From: Than McIntosh <thanm@google.com>
Date: Tue, 30 Jun 2020 14:22:13 +0000 (-0400)
Subject: [dev.link] cmd/link: skip symtab entries for selected file local symbols
X-Git-Tag: go1.16beta1~1378^2~58
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=8aa036e9135f6f24ab6a5f250a4fba47a5d3a083;p=gostls13.git

[dev.link] cmd/link: skip symtab entries for selected file local symbols

Don't emit symbol table entries for compiler-generated file-local
symbols (this category includes .stmp_* temporaries and *.stkobj
symbols). Note that user-written static symbols within assembler
sources will still be added to the symbol table. Apply the same test
when emitting DWARF for global variables.

Change-Id: I4db77a2750a0b575e051dfea895c4742cf6709a6
Reviewed-on: https://go-review.googlesource.com/c/go/+/240539
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
---

diff --git a/src/cmd/internal/goobj2/objfile.go b/src/cmd/internal/goobj2/objfile.go
index 433eafa559..938362901a 100644
--- a/src/cmd/internal/goobj2/objfile.go
+++ b/src/cmd/internal/goobj2/objfile.go
@@ -241,6 +241,7 @@ const SymABIstatic = ^uint16(0)
 const (
 	ObjFlagShared            = 1 << iota // this object is built with -shared
 	ObjFlagNeedNameExpansion             // the linker needs to expand `"".` to package path in symbol names
+	ObjFlagFromAssembly                  // object is from asm src, not go
 )
 
 // Sym.Flag
@@ -742,3 +743,4 @@ func (r *Reader) Flags() uint32 {
 
 func (r *Reader) Shared() bool            { return r.Flags()&ObjFlagShared != 0 }
 func (r *Reader) NeedNameExpansion() bool { return r.Flags()&ObjFlagNeedNameExpansion != 0 }
+func (r *Reader) FromAssembly() bool      { return r.Flags()&ObjFlagFromAssembly != 0 }
diff --git a/src/cmd/internal/obj/objfile2.go b/src/cmd/internal/obj/objfile2.go
index b12b6fe84c..fbd2395d1f 100644
--- a/src/cmd/internal/obj/objfile2.go
+++ b/src/cmd/internal/obj/objfile2.go
@@ -41,6 +41,9 @@ func WriteObjFile(ctxt *Link, b *bio.Writer, pkgpath string) {
 	if pkgpath == "" {
 		flags |= goobj2.ObjFlagNeedNameExpansion
 	}
+	if ctxt.IsAsm {
+		flags |= goobj2.ObjFlagFromAssembly
+	}
 	h := goobj2.Header{
 		Magic:       goobj2.Magic,
 		Fingerprint: ctxt.Fingerprint,
diff --git a/src/cmd/link/internal/ld/dwarf.go b/src/cmd/link/internal/ld/dwarf.go
index d15cde4e38..a574472aa4 100644
--- a/src/cmd/link/internal/ld/dwarf.go
+++ b/src/cmd/link/internal/ld/dwarf.go
@@ -1887,11 +1887,12 @@ func dwarfGenerateDebugInfo(ctxt *Link) {
 		if d.ldr.SymGoType(idx) == 0 {
 			continue
 		}
-
-		sn := d.ldr.SymName(idx)
-		if ctxt.LinkMode != LinkExternal && isStaticTemp(sn) {
+		// Skip file local symbols (this includes static tmps, stack
+		// object symbols, and local symbols in assembler src files).
+		if d.ldr.IsFileLocal(idx) {
 			continue
 		}
+		sn := d.ldr.SymName(idx)
 		if sn == "" {
 			// skip aux symbols
 			continue
diff --git a/src/cmd/link/internal/ld/symtab.go b/src/cmd/link/internal/ld/symtab.go
index b5f4288b6c..fddf85f1c5 100644
--- a/src/cmd/link/internal/ld/symtab.go
+++ b/src/cmd/link/internal/ld/symtab.go
@@ -196,7 +196,14 @@ func genelfsym(ctxt *Link, elfbind int) {
 			return false
 		}
 		// FIXME: avoid having to do name inspections here.
+		// NB: the restrictions below on file local symbols are a bit
+		// arbitrary -- if it turns out we need nameless static
+		// symbols they could be relaxed/removed.
 		sn := ldr.SymName(s)
+		if (sn == "" || sn[0] == '.') && ldr.IsFileLocal(s) {
+			panic(fmt.Sprintf("unexpected file local symbol %d %s<%d>\n",
+				s, sn, ldr.SymVersion(s)))
+		}
 		if (sn == "" || sn[0] == '.') && !ldr.IsFileLocal(s) {
 			return false
 		}
@@ -499,15 +506,14 @@ func (ctxt *Link) symtab() []sym.SymKind {
 	nsym := loader.Sym(ldr.NSym())
 	symGroupType := make([]sym.SymKind, nsym)
 	for s := loader.Sym(1); s < nsym; s++ {
-		name := ldr.SymName(s)
-		if !ctxt.IsExternal() && isStaticTemp(name) {
+		if !ctxt.IsExternal() && ldr.IsFileLocal(s) && !ldr.IsFromAssembly(s) {
 			ldr.SetAttrNotInSymbolTable(s, true)
 		}
-
 		if !ldr.AttrReachable(s) || ldr.AttrSpecial(s) || (ldr.SymType(s) != sym.SRODATA && ldr.SymType(s) != sym.SGOFUNC) {
 			continue
 		}
 
+		name := ldr.SymName(s)
 		switch {
 		case strings.HasPrefix(name, "type."):
 			if !ctxt.DynlinkingGo() {
@@ -768,10 +774,3 @@ func (ctxt *Link) symtab() []sym.SymKind {
 	}
 	return symGroupType
 }
-
-func isStaticTemp(name string) bool {
-	if i := strings.LastIndex(name, "/"); i >= 0 {
-		name = name[i:]
-	}
-	return strings.Contains(name, "..stmp_")
-}
diff --git a/src/cmd/link/internal/loader/loader.go b/src/cmd/link/internal/loader/loader.go
index 3de0ab34b4..28847ad17a 100644
--- a/src/cmd/link/internal/loader/loader.go
+++ b/src/cmd/link/internal/loader/loader.go
@@ -683,7 +683,19 @@ func (l *Loader) SymVersion(i Sym) int {
 	return int(abiToVer(r.Sym(li).ABI(), r.version))
 }
 
-func (l *Loader) IsFileLocal(i Sym) bool { return l.SymVersion(i) >= sym.SymVerStatic }
+func (l *Loader) IsFileLocal(i Sym) bool {
+	return l.SymVersion(i) >= sym.SymVerStatic
+}
+
+// IsFromAssembly returns true if this symbol is derived from an
+// object file generated by the Go assembler.
+func (l *Loader) IsFromAssembly(i Sym) bool {
+	if l.IsExternal(i) {
+		return false
+	}
+	r, _ := l.toLocal(i)
+	return r.FromAssembly()
+}
 
 // Returns the type of the i-th symbol.
 func (l *Loader) SymType(i Sym) sym.SymKind {