On Wed, Jun 10, 2015 at 04:11:04PM +0200, Andi Kleen wrote: > > In most cases there are ways to keep the optimizations. For example: > > > > - grow the function bounds to keep the jump internal > > So you mean moving it after the ret? That still means icache bloat. No, in most cases it just means changing the ELF annotations. See patch 9 for an example. > > - duplicate the destination code inside the function > > - convert the jump to a call > > That all won't work for a lot of cases. Hm, could you give an example? > > Also note that these rules only affect _callable_ functions, so the > > entry code and other non-function asm code can still be a pile of > > spaghetti (though I think Andy is working on improving that). > > Thank you for your kind words. Don't like spaghetti? :-) > > > In fact even gcc with the right options can generate code that violates > > > this. Standard Linux constructions, such as exception handling, > > > also violate this. > > > > > > If your tool needs that your tool is broken. > > > > This tool only validates asm code, so I don't see how whatever gcc does > > is relevant. > > Whoever needs it would need it everywhere, right? If it's not needed > for gcc then it shouldn't be needed for assembler code either. Well, I don't see how that's really a logical conclusion. But we're probably being too vague here... Do you have any examples where you really need to jump outside of a callable function? If we ignore C++, then 99% of the time, C functions are self-contained. The only exception I can think of is for switch statements, which sometimes have an external jump table. -- Josh -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
