cmd/link: remove reading/processing of function Autom records

Remove linker reading and processing of automs (no longer needed, now
that the compiler is emitting R_USETYPE relocations on functions). So
as to avoid changing the object file format, the object still contains
a count of automs, but this count is required to be zero.

Updates #34554.

Change-Id: I10230e191057c5c5705541eeb06f747d5f73c42d
Reviewed-on: https://go-review.googlesource.com/c/go/+/197500Reviewed-by: Jeremy Faller <jeremy@golang.org>

src/cmd/link/internal/ld/deadcode.go

@@ -270,12 +270,6 @@ func (d *deadcodepass) flood() {
 			if d.ctxt.Debugvlog > 1 {
 				d.ctxt.Logf("marktext %s\n", s.Name)
 			}
-			if s.FuncInfo != nil {
-				for _, a := range s.FuncInfo.Autom {
-					d.mark(a.Gotype, s)
-				}
-			}
-
 		}
 
 		if strings.HasPrefix(s.Name, "type.") && s.Name[5] != '.' {

src/cmd/link/internal/ld/lib.go

@@ -2366,7 +2366,6 @@ func genasmsym(ctxt *Link, put func(*Link, *sym.Symbol, string, SymbolType, int6
 		}
 	}
 
-	var off int32
 	for _, s := range ctxt.Textp {
 		put(ctxt, s, s.Name, TextSym, s.Value, s.Gotype)
 
@@ -2380,39 +2379,6 @@ func genasmsym(ctxt *Link, put func(*Link, *sym.Symbol, string, SymbolType, int6
 		if s.FuncInfo == nil {
 			continue
 		}
-		for _, a := range s.FuncInfo.Autom {
-			if a.Name == objabi.A_DELETED_AUTO {
-				put(ctxt, nil, "", DeletedAutoSym, 0, a.Gotype)
-				continue
-			}
-
-			// Emit a or p according to actual offset, even if label is wrong.
-			// This avoids negative offsets, which cannot be encoded.
-			if a.Name != objabi.A_AUTO && a.Name != objabi.A_PARAM {
-				continue
-			}
-
-			// compute offset relative to FP
-			if a.Name == objabi.A_PARAM {
-				off = a.Aoffset
-			} else {
-				off = a.Aoffset - int32(ctxt.Arch.PtrSize)
-			}
-
-			// FP
-			if off >= 0 {
-				put(ctxt, nil, a.Asym.Name, ParamSym, int64(off), a.Gotype)
-				continue
-			}
-
-			// SP
-			if off <= int32(-ctxt.Arch.PtrSize) {
-				put(ctxt, nil, a.Asym.Name, AutoSym, -(int64(off) + int64(ctxt.Arch.PtrSize)), a.Gotype)
-				continue
-			}
-			// Otherwise, off is addressing the saved program counter.
-			// Something underhanded is going on. Say nothing.
-		}
 	}
 
 	if ctxt.Debugvlog != 0 || *flagN {

src/cmd/link/internal/objfile/objfile.go

@@ -55,7 +55,6 @@ type objReader struct {
 	data        []byte
 	reloc       []sym.Reloc
 	pcdata      []sym.Pcdata
-	autom       []sym.Auto
 	funcdata    []*sym.Symbol
 	funcdataoff []int64
 	file        []*sym.Symbol
@@ -193,8 +192,7 @@ func (r *objReader) readSlices() {
 	r.reloc = make([]sym.Reloc, n)
 	n = r.readInt()
 	r.pcdata = make([]sym.Pcdata, n)
-	n = r.readInt()
-	r.autom = make([]sym.Auto, n)
+	_ = r.readInt() // TODO: remove on next object file rev (autom count)
 	n = r.readInt()
 	r.funcdata = make([]*sym.Symbol, n)
 	r.funcdataoff = make([]int64, n)
@@ -328,24 +326,10 @@ overwrite:
 			s.Attr |= sym.AttrTopFrame
 		}
 		n := r.readInt()
-		pc.Autom = r.autom[:n:n]
-		if !isdup {
-			r.autom = r.autom[n:]
+		if n != 0 {
+			log.Fatalf("stale object file: autom count nonzero")
 		}
 
-		for i := 0; i < n; i++ {
-			pc.Autom[i] = sym.Auto{
-				Asym:    r.readSymIndex(),
-				Aoffset: r.readInt32(),
-				Name:    r.readInt16(),
-				Gotype:  r.readSymIndex(),
-			}
-		}
-
-		// Temporary: zero out the autom list after we've read it.
-		// In a subsequent patch we'll remove autom handling more completely.
-		pc.Autom = nil
-
 		pc.Pcsp.P = r.readData()
 		pc.Pcfile.P = r.readData()
 		pc.Pcline.P = r.readData()

src/cmd/link/internal/sym/symbol.go

@@ -518,7 +518,6 @@ func SortSub(l *Symbol) *Symbol {
 type FuncInfo struct {
 	Args        int32
 	Locals      int32
-	Autom       []Auto
 	Pcsp        Pcdata
 	Pcfile      Pcdata
 	Pcline      Pcdata
@@ -542,10 +541,3 @@ type InlinedCall struct {
 type Pcdata struct {
 	P []byte
 }
-
-type Auto struct {
-	Asym    *Symbol
-	Gotype  *Symbol
-	Aoffset int32
-	Name    int16
-}