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Fix UB in vector<bool> by adding missing special case#5726
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AlexGuteniev
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vector<bool> by adding missing special case
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Looks like that the affect statements can be executed in constant execution. Can we add a |
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Adding But I'm against a test case for this specific branch. Think that we should be systematic, and make the entire coverage constexpr, except huge and random. And this larger change looks like out of scope, I want to fix specific bug, for which there is already expected ubsan coverage. |
AlexGuteniev
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Sep 17, 2025
StephanTLavavej
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Sep 17, 2025
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Thanks for the quick fix and clear explanation! 😻 |
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I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed. |
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Fixes #5720.
_IsSingleBlockDesthas special case when that single block touches edge, and_DestEndis greater that_Dest, and_DestEnd._Myoff == 0. This is handled elsewhere:STL/stl/inc/vector
Line 3834 in 43e96b2
STL/stl/inc/vector
Line 3843 in 43e96b2
STL/stl/inc/vector
Line 3860 in 43e96b2
Now we need to add missing handling in the UB causing line. If
_DestEnd._Myoff == 0, we have the only case when the subtraction result is negative. We actually need to subtract from full 32 bits in this case.The UB didn't cause runtime behavior difference, as the shift instruction just ignores high bits.