debug/pe: parse the import directory correctly

This parses the import table properly which allows for debug/pe
to extract import symbols from pecoffs linked with an import
table in a section named something other than ".idata"

The section names in a pecoff object aren't guaranteed to actually
mean anything, so hardcoding a search for the ".idata" section
is not guaranteed to find the import table in all shared libraries.
This resulted in debug/pe being unable to read import symbols
from some libraries.

The proper way to locate the import table is to validate the
number of data directory entries, locate the import entry, and
then use the va to identify the section containing the import
table. This patch does exactly this.

Fixes #16103.

Change-Id: I3ab6de7f896a0c56bb86c3863e504e8dd4c8faf3
GitHub-Last-Rev: ce8077cb15
GitHub-Pull-Request: golang/go#25193
Reviewed-on: https://go-review.googlesource.com/110555
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

src/debug/pe/file.go

@@ -260,19 +260,59 @@ type ImportDirectory struct {
 // It does not return weak symbols.
 func (f *File) ImportedSymbols() ([]string, error) {
 	pe64 := f.Machine == IMAGE_FILE_MACHINE_AMD64
-	ds := f.Section(".idata")
-	if ds == nil {
-		// not dynamic, so no libraries
+
+	// grab the number of data directory entries
+	var dd_length uint32
+	if pe64 {
+		dd_length = f.OptionalHeader.(*OptionalHeader64).NumberOfRvaAndSizes
+	} else {
+		dd_length = f.OptionalHeader.(*OptionalHeader32).NumberOfRvaAndSizes
+	}
+
+	// check that the length of data directory entries is large 
+	// enough to include the imports directory.
+	if dd_length < IMAGE_DIRECTORY_ENTRY_IMPORT + 1 {
 		return nil, nil
 	}
+
+	// grab the import data directory entry
+	var idd DataDirectory
+	if pe64 {
+		idd = f.OptionalHeader.(*OptionalHeader64).DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT]
+	} else {
+		idd = f.OptionalHeader.(*OptionalHeader32).DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT]
+	}
+
+	// figure out which section contains the import directory table
+	var ds *Section
+	ds = nil
+	for _, s := range f.Sections {
+		if s.VirtualAddress <= idd.VirtualAddress && idd.VirtualAddress < s.VirtualAddress + s.VirtualSize {
+			ds = s
+			break
+		}
+	}
+
+	// didn't find a section, so no import libraries were found
+	if ds == nil {
+		return nil, nil
+	}
+
 	d, err := ds.Data()
 	if err != nil {
 		return nil, err
 	}
+
+	// seek to the virtual address specified in the import data directory
+	d = d[idd.VirtualAddress - ds.VirtualAddress:]
+
+	// start decoding the import directory
 	var ida []ImportDirectory
 	for len(d) > 0 {
 		var dt ImportDirectory
 		dt.OriginalFirstThunk = binary.LittleEndian.Uint32(d[0:4])
+		dt.TimeDateStamp = binary.LittleEndian.Uint32(d[4:8])
+		dt.ForwarderChain = binary.LittleEndian.Uint32(d[8:12])
 		dt.Name = binary.LittleEndian.Uint32(d[12:16])
 		dt.FirstThunk = binary.LittleEndian.Uint32(d[16:20])
 		d = d[20:]
@@ -282,7 +322,7 @@ func (f *File) ImportedSymbols() ([]string, error) {
 		ida = append(ida, dt)
 	}
 	// TODO(brainman): this needs to be rewritten
-	//  ds.Data() return contets of .idata section. Why store in variable called "names"?
+	//  ds.Data() returns contents of section containing import table. Why store in variable called "names"?
 	//  Why we are retrieving it second time? We already have it in "d", and it is not modified anywhere.
 	//  getString does not extracts a string from symbol string table (as getString doco says).
 	//  Why ds.Data() called again and again in the loop?

src/debug/pe/file_test.go

@@ -532,3 +532,31 @@ func TestBuildingWindowsGUI(t *testing.T) {
 		t.Fatalf("unexpected OptionalHeader type: have %T, but want *pe.OptionalHeader32 or *pe.OptionalHeader64", oh)
 	}
 }
+
+func TestImportTableInUnknownSection(t *testing.T) {
+	if runtime.GOOS != "windows" {
+		t.Skip("skipping windows only test")
+	}
+
+	// first we need to find this font driver
+	path, err := exec.LookPath("atmfd.dll")
+	if err != nil {
+		t.Fatalf("unable to locate required file %q in search path: %s", "atmfd.dll", err)
+	}
+
+	f, err := Open(path)
+	if err != nil {
+		t.Error(err)
+	}
+	defer f.Close()
+
+	// now we can extract its imports
+	symbols, err := f.ImportedSymbols()
+	if err != nil {
+		t.Error(err)
+	}
+
+	if len(symbols) == 0 {
+		t.Fatalf("unable to locate any imported symbols within file %q.", path)
+	}
+}

src/debug/pe/pe.go

@@ -108,3 +108,23 @@ const (
 	IMAGE_FILE_MACHINE_THUMB     = 0x1c2
 	IMAGE_FILE_MACHINE_WCEMIPSV2 = 0x169
 )
+
+// IMAGE_DIRECTORY_ENTRY constants
+const (
+	IMAGE_DIRECTORY_ENTRY_EXPORT = 0
+	IMAGE_DIRECTORY_ENTRY_IMPORT = 1
+	IMAGE_DIRECTORY_ENTRY_RESOURCE = 2
+	IMAGE_DIRECTORY_ENTRY_EXCEPTION = 3
+	IMAGE_DIRECTORY_ENTRY_SECURITY = 4
+	IMAGE_DIRECTORY_ENTRY_BASERELOC = 5
+	IMAGE_DIRECTORY_ENTRY_DEBUG = 6
+	IMAGE_DIRECTORY_ENTRY_ARCHITECTURE = 7
+	IMAGE_DIRECTORY_ENTRY_GLOBALPTR = 8
+	IMAGE_DIRECTORY_ENTRY_TLS = 9
+	IMAGE_DIRECTORY_ENTRY_LOAD_CONFIG = 10
+	IMAGE_DIRECTORY_ENTRY_BOUND_IMPORT = 11
+	IMAGE_DIRECTORY_ENTRY_IAT = 12
+	IMAGE_DIRECTORY_ENTRY_DELAY_IMPORT = 13
+	IMAGE_DIRECTORY_ENTRY_COM_DESCRIPTOR = 14
+)
+