Support small methods and selector indirection

Author: Mike Richter

Source/CDMachOFile.m

@@ -350,6 +350,13 @@ - (NSString *)stringAtAddress:(NSUInteger)address;
     if (offset == 0)
         return nil;
 
+    // Support small methods referencing selector names in __objc_selrefs.
+    CDSection *section = [segment sectionContainingAddress:address];
+    if ([[section sectionName] isEqualToString:@"__objc_selrefs"]) {
+        const void * reference = [self.data bytes] + offset;
+        offset = ([self ptrSize] == 8) ? *((uint64_t *)reference) : *((uint32_t *)reference);
+    }
+
     ptr = (uint8_t *)[self.data bytes] + offset;
 
     return [[NSString alloc] initWithBytes:ptr length:strlen(ptr) encoding:NSASCIIStringEncoding];

Source/CDMachOFileDataCursor.h

@@ -28,5 +28,6 @@
 
 // Read using the current byteOrder and ptrSize (from the machOFile)
 - (uint64_t)readPtr;
+- (uint64_t)readPtr:(bool)small;
 
 @end

Source/CDMachOFileDataCursor.m

@@ -110,4 +110,15 @@ - (uint64_t)readPtr;
     return 0;
 }
 
+- (uint64_t)readPtr:(bool)small;
+{
+    // "small" pointers are signed 32-bit values
+    if (small) {
+        // The pointers are relative to the location in the image, so get the offset before reading the offset:
+        return [self offset] + [self readInt32];
+    } else {
+        return [self readPtr];
+    }
+}
+
 @end

Source/CDObjectiveC2Processor.h

@@ -5,6 +5,10 @@
 
 #import "CDObjectiveCProcessor.h"
 
+#define METHOD_LIST_T_RESERVED_BITS 0x7FFF0003
+#define METHOD_LIST_T_SMALL_METHOD_FLAG 0x80000000
+#define METHOD_LIST_T_ENTSIZE_MASK (METHOD_LIST_T_RESERVED_BITS|METHOD_LIST_T_SMALL_METHOD_FLAG)
+
 @interface CDObjectiveC2Processor : CDObjectiveCProcessor
 
 @end

Source/CDObjectiveC2Processor.m

@@ -398,17 +398,19 @@ - (NSArray *)loadMethodsAtAddress:(uint64_t)address extendedMethodTypesCursor:(C
 
         struct cd_objc2_list_header listHeader;
 
-        // See getEntsize() from http://www.opensource.apple.com/source/objc4/objc4-532.2/runtime/objc-runtime-new.h
-        listHeader.entsize = [cursor readInt32] & ~(uint32_t)3;
-        listHeader.count   = [cursor readInt32];
-        NSParameterAssert(listHeader.entsize == 3 * [self.machOFile ptrSize]);
-        
+        // See https://opensource.apple.com/source/objc4/objc4-787.1/runtime/objc-runtime-new.h
+        uint32_t value = [cursor readInt32];
+        listHeader.entsize = value & ~METHOD_LIST_T_ENTSIZE_MASK;
+        bool small = (value & METHOD_LIST_T_SMALL_METHOD_FLAG) != 0;
+        listHeader.count = [cursor readInt32];
+        NSParameterAssert(listHeader.entsize == 3 * (small ? sizeof(int32_t) : [self.machOFile ptrSize]));
+
         for (uint32_t index = 0; index < listHeader.count; index++) {
             struct cd_objc2_method objc2Method;
-            
-            objc2Method.name  = [cursor readPtr];
-            objc2Method.types = [cursor readPtr];
-            objc2Method.imp   = [cursor readPtr];
+
+            objc2Method.name  = [cursor readPtr:small];
+            objc2Method.types = [cursor readPtr:small];
+            objc2Method.imp   = [cursor readPtr:small];
             NSString *name    = [self.machOFile stringAtAddress:objc2Method.name];
             NSString *types   = [self.machOFile stringAtAddress:objc2Method.types];
 
@@ -417,7 +419,7 @@ - (NSArray *)loadMethodsAtAddress:(uint64_t)address extendedMethodTypesCursor:(C
                 types = [self.machOFile stringAtAddress:extendedMethodTypes];
             }
 
-            //NSLog(@"%3u: %016lx %016lx %016lx", index, objc2Method.name, objc2Method.types, objc2Method.imp);
+            //NSLog(@"%3u: %016llx %016llx %016llx", index, objc2Method.name, objc2Method.types, objc2Method.imp);
             //NSLog(@"name: %@", name);
             //NSLog(@"types: %@", types);