On Fri, Mar 20, 2020 at 09:26:13AM +0100, Peter Zijlstra wrote: > On Thu, Mar 19, 2020 at 12:45:50PM -0500, Josh Poimboeuf wrote: > > > On Thu, Mar 19, 2020 at 12:33:31PM -0500, Josh Poimboeuf wrote: > > > > > Actually I suspect it's the __builtin_unreachable() annotation which is > > > > making UBSAN add the __builtin_trap()... because I don't see any double > > > > UD2s for WARNs. > > > Actually, removing __builtin_unreachable() *does* make the extra UD2 go > > away -- I forgot I had some silly debug code. > > LOL, check this: > > "Built-in Function: void __builtin_unreachable (void) > > If control flow reaches the point of the __builtin_unreachable, the > program is undefined. It is useful in situations where the compiler > cannot deduce the unreachability of the code. " > > Which, I bet, is what makes UBSAN insert that __builtin_trap(). > > What a friggin mess :/ What I'd like is to be able to specify to UBSAN what function to call for the trap. I'd prefer to specify a well-defined exception handler, but at present, UBSAN just inserts __builtin_trap(). Can't objtool be told to ignore a ud2 that lacks an execution path to it? -- Kees Cook
