[dpdk-dev] [RFC PATCH v1] build: kni gcc cross-compilation support

[Juraj Linkeš]

> -----Original Message-----
> From: Bruce Richardson <bruce.richardson at intel.com>
> Sent: Friday, January 29, 2021 2:51 PM
> To: Juraj Linkeš <juraj.linkes at pantheon.tech>
> Cc: thomas at monjalon.net; Ruifeng.Wang at arm.com; jerinjacobk at gmail.com;
> hemant.agrawal at nxp.com; ferruh.yigit at intel.com; aboyer at pensando.io;
> dev at dpdk.org
> Subject: Re: [RFC PATCH v1] build: kni gcc cross-compilation support
> 
> On Fri, Jan 29, 2021 at 12:33:06PM +0000, Juraj Linkeš wrote:
> >
> >
> > > -----Original Message-----
> > > From: Bruce Richardson <bruce.richardson at intel.com>
> > > Sent: Friday, January 29, 2021 12:44 PM
> > > To: Juraj Linkeš <juraj.linkes at pantheon.tech>
> > > Cc: thomas at monjalon.net; Ruifeng.Wang at arm.com;
> > > jerinjacobk at gmail.com; hemant.agrawal at nxp.com;
> > > ferruh.yigit at intel.com; aboyer at pensando.io; dev at dpdk.org
> > > Subject: Re: [RFC PATCH v1] build: kni gcc cross-compilation support
> > >
> > > On Fri, Jan 29, 2021 at 11:29:19AM +0100, Juraj Linkeš wrote:
> > > > The kni linux module is using a custom target for building, which
> > > > doesn't take into account any cross compilation arguments. The
> > > > arguments in question are ARCH and CROSS_COMPILE. Get those from
> > > > the cross file and pass them to the custom target.
> > > >
> > > > The user supplied path may not contain the 'build' directory, such
> > > > as when using cross-compiled headers, so only append that in the
> > > > default case (when no path is supplied in native builds) and use
> > > > the unmodified path from the user otherwise.
> > > >
> > > > Signed-off-by: Juraj Linkeš <juraj.linkes at pantheon.tech>
> > > > ---
> > > >  kernel/linux/kni/meson.build |  4 ++--
> > > >  kernel/linux/meson.build     | 33 +++++++++++++++++++++++++++++----
> > > >  2 files changed, 31 insertions(+), 6 deletions(-)
> > > >
> > > > diff --git a/kernel/linux/kni/meson.build
> > > > b/kernel/linux/kni/meson.build index 07e0c9dae..0fbf52c93 100644
> > > > --- a/kernel/linux/kni/meson.build
> > > > +++ b/kernel/linux/kni/meson.build
> > > > @@ -13,7 +13,7 @@ kni_sources = files(  custom_target('rte_kni',
> > > >  	input: kni_sources,
> > > >  	output: 'rte_kni.ko',
> > > > -	command: ['make', '-j4', '-C', kernel_dir + '/build',
> > > > +	command: ['make', '-j4', '-C', kernel_dir,
> > > >  		'M=' + meson.current_build_dir(),
> > > >  		'src=' + meson.current_source_dir(),
> > > >  		'MODULE_CFLAGS=-include ' + meson.source_root() +
> > > > '/config/rte_config.h' + @@ -21,7 +21,7 @@ custom_target('rte_kni',
> > > >  		' -I' + meson.source_root() + '/lib/librte_kni' +
> > > >  		' -I' + meson.build_root() +
> > > >  		' -I' + meson.current_source_dir(),
> > > > -		'modules'],
> > > > +		'modules'] + cross_args,
> > > >  	depends: kni_mkfile,
> > > >  	install: true,
> > > >  	install_dir: kernel_dir + '/extra/dpdk', diff --git
> > > > a/kernel/linux/meson.build b/kernel/linux/meson.build index
> > > > 5c864a465..57ed9bc48 100644
> > > > --- a/kernel/linux/meson.build
> > > > +++ b/kernel/linux/meson.build
> > > > @@ -3,20 +3,45 @@
> > > >
> > > >  subdirs = ['kni']
> > > >
> > > > +cross_args = []
> > > >  # if we are cross-compiling we need kernel_dir specified -if
> > > > get_option('kernel_dir') == '' and meson.is_cross_build()
> > > > -	error('Need "kernel_dir" option for kmod compilation when cross-
> > > compiling')
> > > > +if meson.is_cross_build()
> > > > +	if get_option('kernel_dir') == ''
> > > > +		error('Need "kernel_dir" option for kmod compilation when
> > > cross-compiling')
> > > > +	else
> > > > +		cross_compiler = find_program('c').path()
> > > > +		if cross_compiler.endswith('gcc')
> > > > +			cross_prefix = ''
> > > > +			# remove the 'gcc' suffix
> > > > +			# meson doesn't support removing elements from an
> > > array
> > > > +			# nor does it support slicing, so do it on our own
> > > > +			foreach element : cross_compiler.split('-')
> > > > +				if element != 'gcc'
> > > > +					cross_prefix += '@0 at -
> > > '.format(element)
> > > > +				endif
> > > > +			endforeach
> > > > +		else
> > > > +			error('Unsupported cross compiler:
> > > @0@'.format(cross_compiler))
> > > > +		endif
> > >
> > > Rather than splitting manually, might it be better to just define a
> > > new property in the cross-file to hold the prefix?
> >
> > That would by one more unnecessary input, so I don't like that.
> >
> > > Alternatively, rather than meson looping, why not just use
> > > "run_command" to use shell or python to do the job, e.g. [untested]
> > >
> > > run_command([py3, '-c',
> > > 	'print("-".join("' + cross_compiler + '".split("-")[:-1]))')
> > >
> > > run_command('bash', '-c',
> > > 	'echo ' + cross_compiler + ' | sed "s/gcc$//"')
> > >
> >
> > Since there isn't a better way to do this in Meson, it makes sense to use an
> external tool.
> > On top of that, this would save lines and wouldn't need as many code
> comments. I'll change it.
> >
> > > > +		if host_machine.cpu_family() == 'aarch64'
> > > > +			cross_arch = 'arm64'
> > > > +		else
> > > > +			cross_arch = build_machine.cpu_family()
> > > > +		endif
> > > > +		cross_args = ['ARCH=@0@'.format(cross_arch),
> > > > +			'CROSS_COMPILE=@0@'.format(cross_prefix)]
> > > > +	endif
> > > >  endif
> > > >
> > > >  kernel_dir = get_option('kernel_dir')  if kernel_dir == ''
> > > >  	# use default path for native builds
> > > >  	kernel_version = run_command('uname', '-r').stdout().strip()
> > > > -	kernel_dir = '/lib/modules/' + kernel_version
> > > > +	kernel_dir = '/lib/modules/' + kernel_version + '/build'
> > > >  endif
> > >
> > > The reason we don't keep the "build" off the kernel_dir is to ensure
> > > that the kernel modules install to the correct place. With this
> > > change the modules will go in
> > > "/lib/modules/<version>/build/extra/dpdk", rather than
> "/lib/modules/<version>/extra/dpdk".
> > >
> >
> > Ah, I see. The modules will be installed during meson install. This should also
> be changed, then, as we always want to install them to '/lib/modules/<version>'
> (not necessarily to 'kernel_dir', as the user may change that) and only for native
> builds, right?
> >
> Well, we definitely want it for native builds, but I'd imagine it would be useful for
> cross-builds too, no?

I guess it would be useful for setups with shared storage. Did you have something else in mind?

> Can we find some way of getting it working for both cases.
> For native builds we want:
> 
> * build kernel-dir = /lib/modules/<ver>/build
> * install dir = /lib/modules/<ver>/extra/dpdk
> 
> What are the expected equivalent paths for cross building?
> 

The ubuntu1804 packages are installing aarch64 cross files to /usr/aarch64-linux-gnu, so we could install it to /usr/aarch64-linux-gnu/lib/modules/<ver>/extra/dpdk, or /usr/<cross_triple>/lib/modules/<ver>/extra/dpdk in general. I think we can get <ver> from 'make kernelversion', so that would work, although I'm not sure this is the right place.

A note: all this works just for gcc. Should I also add support for clang?

> /Bruce