fix(asm): reject duplicate symbol declarations like the toolchain

Assisted-by: GLM 5.3 Flash

asm/link.go

@@ -557,11 +557,66 @@ type dataSym struct {
 	relocs []Reloc
 }
 
+// checkDuplicateDecls rejects a symbol the file declares twice, the
+// toolchain's OnList rule (cmd/internal/obj, InitTextSym and GloblPos,
+// measured with go tool asm): the second declaration of a symbol is
+// diagnosed as a redeclaration whether the pair is two TEXTs, two GLOBLs
+// or one of each, and a second TEXT carries the other declaration's line
+// the way the toolchain's note does.  The DUPOK flag plays no part at
+// assembly time: it legalises duplicate definitions across files
+// (AttrDuplicateOK, which the linker resolves), never two declarations
+// inside one file, so a DUPOK pair here is rejected exactly like a plain
+// one.  Symbol identity follows the object model: the package prefix and
+// the <> static marker are part of the name (foo(SB), foo<>(SB) and
+// other·foo(SB) are three symbols); the ABI selector is not, because
+// outside the runtime package, where alone it is legal, foo<ABIInternal>(SB)
+// resolves to foo(SB) and is a redeclaration.
+func checkDuplicateDecls(f *ast.File) error {
+	type decl struct {
+		text bool
+		line int
+	}
+	seen := make(map[string]decl)
+	symKey := func(s *ast.Symbol) string {
+		key := s.Pkg + "\x00" + s.Name
+		if s.Static {
+			key += "\x00<>"
+		}
+		return key
+	}
+	for _, d := range f.Decls {
+		switch t := d.(type) {
+		case *ast.Text:
+			if first, dup := seen[symKey(t.Name)]; dup {
+				if first.text {
+					return fmt.Errorf("symbol %q redeclared (other declaration on line %d)", t.Name.Name, first.line)
+				}
+				return fmt.Errorf("symbol %q redeclared", t.Name.Name)
+			}
+			seen[symKey(t.Name)] = decl{text: true, line: t.Pos().Line}
+		case *ast.Globl:
+			if t.Name == nil || t.Name.Pseudo != "SB" {
+				continue
+			}
+			if _, dup := seen[symKey(t.Name)]; dup {
+				return fmt.Errorf("symbol %q redeclared", t.Name.Name)
+			}
+			seen[symKey(t.Name)] = decl{line: t.Pos().Line}
+		}
+	}
+	return nil
+}
+
 // collectData gathers the file's static symbols (GLOBL) and their initial
 // contents (DATA) into byte buffers.  Two passes: the Plan 9 convention puts
 // every DATA line before its symbol's GLOBL, so the symbols are registered
-// before the initialisers are applied.
+// before the initialisers are applied.  Every per-architecture entry point
+// collects data before assembling text, so the duplicate-declaration check
+// rides here and covers them all.
 func collectData(f *ast.File) ([]dataSym, error) {
+	if err := checkDuplicateDecls(f); err != nil {
+		return nil, err
+	}
 	index := map[string]int{}
 	var syms []dataSym
 	for _, d := range f.Decls {
@@ -573,9 +628,6 @@ func collectData(f *ast.File) ([]dataSym, error) {
 			continue
 		}
 		name := gd.Name.Name
-		if _, dup := index[name]; dup {
-			return nil, fmt.Errorf("duplicate GLOBL %q", name)
-		}
 		size := 0
 		if gd.Size != nil && gd.Size.Imm.HasVal {
 			size = int(gd.Size.Imm.Val)