Re: [libvirt] [PATCH] Rewrite the way mockable functions are handled.

On Thu, Jul 13, 2017 at 12:25:50PM +0100, Daniel P. Berrange wrote: > On Thu, Jul 13, 2017 at 01:14:12PM +0200, Martin Kletzander wrote: > > On Wed, Jul 12, 2017 at 05:06:22PM +0100, Daniel P. Berrange wrote: > > > Currently any mockable functions are marked with attributes > > > noinline, noclone and weak. This prevents the compiler from > > > optimizing away the impl of these functions. > > > > > > It has an unfortunate side effect with the libtool convenience > > > libraries, if executables directly link to them. For example > > > virlockd, virlogd both link to libvirt_util.la When this is > > > done, the linker does not consider weak symbols as being > > > undefined, so it never copies them into the final executable. > > > > > > In this new approach, we stop annotating the headers entirely. > > > Instead we create a weak function alias in the source. > > > > > > int fooImpl(void) { > > > ..the real code.. > > > } > > > > > > int foo(void) __attribute__((noinline, noclone, weak, alias("fooImpl")) > > > > > > If any functions in the same file call "foo", this prevents the > > > optimizer from inlining any part of fooImpl. When linking to the > > > libtool convenience static library, we also get all the symbols > > > present. Finally the test suite can just directly define a > > > 'foo' function in its source, removing the need to use LD_PRELOAD > > > (though removal of LD_PRELOADS is left for a future patch). > > > > > > > What are you using for tag navigation? With this macro-defined > > functions I cannot easily jump to them (the main reason why I don't like > > macros defining functions). > > Grep & historic knowledge :-) > > > I would very much prefer if > > ATTRIBUTE_MOCKABLE just took a parameter like this: > > > > #define ATTRIBUTE_MOCKABLE(func) __attribute__((noinline, noclone, weak, alias(#func "Impl")) > > > > (written by hand, don't take mu word for it working out of the box) and > > the original function would be left untouched. > > Yeah, that is certainly a valid alternative. I was not entirely happy > with the results I get here. As long as we don't mind repeating the > arg list in both places, your approach is more attractive, despite > the duplication. > I think we don't if we do: #define VIR_MOCKABLE(ret, name) typeof(name ## Impl) name \ __attribute__((noinline, weak, __alias__(#name "Impl"))); or can't this be done for functions? It worked when I tried it now.

I have one more idea, though. So that we don't have to double-type the actual definition of the Impl function, we can make it static. What if we make *all* functions static and only add weak aliases to those that are supposed to be used outside the file? That is after we deal with the Darwin case, of course.