[Lldb-commits] [lldb] [lldb] [ObjC runtime] Don't cast to signed when left shifting (PR #86605)

[Jason Molenda via lldb-commits]

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@@ -3154,7 +3154,7 @@ AppleObjCRuntimeV2::TaggedPointerVendorExtended::GetClassDescriptor(
                             << m_objc_debug_taggedpointer_ext_payload_lshift) >>
                            m_objc_debug_taggedpointer_ext_payload_rshift);
   int64_t data_payload_signed =
-      ((int64_t)((int64_t)unobfuscated
+      ((int64_t)((uint64_t)unobfuscated
                  << m_objc_debug_taggedpointer_ext_payload_lshift) >>
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jasonmolenda wrote:

I suspect the runtime gave us these "left & right shift" values, and the person who wrote this used the obvious implementation.  It could be expressed as a bit slice with a little subtraction, true.  Just to be clear, we're not fixing a real bug here, we were saying a UInt64 was signed and then ubsan got all shirty when we shifted away some bits that would indicate sign.

https://github.com/llvm/llvm-project/pull/86605