tree 29f679765d67c7b411345c43c69ca8c251bd0b4e
parent 21a2db4ee679d4efa8898326245ffd26a055cd4c
author Vedant Kumar <vsk@apple.com> 1498087489 -0700
committer Vedant Kumar <vsk@apple.com> 1498093930 -0700

[ubsan] Teach the pointer overflow check that "p - <unsigned> <= p" (PR33430)

The pointer overflow check gives false negatives when dealing with
expressions in which an unsigned value is subtracted from a pointer.
This is summarized in PR33430 [1]: ubsan permits the result of the
subtraction to be greater than "p", but it should not.

To fix the issue, we should track whether or not the pointer expression
is a subtraction. If it is, and the indices are unsigned, we know to
expect "p - <unsigned> <= p".

I've tested this by running check-{llvm,clang} with a stage2 ubsan-enabled build. I've also added some tests to compiler-rt, which I'll upload in a separate patch.

[1] https://bugs.llvm.org/show_bug.cgi?id=33430