Merge "symbols_map: don't error on bad elf files"

cmd/symbols_map/elf.go

@@ -18,8 +18,10 @@ import (
 	"debug/elf"
 	"encoding/binary"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"io"
+	"os"
 )
 
 const gnuBuildID = "GNU\x00"
@@ -27,12 +29,33 @@ const gnuBuildID = "GNU\x00"
 // elfIdentifier extracts the elf build ID from an elf file.  If allowMissing is true it returns
 // an empty identifier if the file exists but the build ID note does not.
 func elfIdentifier(filename string, allowMissing bool) (string, error) {
-	f, err := elf.Open(filename)
+	f, err := os.Open(filename)
 	if err != nil {
 		return "", fmt.Errorf("failed to open %s: %w", filename, err)
 	}
 	defer f.Close()
 
+	return elfIdentifierFromReaderAt(f, filename, allowMissing)
+}
+
+// elfIdentifier extracts the elf build ID from a ReaderAt.  If allowMissing is true it returns
+// an empty identifier if the file exists but the build ID note does not.
+func elfIdentifierFromReaderAt(r io.ReaderAt, filename string, allowMissing bool) (string, error) {
+	f, err := elf.NewFile(r)
+	if err != nil {
+		if allowMissing {
+			if errors.Is(err, io.EOF) {
+				return "", nil
+			}
+			if _, ok := err.(*elf.FormatError); ok {
+				// The file was not an elf file.
+				return "", nil
+			}
+		}
+		return "", fmt.Errorf("failed to parse elf file %s: %w", filename, err)
+	}
+	defer f.Close()
+
 	buildIDNote := f.Section(".note.gnu.build-id")
 	if buildIDNote == nil {
 		if allowMissing {

cmd/symbols_map/elf_test.go

@@ -16,11 +16,46 @@ package main
 
 import (
 	"bytes"
+	"debug/elf"
 	"encoding/binary"
 	"reflect"
 	"testing"
 )
 
+func Test_elfIdentifierFromReaderAt_BadElfFile(t *testing.T) {
+	tests := []struct {
+		name     string
+		contents string
+	}{
+		{
+			name:     "empty",
+			contents: "",
+		},
+		{
+			name:     "text",
+			contents: "#!/bin/bash\necho foobar",
+		},
+		{
+			name:     "empty elf",
+			contents: emptyElfFile(),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			buf := bytes.NewReader([]byte(tt.contents))
+			_, err := elfIdentifierFromReaderAt(buf, "<>", false)
+			if err == nil {
+				t.Errorf("expected error reading bad elf file without allowMissing")
+			}
+			_, err = elfIdentifierFromReaderAt(buf, "<>", true)
+			if err != nil {
+				t.Errorf("expected no error reading bad elf file with allowMissing, got %q", err.Error())
+			}
+		})
+	}
+}
+
 func Test_readNote(t *testing.T) {
 	note := []byte{
 		0x04, 0x00, 0x00, 0x00,
@@ -43,3 +78,36 @@ func Test_readNote(t *testing.T) {
 		t.Errorf("incorrect return, want %#v got %#v", expectedDescs, descs)
 	}
 }
+
+// emptyElfFile returns an elf file header with no program headers or sections.
+func emptyElfFile() string {
+	ident := [elf.EI_NIDENT]byte{}
+	identBuf := bytes.NewBuffer(ident[0:0:elf.EI_NIDENT])
+	binary.Write(identBuf, binary.LittleEndian, []byte("\x7fELF"))
+	binary.Write(identBuf, binary.LittleEndian, elf.ELFCLASS64)
+	binary.Write(identBuf, binary.LittleEndian, elf.ELFDATA2LSB)
+	binary.Write(identBuf, binary.LittleEndian, elf.EV_CURRENT)
+	binary.Write(identBuf, binary.LittleEndian, elf.ELFOSABI_LINUX)
+	binary.Write(identBuf, binary.LittleEndian, make([]byte, 8))
+
+	header := elf.Header64{
+		Ident:     ident,
+		Type:      uint16(elf.ET_EXEC),
+		Machine:   uint16(elf.EM_X86_64),
+		Version:   uint32(elf.EV_CURRENT),
+		Entry:     0,
+		Phoff:     uint64(binary.Size(elf.Header64{})),
+		Shoff:     uint64(binary.Size(elf.Header64{})),
+		Flags:     0,
+		Ehsize:    uint16(binary.Size(elf.Header64{})),
+		Phentsize: 0x38,
+		Phnum:     0,
+		Shentsize: 0x40,
+		Shnum:     0,
+		Shstrndx:  0,
+	}
+
+	buf := &bytes.Buffer{}
+	binary.Write(buf, binary.LittleEndian, header)
+	return buf.String()
+}