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Re: [Qemu-devel] [PATCH v4] buildsys: Move crypto cflags/libs to per obj
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [PATCH v4] buildsys: Move crypto cflags/libs to per object variables |
Date: |
Fri, 8 Sep 2017 18:27:01 +0800 |
User-agent: |
Mutt/1.8.3 (2017-05-23) |
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 <address@hidden>
> >
> > ---
> >
> > v4: Merge into one patch which is supposedly easier to manage and
> > review, and use .mo appraoch to avoid $(foreach) and $(eval) magics.
>
> I don't think using .mo is suitable here. You've used it as a generic
> mechanism for grouping .o files, but that is not what it does. There
> are special semantics around .mo rules that affect how the final
> binaries are linked.
Using .mo is okay here, but after a hindsight I think grouping by library
(nettle.mo, gcrypt.mo, etc.) is better than grouping by functionality, for
modularization in the future. But that also means assigning the cflags/libs
variable cannot be simplified like this.
>
> eg looking back at the description of .mo files
>
> [quote]
> commit c261d774fb9093d00e0938a19f502fb220f62718
> Author: Fam Zheng <address@hidden>
> Date: Mon Sep 1 18:35:10 2014 +0800
>
> [...snip...]
>
> 3) When linking an executable, those .mo files in its "-y" variables are
> filtered out, and replaced by one or more -Wl,-u,$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
- [Qemu-devel] [PATCH v4] buildsys: Move crypto cflags/libs to per object variables, Fam Zheng, 2017/09/06
- Re: [Qemu-devel] [PATCH v4] buildsys: Move crypto cflags/libs to per object variables, Fam Zheng, 2017/09/08
- Re: [Qemu-devel] [PATCH v4] buildsys: Move crypto cflags/libs to per object variables, Daniel P. Berrange, 2017/09/08
- Re: [Qemu-devel] [PATCH v4] buildsys: Move crypto cflags/libs to per object variables,
Fam Zheng <=
- Re: [Qemu-devel] [PATCH v4] buildsys: Move crypto cflags/libs to per object variables, Daniel P. Berrange, 2017/09/08
- Re: [Qemu-devel] [PATCH v4] buildsys: Move crypto cflags/libs to per object variables, Fam Zheng, 2017/09/08
- Re: [Qemu-devel] [PATCH v4] buildsys: Move crypto cflags/libs to per object variables, Daniel P. Berrange, 2017/09/08
- Re: [Qemu-devel] [PATCH v4] buildsys: Move crypto cflags/libs to per object variables, Fam Zheng, 2017/09/08
- Re: [Qemu-devel] [PATCH v4] buildsys: Move crypto cflags/libs to per object variables, Daniel P. Berrange, 2017/09/08