src/cmd/internal/obj/sym.go

// Derived from Inferno utils/6l/obj.c and utils/6l/span.c
// https://bitbucket.org/inferno-os/inferno-os/src/default/utils/6l/obj.c
// https://bitbucket.org/inferno-os/inferno-os/src/default/utils/6l/span.c
//
//	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
//	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
//	Portions Copyright © 1997-1999 Vita Nuova Limited
//	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
//	Portions Copyright © 2004,2006 Bruce Ellis
//	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
//	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
//	Portions Copyright © 2009 The Go Authors. All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

package obj

import (
	"cmd/internal/goobj2"
	"cmd/internal/objabi"
	"crypto/md5"
	"fmt"
	"log"
	"math"
	"sort"
)

func Linknew(arch *LinkArch) *Link {
	ctxt := new(Link)
	ctxt.hash = make(map[string]*LSym)
	ctxt.funchash = make(map[string]*LSym)
	ctxt.statichash = make(map[string]*LSym)
	ctxt.Arch = arch
	ctxt.Pathname = objabi.WorkingDir()

	if err := ctxt.Headtype.Set(objabi.GOOS); err != nil {
		log.Fatalf("unknown goos %s", objabi.GOOS)
	}

	ctxt.Flag_optimize = true
	ctxt.Framepointer_enabled = objabi.Framepointer_enabled(objabi.GOOS, arch.Name)
	return ctxt
}

// LookupDerived looks up or creates the symbol with name name derived from symbol s.
// The resulting symbol will be static iff s is.
func (ctxt *Link) LookupDerived(s *LSym, name string) *LSym {
	if s.Static() {
		return ctxt.LookupStatic(name)
	}
	return ctxt.Lookup(name)
}

// LookupStatic looks up the static symbol with name name.
// If it does not exist, it creates it.
func (ctxt *Link) LookupStatic(name string) *LSym {
	s := ctxt.statichash[name]
	if s == nil {
		s = &LSym{Name: name, Attribute: AttrStatic}
		ctxt.statichash[name] = s
	}
	return s
}

// LookupABI looks up a symbol with the given ABI.
// If it does not exist, it creates it.
func (ctxt *Link) LookupABI(name string, abi ABI) *LSym {
	return ctxt.LookupABIInit(name, abi, nil)
}

// LookupABI looks up a symbol with the given ABI.
// If it does not exist, it creates it and
// passes it to init for one-time initialization.
func (ctxt *Link) LookupABIInit(name string, abi ABI, init func(s *LSym)) *LSym {
	var hash map[string]*LSym
	switch abi {
	case ABI0:
		hash = ctxt.hash
	case ABIInternal:
		hash = ctxt.funchash
	default:
		panic("unknown ABI")
	}

	ctxt.hashmu.Lock()
	s := hash[name]
	if s == nil {
		s = &LSym{Name: name}
		s.SetABI(abi)
		hash[name] = s
		if init != nil {
			init(s)
		}
	}
	ctxt.hashmu.Unlock()
	return s
}

// Lookup looks up the symbol with name name.
// If it does not exist, it creates it.
func (ctxt *Link) Lookup(name string) *LSym {
	return ctxt.LookupInit(name, nil)
}

// LookupInit looks up the symbol with name name.
// If it does not exist, it creates it and
// passes it to init for one-time initialization.
func (ctxt *Link) LookupInit(name string, init func(s *LSym)) *LSym {
	ctxt.hashmu.Lock()
	s := ctxt.hash[name]
	if s == nil {
		s = &LSym{Name: name}
		ctxt.hash[name] = s
		if init != nil {
			init(s)
		}
	}
	ctxt.hashmu.Unlock()
	return s
}

func (ctxt *Link) Float32Sym(f float32) *LSym {
	i := math.Float32bits(f)
	name := fmt.Sprintf("$f32.%08x", i)
	return ctxt.LookupInit(name, func(s *LSym) {
		s.Size = 4
		s.Set(AttrLocal, true)
	})
}

func (ctxt *Link) Float64Sym(f float64) *LSym {
	i := math.Float64bits(f)
	name := fmt.Sprintf("$f64.%016x", i)
	return ctxt.LookupInit(name, func(s *LSym) {
		s.Size = 8
		s.Set(AttrLocal, true)
	})
}

func (ctxt *Link) Int64Sym(i int64) *LSym {
	name := fmt.Sprintf("$i64.%016x", uint64(i))
	return ctxt.LookupInit(name, func(s *LSym) {
		s.Size = 8
		s.Set(AttrLocal, true)
	})
}

// Assign index to symbols.
// asm is set to true if this is called by the assembler (i.e. not the compiler),
// in which case all the symbols are non-package (for now).
func (ctxt *Link) NumberSyms(asm bool) {
	if !ctxt.Flag_go115newobj {
		return
	}

	if ctxt.Headtype == objabi.Haix {
		// Data must be sorted to keep a constant order in TOC symbols.
		// As they are created during Progedit, two symbols can be switched between
		// two different compilations. Therefore, BuildID will be different.
		// TODO: find a better place and optimize to only sort TOC symbols
		sort.Slice(ctxt.Data, func(i, j int) bool {
			return ctxt.Data[i].Name < ctxt.Data[j].Name
		})
	}

	ctxt.pkgIdx = make(map[string]int32)
	ctxt.defs = []*LSym{}
	ctxt.nonpkgdefs = []*LSym{}

	var idx, nonpkgidx int32 = 0, 0
	ctxt.traverseSyms(traverseDefs, func(s *LSym) {
		if isNonPkgSym(ctxt, asm, s) {
			s.PkgIdx = goobj2.PkgIdxNone
			s.SymIdx = nonpkgidx
			if nonpkgidx != int32(len(ctxt.nonpkgdefs)) {
				panic("bad index")
			}
			ctxt.nonpkgdefs = append(ctxt.nonpkgdefs, s)
			nonpkgidx++
		} else {
			s.PkgIdx = goobj2.PkgIdxSelf
			s.SymIdx = idx
			if idx != int32(len(ctxt.defs)) {
				panic("bad index")
			}
			ctxt.defs = append(ctxt.defs, s)
			idx++
		}
		s.Set(AttrIndexed, true)
	})

	ipkg := int32(1) // 0 is invalid index
	nonpkgdef := nonpkgidx
	ctxt.traverseSyms(traverseRefs|traverseAux, func(rs *LSym) {
		if rs.PkgIdx != goobj2.PkgIdxInvalid {
			return
		}
		if !ctxt.Flag_linkshared {
			// Assign special index for builtin symbols.
			// Don't do it when linking against shared libraries, as the runtime
			// may be in a different library.
			if i := goobj2.BuiltinIdx(rs.Name, int(rs.ABI())); i != -1 {
				rs.PkgIdx = goobj2.PkgIdxBuiltin
				rs.SymIdx = int32(i)
				rs.Set(AttrIndexed, true)
				return
			}
		}
		pkg := rs.Pkg
		if pkg == "" || pkg == "\"\"" || pkg == "_" || !rs.Indexed() {
			rs.PkgIdx = goobj2.PkgIdxNone
			rs.SymIdx = nonpkgidx
			rs.Set(AttrIndexed, true)
			if nonpkgidx != nonpkgdef+int32(len(ctxt.nonpkgrefs)) {
				panic("bad index")
			}
			ctxt.nonpkgrefs = append(ctxt.nonpkgrefs, rs)
			nonpkgidx++
			return
		}
		if k, ok := ctxt.pkgIdx[pkg]; ok {
			rs.PkgIdx = k
			return
		}
		rs.PkgIdx = ipkg
		ctxt.pkgIdx[pkg] = ipkg
		ipkg++
	})

	// Compute a fingerprint of the indices, for exporting.
	if !asm {
		h := md5.New()
		for _, s := range ctxt.defs {
			h.Write([]byte(s.Name))
		}
		copy(ctxt.Fingerprint[:], h.Sum(nil)[:])
	}
}

// Returns whether s is a non-package symbol, which needs to be referenced
// by name instead of by index.
func isNonPkgSym(ctxt *Link, asm bool, s *LSym) bool {
	if asm && !s.Static() {
		// asm symbols are referenced by name only, except static symbols
		// which are file-local and can be referenced by index.
		return true
	}
	if ctxt.Flag_linkshared {
		// The referenced symbol may be in a different shared library so
		// the linker cannot see its index.
		return true
	}
	if s.Pkg == "_" {
		// The frontend uses package "_" to mark symbols that should not
		// be referenced by index, e.g. linkname'd symbols.
		return true
	}
	if s.DuplicateOK() {
		// Dupok symbol needs to be dedup'd by name.
		return true
	}
	return false
}

type traverseFlag uint32

const (
	traverseDefs traverseFlag = 1 << iota
	traverseRefs
	traverseAux

	traverseAll = traverseDefs | traverseRefs | traverseAux
)

// Traverse symbols based on flag, call fn for each symbol.
func (ctxt *Link) traverseSyms(flag traverseFlag, fn func(*LSym)) {
	lists := [][]*LSym{ctxt.Text, ctxt.Data, ctxt.ABIAliases}
	for _, list := range lists {
		for _, s := range list {
			if flag&traverseDefs != 0 {
				fn(s)
			}
			if flag&traverseRefs != 0 {
				for _, r := range s.R {
					if r.Sym != nil {
						fn(r.Sym)
					}
				}
			}
			if flag&traverseAux != 0 {
				if s.Gotype != nil {
					fn(s.Gotype)
				}
				if s.Type == objabi.STEXT {
					f := func(parent *LSym, aux *LSym) {
						fn(aux)
					}
					ctxt.traverseFuncAux(flag, s, f)
				}
			}
		}
	}
}

func (ctxt *Link) traverseFuncAux(flag traverseFlag, fsym *LSym, fn func(parent *LSym, aux *LSym)) {
	pc := &fsym.Func.Pcln
	if flag&traverseAux == 0 {
		// NB: should it become necessary to walk aux sym reloc references
		// without walking the aux syms themselves, this can be changed.
		panic("should not be here")
	}
	for _, d := range pc.Funcdata {
		if d != nil {
			fn(fsym, d)
		}
	}
	for _, f := range pc.File {
		if filesym := ctxt.Lookup(f); filesym != nil {
			fn(fsym, filesym)
		}
	}
	for _, call := range pc.InlTree.nodes {
		if call.Func != nil {
			fn(fsym, call.Func)
		}
		f, _ := linkgetlineFromPos(ctxt, call.Pos)
		if filesym := ctxt.Lookup(f); filesym != nil {
			fn(fsym, filesym)
		}
	}
	dwsyms := []*LSym{fsym.Func.dwarfRangesSym, fsym.Func.dwarfLocSym, fsym.Func.dwarfDebugLinesSym, fsym.Func.dwarfInfoSym}
	for _, dws := range dwsyms {
		if dws == nil || dws.Size == 0 {
			continue
		}
		fn(fsym, dws)
		if flag&traverseRefs != 0 {
			for _, r := range dws.R {
				if r.Sym != nil {
					fn(dws, r.Sym)
				}
			}
		}
	}
}

// Traverse aux symbols, calling fn for each sym/aux pair.
func (ctxt *Link) traverseAuxSyms(flag traverseFlag, fn func(parent *LSym, aux *LSym)) {
	lists := [][]*LSym{ctxt.Text, ctxt.Data, ctxt.ABIAliases}
	for _, list := range lists {
		for _, s := range list {
			if s.Gotype != nil {
				if flag&traverseDefs != 0 {
					fn(s, s.Gotype)
				}
			}
			if s.Type != objabi.STEXT {
				continue
			}
			ctxt.traverseFuncAux(flag, s, fn)
		}
	}
}