On Fri, Mar 20, 2020 at 11:35:37AM -0700, Kees Cook wrote: > 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? It can ignore unreachable UD2s, if we think that's the right fix. I was hoping we could find a way to get rid of the double UD2s, but I couldn't figure out a way to do that when I looked at it last week. -- Josh
