[cfe-dev] -ftrapv

[David Chisnall]

I've attached a diff which adds -ftrapv to clang-cc (not to clang; the  
driver code scares me) which uses the new LLVM overflow-checked  
operations for +, - and * (not ++ or -- yet).  When an overflow is  
detected, it calls a function in a supporting library to handle it.   
I've provided a default implementation in overflowlib.c.  This can be  
replaced in compiled code by some other function if required.  For  
100% GCC compatibility just add:

__overflow_handler = abort;

somewhere before the operations that may overflow.

The overflow.c file provided here shows a simple case where an  
overflow occurs (the volatiles are just there to make absolutely sure  
no optimisation passes decide to calculate the result at compile  
time).  When you run this (linked against overflowlib.c), you get:

$ ./a.out
Integer overflow!  Op unsigned add on 32-bit values, Aborting!
Abort trap: 6 (core dumped)

David

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