From 77c27c31026f758768c981c45704c7931e7046d1 Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Wed, 11 Oct 2017 11:05:58 -0400 Subject: [PATCH] cmd/link: eliminate .debug_aranges The .debug_aranges section is an odd vestige of DWARF, since its contents are easy and efficient for a debugger to reconstruct from the attributes of the top-level compilation unit DIEs. Neither GCC nor clang emit it by default these days. GDB and Delve ignore it entirely. LLDB will use it if present, but is happy to construct the index from the compilation unit attributes (and, indeed, a remarkable variety of other ways if those aren't available either). We're about to split up the compilation units by package, which means they'll have discontiguous PC ranges, which is going to make .debug_aranges harder to construct (and larger). Rather than try to maintain this essentially unused code, let's simplify things and remove it. Change-Id: I8e0ccc033b583b5b8908cbb2c879b2f2d5f9a50b Reviewed-on: https://go-review.googlesource.com/69972 Run-TryBot: Austin Clements Reviewed-by: Heschi Kreinick Reviewed-by: Than McIntosh --- src/cmd/link/internal/ld/dwarf.go | 52 -------------------- src/runtime/runtime-lldb_test.go | 82 ------------------------------- 2 files changed, 134 deletions(-) diff --git a/src/cmd/link/internal/ld/dwarf.go b/src/cmd/link/internal/ld/dwarf.go index dd6d983f56..02eea54435 100644 --- a/src/cmd/link/internal/ld/dwarf.go +++ b/src/cmd/link/internal/ld/dwarf.go @@ -1308,9 +1308,6 @@ func writeinfo(ctxt *Link, syms []*sym.Symbol, funcs, consts []*sym.Symbol, abbr infosec.Attr |= sym.AttrReachable syms = append(syms, infosec) - arangessec := ctxt.Syms.Lookup(".dwarfaranges", 0) - arangessec.R = arangessec.R[:0] - var dwarfctxt dwarf.Context = dwctxt{ctxt} for compunit := dwroot.Child; compunit != nil; compunit = compunit.Link { @@ -1406,52 +1403,6 @@ func writepub(ctxt *Link, sname string, ispub func(*dwarf.DWDie) bool, syms []*s return syms } -/* - * emit .debug_aranges. _info must have been written before, - * because we need die->offs of dwarf.DW_globals. - */ -func writearanges(ctxt *Link, syms []*sym.Symbol) []*sym.Symbol { - s := ctxt.Syms.Lookup(".debug_aranges", 0) - s.Type = sym.SDWARFSECT - // The first tuple is aligned to a multiple of the size of a single tuple - // (twice the size of an address) - headersize := int(Rnd(4+2+4+1+1, int64(ctxt.Arch.PtrSize*2))) // don't count unit_length field itself - - for compunit := dwroot.Child; compunit != nil; compunit = compunit.Link { - b := getattr(compunit, dwarf.DW_AT_low_pc) - if b == nil { - continue - } - e := getattr(compunit, dwarf.DW_AT_high_pc) - if e == nil { - continue - } - - // Write .debug_aranges Header + entry (sec 6.1.2) - unitlength := uint32(headersize) + 4*uint32(ctxt.Arch.PtrSize) - 4 - s.AddUint32(ctxt.Arch, unitlength) // unit_length (*) - s.AddUint16(ctxt.Arch, 2) // dwarf version (appendix F) - - adddwarfref(ctxt, s, dtolsym(compunit.Sym), 4) - - s.AddUint8(uint8(ctxt.Arch.PtrSize)) // address_size - s.AddUint8(0) // segment_size - padding := headersize - (4 + 2 + 4 + 1 + 1) - for i := 0; i < padding; i++ { - s.AddUint8(0) - } - - s.AddAddrPlus(ctxt.Arch, b.Data.(*sym.Symbol), b.Value-(b.Data.(*sym.Symbol)).Value) - s.AddUintXX(ctxt.Arch, uint64(e.Value-b.Value), ctxt.Arch.PtrSize) - s.AddUintXX(ctxt.Arch, 0, ctxt.Arch.PtrSize) - s.AddUintXX(ctxt.Arch, 0, ctxt.Arch.PtrSize) - } - if s.Size > 0 { - syms = append(syms, s) - } - return syms -} - func writegdbscript(ctxt *Link, syms []*sym.Symbol) []*sym.Symbol { if ctxt.LinkMode == LinkExternal && Headtype == objabi.Hwindows && ctxt.BuildMode == BuildModeCArchive { // gcc on Windows places .debug_gdb_scripts in the wrong location, which @@ -1584,7 +1535,6 @@ func dwarfgeneratedebugsyms(ctxt *Link) { syms = writepub(ctxt, ".debug_pubnames", ispubname, syms) syms = writepub(ctxt, ".debug_pubtypes", ispubtype, syms) - syms = writearanges(ctxt, syms) syms = writegdbscript(ctxt, syms) syms = append(syms, infosyms...) syms = collectlocs(ctxt, syms, funcs) @@ -1625,7 +1575,6 @@ func dwarfaddshstrings(ctxt *Link, shstrtab *sym.Symbol) { } Addstring(shstrtab, ".debug_abbrev") - Addstring(shstrtab, ".debug_aranges") Addstring(shstrtab, ".debug_frame") Addstring(shstrtab, ".debug_info") Addstring(shstrtab, ".debug_loc") @@ -1637,7 +1586,6 @@ func dwarfaddshstrings(ctxt *Link, shstrtab *sym.Symbol) { if ctxt.LinkMode == LinkExternal { Addstring(shstrtab, elfRelType+".debug_info") Addstring(shstrtab, elfRelType+".debug_loc") - Addstring(shstrtab, elfRelType+".debug_aranges") Addstring(shstrtab, elfRelType+".debug_line") Addstring(shstrtab, elfRelType+".debug_frame") Addstring(shstrtab, elfRelType+".debug_pubnames") diff --git a/src/runtime/runtime-lldb_test.go b/src/runtime/runtime-lldb_test.go index 98bc906666..6889e32601 100644 --- a/src/runtime/runtime-lldb_test.go +++ b/src/runtime/runtime-lldb_test.go @@ -5,11 +5,7 @@ package runtime_test import ( - "debug/elf" - "debug/macho" - "encoding/binary" "internal/testenv" - "io" "io/ioutil" "os" "os/exec" @@ -182,81 +178,3 @@ func TestLldbPython(t *testing.T) { t.Fatalf("Unexpected lldb output:\n%s", got) } } - -// Check that aranges are valid even when lldb isn't installed. -func TestDwarfAranges(t *testing.T) { - testenv.MustHaveGoBuild(t) - dir, err := ioutil.TempDir("", "go-build") - if err != nil { - t.Fatalf("failed to create temp directory: %v", err) - } - defer os.RemoveAll(dir) - - src := filepath.Join(dir, "main.go") - err = ioutil.WriteFile(src, []byte(lldbHelloSource), 0644) - if err != nil { - t.Fatalf("failed to create file: %v", err) - } - - cmd := exec.Command(testenv.GoToolPath(t), "build", "-o", "a.exe") - cmd.Dir = dir - out, err := cmd.CombinedOutput() - if err != nil { - t.Fatalf("building source %v\n%s", err, out) - } - - filename := filepath.Join(dir, "a.exe") - if f, err := elf.Open(filename); err == nil { - sect := f.Section(".debug_aranges") - if sect == nil { - t.Fatal("Missing aranges section") - } - verifyAranges(t, f.ByteOrder, sect.Open()) - } else if f, err := macho.Open(filename); err == nil { - sect := f.Section("__debug_aranges") - if sect == nil { - t.Fatal("Missing aranges section") - } - verifyAranges(t, f.ByteOrder, sect.Open()) - } else { - t.Skip("Not an elf or macho binary.") - } -} - -func verifyAranges(t *testing.T, byteorder binary.ByteOrder, data io.ReadSeeker) { - var header struct { - UnitLength uint32 // does not include the UnitLength field - Version uint16 - Offset uint32 - AddressSize uint8 - SegmentSize uint8 - } - for { - offset, err := data.Seek(0, io.SeekCurrent) - if err != nil { - t.Fatalf("Seek error: %v", err) - } - if err = binary.Read(data, byteorder, &header); err == io.EOF { - return - } else if err != nil { - t.Fatalf("Error reading arange header: %v", err) - } - tupleSize := int64(header.SegmentSize) + 2*int64(header.AddressSize) - lastTupleOffset := offset + int64(header.UnitLength) + 4 - tupleSize - if lastTupleOffset%tupleSize != 0 { - t.Fatalf("Invalid arange length %d, (addr %d, seg %d)", header.UnitLength, header.AddressSize, header.SegmentSize) - } - if _, err = data.Seek(lastTupleOffset, io.SeekStart); err != nil { - t.Fatalf("Seek error: %v", err) - } - buf := make([]byte, tupleSize) - if n, err := data.Read(buf); err != nil || int64(n) < tupleSize { - t.Fatalf("Read error: %v", err) - } - for _, val := range buf { - if val != 0 { - t.Fatalf("Invalid terminator") - } - } - } -}