Miscellaneous fixes for big-endian systems

[uweigand]

Summary

This patch fixes a bunch of issues that show up on big-endian systems:

• The gnu_libstdcpp.py script doesn't follow the way libstdc++ encodes bit vectors: it should identify the enclosing *word* and then access the appropriate bit within that word. Instead, the script simply operates on bytes. This gives the same result on little-endian systems, but not on big-endian.

• lldb_private::formatters::WCharSummaryProvider always assumes wchar_t is UTF16, even though it could also be UTF8 or UTF32. This is mostly not an issue on little-endian systems, but immediately fails on BE. Fixed by checking the size of wchar_t like WCharStringSummaryProvider already does.

• ClangASTContext::GetChildCompilerTypeAtIndex uses uint32_t to access the virtual base offset stored in the vtable, even though the size of this field matches the target pointer size according to the C++ ABI. Again, this is mostly not visible on LE, but fails on BE.

• Process::ReadStringFromMemory uses strncmp to search for a terminator consisting of multiple zero bytes. This doesn't work since strncmp will stop already at the first zero byte. Use memcmp instead.

[clayborg]

Looks good.

lldb/trunk/examples/synthetic/gnu_libstdcpp.py

def num_children(self):
         offset = self.offset.GetValueAsUnsigned(0)
         if finish >= start:
           return (finish - start) * 8 + offset
       return 0
 
     def get_child_at_index(self, index):
       if index >= self.num_children():
         return None
-      byte_offset = index / 8
-      bit_offset = index % 8
-      element_size = self.start_p.GetType().GetPointeeType().GetByteSize()
-      data = self.start_p.GetPointeeData(byte_offset / element_size)
-      bit = data.GetUnsignedInt8(lldb.SBError(), byte_offset % element_size) & (1 << bit_offset)
+      element_type = self.start_p.GetType().GetPointeeType()
+      element_bits = 8 * element_type.GetByteSize()
+      element_offset = index / element_bits
+      bit_offset = index % element_bits
+      element = self.start_p.CreateChildAtOffset('['+str(index)+']',element_offset,element_type)
+      bit = element.GetValueAsUnsigned(0) & (1 << bit_offset)
       if bit != 0:
         value_expr = "(bool)true"
       else:
         value_expr = "(bool)false"
       return self.valobj.CreateValueFromExpression("[%d]" % index, value_expr)
 
     def update(self):
       try:

lldb/trunk/source/Plugins/Language/CPlusPlus/CxxStringTypes.cpp

 {
     DataExtractor data;
     Error error;
     valobj.GetData(data, error);
     
     if (error.Fail())
         return false;
     
+    // Get a wchar_t basic type from the current type system
+    CompilerType wchar_compiler_type = valobj.GetCompilerType().GetBasicTypeFromAST(lldb::eBasicTypeWChar);
+
+    if (!wchar_compiler_type)
+        return false;
+
+    const uint32_t wchar_size = wchar_compiler_type.GetBitSize(nullptr); // Safe to pass NULL for exe_scope here
+
     StringPrinter::ReadBufferAndDumpToStreamOptions options(valobj);
     options.SetData(data);
     options.SetStream(&stream);
     options.SetPrefixToken("L");
     options.SetQuote('\'');
     options.SetSourceSize(1);
     options.SetBinaryZeroIsTerminator(false);
     
+    switch (wchar_size)
+    {
+        case 8:
+            return StringPrinter::ReadBufferAndDumpToStream<StringPrinter::StringElementType::UTF8>(options);
+        case 16:
             return StringPrinter::ReadBufferAndDumpToStream<StringPrinter::StringElementType::UTF16>(options);
+        case 32:
+            return StringPrinter::ReadBufferAndDumpToStream<StringPrinter::StringElementType::UTF32>(options);
+        default:
+            stream.Printf("size for wchar_t is not valid");
+            return true;
+    }
+    return true;
 }

lldb/trunk/source/Symbol/ClangASTContext.cpp

switch (parent_type_class)
                                                     clang::ItaniumVTableContext *itanium_vtable_ctx = static_cast<clang::ItaniumVTableContext *>(vtable_ctx);
                                                     if (vtable_ptr_addr)
                                                     {
                                                         const lldb::addr_t vtable_ptr = process->ReadPointerFromMemory(vtable_ptr_addr, err);
                                                         if (vtable_ptr != LLDB_INVALID_ADDRESS)
                                                         {
                                                             clang::CharUnits base_offset_offset = itanium_vtable_ctx->getVirtualBaseOffsetOffset(cxx_record_decl, base_class_decl);
                                                             const lldb::addr_t base_offset_addr = vtable_ptr + base_offset_offset.getQuantity();
-                                                            const uint32_t base_offset = process->ReadUnsignedIntegerFromMemory(base_offset_addr, 4, UINT32_MAX, err);
-                                                            if (base_offset != UINT32_MAX)
+                                                            const uint32_t base_offset_size = process->GetAddressByteSize();
+                                                            const uint64_t base_offset = process->ReadUnsignedIntegerFromMemory(base_offset_addr, base_offset_size, UINT32_MAX, err);
+                                                            if (base_offset < UINT32_MAX)
                                                             {
                                                                 handled = true;
                                                                 bit_offset = base_offset * 8;
                                                             }
                                                         }
                                                     }
                                                 }
                                             }

lldb/trunk/source/Target/Process.cpp

if (dst && max_bytes && type_width && max_bytes >= type_width)
             size_t bytes_read = ReadMemory (curr_addr, curr_dst, bytes_to_read, error);
 
             if (bytes_read == 0)
                 break;
 
             // Search for a null terminator of correct size and alignment in bytes_read
             size_t aligned_start = total_bytes_read - total_bytes_read % type_width;
             for (size_t i = aligned_start; i + type_width <= total_bytes_read + bytes_read; i += type_width)
-                if (::strncmp(&dst[i], terminator, type_width) == 0)
+                if (::memcmp(&dst[i], terminator, type_width) == 0)
                 {
                     error.Clear();
                     return i;
                 }
 
             total_bytes_read += bytes_read;
             curr_dst += bytes_read;
             curr_addr += bytes_read;