[llvm] r223402 - Fix UBSan report in StringMap implementation.

[David Blaikie]

On Thu, Dec 4, 2014 at 2:45 PM, Alexey Samsonov <vonosmas at gmail.com> wrote:

> Author: samsonov
> Date: Thu Dec  4 16:45:31 2014
> New Revision: 223402
>
> URL: http://llvm.org/viewvc/llvm-project?rev=223402&view=rev
> Log:
> Fix UBSan report in StringMap implementation.
>
> Use offsetof() instead of a member access within null pointer.
>
> Modified:
>     llvm/trunk/include/llvm/ADT/StringMap.h
>
> Modified: llvm/trunk/include/llvm/ADT/StringMap.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/StringMap.h?rev=223402&r1=223401&r2=223402&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/ADT/StringMap.h (original)
> +++ llvm/trunk/include/llvm/ADT/StringMap.h Thu Dec  4 16:45:31 2014
> @@ -182,10 +182,7 @@ public:
>    /// GetStringMapEntryFromValue - Given a value that is known to be
> embedded
>    /// into a StringMapEntry, return the StringMapEntry itself.
>    static StringMapEntry &GetStringMapEntryFromValue(ValueTy &V) {
> -    StringMapEntry *EPtr = 0;
> -    char *Ptr = reinterpret_cast<char*>(&V) -
> -                  (reinterpret_cast<char*>(&EPtr->second) -
> -                   reinterpret_cast<char*>(EPtr));
> +    char *Ptr = reinterpret_cast<char *>(&V) - offsetof(StringMapEntry,
> second);
>

llvm/src/include/llvm/ADT/StringMap.h:185:48: error: offset of on
non-standard-layout type 'llvm::StringMapEntry<llvm::MDString>'
[-Werror,-Winvalid-offsetof]
    char *Ptr = reinterpret_cast<char *>(&V) - offsetof(StringMapEntry,
second);
                                               ^
 ~~~~~~


>      return *reinterpret_cast<StringMapEntry*>(Ptr);
>    }
>    static const StringMapEntry &GetStringMapEntryFromValue(const ValueTy
> &V) {
>
>
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