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Subject: Re: [RFC 01/19] kbuild: Fixes to rules for host-cshlib and
 host-cxxshlib
From:   Knut Omang <knut.omang@oracle.com>
To:     Masahiro Yamada <yamada.masahiro@socionext.com>
Cc:     "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Shuah Khan <shuah@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Michal Marek <michal.lkml@markovi.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Shreyans Devendra Doshi <0xinfosect0r@gmail.com>,
        Alan Maguire <alan.maguire@oracle.com>,
        Brendan Higgins <brendanhiggins@google.com>,
        Kevin Hilman <khilman@baylibre.com>,
        Hidenori Yamaji <hidenori.yamaji@sony.com>,
        Frank Rowand <frowand.list@gmail.com>,
        Timothy Bird <Tim.Bird@sony.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        "Theodore Ts'o" <tytso@mit.edu>, Daniel Vetter <daniel@ffwll.ch>,
        Stephen Boyd <sboyd@kernel.org>
Date:   Wed, 21 Aug 2019 06:03:39 +0200
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On Wed, 2019-08-21 at 10:47 +0900, Masahiro Yamada wrote:
> On Wed, Aug 14, 2019 at 9:53 PM Knut Omang <knut.omang@oracle.com> wrote:
> >
> > On Wed, 2019-08-14 at 07:52 +0200, Knut Omang wrote:
> > > On Wed, 2019-08-14 at 11:02 +0900, Masahiro Yamada wrote:
> > > > Hi Knut,
> > > >
> > > > On Wed, Aug 14, 2019 at 1:19 AM Knut Omang <knut.omang@oracle.com> wrote:
> > > > > On Tue, 2019-08-13 at 23:01 +0900, Masahiro Yamada wrote:
> > > > > > On Tue, Aug 13, 2019 at 3:13 PM Knut Omang <knut.omang@oracle.com> wrote:
> > > > > > > C++ libraries interfacing to C APIs might sometimes need some glue
> > > > > > > logic more easily written in C.
> > > > > > > Allow a C++ library to also contain 0 or more C objects.
> > > > > > >
> > > > > > > Also fix rules for both C and C++ shared libraries:
> > > > > > > - C++ shared libraries depended on .c instead of .cc files
> > > > > > > - Rules were referenced as -objs instead of the intended
> > > > > > >   -cobjs and -cxxobjs following the pattern from hostprogs*.
> > > > > > >
> > > > > > > Signed-off-by: Knut Omang <knut.omang@oracle.com>
> > > > > >
> > > > > > How is this patch related to the rest of this series?
> > > > >
> > > > > This is just my (likely naive) way I to get what I had working
> > > > > using autotools in the Github version of KTF) translated into something
> > > > > comparable using kbuild only. We need to build a shared library consisting
> > > > > of a few C++ files and a very simple C file, and a couple of simple binaries,
> > > > > and the rule in there does seem to take .c files and subject them to the
> > > > > C++ compiler, which makes this difficult to achieve?
> > > >
> > > > Looking at the diff stat of the cover-letter,
> > > > the rest of this patch series is touching only
> > > > Documentation/ and tools/testing/kselftests/.
> > > >
> > > > So, this one is unused by the rest of the changes, isn't it?
> > > > Am I missing something?
> > > >
> > > >
> > > >
> > > > > > This patch breaks GCC-plugins.
> > > > > > Did you really compile-test this patch before the submission?
> > > > >
> > > > > Sorry for my ignorance here:
> > > > > I ran through the kernel build and installed the resulting kernel
> > > > > on a VM that I used to test this, if that's what you are asking
> > > > > about?
> > > > >
> > > > > Do I need some unusual .config options or run a special make target
> > > > > to trigger the problem you see?
> > > > >
> > > > > I used a recent Fedora config with default values for new options,
> > > > > and ran the normal default make target (also with O=) and make selftests
> > > > > to test the patch itself.
> > > >
> > > > I just built allmodconfig for arm.
> > > >
> > > > (The 0-day bot tests allmodconfig for most of architectures,
> > > > so you may receive error reports anyway.)
> > > >
> > > >
> > > > With your patch, I got the following:
> > > >
> > > >
> > > > masahiro@grover:~/ref/linux$ make  ARCH=arm
> > > > CROSS_COMPILE=-  allmodconfig all
> > > >   HOSTCC  scripts/basic/fixdep
> > > >   HOSTCC  scripts/kconfig/conf.o
> > > >   HOSTCC  scripts/kconfig/confdata.o
> > > >   HOSTCC  scripts/kconfig/expr.o
> > > >   LEX     scripts/kconfig/lexer.lex.c
> > > >   YACC    scripts/kconfig/parser.tab.h
> > > >   HOSTCC  scripts/kconfig/lexer.lex.o
> > > >   YACC    scripts/kconfig/parser.tab.c
> > > >   HOSTCC  scripts/kconfig/parser.tab.o
> > > >   HOSTCC  scripts/kconfig/preprocess.o
> > > >   HOSTCC  scripts/kconfig/symbol.o
> > > >   HOSTLD  scripts/kconfig/conf
> > > > scripts/kconfig/conf  --allmodconfig Kconfig
> > > > #
> > > > # configuration written to .config
> > > > #
> > > >   SYSHDR  arch/arm/include/generated/uapi/asm/unistd-common.h
> > > >   SYSHDR  arch/arm/include/generated/uapi/asm/unistd-oabi.h
> > > >   SYSHDR  arch/arm/include/generated/uapi/asm/unistd-eabi.h
> > > >   HOSTCC  scripts/dtc/dtc.o
> > > >   HOSTCC  scripts/dtc/flattree.o
> > > >   HOSTCC  scripts/dtc/fstree.o
> > > >   HOSTCC  scripts/dtc/data.o
> > > >   HOSTCC  scripts/dtc/livetree.o
> > > >   HOSTCC  scripts/dtc/treesource.o
> > > >   HOSTCC  scripts/dtc/srcpos.o
> > > >   HOSTCC  scripts/dtc/checks.o
> > > >   HOSTCC  scripts/dtc/util.o
> > > >   LEX     scripts/dtc/dtc-lexer.lex.c
> > > >   YACC    scripts/dtc/dtc-parser.tab.h
> > > >   HOSTCC  scripts/dtc/dtc-lexer.lex.o
> > > >   YACC    scripts/dtc/dtc-parser.tab.c
> > > >   HOSTCC  scripts/dtc/dtc-parser.tab.o
> > > >   HOSTCC  scripts/dtc/yamltree.o
> > > >   HOSTLD  scripts/dtc/dtc
> > > >   CC      scripts/gcc-plugins/latent_entropy_plugin.o
> > > > cc1: error: cannot load plugin ./scripts/gcc-plugins/arm_ssp_per_task_plugin.so
> > > >    ./scripts/gcc-plugins/arm_ssp_per_task_plugin.so: cannot open
> > > > shared object file: No such file or directory
> > > > cc1: error: cannot load plugin ./scripts/gcc-plugins/structleak_plugin.so
> > > >    ./scripts/gcc-plugins/structleak_plugin.so: cannot open shared
> > > > object file: No such file or directory
> > > > cc1: error: cannot load plugin ./scripts/gcc-plugins/latent_entropy_plugin.so
> > > >    ./scripts/gcc-plugins/latent_entropy_plugin.so: cannot open shared
> > > > object file: No such file or directory
> > > > cc1: error: cannot load plugin ./scripts/gcc-plugins/randomize_layout_plugin.so
> > > >    ./scripts/gcc-plugins/randomize_layout_plugin.so: cannot open
> > > > shared object file: No such file or directory
> > > > make[3]: *** [scripts/Makefile.build;281:
> > > > scripts/gcc-plugins/latent_entropy_plugin.o] Error 1
> > > > make[2]: *** [scripts/Makefile.build;497: scripts/gcc-plugins] Error 2
> > > > make[1]: *** [Makefile;1097: scripts] Error 2
> > > > make: *** [Makefile;330: __build_one_by_one] Error 2
> > >
> > > Ok, I see!
> > >
> > > I'll recall this target and look into it!
> >
> > Ok, so I have tried installing the arm-linux-gnueabihf cross compiler and compiled the
> kernel for arm,
> > but allmodconfig does not seem to enable any GCC plugins per default even on ARM and I
> haven't been able
> > to figure out how to enable any.
> 
> 
> Linaro toolchain supports gcc plugins.
> 
> https://releases.linaro.org/components/toolchain/binaries/latest-7/arm-linux-gnueabihf/
> 
> 
> kernel.org one supports it as well.
> 
> https://mirrors.edge.kernel.org/pub/tools/crosstool/
> 
> 
> 
> 
> 
> > A plain allmodconfig generated config compiles perfectly for me both native x86 and
> w/arm cross compile,
> > but it doesn't seem to enable any gcc plugins.
> >
> > Anyway, maybe I am getting this wrong anyway:
> > Having played with cross compile, it starts to become clear to me that HOSTCC rules
> > might not be the right rules to use, as it will generate host user land binaries as
> opposed to
> > target user land binaries (in a cross compile world obviously these differ)
> >
> > Now, I started off with using the rules in the selftests makefiles for this, but they
> do not play that well with
> > kernel module building. My goal is to be able to do both user land and kernel module
> **target** compiles
> > from the same subtree. Any hints on how to accomplish this appreciated :-)
> 
> 
> tools/ is out of scope of kbuild because it adopted a different (more
> adhoc) build system.

That resonates with my understanding, thanks!
I think that's what I am trying to understand how to improve:

To sum up, my conclusion so far is that there's a need for a set of more integrated Kbuild
rules for target platform binaries and libraries similar to the host* rules. The rules in
tools/ could then be modified to use that generic support instead of the current adhoc
approach. That would allow the needs of tests that have both user space and kernel space
code to be more nicely co-located, with several benefits IMHO.

Any further insights appreciated!

> I have no idea. Please talk to the kselftest maintainer.

She's on the Cc:-list, I was hoping to get a some of the challenges/choices highlighted
here ;-)

Thanks!
Knut