[PATCH] D67122: [UBSan][clang][compiler-rt] Applying non-zero offset to nullptr is undefined behaviour

[Jordan Rupprecht via Phabricator via cfe-commits]

rupprecht added a comment.

> Still think this looks good. Have you tried running this on the llvm test suite, or some other interesting corpus? Would be curious to see any pre/post patch numbers.

I finally had time this morning to patch this in and give it a shot. (Sorry for the delay... it's been a real busy week :( )

First, starting off with the good news: I reverted all the fixes I made, and now all the tests fail when running w/ ubsan. Yay!

The error we see in each case is `UndefinedBehaviorSanitizer: nullptr-with-nonzero-offset` with the logs containing `runtime error: applying non-zero offset <non-zero> to null pointer`. Which catches the two places where we were adding some non-zero offset to nullptr, but doesn't seem to catch the nullptr-after-nonzero-offset case in https://github.com/google/filament/pull/1566 -- instead, it fails later, when the pointer with a value of nullptr is incremented. (Or... maybe this is actually a separate bug. Hmm. Needs some more testing...)

At any rate, I have some more tests to run to get some idea of what % of code this would flag as being bad.


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