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cmd/link: eliminate .debug_aranges

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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 <austin@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
This commit is contained in:
Austin Clements 2017-10-11 11:05:58 -04:00
parent a0402b6bf8
commit 77c27c3102
2 changed files with 0 additions and 134 deletions
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52
src/cmd/link/internal/ld/dwarf.go
View file

@ -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")