debug/elf: make check for empty symbol section consistent for 64-bit and 32-bit binaries

The check for whether a binary's symbols section is empty is
inconsistent across the 32-bit and 64-bit flows.

Change-Id: I1abc235320a53cf957cfb83c9e7bcad6e52bc529
GitHub-Last-Rev: f264915
GitHub-Pull-Request: #75334
Reviewed-on: https://go-review.googlesource.com/c/go/+/702195
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Keith Randall <khr@google.com>

Author: adityasaky

src/debug/elf/file.go

@@ -641,7 +641,7 @@ func (f *File) getSymbols32(typ SectionType) ([]Symbol, []byte, error) {
 		return nil, nil, fmt.Errorf("cannot load symbol section: %w", err)
 	}
 	if len(data) == 0 {
-		return nil, nil, errors.New("symbol section is empty")
+		return nil, nil, ErrNoSymbols
 	}
 	if len(data)%Sym32Size != 0 {
 		return nil, nil, errors.New("length of symbol section is not a multiple of SymSize")
@@ -690,12 +690,12 @@ func (f *File) getSymbols64(typ SectionType) ([]Symbol, []byte, error) {
 	if err != nil {
 		return nil, nil, fmt.Errorf("cannot load symbol section: %w", err)
 	}
-	if len(data)%Sym64Size != 0 {
-		return nil, nil, errors.New("length of symbol section is not a multiple of Sym64Size")
-	}
 	if len(data) == 0 {
 		return nil, nil, ErrNoSymbols
 	}
+	if len(data)%Sym64Size != 0 {
+		return nil, nil, errors.New("length of symbol section is not a multiple of Sym64Size")
+	}
 
 	strdata, err := f.stringTable(symtabSection.Link)
 	if err != nil {