debug/pe: rework reading of aux symbols to fix endianity problems

This patch reworks CL 394534 to fix things so that reading auxiliary
symbol info works properly in a cross-endian mode (running
debug/pe-based tool on a big-endian system). The previous
implementation read in all symbol records using the primary symbol
format, then just used a pointer cast to convert to the auxiliary
format, which doesn't play well if host and target have different
endianness.

Fixes #52079.

Change-Id: I143d94d9313a265f11ca7befd254bdb150698834
Reviewed-on: https://go-review.googlesource.com/c/go/+/397485
Run-TryBot: Than McIntosh <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Alex Brainman <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: thanm

src/debug/pe/symbol.go

@@ -23,6 +23,29 @@ type COFFSymbol struct {
 	NumberOfAuxSymbols uint8
 }
 
+// readCOFFSymbols reads in the symbol table for a PE file, returning
+// a slice of COFFSymbol objects. The PE format includes both primary
+// symbols (whose fields are described by COFFSymbol above) and
+// auxiliary symbols; all symbols are 18 bytes in size. The auxiliary
+// symbols for a given primary symbol are placed following it in the
+// array, e.g.
+//
+//   ...
+//   k+0:  regular sym k
+//   k+1:    1st aux symbol for k
+//   k+2:    2nd aux symbol for k
+//   k+3:  regular sym k+3
+//   k+4:    1st aux symbol for k+3
+//   k+5:  regular sym k+5
+//   k+6:  regular sym k+6
+//
+// The PE format allows for several possible aux symbol formats. For
+// more info see:
+//
+//     https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#auxiliary-symbol-records
+//
+// At the moment this package only provides APIs for looking at
+// aux symbols of format 5 (associated with section definition symbols).
 func readCOFFSymbols(fh *FileHeader, r io.ReadSeeker) ([]COFFSymbol, error) {
 	if fh.PointerToSymbolTable == 0 {
 		return nil, nil
@@ -35,9 +58,31 @@ func readCOFFSymbols(fh *FileHeader, r io.ReadSeeker) ([]COFFSymbol, error) {
 		return nil, fmt.Errorf("fail to seek to symbol table: %v", err)
 	}
 	syms := make([]COFFSymbol, fh.NumberOfSymbols)
-	err = binary.Read(r, binary.LittleEndian, syms)
-	if err != nil {
-		return nil, fmt.Errorf("fail to read symbol table: %v", err)
+	naux := 0
+	for k := range syms {
+		if naux == 0 {
+			// Read a primary symbol.
+			err = binary.Read(r, binary.LittleEndian, &syms[k])
+			if err != nil {
+				return nil, fmt.Errorf("fail to read symbol table: %v", err)
+			}
+			// Record how many auxiliary symbols it has.
+			naux = int(syms[k].NumberOfAuxSymbols)
+		} else {
+			// Read an aux symbol. At the moment we assume all
+			// aux symbols are format 5 (obviously this doesn't always
+			// hold; more cases will be needed below if more aux formats
+			// are supported in the future).
+			naux--
+			aux := (*COFFSymbolAuxFormat5)(unsafe.Pointer(&syms[k]))
+			err = binary.Read(r, binary.LittleEndian, aux)
+			if err != nil {
+				return nil, fmt.Errorf("fail to read symbol table: %v", err)
+			}
+		}
+	}
+	if naux != 0 {
+		return nil, fmt.Errorf("fail to read symbol table: %d aux symbols unread", naux)
 	}
 	return syms, nil
 }

src/debug/pe/symbols_test.go

@@ -6,7 +6,6 @@ package pe
 
 import (
 	"fmt"
-	"runtime"
 	"testing"
 )
 
@@ -18,13 +17,6 @@ type testpoint struct {
 }
 
 func TestReadCOFFSymbolAuxInfo(t *testing.T) {
-
-	switch runtime.GOARCH {
-	case "mips", "mips64", "ppc64", "s390x":
-		t.Skipf("Skipping on %s (big endian) until issue #52079 fixed",
-			runtime.GOARCH)
-	}
-
 	testpoints := map[int]testpoint{
 		39: testpoint{
 			name:   ".rdata$.refptr.__native_startup_lock",