Re: [PATCH v4] config: Allow kernel installation packaging to override pkg-config

[Nick Desaulniers <ndesaulniers@google.com>]

On Tue, Mar 22, 2022 at 12:44 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Wed, Mar 16, 2022 at 11:51 AM Chun-Tse Shao <ctshao@google.com> wrote:
> >
> > Tue, Mar 08, 2022 at 01:01:45PM +0900, Masahiro Yamada wrote:
> > > On Tue, Mar 8, 2022 at 7:50 AM Chun-Tse Shao <ctshao@google.com> wrote:
> > > >
> > > > On Mon, Mar 07, 2022 at 10:17:17AM -0800, Nick Desaulniers wrote:
> > > > > On Sun, Mar 6, 2022 at 2:39 PM Chun-Tse Shao <ctshao@google.com> wrote:
> > > > > >
> > > > > > Add HOSTPKG_CONFIG to allow tooling that builds the kernel to override
> > > > > > what pkg-config and parameters are used.
> > > > >
> > > > > Sorry, kind a late thought here for v4, but we don't seem to prefix
> > > > > many other host side tools with HOST_, i.e. LEX, YACC, AWK, PERL,
> > > > > PYTHON3, etc.  Maybe just having the variable identifier be simply
> > > > > PKGCONFIG rather than HOSTPKG_CONFIG then put it at the end of the
> > > > > list in the top level Makefile after ZSTD (i.e. the list of host
> > > > > tools)?  There's HOST_ prefixes when there's more than one tool
> > > > > involved (i.e. host compiler vs target compiler), but I suspect
> > > > > there's no such distinction for the existing uses of pkg-config?
> > > > >
> > > > Thanks for your suggestion, Nick! Yes I think it makes sense with PKGCONFIG
> > > > instead of HOSTPKG_CONFIG since there is only one tool involved. I will
> > > > work on it and submit a new patch.
> > > >
> > >
> > > Please hold on.
> > >
> > > I was also wondering what to do with the "HOST" prefix.
> > >
> > > Libraries are usually arch-dependent.
> > > (in other words, pkg-config should return different library paths
> > > for $(CC) and $(HOSTCC) )
> > >
> > > You already understood this, so you added "HOST" prefix.
> > >
> > >
> > > Please let me take time for further discussion.
> > > I will come back to this when I get some time.
> > >
> > >
> >
> > Hi Mashiro,
> >
> > I was wondering if you were able to look more into this.
> >
> > Thank you!
> >
> > -CT
> >
> > > In the meantime,
> > >   a8a5cd8b472ca20e5b8fa649c43b3756867322f8
> > > as reference info if you have not seen it.
> > >
> > >
> > > How many distros support something like
> > > "aarch64-linux-gnu-pkg-config"  ?
> > >
> > > Ubuntu 18.04 and 20.04 seem to support it.
> > > I do not know for others.
> > >
> > >
> > >
> > >
>
>
>
> Sorry for the delay.
> I am OK with the idea of allowing users to override the pkg-config command,
> but I tend to take time before making a decision.
>
>
>
>
> Does anybody have any insight / thoughts about the following points?
>
>
>
>
>
>
> [Q1]   with/without "HOST" prefix
>
>
> Apparently, "pkg-config" should return different libs/cflags
> for $(CC) and $(HOSTCC).
>
> I think the non-prefixed macro name "PKG_CONFIG" should be
> reserved for $(CC)  (building for the target system).

Ok. I retract my comment on v4 about removing the HOST prefix then.

>
> "HOSTPKG_CONFIG" looks unbalanced
> due to the underscore.
>
> Perhaps, "HOST_PKG_CONFIG" might be better?

I'm fine with HOSTPKG_CONFIG (what's in v4); follows the style of
HOSTCC and HOSTCXX.

>
>
>
>
> [Q2]    "pkg-config" vs "pkgconf"
>
> The traditional pkg-config implementation [1] is not actively
> maintained these days.
> The last commit was more than one year ago.
>
> The alternative one 'pkgconf' [2] is more active.
>
> In fact, Fedora already switched to 'pkgconf' [3].
> Now 'pkg-config' is just a wrapper of 'pkgconf'.
> Many distributions already support pkgconf.
>
>
> I considered the shorter macro name "HOSTPKGCONF" and
>
>    HOSTPKGCONF  = pkgconf
>
> but I am not sure if this is the right decision.
> Maybe we should stick to "PKG_CONFIG" / "HOST_PKG_CONFIG"
> for the macro names.
>
>
>   [1]  https://gitlab.freedesktop.org/pkg-config/pkg-config.git
>   [2]  https://github.com/pkgconf/pkgconf.git
>   [3]  https://fedoraproject.org/wiki/Changes/pkgconf_as_system_pkg-config_implementation

If the folks sending this are working on CrOS, better find what's in
their build system. Chun-Tse?

(I feel like I'm behind the times again, like when `apt-get install`
became old news in favor of `apt install`...)

>
>
>
>
>
> [Q3] What is the trend of handling cross-compile by pkg-config (or pkgconf).
>
>
> By default, pkg-config returns the libs/cflags for native builds.
>
> For cross builds, the search paths for the *.pc files must be changed
> via the "PKG_CONFIG_LIBDIR" environment variable.
>
> To ease this, some distributions provide  <triplet>-pkg-config
> (for example,   aarch64-linux-gnu-pkg-config).
> This became the nationale for tools/build/feature/Makefile defining:
>
>    PKG_CONFIG ?= $(CROSS_COMPILE)pkg-config
>
> But, this wrapper shell script is not always available.
> I do not know how to do it with the LLVM tool suite.
> I am not quite sure if this is the global solution.
>
>
> These days, pkgconf supports another way, .personality file [4]
> to specify the .pc search paths for cross builds.
>
> Is it reasonable to use an option to distinguish native / cross builds
> and use the same macro   "PKG_CONFIG = pkg-config" everywhere ?
>
>
> [4] http://manpages.ubuntu.com/manpages/focal/en/man5/pkgconf-personality.5.html

I'm not sure, but do we need to cross that bridge for this patch if
it's just adding support for the HOST? No cross pkg-config necessary,
yet. (Famous last words).
-- 
Thanks,
~Nick Desaulniers