
  		if started {
  			addvarint(dst, uint32((p.Pc-pc)/int64(ctxt.Arch.MinLC)))
  			pc = p.Pc
  		}
  
  		delta = uint32(val) - uint32(oldval)
  		if delta>>31 != 0 {
  			delta = 1 | ^(delta << 1)
  		} else {
  			delta <<= 1
  		}
  		addvarint(dst, delta)
  		oldval = val
  		started = true
  		val = valfunc(ctxt, func_, val, p, 1, arg)
  	}
  
  	if started {
  		if dbg {
  			ctxt.Logf("%6x done\n", uint64(func_.Func.Text.Pc+func_.Size))
  		}
  		addvarint(dst, uint32((func_.Size-pc)/int64(ctxt.Arch.MinLC)))
  		addvarint(dst, 0) // terminator
  	}
  
  	if dbg {
  		ctxt.Logf("wrote %d bytes to %p\n", len(dst.P), dst)
  		for i := 0; i < len(dst.P); i++ {
  			ctxt.Logf(" %02x", dst.P[i])
  		}
  		ctxt.Logf("\n")
  	}
  }
  
  // pctofileline computes either the file number (arg == 0)
  // or the line number (arg == 1) to use at p.
  // Because p.Pos applies to p, phase == 0 (before p)
  // takes care of the update.
  func pctofileline(ctxt *Link, sym *LSym, oldval int32, p *Prog, phase int32, arg interface{}) int32 {
  	if p.As == ATEXT || p.As == ANOP || p.Pos.Line() == 0 || phase == 1 {
  		return oldval
  	}
  	f, l := linkgetlineFromPos(ctxt, p.Pos)
  	if arg == nil {
  		return l
  	}
  	pcln := arg.(*Pcln)
  
  	if f == pcln.Lastfile {
  		return int32(pcln.Lastindex)
  	}
  
  	for i, file := range pcln.File {
  		if file == f {
  			pcln.Lastfile = f
  			pcln.Lastindex = i
  			return int32(i)
  		}
  	}
  	i := len(pcln.File)
  	pcln.File = append(pcln.File, f)
  	pcln.Lastfile = f
  	pcln.Lastindex = i
  	return int32(i)
  }
  
  // pcinlineState holds the state used to create a function's inlining
  // tree and the PC-value table that maps PCs to nodes in that tree.
  type pcinlineState struct {
  	globalToLocal map[int]int
  	localTree     InlTree
  }
  
  // addBranch adds a branch from the global inlining tree in ctxt to
  // the function's local inlining tree, returning the index in the local tree.
  func (s *pcinlineState) addBranch(ctxt *Link, globalIndex int) int {
  	if globalIndex < 0 {
  		return -1
  	}
  
  	localIndex, ok := s.globalToLocal[globalIndex]
  	if ok {
  		return localIndex
  	}
  
  	// Since tracebacks don't include column information, we could
  	// use one node for multiple calls of the same function on the
  	// same line (e.g., f(x) + f(y)). For now, we use one node for
  	// each inlined call.
  	call := ctxt.InlTree.nodes[globalIndex]
  	call.Parent = s.addBranch(ctxt, call.Parent)
  	localIndex = len(s.localTree.nodes)
  	s.localTree.nodes = append(s.localTree.nodes, call)
  	s.globalToLocal[globalIndex] = localIndex
  	return localIndex
  }
  
  // pctoinline computes the index into the local inlining tree to use at p.
  // If p is not the result of inlining, pctoinline returns -1. Because p.Pos
  // applies to p, phase == 0 (before p) takes care of the update.
  func (s *pcinlineState) pctoinline(ctxt *Link, sym *LSym, oldval int32, p *Prog, phase int32, arg interface{}) int32 {
  	if phase == 1 {
  		return oldval
  	}
  
  	posBase := ctxt.PosTable.Pos(p.Pos).Base()
  	if posBase == nil {
  		return -1
  	}
  
  	globalIndex := posBase.InliningIndex()
  	if globalIndex < 0 {
  		return -1
  	}
  
  	if s.globalToLocal == nil {
  		s.globalToLocal = make(map[int]int)
  	}
  
  	return int32(s.addBranch(ctxt, globalIndex))
  }
  
  // pctospadj computes the sp adjustment in effect.
  // It is oldval plus any adjustment made by p itself.
  // The adjustment by p takes effect only after p, so we
  // apply the change during phase == 1.
  func pctospadj(ctxt *Link, sym *LSym, oldval int32, p *Prog, phase int32, arg interface{}) int32 {
  	if oldval == -1 { // starting
  		oldval = 0
  	}
  	if phase == 0 {
  		return oldval
  	}
  	if oldval+p.Spadj < -10000 || oldval+p.Spadj > 1100000000 {
  		ctxt.Diag("overflow in spadj: %d + %d = %d", oldval, p.Spadj, oldval+p.Spadj)
  		log.Fatalf("bad code")
  	}
  
  	return oldval + p.Spadj
  }
  
  // pctopcdata computes the pcdata value in effect at p.
  // A PCDATA instruction sets the value in effect at future
  // non-PCDATA instructions.
  // Since PCDATA instructions have no width in the final code,
  // it does not matter which phase we use for the update.
  func pctopcdata(ctxt *Link, sym *LSym, oldval int32, p *Prog, phase int32, arg interface{}) int32 {
  	if phase == 0 || p.As != APCDATA || p.From.Offset != int64(arg.(uint32)) {
  		return oldval
  	}
  	if int64(int32(p.To.Offset)) != p.To.Offset {
  		ctxt.Diag("overflow in PCDATA instruction: %v", p)
  		log.Fatalf("bad code")
  	}
  
  	return int32(p.To.Offset)
  }
  
  func linkpcln(ctxt *Link, cursym *LSym) {
  	pcln := &cursym.Func.Pcln
  
  	npcdata := 0
  	nfuncdata := 0
  	for p := cursym.Func.Text; p != nil; p = p.Link {
  		// Find the highest ID of any used PCDATA table. This ignores PCDATA table
  		// that consist entirely of "-1", since that's the assumed default value.
  		//   From.Offset is table ID
  		//   To.Offset is data
  		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
  			npcdata = int(p.From.Offset + 1)
  		}
  		// Find the highest ID of any FUNCDATA table.
  		//   From.Offset is table ID
  		if p.As == AFUNCDATA && p.From.Offset >= int64(nfuncdata) {
  			nfuncdata = int(p.From.Offset + 1)
  		}
  	}
  
  	pcln.Pcdata = make([]Pcdata, npcdata)
  	pcln.Pcdata = pcln.Pcdata[:npcdata]
  	pcln.Funcdata = make([]*LSym, nfuncdata)
  	pcln.Funcdataoff = make([]int64, nfuncdata)
  	pcln.Funcdataoff = pcln.Funcdataoff[:nfuncdata]
  
  	funcpctab(ctxt, &pcln.Pcsp, cursym, "pctospadj", pctospadj, nil)
  	funcpctab(ctxt, &pcln.Pcfile, cursym, "pctofile", pctofileline, pcln)
  	funcpctab(ctxt, &pcln.Pcline, cursym, "pctoline", pctofileline, nil)
  
  	pcinlineState := new(pcinlineState)
  	funcpctab(ctxt, &pcln.Pcinline, cursym, "pctoinline", pcinlineState.pctoinline, nil)
  	pcln.InlTree = pcinlineState.localTree
  	if ctxt.Debugpcln == "pctoinline" && len(pcln.InlTree.nodes) > 0 {
  		ctxt.Logf("-- inlining tree for %s:\n", cursym)
  		dumpInlTree(ctxt, pcln.InlTree)
  		ctxt.Logf("--\n")
  	}
  
  	// tabulate which pc and func data we have.
  	havepc := make([]uint32, (npcdata+31)/32)
  	havefunc := make([]uint32, (nfuncdata+31)/32)
  	for p := cursym.Func.Text; p != nil; p = p.Link {
  		if p.As == AFUNCDATA {
  			if (havefunc[p.From.Offset/32]>>uint64(p.From.Offset%32))&1 != 0 {
  				ctxt.Diag("multiple definitions for FUNCDATA $%d", p.From.Offset)
  			}
  			havefunc[p.From.Offset/32] |= 1 << uint64(p.From.Offset%32)
  		}
  
  		if p.As == APCDATA && p.To.Offset != -1 {
  			havepc[p.From.Offset/32] |= 1 << uint64(p.From.Offset%32)
  		}
  	}
  
  	// pcdata.
  	for i := 0; i < npcdata; i++ {
  		if (havepc[i/32]>>uint(i%32))&1 == 0 {
  			continue
  		}
  		funcpctab(ctxt, &pcln.Pcdata[i], cursym, "pctopcdata", pctopcdata, interface{}(uint32(i)))
  	}
  
  	// funcdata
  	if nfuncdata > 0 {
  		var i int
  		for p := cursym.Func.Text; p != nil; p = p.Link {
  			if p.As == AFUNCDATA {
  				i = int(p.From.Offset)
  				pcln.Funcdataoff[i] = p.To.Offset
  				if p.To.Type != TYPE_CONST {
  					// TODO: Dedup.
  					//funcdata_bytes += p->to.sym->size;
  					pcln.Funcdata[i] = p.To.Sym
  				}
  			}
  		}
  	}
  }
  

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