On Tue, Apr 28, 2015 at 02:16:06PM +0200, Peter Zijlstra wrote: > On Mon, Apr 27, 2015 at 08:56:27AM -0500, Josh Poimboeuf wrote: > > Frame pointer based stack traces aren't always reliable. One big reason > > is that most asm functions don't set up the frame pointer. > > > > Fix that by enforcing that all asm functions honor CONFIG_FRAME_POINTER. > > This is done with a new stackvalidate host tool which is automatically > > run for every compiled .S file and which validates that every asm > > function does the proper frame pointer setup. > > Would it make sense (maybe as an additional CONFIG_*_DEBUG thing) to > also process the output of GCC with this tool? To both double check GCC > and to give the tool more input? I tried that, but I discovered that gcc's usage of frame pointers would be a lot harder to validate. It only sets up the frame pointer in code paths which have call instructions. There are a lot of functions which have conditional jumps at the beginning which can jump straight to a return instruction without first doing the frame pointer setup. So it would really need to have a much more sophisticated static code analysis. But I think the possibility of gcc messing up frame pointers is very slim. I doubt it would be worth the complexity (and added compile time) needed to try to find any gcc bugs there. -- 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
