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

-----Original Message-----
From: Bruce Richardson <redacted>
Sent: Friday, January 29, 2021 12:44 PM
To: Juraj Linkeš <redacted>
Cc: thomas@monjalon.net; Ruifeng.Wang@arm.com; jerinjacobk@gmail.com;
hemant.agrawal@nxp.com; ferruh.yigit@intel.com; aboyer@pensando.io;
dev@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:

quoted

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 <redacted>
---
 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')

quoted

+if meson.is_cross_build()
+	if get_option('kernel_dir') == ''
+		error('Need "kernel_dir" option for kmod compilation when

cross-compiling')

quoted

+	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

quoted

+			# nor does it support slicing, so do it on our own
+			foreach element : cross_compiler.split('-')
+				if element != 'gcc'
+					cross_prefix += '@0@-

'.format(element)

quoted

+				endif
+			endforeach
+		else
+			error('Unsupported cross compiler:

@0@'.format(cross_compiler))

quoted

+		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.

quoted

+		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?

quoted

 # test running make in kernel directory, using "make kernelversion"
-make_returncode = run_command('make', '-sC', kernel_dir + '/build',
+make_returncode = run_command('make', '-sC', kernel_dir,
 		'kernelversion').returncode()
 if make_returncode != 0
 	error('Cannot compile kernel modules as requested - are kernel
headers installed?')
--
2.20.1