Check pointer arithmetic for overflow.
For some more background on this check, see:
Patch by Will Dietz and John Regehr!
This version of the patch is different from the original in a few ways:
- It introduces the EmitCheckedInBoundsGEP utility which inserts checks when the pointer overflow check is enabled.
- It does some constant-folding to reduce instrumentation overhead.
- It does not check some GEPs in CGExprCXX. I'm not sure that inserting checks here, or in CGClass, would catch many bugs.
Possible future directions for this check:
- Introduce CGF.EmitCheckedStructGEP, to detect overflows when accessing structures.
Testing: Apart from the added lit test, I ran check-llvm and check-clang
with a stage2, ubsan-instrumented clang. I found one overflow (see: