internal/ld/pcln.go

// 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 ld

import (
	"cmd/internal/obj"
	"cmd/internal/objabi"
	"cmd/internal/src"
	"cmd/internal/sys"
	"cmd/link/internal/sym"
	"encoding/binary"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"strings"
)

func ftabaddstring(ftab *sym.Symbol, s string) int32 {
	start := len(ftab.P)
	ftab.Grow(int64(start + len(s) + 1)) // make room for s plus trailing NUL
	copy(ftab.P[start:], s)
	return int32(start)
}

// numberfile assigns a file number to the file if it hasn't been assigned already.
func numberfile(ctxt *Link, file *sym.Symbol) {
	if file.Type != sym.SFILEPATH {
		ctxt.Filesyms = append(ctxt.Filesyms, file)
		file.Value = int64(len(ctxt.Filesyms))
		file.Type = sym.SFILEPATH
		path := file.Name[len(src.FileSymPrefix):]
		file.Name = expandGoroot(path)
	}
}

func renumberfiles(ctxt *Link, files []*sym.Symbol, d *sym.Pcdata) {
	// Give files numbers.
	for _, f := range files {
		numberfile(ctxt, f)
	}

	buf := make([]byte, binary.MaxVarintLen32)
	newval := int32(-1)
	var out sym.Pcdata
	it := obj.NewPCIter(uint32(ctxt.Arch.MinLC))
	for it.Init(d.P); !it.Done; it.Next() {
		// value delta
		oldval := it.Value

		var val int32
		if oldval == -1 {
			val = -1
		} else {
			if oldval < 0 || oldval >= int32(len(files)) {
				log.Fatalf("bad pcdata %d", oldval)
			}
			val = int32(files[oldval].Value)
		}

		dv := val - newval
		newval = val

		// value
		n := binary.PutVarint(buf, int64(dv))
		out.P = append(out.P, buf[:n]...)

		// pc delta
		pc := (it.NextPC - it.PC) / it.PCScale
		n = binary.PutUvarint(buf, uint64(pc))
		out.P = append(out.P, buf[:n]...)
	}

	// terminating value delta
	// we want to write varint-encoded 0, which is just 0
	out.P = append(out.P, 0)

	*d = out
}

// onlycsymbol reports whether this is a symbol that is referenced by C code.
func onlycsymbol(s *sym.Symbol) bool {
	switch s.Name {
	case "_cgo_topofstack", "__cgo_topofstack", "_cgo_panic", "crosscall2":
		return true
	}
	if strings.HasPrefix(s.Name, "_cgoexp_") {
		return true
	}
	return false
}

func emitPcln(ctxt *Link, s *sym.Symbol) bool {
	if s == nil {
		return true
	}
	if ctxt.BuildMode == BuildModePlugin && ctxt.HeadType == objabi.Hdarwin && onlycsymbol(s) {
		return false
	}
	// We want to generate func table entries only for the "lowest level" symbols,
	// not containers of subsymbols.
	return !s.Attr.Container()
}

// pclntab initializes the pclntab symbol with
// runtime function and file name information.

var pclntabZpcln sym.FuncInfo

// These variables are used to initialize runtime.firstmoduledata, see symtab.go:symtab.
var pclntabNfunc int32
var pclntabFiletabOffset int32
var pclntabPclntabOffset int32
var pclntabFirstFunc *sym.Symbol
var pclntabLastFunc *sym.Symbol

func (ctxt *Link) pclntab() {
	funcdataBytes := int64(0)
	ftab := ctxt.Syms.Lookup("runtime.pclntab", 0)
	ftab.Type = sym.SPCLNTAB
	ftab.Attr |= sym.AttrReachable

	// See golang.org/s/go12symtab for the format. Briefly:
	//	8-byte header
	//	nfunc [thearch.ptrsize bytes]
	//	function table, alternating PC and offset to func struct [each entry thearch.ptrsize bytes]
	//	end PC [thearch.ptrsize bytes]
	//	offset to file table [4 bytes]

	// Find container symbols and mark them as such.
	for _, s := range ctxt.Textp {
		if s.Outer != nil {
			s.Outer.Attr |= sym.AttrContainer
		}
	}

	// Gather some basic stats and info.
	var nfunc int32
	prevSect := ctxt.Textp[0].Sect
	for _, s := range ctxt.Textp {
		if !emitPcln(ctxt, s) {
			continue
		}
		nfunc++
		if pclntabFirstFunc == nil {
			pclntabFirstFunc = s
		}
		if s.Sect != prevSect {
			// With multiple text sections, the external linker may insert functions
			// between the sections, which are not known by Go. This leaves holes in
			// the PC range covered by the func table. We need to generate an entry
			// to mark the hole.
			nfunc++
			prevSect = s.Sect
		}
	}

	pclntabNfunc = nfunc
	ftab.Grow(8 + int64(ctxt.Arch.PtrSize) + int64(nfunc)*2*int64(ctxt.Arch.PtrSize) + int64(ctxt.Arch.PtrSize) + 4)
	ftab.SetUint32(ctxt.Arch, 0, 0xfffffffb)
	ftab.SetUint8(ctxt.Arch, 6, uint8(ctxt.Arch.MinLC))
	ftab.SetUint8(ctxt.Arch, 7, uint8(ctxt.Arch.PtrSize))
	ftab.SetUint(ctxt.Arch, 8, uint64(nfunc))
	pclntabPclntabOffset = int32(8 + ctxt.Arch.PtrSize)

	funcnameoff := make(map[string]int32)
	nameToOffset := func(name string) int32 {
		nameoff, ok := funcnameoff[name]
		if !ok {
			nameoff = ftabaddstring(ftab, name)
			funcnameoff[name] = nameoff
		}
		return nameoff
	}

	pctaboff := make(map[string]uint32)
	writepctab := func(off int32, p []byte) int32 {
		start, ok := pctaboff[string(p)]
		if !ok {
			if len(p) > 0 {
				start = uint32(len(ftab.P))
				ftab.AddBytes(p)
			}
			pctaboff[string(p)] = start
		}
		newoff := int32(ftab.SetUint32(ctxt.Arch, int64(off), start))
		return newoff
	}

	nfunc = 0 // repurpose nfunc as a running index
	prevFunc := ctxt.Textp[0]
	for _, s := range ctxt.Textp {
		if !emitPcln(ctxt, s) {
			continue
		}

		if s.Sect != prevFunc.Sect {
			// With multiple text sections, there may be a hole here in the address
			// space (see the comment above). We use an invalid funcoff value to
			// mark the hole.
			// See also runtime/symtab.go:findfunc
			ftab.SetAddrPlus(ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize), prevFunc, prevFunc.Size)
			ftab.SetUint(ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize)+int64(ctxt.Arch.PtrSize), ^uint64(0))
			nfunc++
		}
		prevFunc = s

		pcln := s.FuncInfo
		if pcln == nil {
			pcln = &pclntabZpcln
		}

		if len(pcln.InlTree) > 0 {
			if len(pcln.Pcdata) <= objabi.PCDATA_InlTreeIndex {
				// Create inlining pcdata table.
				pcdata := make([]sym.Pcdata, objabi.PCDATA_InlTreeIndex+1)
				copy(pcdata, pcln.Pcdata)
				pcln.Pcdata = pcdata
			}

			if len(pcln.Funcdataoff) <= objabi.FUNCDATA_InlTree {
				// Create inline tree funcdata.
				funcdata := make([]*sym.Symbol, objabi.FUNCDATA_InlTree+1)
				funcdataoff := make([]int64, objabi.FUNCDATA_InlTree+1)
				copy(funcdata, pcln.Funcdata)
				copy(funcdataoff, pcln.Funcdataoff)
				pcln.Funcdata = funcdata
				pcln.Funcdataoff = funcdataoff
			}
		}

		funcstart := int32(len(ftab.P))
		funcstart += int32(-len(ftab.P)) & (int32(ctxt.Arch.PtrSize) - 1) // align to ptrsize

		ftab.SetAddr(ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize), s)
		ftab.SetUint(ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize)+int64(ctxt.Arch.PtrSize), uint64(funcstart))

		// Write runtime._func. Keep in sync with ../../../../runtime/runtime2.go:/_func
		// and package debug/gosym.

		// fixed size of struct, checked below
		off := funcstart

		end := funcstart + int32(ctxt.Arch.PtrSize) + 3*4 + 5*4 + int32(len(pcln.Pcdata))*4 + int32(len(pcln.Funcdata))*int32(ctxt.Arch.PtrSize)
		if len(pcln.Funcdata) > 0 && (end&int32(ctxt.Arch.PtrSize-1) != 0) {
			end += 4
		}
		ftab.Grow(int64(end))

		// entry uintptr
		off = int32(ftab.SetAddr(ctxt.Arch, int64(off), s))

		// name int32
		nameoff := nameToOffset(s.Name)
		off = int32(ftab.SetUint32(ctxt.Arch, int64(off), uint32(nameoff)))

		// args int32
		// TODO: Move into funcinfo.
		args := uint32(0)
		if s.FuncInfo != nil {
			args = uint32(s.FuncInfo.Args)
		}
		off = int32(ftab.SetUint32(ctxt.Arch, int64(off), args))

		// deferreturn
		deferreturn := uint32(0)
		lastWasmAddr := uint32(0)
		for _, r := range s.R {
			if ctxt.Arch.Family == sys.Wasm && r.Type == objabi.R_ADDR {
				// Wasm does not have a live variable set at the deferreturn
				// call itself. Instead it has one identified by the
				// resumption point immediately preceding the deferreturn.
				// The wasm code has a R_ADDR relocation which is used to
				// set the resumption point to PC_B.
				lastWasmAddr = uint32(r.Add)
			}
			if r.Type.IsDirectCall() && r.Sym != nil && r.Sym.Name == "runtime.deferreturn" {
				if ctxt.Arch.Family == sys.Wasm {
					deferreturn = lastWasmAddr - 1
				} else {
					// Note: the relocation target is in the call instruction, but
					// is not necessarily the whole instruction (for instance, on
					// x86 the relocation applies to bytes [1:5] of the 5 byte call
					// instruction).
					deferreturn = uint32(r.Off)
					switch ctxt.Arch.Family {
					case sys.AMD64, sys.I386:
						deferreturn--
					case sys.PPC64, sys.ARM, sys.ARM64, sys.MIPS, sys.MIPS64:
						// no change
					case sys.RISCV64:
						// TODO(jsing): The JALR instruction is marked with
						// R_CALLRISCV, whereas the actual reloc is currently
						// one instruction earlier starting with the AUIPC.
						deferreturn -= 4
					case sys.S390X:
						deferreturn -= 2
					default:
						panic(fmt.Sprint("Unhandled architecture:", ctxt.Arch.Family))
					}
				}
				break // only need one
			}
		}
		off = int32(ftab.SetUint32(ctxt.Arch, int64(off), deferreturn))

		if pcln != &pclntabZpcln {
			renumberfiles(ctxt, pcln.File, &pcln.Pcfile)
			if false {
				// Sanity check the new numbering
				it := obj.NewPCIter(uint32(ctxt.Arch.MinLC))
				for it.Init(pcln.Pcfile.P); !it.Done; it.Next() {
					if it.Value < 1 || it.Value > int32(len(ctxt.Filesyms)) {
						Errorf(s, "bad file number in pcfile: %d not in range [1, %d]\n", it.Value, len(ctxt.Filesyms))
						errorexit()
					}
				}
			}
		}

		if len(pcln.InlTree) > 0 {
			inlTreeSym := ctxt.Syms.Lookup("inltree."+s.Name, 0)
			inlTreeSym.Type = sym.SRODATA
			inlTreeSym.Attr |= sym.AttrReachable | sym.AttrDuplicateOK

			for i, call := range pcln.InlTree {
				// Usually, call.File is already numbered since the file
				// shows up in the Pcfile table. However, two inlined calls
				// might overlap exactly so that only the innermost file
				// appears in the Pcfile table. In that case, this assigns
				// the outer file a number.
				numberfile(ctxt, call.File)
				nameoff := nameToOffset(call.Func)

				inlTreeSym.SetUint16(ctxt.Arch, int64(i*20+0), uint16(call.Parent))
				inlTreeSym.SetUint8(ctxt.Arch, int64(i*20+2), uint8(objabi.GetFuncID(call.Func, "")))
				// byte 3 is unused
				inlTreeSym.SetUint32(ctxt.Arch, int64(i*20+4), uint32(call.File.Value))
				inlTreeSym.SetUint32(ctxt.Arch, int64(i*20+8), uint32(call.Line))
				inlTreeSym.SetUint32(ctxt.Arch, int64(i*20+12), uint32(nameoff))
				inlTreeSym.SetUint32(ctxt.Arch, int64(i*20+16), uint32(call.ParentPC))
			}

			pcln.Funcdata[objabi.FUNCDATA_InlTree] = inlTreeSym
			pcln.Pcdata[objabi.PCDATA_InlTreeIndex] = pcln.Pcinline
		}

		// pcdata
		off = writepctab(off, pcln.Pcsp.P)
		off = writepctab(off, pcln.Pcfile.P)
		off = writepctab(off, pcln.Pcline.P)
		off = int32(ftab.SetUint32(ctxt.Arch, int64(off), uint32(len(pcln.Pcdata))))

		// funcID uint8
		var file string
		if s.FuncInfo != nil && len(s.FuncInfo.File) > 0 {
			file = s.FuncInfo.File[0].Name
		}
		funcID := objabi.GetFuncID(s.Name, file)

		off = int32(ftab.SetUint8(ctxt.Arch, int64(off), uint8(funcID)))

		// unused
		off += 2

		// nfuncdata must be the final entry.
		off = int32(ftab.SetUint8(ctxt.Arch, int64(off), uint8(len(pcln.Funcdata))))
		for i := range pcln.Pcdata {
			off = writepctab(off, pcln.Pcdata[i].P)
		}

		// funcdata, must be pointer-aligned and we're only int32-aligned.
		// Missing funcdata will be 0 (nil pointer).
		if len(pcln.Funcdata) > 0 {
			if off&int32(ctxt.Arch.PtrSize-1) != 0 {
				off += 4
			}
			for i := range pcln.Funcdata {
				dataoff := int64(off) + int64(ctxt.Arch.PtrSize)*int64(i)
				if pcln.Funcdata[i] == nil {
					ftab.SetUint(ctxt.Arch, dataoff, uint64(pcln.Funcdataoff[i]))
					continue
				}
				// TODO: Dedup.
				funcdataBytes += pcln.Funcdata[i].Size
				ftab.SetAddrPlus(ctxt.Arch, dataoff, pcln.Funcdata[i], pcln.Funcdataoff[i])
			}
			off += int32(len(pcln.Funcdata)) * int32(ctxt.Arch.PtrSize)
		}

		if off != end {
			Errorf(s, "bad math in functab: funcstart=%d off=%d but end=%d (npcdata=%d nfuncdata=%d ptrsize=%d)", funcstart, off, end, len(pcln.Pcdata), len(pcln.Funcdata), ctxt.Arch.PtrSize)
			errorexit()
		}

		nfunc++
	}

	last := ctxt.Textp[len(ctxt.Textp)-1]
	pclntabLastFunc = last
	// Final entry of table is just end pc.
	ftab.SetAddrPlus(ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize), last, last.Size)

	// Start file table.
	start := int32(len(ftab.P))

	start += int32(-len(ftab.P)) & (int32(ctxt.Arch.PtrSize) - 1)
	pclntabFiletabOffset = start
	ftab.SetUint32(ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize)+int64(ctxt.Arch.PtrSize), uint32(start))

	ftab.Grow(int64(start) + (int64(len(ctxt.Filesyms))+1)*4)
	ftab.SetUint32(ctxt.Arch, int64(start), uint32(len(ctxt.Filesyms)+1))
	for i := len(ctxt.Filesyms) - 1; i >= 0; i-- {
		s := ctxt.Filesyms[i]
		ftab.SetUint32(ctxt.Arch, int64(start)+s.Value*4, uint32(ftabaddstring(ftab, s.Name)))
	}

	ftab.Size = int64(len(ftab.P))

	if ctxt.Debugvlog != 0 {
		ctxt.Logf("pclntab=%d bytes, funcdata total %d bytes\n", ftab.Size, funcdataBytes)
	}
}

func gorootFinal() string {
	root := objabi.GOROOT
	if final := os.Getenv("GOROOT_FINAL"); final != "" {
		root = final
	}
	return root
}

func expandGoroot(s string) string {
	const n = len("$GOROOT")
	if len(s) >= n+1 && s[:n] == "$GOROOT" && (s[n] == '/' || s[n] == '\\') {
		return filepath.ToSlash(filepath.Join(gorootFinal(), s[n:]))
	}
	return s
}

const (
	BUCKETSIZE    = 256 * MINFUNC
	SUBBUCKETS    = 16
	SUBBUCKETSIZE = BUCKETSIZE / SUBBUCKETS
	NOIDX         = 0x7fffffff
)

// findfunctab generates a lookup table to quickly find the containing
// function for a pc. See src/runtime/symtab.go:findfunc for details.
func (ctxt *Link) findfunctab() {
	t := ctxt.Syms.Lookup("runtime.findfunctab", 0)
	t.Type = sym.SRODATA
	t.Attr |= sym.AttrReachable
	t.Attr |= sym.AttrLocal

	// find min and max address
	min := ctxt.Textp[0].Value
	lastp := ctxt.Textp[len(ctxt.Textp)-1]
	max := lastp.Value + lastp.Size

	// for each subbucket, compute the minimum of all symbol indexes
	// that map to that subbucket.
	n := int32((max - min + SUBBUCKETSIZE - 1) / SUBBUCKETSIZE)

	indexes := make([]int32, n)
	for i := int32(0); i < n; i++ {
		indexes[i] = NOIDX
	}
	idx := int32(0)
	for i, s := range ctxt.Textp {
		if !emitPcln(ctxt, s) {
			continue
		}
		p := s.Value
		var e *sym.Symbol
		i++
		if i < len(ctxt.Textp) {
			e = ctxt.Textp[i]
		}
		for !emitPcln(ctxt, e) && i < len(ctxt.Textp) {
			e = ctxt.Textp[i]
			i++
		}
		q := max
		if e != nil {
			q = e.Value
		}

		//print("%d: [%lld %lld] %s\n", idx, p, q, s->name);
		for ; p < q; p += SUBBUCKETSIZE {
			i = int((p - min) / SUBBUCKETSIZE)
			if indexes[i] > idx {
				indexes[i] = idx
			}
		}

		i = int((q - 1 - min) / SUBBUCKETSIZE)
		if indexes[i] > idx {
			indexes[i] = idx
		}
		idx++
	}

	// allocate table
	nbuckets := int32((max - min + BUCKETSIZE - 1) / BUCKETSIZE)

	t.Grow(4*int64(nbuckets) + int64(n))

	// fill in table
	for i := int32(0); i < nbuckets; i++ {
		base := indexes[i*SUBBUCKETS]
		if base == NOIDX {
			Errorf(nil, "hole in findfunctab")
		}
		t.SetUint32(ctxt.Arch, int64(i)*(4+SUBBUCKETS), uint32(base))
		for j := int32(0); j < SUBBUCKETS && i*SUBBUCKETS+j < n; j++ {
			idx = indexes[i*SUBBUCKETS+j]
			if idx == NOIDX {
				Errorf(nil, "hole in findfunctab")
			}
			if idx-base >= 256 {
				Errorf(nil, "too many functions in a findfunc bucket! %d/%d %d %d", i, nbuckets, j, idx-base)
			}

			t.SetUint8(ctxt.Arch, int64(i)*(4+SUBBUCKETS)+4+int64(j), uint8(idx-base))
		}
	}
}