[dev.link] cmd/link: stop emitting .debug_pubnames/.debug_pubtypes

Don't emit the .debug_pubnames/.debug_pubtypes sections. These sections
are not used by either GDB or Delve, and C++ compilers [notably GCC
and Clang] no longer emit the sections by default.

Change-Id: Ic3309755e88c8e1aa28a29366bc7f0df1748fe64
Reviewed-on: https://go-review.googlesource.com/c/go/+/237426
Reviewed-by: Jeremy Faller <jeremy@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

diff --git a/src/cmd/link/internal/ld/dwarf.go b/src/cmd/link/internal/ld/dwarf.go
index 78162515d3997111b8401a071a97b0ba5a5d2ddc..da05d1bd2ec4540c5aadc9e6bd2d9fb932c437c5 100644 (file)
--- a/src/cmd/link/internal/ld/dwarf.go
+++ b/src/cmd/link/internal/ld/dwarf.go
@@ -1518,7 +1518,7 @@ func appendSyms(syms []loader.Sym, src []sym.LoaderSym) []loader.Sym {
        return syms
 }
 
-func (d *dwctxt) writeinfo(units []*sym.CompilationUnit, abbrevsym loader.Sym, pubNames, pubTypes *pubWriter) dwarfSecInfo {
+func (d *dwctxt) writeinfo(units []*sym.CompilationUnit, abbrevsym loader.Sym) dwarfSecInfo {
 
        infosec := d.ldr.LookupOrCreateSym(".debug_info", 0)
        disu := d.ldr.MakeSymbolUpdater(infosec)
@@ -1535,9 +1535,6 @@ func (d *dwctxt) writeinfo(units []*sym.CompilationUnit, abbrevsym loader.Sym, p
                        continue
                }
 
-               pubNames.beginCompUnit(compunit)
-               pubTypes.beginCompUnit(compunit)
-
                // Write .debug_info Compilation Unit Header (sec 7.5.1)
                // Fields marked with (*) must be changed for 64-bit dwarf
                // This must match COMPUNITHEADERSIZE above.
@@ -1568,12 +1565,6 @@ func (d *dwctxt) writeinfo(units []*sym.CompilationUnit, abbrevsym loader.Sym, p
                        l := len(cu)
                        lastSymSz := int64(len(d.ldr.Data(cu[l-1])))
                        cu = d.putdie(cu, die)
-                       if ispubname(die) {
-                               pubNames.add(die, cusize)
-                       }
-                       if ispubtype(die) {
-                               pubTypes.add(die, cusize)
-                       }
                        if lastSymSz != int64(len(d.ldr.Data(cu[l-1]))) {
                                // putdie will sometimes append directly to the last symbol of the list
                                cusize = cusize - lastSymSz + int64(len(d.ldr.Data(cu[l-1])))
@@ -1598,87 +1589,12 @@ func (d *dwctxt) writeinfo(units []*sym.CompilationUnit, abbrevsym loader.Sym, p
                        cusize -= 4 // exclude the length field.
                        su.SetUint32(d.arch, 0, uint32(cusize))
                }
-               pubNames.endCompUnit(compunit, uint32(cusize)+4)
-               pubTypes.endCompUnit(compunit, uint32(cusize)+4)
                syms = append(syms, cu...)
        }
 
        return dwarfSecInfo{syms: syms}
 }
 
-/*
- *  Emit .debug_pubnames/_types.  _info must have been written before,
- *  because we need die->offs and infoo/infosize;
- */
-
-type pubWriter struct {
-       d     *dwctxt
-       s     loader.Sym
-       su    *loader.SymbolBuilder
-       sname string
-
-       sectionstart int64
-       culengthOff  int64
-}
-
-func newPubWriter(d *dwctxt, sname string) *pubWriter {
-       s := d.ldr.LookupOrCreateSym(sname, 0)
-       u := d.ldr.MakeSymbolUpdater(s)
-       u.SetType(sym.SDWARFSECT)
-       return &pubWriter{d: d, s: s, su: u, sname: sname}
-}
-
-func (pw *pubWriter) beginCompUnit(compunit *dwarf.DWDie) {
-       pw.sectionstart = pw.su.Size()
-
-       // Write .debug_pubnames/types  Header (sec 6.1.1)
-       pw.d.createUnitLength(pw.su, 0)                         // unit_length (*), will be filled in later.
-       pw.su.AddUint16(pw.d.arch, 2)                           // dwarf version (appendix F)
-       pw.d.addDwarfAddrRef(pw.su, pw.d.dtolsym(compunit.Sym)) // debug_info_offset (of the Comp unit Header)
-       pw.culengthOff = pw.su.Size()
-       pw.d.addDwarfAddrField(pw.su, uint64(0)) // debug_info_length, will be filled in later.
-}
-
-func (pw *pubWriter) add(die *dwarf.DWDie, offset int64) {
-       dwa := getattr(die, dwarf.DW_AT_name)
-       name := dwa.Data.(string)
-       if pw.d.dtolsym(die.Sym) == 0 {
-               fmt.Println("Missing sym for ", name)
-       }
-       pw.d.addDwarfAddrField(pw.su, uint64(offset))
-       pw.su.Addstring(name)
-}
-
-func (pw *pubWriter) endCompUnit(compunit *dwarf.DWDie, culength uint32) {
-       pw.d.addDwarfAddrField(pw.su, 0) // Null offset
-
-       // On AIX, save the current size of this compilation unit.
-       if pw.d.linkctxt.HeadType == objabi.Haix {
-               saveDwsectCUSize(pw.sname, pw.d.getPkgFromCUSym(pw.d.dtolsym(compunit.Sym)), uint64(pw.su.Size()-pw.sectionstart))
-       }
-       if isDwarf64(pw.d.linkctxt) {
-               pw.su.SetUint(pw.d.arch, pw.sectionstart+4, uint64(pw.su.Size()-pw.sectionstart)-12) // exclude the length field.
-               pw.su.SetUint(pw.d.arch, pw.culengthOff, uint64(culength))
-       } else {
-               pw.su.SetUint32(pw.d.arch, pw.sectionstart, uint32(pw.su.Size()-pw.sectionstart)-4) // exclude the length field.
-               pw.su.SetUint32(pw.d.arch, pw.culengthOff, culength)
-       }
-}
-
-func ispubname(die *dwarf.DWDie) bool {
-       switch die.Abbrev {
-       case dwarf.DW_ABRV_FUNCTION, dwarf.DW_ABRV_VARIABLE:
-               a := getattr(die, dwarf.DW_AT_external)
-               return a != nil && a.Value != 0
-       }
-
-       return false
-}
-
-func ispubtype(die *dwarf.DWDie) bool {
-       return die.Abbrev >= dwarf.DW_ABRV_NULLTYPE
-}
-
 func (d *dwctxt) writegdbscript() dwarfSecInfo {
        // TODO (aix): make it available
        if d.linkctxt.HeadType == objabi.Haix {
@@ -2019,9 +1935,9 @@ func dwarfGenerateDebugInfo(ctxt *Link) {
        // every DIE constructed and convert the symbols.
 }
 
-// dwarfGenerateDebugSyms constructs debug_line, debug_frame, debug_loc,
-// debug_pubnames and debug_pubtypes. It also writes out the debug_info
-// section using symbols generated in dwarfGenerateDebugInfo2.
+// dwarfGenerateDebugSyms constructs debug_line, debug_frame, and
+// debug_loc. It also writes out the debug_info section using symbols
+// generated in dwarfGenerateDebugInfo2.
 func dwarfGenerateDebugSyms(ctxt *Link) {
        if !dwarfEnabled(ctxt) {
                return
@@ -2070,15 +1986,10 @@ func (d *dwctxt) dwarfGenerateDebugSyms() {
        reversetree(&dwtypes.Child)
        movetomodule(d.linkctxt, &dwtypes)
 
-       pubNames := newPubWriter(d, ".debug_pubnames")
-       pubTypes := newPubWriter(d, ".debug_pubtypes")
-
-       infoSec := d.writeinfo(d.linkctxt.compUnits, abbrevSec.secSym(), pubNames, pubTypes)
+       infoSec := d.writeinfo(d.linkctxt.compUnits, abbrevSec.secSym())
 
        framesSec := d.writeframes()
        dwarfp = append(dwarfp, framesSec)
-       dwarfp = append(dwarfp, dwarfSecInfo{syms: []loader.Sym{pubNames.s}})
-       dwarfp = append(dwarfp, dwarfSecInfo{syms: []loader.Sym{pubTypes.s}})
        gdbScriptSec := d.writegdbscript()
        if gdbScriptSec.secSym() != 0 {
                dwarfp = append(dwarfp, gdbScriptSec)
@@ -2142,7 +2053,7 @@ func dwarfaddshstrings(ctxt *Link, shstrtab *loader.SymbolBuilder) {
                return
        }
 
-       secs := []string{"abbrev", "frame", "info", "loc", "line", "pubnames", "pubtypes", "gdb_scripts", "ranges"}
+       secs := []string{"abbrev", "frame", "info", "loc", "line", "gdb_scripts", "ranges"}
        for _, sec := range secs {
                shstrtab.Addstring(".debug_" + sec)
                if ctxt.IsExternal() {