On Fri, 09/08 11:05, Daniel P. Berrange wrote: > On Wed, Sep 06, 2017 at 08:49:00PM +0800, Fam Zheng wrote: > > This patch groups the crypto objects into a few .mo objects based on > > functional submodules, and moves inclusion conditions to *-objs > > variables, then moves the global cflags/libs to the *-cflags and *-libs > > variables. > > > > For init.o and cipher.o, which may or may not need the library flags > > depending on config, adding flags and libs unconditionally doesn't hurt, > > because if the library is not available, the variables are empty. This > > makes less code. > > > > Signed-off-by: Fam Zheng <f...@redhat.com> > > > > --- > > > > v4: Merge into one patch which is supposedly easier to manage and > > review, and use .mo appraoch to avoid $(foreach) and $(eval) magics. > > I don't think using .mo is suitable here. You've used it as a generic > mechanism for grouping .o files, but that is not what it does. There > are special semantics around .mo rules that affect how the final > binaries are linked.
Using .mo is okay here, but after a hindsight I think grouping by library (nettle.mo, gcrypt.mo, etc.) is better than grouping by functionality, for modularization in the future. But that also means assigning the cflags/libs variable cannot be simplified like this. > > eg looking back at the description of .mo files > > [quote] > commit c261d774fb9093d00e0938a19f502fb220f62718 > Author: Fam Zheng <f...@redhat.com> > Date: Mon Sep 1 18:35:10 2014 +0800 > > [...snip...] > > 3) When linking an executable, those .mo files in its "-y" variables are > filtered out, and replaced by one or more -Wl,-u,$symbol flags. This > is done in the added macro "process-archive-undefs". > > These "-Wl,-u,$symbol" flags will force ld to pull in the function > definition from the archives when linking. > > Note that the .mo objects, that are actually meant to be linked in > the executables, are already expanded in unnest-vars, before the > linking command. So we are safe to simply filter out .mo for the > purpose of pulling undefined symbols. > > process-archive-undefs works as this: For each ".mo", find all the > undefined symbols in it, filter ones that are defined in the > archives. For each of these symbols, generate a "-Wl,-u,$symbol" in > the link command, and put them before archive names in the command > line. > [/quote] > > Based on this, I don't think I can ack this patch, because it can > have unexpected consequences. This described the process-archive-undefs semantics of .mo, but not the essence of it. Basically .mo is just partial linking with the additional services of -cflags, -libs and the above -Wl,-u thing. I cannot think of any unexpected consequences with this change. We've had sdl.mo in ui/Makefile.objs for long, just for the same purpose of this patch, with no problem. Fam
