Handle UTF-16 and UTF-32 constant CFStrings

[spyffe]

Summary

We have a longstanding issue where the expression parser does not handle wide CFStrings (e.g., @"凸凹") correctly, producing the useless error message

Internal error [IRForTarget]: An Objective-C constant string's string initializer is not an array
error: warning: expression result unused
error: The expression could not be prepared to run in the target

This is just a side effect of the fact that we don't handle wide string constants when converting these to CFStringCreateWithBytes. That function takes the string's encoding as an argument, so I made it work and added a testcase.

[jingham]

Other than the request for a more logging, this seems fine.

source/Plugins/ExpressionParser/Clang/IRForTarget.cpp

514–515

The default case here expresses "I don't know what this string is so I'm just going to try ASCII". That's fine, but we should log the unknown kind so that when this happens in the wild and we can't get a repro case, we'll be able to figure out something from the log.

[spyffe]

Updated to reflect Jim's comments.

[jingham]

Looks good.

packages/Python/lldbsuite/test/lang/objc/unicode-string/TestUnicodeString.py

+from lldbsuite.test import lldbinline
+from lldbsuite.test import decorators
+
+lldbinline.MakeInlineTest(
+    __file__, globals(), [
+        decorators.skipUnlessDarwin])

packages/Python/lldbsuite/test/lang/objc/unicode-string/main.m

+#import <Foundation/Foundation.h>
+
+int main() {
+  NSLog(@"凸"); //% self.expect("po @\"凹\"", DATA_TYPES_DISPLAYED_CORRECTLY, substrs = ["凹"])
+}

source/Plugins/ExpressionParser/Clang/IRForTarget.cpp

bool IRForTarget::RewriteObjCConstString(llvm::GlobalVariable *ns_str,
 
   if (cstr)
     string_array = dyn_cast<ConstantDataSequential>(cstr->getInitializer());
 
   Constant *alloc_arg = Constant::getNullValue(i8_ptr_ty);
   Constant *bytes_arg = cstr ? ConstantExpr::getBitCast(cstr, i8_ptr_ty)
                              : Constant::getNullValue(i8_ptr_ty);
   Constant *numBytes_arg = ConstantInt::get(
-      m_intptr_ty, cstr ? string_array->getNumElements() - 1 : 0, false);
-  Constant *encoding_arg = ConstantInt::get(
-      i32_ty, 0x0600, false); /* 0x0600 is kCFStringEncodingASCII */
-  Constant *isExternal_arg =
-      ConstantInt::get(i8_ty, 0x0, false); /* 0x0 is false */
+      m_intptr_ty, cstr ? (string_array->getNumElements() - 1) * string_array->getElementByteSize() : 0, false);
+ int encoding_flags = 0;
+ switch (string_array->getElementByteSize()) {
+ case 1:
+   encoding_flags = 0x08000100; /* 0x08000100 is kCFStringEncodingUTF8 */
+   break;
+ case 2:
+   encoding_flags = 0x0100; /* 0x0100 is kCFStringEncodingUTF16 */
+   break;
+ case 4:
+   encoding_flags = 0x0c000100; /* 0x0c000100 is kCFStringEncodingUTF32 */
+   break;
+ default:
+   encoding_flags = 0x0600; /* fall back to 0x0600, kCFStringEncodingASCII */
+   if (log) {
+     log->Printf("Encountered an Objective-C constant string with unusual "
+                 "element size %llu",
+                 string_array->getElementByteSize());
+   }
+ }
+ Constant *encoding_arg = ConstantInt::get(i32_ty, encoding_flags, false);
 
-  Value *argument_array[5];
 
-  argument_array[0] = alloc_arg;
-  argument_array[1] = bytes_arg;
-  argument_array[2] = numBytes_arg;
-  argument_array[3] = encoding_arg;
-  argument_array[4] = isExternal_arg;
 
-  ArrayRef<Value *> CFSCWB_arguments(argument_array, 5);
 
-  FunctionValueCache CFSCWB_Caller(
-      [this, &CFSCWB_arguments](llvm::Function *function) -> llvm::Value * {
-        return CallInst::Create(
-            m_CFStringCreateWithBytes, CFSCWB_arguments,
-            "CFStringCreateWithBytes",
-            llvm::cast<Instruction>(
-                m_entry_instruction_finder.GetValue(function)));
-      });
 
-  if (!UnfoldConstant(ns_str, nullptr, CFSCWB_Caller,
-                      m_entry_instruction_finder, m_error_stream)) {
-    if (log)
-      log->PutCString(
-          "Couldn't replace the NSString with the result of the call");
+ if (!UnfoldConstant(ns_str, nullptr, CFSCWB_Caller, m_entry_instruction_finder,
+                     m_error_stream)) {
 
-    m_error_stream.Printf("error [IRForTarget internal]: Couldn't replace an "
-                          "Objective-C constant string with a dynamic "
-                          "string\n");
 
-    return false;
   }
 
   ns_str->eraseFromParent();
 
   return true;
 }
 
 bool IRForTarget::RewriteObjCConstStrings() {
if (strstr(value_name_cstr, "_unnamed_cfstring_")) {
 
         m_error_stream.Printf("Internal error [IRForTarget]: An Objective-C "
                               "constant string's string initializer is not "
                               "constant\n");
 
         return false;
       }
 
-      if (nsstring_expr->getOpcode() != Instruction::GetElementPtr) {
-        if (log)
-          log->Printf("NSString initializer's str element is not a "
-                      "GetElementPtr expression, it's a %s",
-                      nsstring_expr->getOpcodeName());
-
-        m_error_stream.Printf("Internal error [IRForTarget]: An Objective-C "
-                              "constant string's string initializer is not an "
-                              "array\n");
-
-        return false;
-      }
+      GlobalVariable *cstr_global = nullptr;
 
+      if (nsstring_expr->getOpcode() == Instruction::GetElementPtr) {
         Constant *nsstring_cstr = nsstring_expr->getOperand(0);
-
-      GlobalVariable *cstr_global = dyn_cast<GlobalVariable>(nsstring_cstr);
+        cstr_global = dyn_cast<GlobalVariable>(nsstring_cstr);
+      } else if (nsstring_expr->getOpcode() == Instruction::BitCast) {
+        Constant *nsstring_cstr = nsstring_expr->getOperand(0);
+        cstr_global = dyn_cast<GlobalVariable>(nsstring_cstr);
+      }
 
       if (!cstr_global) {
         if (log)
           log->PutCString(
               "NSString initializer's str element is not a GlobalVariable");
 
-        m_error_stream.Printf("Internal error [IRForTarget]: An Objective-C "
-                              "constant string's string initializer doesn't "
-                              "point to a global\n");
+        m_error_stream.Printf("Internal error [IRForTarget]: Unhandled"
+                              "constant string initializer\n");
 
         return false;
       }
 
       if (!cstr_global->hasInitializer()) {
         if (log)
           log->PutCString("NSString initializer's str element does not have an "
                           "initializer");