[PATCH] -fcatch-undefined-behavior with trapping implementation

[Chad Rosier]

All,
The attached patch implements the -fcatch-undefined-behavior flag using a trapping implementation; this is much more inline with the original implementation (i.e., pre-Ubsan) and does not require run-time library support.

I've added a the 'undefined-trap' SANITIZER_GROUP that includes all the sanitizers which have low overhead, no ABI or address space layout implications, only catch undefined behavior, *and* do not require run-time library support.  This group should be used in conjunction with the new -fsanitize-undefined-trap-on-error flag.  Thus, the trapping implementation can be invoked using either '-fcatch-undefined-behavior' or '-fsanitize=undefined-trap -fsanitize-undefined-trap-on-error'.  Per a discussion between Richard, Chandler, and I, we are going to continue deprecating the -fcatch-undefined-behavior flag, but don't expect the flag to be removed until after a few releases.

Please take a look.

Thanks to Richard for a great deal of feedback prior to my submission to the list.

  Chad

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