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cmd/link: one DWARF compilation unit per package

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Currently, the linker generates one huge DWARF compilation unit for
the entire Go binary. This commit creates a separate compilation unit
and line table per Go package.

We temporarily lose compilation unit PC range information, since it's
now discontiguous, so harder to emit. We'll bring it back in the next
commit.

Beyond being "more traditional", this has various technical
advantages:

* It should speed up line table lookup, since that requires a
  sequential scan of the line table. With this change, a debugger can
  first locate the per-package line table and then scan only that line
  table.

* Once we emit compilation unit PC ranges again, this should also
  speed up various other debugger reverse PC lookups.

* It puts us in a good position to move more DWARF generation into the
  compiler, which could produce at least the CU header, per-function
  line table fragments, and per-function frame unwinding info that the
  linker could simply paste together.

* It will let us record a per-package compiler command-line flags
  (#22168).

Change-Id: Ibac642890984636b3ef1d4b37fe97f4453c2cc84
Reviewed-on: https://go-review.googlesource.com/69973
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Austin Clements 2017-10-09 16:19:56 -04:00
parent ce6e0b089f
commit d4dda76b5f
4 changed files with 110 additions and 64 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/cmd/internal/dwarf/dwarf.go
View File

@ -281,8 +281,6 @@ var abbrevs = [DW_NABRV]dwAbbrev{
[]dwAttrForm{
{DW_AT_name, DW_FORM_string},
{DW_AT_language, DW_FORM_data1},
{DW_AT_low_pc, DW_FORM_addr},
{DW_AT_high_pc, DW_FORM_addr},
{DW_AT_stmt_list, DW_FORM_sec_offset},
{DW_AT_comp_dir, DW_FORM_string},
{DW_AT_producer, DW_FORM_string},

148
src/cmd/link/internal/ld/dwarf.go
View File

@ -134,6 +134,10 @@ func newdie(ctxt *Link, parent *dwarf.DWDie, abbrev int, name string, version in
if name != "" && (abbrev <= dwarf.DW_ABRV_VARIABLE || abbrev >= dwarf.DW_ABRV_NULLTYPE) {
if abbrev != dwarf.DW_ABRV_VARIABLE || version == 0 {
if abbrev == dwarf.DW_ABRV_COMPUNIT {
// Avoid collisions with "real" symbol names.
name = ".pkg." + name
}
s := ctxt.Syms.Lookup(dwarf.InfoPrefix+name, version)
s.Attr |= sym.AttrNotInSymbolTable
s.Type = sym.SDWARFINFO
@ -832,6 +836,39 @@ func defdwsymb(ctxt *Link, s *sym.Symbol, str string, t SymbolType, v int64, got
}
}
// compilationUnit is per-compilation unit (equivalently, per-package)
// debug-related data.
type compilationUnit struct {
lib *sym.Library
textp []*sym.Symbol // Function symbols in this package
consts *sym.Symbol // Package constants DIEs
dwinfo *dwarf.DWDie // CU root DIE
funcDIEs []*sym.Symbol // Function DIE subtrees
}
// getCompilationUnits divides the symbols in ctxt.Textp by package.
func getCompilationUnits(ctxt *Link) []*compilationUnit {
units := []*compilationUnit{}
index := make(map[*sym.Library]*compilationUnit)
for _, s := range ctxt.Textp {
if s.FuncInfo == nil {
continue
}
unit := index[s.Lib]
if unit == nil {
unit = &compilationUnit{lib: s.Lib}
if s := ctxt.Syms.ROLookup(dwarf.ConstInfoPrefix+s.Lib.Pkg, 0); s != nil {
importInfoSymbol(ctxt, s)
unit.consts = s
}
units = append(units, unit)
index[s.Lib] = unit
}
unit.textp = append(unit.textp, s)
}
return units
}
func movetomodule(parent *dwarf.DWDie) {
die := dwroot.Child.Child
if die == nil {
@ -989,34 +1026,25 @@ func importInfoSymbol(ctxt *Link, dsym *sym.Symbol) {
}
}
func writelines(ctxt *Link, syms []*sym.Symbol) ([]*sym.Symbol, []*sym.Symbol) {
func writelines(ctxt *Link, lib *sym.Library, textp []*sym.Symbol, ls *sym.Symbol) (dwinfo *dwarf.DWDie, funcs []*sym.Symbol) {
var dwarfctxt dwarf.Context = dwctxt{ctxt}
ls := ctxt.Syms.Lookup(".debug_line", 0)
ls.Type = sym.SDWARFSECT
syms = append(syms, ls)
var funcs []*sym.Symbol
unitstart := int64(-1)
headerstart := int64(-1)
headerend := int64(-1)
epc := int64(0)
var epcs *sym.Symbol
var dwinfo *dwarf.DWDie
lang := dwarf.DW_LANG_Go
s := ctxt.Textp[0]
if ctxt.DynlinkingGo() && Headtype == objabi.Hdarwin {
s = ctxt.Textp[1] // skip runtime.text
}
// TODO: Generate DW_AT_ranges for dwinfo.
dwinfo = newdie(ctxt, &dwroot, dwarf.DW_ABRV_COMPUNIT, "go", 0)
dwinfo = newdie(ctxt, &dwroot, dwarf.DW_ABRV_COMPUNIT, lib.Pkg, 0)
newattr(dwinfo, dwarf.DW_AT_language, dwarf.DW_CLS_CONSTANT, int64(lang), 0)
newattr(dwinfo, dwarf.DW_AT_stmt_list, dwarf.DW_CLS_PTR, 0, ls)
newattr(dwinfo, dwarf.DW_AT_low_pc, dwarf.DW_CLS_ADDRESS, s.Value, s)
newattr(dwinfo, dwarf.DW_AT_stmt_list, dwarf.DW_CLS_PTR, ls.Size, ls)
// OS X linker requires compilation dir or absolute path in comp unit name to output debug info.
compDir := getCompilationDir()
// TODO: Make this be the actual compilation directory, not
// the linker directory. If we move CU construction into the
// compiler, this should happen naturally.
newattr(dwinfo, dwarf.DW_AT_comp_dir, dwarf.DW_CLS_STRING, int64(len(compDir)), compDir)
producer := "Go cmd/compile " + objabi.Version
newattr(dwinfo, dwarf.DW_AT_producer, dwarf.DW_CLS_STRING, int64(len(producer)), producer)
@ -1048,12 +1076,22 @@ func writelines(ctxt *Link, syms []*sym.Symbol) ([]*sym.Symbol, []*sym.Symbol) {
ls.AddUint8(1) // standard_opcode_lengths[9]
ls.AddUint8(0) // include_directories (empty)
for _, f := range ctxt.Filesyms {
// Create the file table. fileNums maps from global file
// indexes (created by numberfile) to CU-local indexes.
fileNums := make(map[int]int)
for _, s := range textp {
for _, f := range s.FuncInfo.File {
if _, ok := fileNums[int(f.Value)]; ok {
continue
}
// File indexes are 1-based.
fileNums[int(f.Value)] = len(fileNums) + 1
Addstring(ls, f.Name)
ls.AddUint8(0)
ls.AddUint8(0)
ls.AddUint8(0)
}
}
// 4 zeros: the string termination + 3 fields.
ls.AddUint8(0)
@ -1064,6 +1102,7 @@ func writelines(ctxt *Link, syms []*sym.Symbol) ([]*sym.Symbol, []*sym.Symbol) {
dwarf.Uleb128put(dwarfctxt, ls, 1+int64(ctxt.Arch.PtrSize))
ls.AddUint8(dwarf.DW_LNE_set_address)
s := textp[0]
pc := s.Value
line := 1
file := 1
@ -1071,13 +1110,7 @@ func writelines(ctxt *Link, syms []*sym.Symbol) ([]*sym.Symbol, []*sym.Symbol) {
var pcfile Pciter
var pcline Pciter
for _, s := range ctxt.Textp {
if s.FuncInfo == nil {
continue
}
epcs = s
for _, s := range textp {
dsym := ctxt.Syms.Lookup(dwarf.InfoPrefix+s.Name, int(s.Version))
importInfoSymbol(ctxt, dsym)
funcs = append(funcs, dsym)
@ -1086,7 +1119,7 @@ func writelines(ctxt *Link, syms []*sym.Symbol) ([]*sym.Symbol, []*sym.Symbol) {
pciterinit(ctxt, &pcfile, &s.FuncInfo.Pcfile)
pciterinit(ctxt, &pcline, &s.FuncInfo.Pcline)
epc = pc
epc := pc
for pcfile.done == 0 && pcline.done == 0 {
if epc-s.Value >= int64(pcfile.nextpc) {
pciternext(&pcfile)
@ -1100,7 +1133,11 @@ func writelines(ctxt *Link, syms []*sym.Symbol) ([]*sym.Symbol, []*sym.Symbol) {
if int32(file) != pcfile.value {
ls.AddUint8(dwarf.DW_LNS_set_file)
dwarf.Uleb128put(dwarfctxt, ls, int64(pcfile.value))
idx, ok := fileNums[int(pcfile.value)]
if !ok {
Exitf("pcln table file missing from DWARF line table")
}
dwarf.Uleb128put(dwarfctxt, ls, int64(idx))
file = int(pcfile.value)
}
@ -1121,12 +1158,10 @@ func writelines(ctxt *Link, syms []*sym.Symbol) ([]*sym.Symbol, []*sym.Symbol) {
dwarf.Uleb128put(dwarfctxt, ls, 1)
ls.AddUint8(dwarf.DW_LNE_end_sequence)
newattr(dwinfo, dwarf.DW_AT_high_pc, dwarf.DW_CLS_ADDRESS, epc+1, epcs)
ls.SetUint32(ctxt.Arch, unitLengthOffset, uint32(ls.Size-unitstart))
ls.SetUint32(ctxt.Arch, headerLengthOffset, uint32(headerend-headerstart))
return syms, funcs
return dwinfo, funcs
}
/*
@ -1298,7 +1333,7 @@ const (
COMPUNITHEADERSIZE = 4 + 2 + 4 + 1
)
func writeinfo(ctxt *Link, syms []*sym.Symbol, funcs, consts []*sym.Symbol, abbrevsym *sym.Symbol) []*sym.Symbol {
func writeinfo(ctxt *Link, syms []*sym.Symbol, units []*compilationUnit, abbrevsym *sym.Symbol) []*sym.Symbol {
infosec := ctxt.Syms.Lookup(".debug_info", 0)
infosec.Type = sym.SDWARFINFO
infosec.Attr |= sym.AttrReachable
@ -1306,8 +1341,15 @@ func writeinfo(ctxt *Link, syms []*sym.Symbol, funcs, consts []*sym.Symbol, abbr
var dwarfctxt dwarf.Context = dwctxt{ctxt}
// Re-index per-package information by its CU die.
unitByDIE := make(map[*dwarf.DWDie]*compilationUnit)
for _, u := range units {
unitByDIE[u.dwinfo] = u
}
for compunit := dwroot.Child; compunit != nil; compunit = compunit.Link {
s := dtolsym(compunit.Sym)
u := unitByDIE[compunit]
// Write .debug_info Compilation Unit Header (sec 7.5.1)
// Fields marked with (*) must be changed for 64-bit dwarf
@ -1324,13 +1366,9 @@ func writeinfo(ctxt *Link, syms []*sym.Symbol, funcs, consts []*sym.Symbol, abbr
dwarf.PutAttrs(dwarfctxt, s, compunit.Abbrev, compunit.Attr)
cu := []*sym.Symbol{s}
if funcs != nil {
cu = append(cu, funcs...)
funcs = nil
}
if consts != nil {
cu = append(cu, consts...)
consts = nil
cu = append(cu, u.funcDIEs...)
if u.consts != nil {
cu = append(cu, u.consts)
}
cu = putdies(ctxt, dwarfctxt, cu, compunit.Child)
var cusize int64
@ -1339,6 +1377,8 @@ func writeinfo(ctxt *Link, syms []*sym.Symbol, funcs, consts []*sym.Symbol, abbr
}
cusize -= 4 // exclude the length field.
s.SetUint32(ctxt.Arch, 0, uint32(cusize))
// Leave a breadcrumb for writepub. This does not
// appear in the DWARF output.
newattr(compunit, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, cusize, 0)
syms = append(syms, cu...)
}
@ -1500,24 +1540,27 @@ func dwarfgeneratedebugsyms(ctxt *Link) {
genasmsym(ctxt, defdwsymb)
var consts []*sym.Symbol
for _, lib := range ctxt.Library {
if s := ctxt.Syms.ROLookup(dwarf.ConstInfoPrefix+lib.Pkg, 0); s != nil {
importInfoSymbol(ctxt, s)
consts = append(consts, s)
}
}
abbrev := writeabbrev(ctxt)
syms := []*sym.Symbol{abbrev}
syms, funcs := writelines(ctxt, syms)
syms = writeframes(ctxt, syms)
units := getCompilationUnits(ctxt)
// Write per-package line tables and start their CU DIEs.
debugLine := ctxt.Syms.Lookup(".debug_line", 0)
debugLine.Type = sym.SDWARFSECT
syms = append(syms, debugLine)
for _, u := range units {
u.dwinfo, u.funcDIEs = writelines(ctxt, u.lib, u.textp, debugLine)
}
synthesizestringtypes(ctxt, dwtypes.Child)
synthesizeslicetypes(ctxt, dwtypes.Child)
synthesizemaptypes(ctxt, dwtypes.Child)
synthesizechantypes(ctxt, dwtypes.Child)
// newdie adds DIEs to the *beginning* of the parent's DIE list.
// Now that we're done creating DIEs, reverse the trees so DIEs
// appear in the order they were created.
reversetree(&dwroot.Child)
reversetree(&dwtypes.Child)
reversetree(&dwglobals.Child)
@ -1527,20 +1570,22 @@ func dwarfgeneratedebugsyms(ctxt *Link) {
// Need to reorder symbols so sym.SDWARFINFO is after all sym.SDWARFSECT
// (but we need to generate dies before writepub)
infosyms := writeinfo(ctxt, nil, funcs, consts, abbrev)
infosyms := writeinfo(ctxt, nil, units, abbrev)
syms = writeframes(ctxt, syms)
syms = writepub(ctxt, ".debug_pubnames", ispubname, syms)
syms = writepub(ctxt, ".debug_pubtypes", ispubtype, syms)
syms = writegdbscript(ctxt, syms)
syms = append(syms, infosyms...)
syms = collectlocs(ctxt, syms, funcs)
syms = collectlocs(ctxt, syms, units)
syms = writeranges(ctxt, syms)
dwarfp = syms
}
func collectlocs(ctxt *Link, syms []*sym.Symbol, funcs []*sym.Symbol) []*sym.Symbol {
func collectlocs(ctxt *Link, syms []*sym.Symbol, units []*compilationUnit) []*sym.Symbol {
empty := true
for _, fn := range funcs {
for _, u := range units {
for _, fn := range u.funcDIEs {
for _, reloc := range fn.R {
if reloc.Type == objabi.R_DWARFREF && strings.HasPrefix(reloc.Sym.Name, dwarf.LocPrefix) {
reloc.Sym.Attr |= sym.AttrReachable | sym.AttrNotInSymbolTable
@ -1551,6 +1596,7 @@ func collectlocs(ctxt *Link, syms []*sym.Symbol, funcs []*sym.Symbol) []*sym.Sym
}
}
}
}
// Don't emit .debug_loc if it's empty -- it makes the ARM linker mad.
if !empty {
locsym := ctxt.Syms.Lookup(".debug_loc", 0)

1
src/cmd/link/internal/objfile/objfile.go
View File

@ -318,6 +318,7 @@ overwrite:
pc.InlTree[i].Func = r.readSymIndex()
}
s.Lib = r.lib
if !dupok {
if s.Attr.OnList() {
log.Fatalf("symbol %s listed multiple times", s.Name)

1
src/cmd/link/internal/sym/symbol.go
View File

@ -41,6 +41,7 @@ type Symbol struct {
Dynimpvers string
Sect *Section
FuncInfo *FuncInfo
Lib *Library // Package defining this symbol
// P contains the raw symbol data.
P []byte
R []Reloc