https://llvm.org/bugs/show_bug.cgi?id=23413
Bug ID: 23413
Summary: UBSan reports downcast/upcast of misaligned address in
std::set<long long>
Product: clang
Version: 3.6
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: -New Bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Created attachment 14283
--> https://llvm.org/bugs/attachment.cgi?id=14283&action=edit
Test program and output after building with Clang 3.6 (using GCC toolchain 4.9)
Using `long long' as std::set's value type causes UBSan as included in Clang
3.5 and 3.6 to report an downcast/upcast of a misaligned address at runtime.
Platform: Debian 8 (Jessie) on Intel x86 (32 bit)
C++ library: libstdc++
Reproduced using:
- Clang 3.5 w/ GCC toolchain 4.9
- Clang 3.6 w/ GCC toolchain 4.9
- Clang 3.6 w/ GCC toolchain 5.1.0
The issue does not occur with libc++. Shorter value types for std::set, e.g.
`long' or `char', work. Packaging the `long long' in another type, e.g. a
struct, works too.
The fact that this is not reproducible when building with GCC 5.1.0 (with
-fsanitize=alignment) and neither when compiling for x86-64 leads me to believe
that this is an issue in Clang's implementation of UBSan.
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