On Fri, 09/08 11:36, Daniel P. Berrange wrote:
> On Fri, Sep 08, 2017 at 06:27:01PM +0800, Fam Zheng wrote:
> > 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.
>
> While I'm in favour of moving the linker/compiler flags out of the global
> vars, I'm not convinced this impl is a step forward.
>
> We already have a mechanism for grouping object files - the 'NNNN-obj-y'
> variables we use throughout our Makefiles.
>
> This patch is adding a second level of grouping purely to work around the
> fact that we can't set linker/compiler flags on the NNN-obj-y variables
> we use. I think this second level of grouping makes the makefiles more
> complex than they ought to be.
Not quite, it is actually a required step to modularization, which I'm inclined
to get my hands on next. That is also why .mo was introduced.
>
> IOW, I'd rather see the rules fixed so that we can set variables against
> the existing grouping we have. eg
>
> crypto-obj-y-cflags := ...
> crypto-obj-y-libs := ...
>
> so we avoid having to introduce second level groups every time we want
> to set these cflags/libs.
This is certainly true, but taking the modularization work into account, .mo
based -cflags and -libs are more natural and consistent. IMO we already have the
latter, so other mechanisms are not really necessary. Remember how complex the
general unnest-vars code is? I believe adding support to crypto-obj-y-cflags is
more complex than (ab)using .mo objects, even if just for flags/libs
localization.
If you don't like introducing {nettle,gcrypt,gnutls}.mo for now, we can probably
defer it to the time when crypto subsystem is modularized.
Either way let's drop this patch for now.
Fam
