On Mon, 27 Jun 2016, Pavel Machek wrote: > > Live patching, as we use it, deliberately disrupts the fabric of > > compile units; thus all assumptions a compiler can make about the > > control flow may be invalid. As an example, it could analyse that a > > callee does not touch a caller-saved register at all, so why waste > > memory bandwidth saving it? The register allocations for the live > > patch replacement function may however be quite different. > > > > Starting with this example, disable all compiler optimisations that > > do not strictly comply with the established calling conventions. > > I thought that in such case, person creating the live patch should > notice and adjust patch appropriately, at assembly level if > neccessary..? Yes, that still holds; a lot of things could be automated though, and creating the automation tools is one of the big TODO items. > If this is not true, and we want gcc to help us, what other > optimalizations do we need to disable? Even changes inside one compiler > unit can be "interesting"... What would actually be helpful is gcc providing us with a list of functions where it performed this ABI-violating optimization (similarly, we're already obtaining list of "what got inlined where"). Unfortunately, -fdump-ipa-ra is currently missing; I'm talking to gcc guys now to have it implemented. -- Jiri Kosina SUSE Labs -- 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
