[lldb] Fix misaligned loads violation in DataExtractor

[bulbazord]

The implementation of the templated Get function contains UB. For example, the "GetDoubleUnaligned" unit test causes Get to perform an unaligned 8 byte read. This violates the double alignment requirement. Furthermore, it violates strict aliasing rules in C++. (We construct a const double * from a const uint8_t * and perform a read on the resulting double pointer).

DataExtractor should be able to read unaligned data to deal with different data formats, but we need to be careful to not perform unaligned reads/writes or violate strict aliasing rules.

rdar://160385383

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Alex Langford (bulbazord)

Changes

The implementation of the templated Get function contains UB. For example, the "GetDoubleUnaligned" unit test causes Get to perform an unaligned 8 byte read. This violates the double alignment requirement. Furthermore, it violates strict aliasing rules in C++. (We construct a const double * from a const uint8_t * and perform a read on the resulting double pointer).

DataExtractor should be able to read unaligned data to deal with different data formats, but we need to be careful to not perform unaligned reads/writes or violate strict aliasing rules.

rdar://160385383

---

Full diff: https://github.com/llvm/llvm-project/pull/163880.diff

1 Files Affected:

• (modified) lldb/include/lldb/Utility/DataExtractor.h (+1-1)

diff --git a/lldb/include/lldb/Utility/DataExtractor.h b/lldb/include/lldb/Utility/DataExtractor.h
index 0b7e771ed4f86..b4960f5e87c85 100644
--- a/lldb/include/lldb/Utility/DataExtractor.h
+++ b/lldb/include/lldb/Utility/DataExtractor.h
@@ -994,7 +994,7 @@ class DataExtractor {
     constexpr size_t src_size = sizeof(T);
     T val = fail_value;
 
-    const T *src = static_cast<const T *>(GetData(offset_ptr, src_size));
+    const void *src = GetData(offset_ptr, src_size);
     if (!src)
       return val;