Re: [dpdk-dev] [PATCH v5] build: kni cross-compilation support

-----Original Message-----
From: Bruce Richardson <redacted>
Sent: Tuesday, February 9, 2021 12:51 PM
To: Juraj Linkeš <redacted>
Cc: thomas@monjalon.net; Ruifeng.Wang@arm.com;
Honnappa.Nagarahalli@arm.com; jerinjacobk@gmail.com;
hemant.agrawal@nxp.com; ferruh.yigit@intel.com; aboyer@pensando.io;
dev@dpdk.org
Subject: Re: [PATCH v5] build: kni cross-compilation support

On Tue, Feb 09, 2021 at 09:47:05AM +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, CROSS_COMPILE (for gcc, clang) and CC,
LD (for clang). 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. Also modify the install path

accordingly.

quoted

Signed-off-by: Juraj Linkeš <redacted>

Reviewed-by: Bruce Richardson <redacted>

Couple of small comments inline below.

quoted

---
 kernel/linux/kni/meson.build |  8 +--
 kernel/linux/meson.build     | 94 +++++++++++++++++++++++++++++++-----
 meson_options.txt            |  2 +-
 3 files changed, 86 insertions(+), 18 deletions(-)

diff --git a/kernel/linux/kni/meson.build

b/kernel/linux/kni/meson.build index 07e0c9dae7..46b71c7418 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_build_dir,
 		'M=' + meson.current_build_dir(),
 		'src=' + meson.current_source_dir(),
 		'MODULE_CFLAGS=-include ' + meson.source_root() +

'/config/rte_config.h' + @@ -21,8 +21,8 @@ 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',
+	install: install,
+	install_dir: kernel_install_dir,
 	build_by_default: get_option('enable_kmods')) diff --git
a/kernel/linux/meson.build b/kernel/linux/meson.build index
5c864a4653..67c1cbd7e0 100644

--- a/kernel/linux/meson.build
+++ b/kernel/linux/meson.build

@@ -3,25 +3,93 @@

 subdirs = ['kni']

-# 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

-endif
+kernel_build_dir = get_option('kernel_dir') kernel_install_dir = ''
+install = not meson.is_cross_build()
+cross_args = []

-kernel_dir = get_option('kernel_dir') -if kernel_dir == ''
-	# use default path for native builds
+if not meson.is_cross_build()
+	# native build
 	kernel_version = run_command('uname', '-r').stdout().strip()
-	kernel_dir = '/lib/modules/' + kernel_version
+	kernel_install_dir = '/lib/modules/' + kernel_version + '/extra/dpdk'
+	if kernel_build_dir == ''
+		# use default path for native builds
+		kernel_build_dir = '/lib/modules/' + kernel_version + '/build'
+	endif
+
+	# test running make in kernel directory, using "make kernelversion"
+	make_returncode = run_command('make', '-sC', kernel_build_dir,
+			'kernelversion').returncode()
+	if make_returncode != 0
+		# backwards compatibility:
+		# the headers could still be in the 'build' subdir
+		if not kernel_build_dir.endswith('build') and not

kernel_build_dir.endswith('build/')

quoted

+			kernel_build_dir = join_paths(kernel_build_dir, 'build')
+			make_returncode = run_command('make', '-sC',

kernel_build_dir,

quoted

+					'kernelversion').returncode()
+			if make_returncode == 0
+				warning('Deprecation notice: Specifying

kernel_dir ' +

quoted

+					'without the build dir will be deprecated

in the future.')

quoted

+			endif

I don't really think we need to deprecate this, since this should adequately
support both options. Therefore, I suggest just dropping these last 4 lines and
accepting both options.

Ok, I'll remove the lines.

quoted

+		endif
+	endif
+
+	if make_returncode != 0
+		error('Cannot compile kernel modules as requested - are kernel

headers installed?')

quoted

+	endif
+
+	# DO ACTUAL MODULE BUILDING
+	foreach d:subdirs
+		subdir(d)
+	endforeach
+
+	subdir_done()
 endif

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

installed?')

quoted

+# cross build
+# if we are cross-compiling we need kernel_build_dir specified if
+kernel_build_dir == ''
+	error('Need "kernel_dir" option for kmod compilation when
+cross-compiling') endif cross_compiler = find_program('c').path() if
+cross_compiler.endswith('gcc')
+	cross_prefix = run_command([py3, '-c', 'print("' + cross_compiler +
+'"[:-3])']).stdout().strip() elif cross_compiler.endswith('clang')
+	cross_prefix = ''
+	found_target = false
+	# search for '-target' and use the arg that follows
+	# (i.e. the value of '-target') as cross_prefix
+	foreach cross_c_arg : meson.get_cross_property('c_args')
+		if found_target and cross_prefix == ''
+			cross_prefix = cross_c_arg
+		endif
+		if cross_c_arg == '-target'
+			found_target = true
+		endif
+	endforeach
+	if cross_prefix == ''
+		error('Didn\'t find -target and its value in' +
+		      ' c_args in input cross-file.')
+	endif
+	linker = 'lld'
+	foreach cross_c_link_arg : meson.get_cross_property('c_link_args')
+		if cross_c_link_arg.startswith('-fuse-ld')
+			linker = cross_c_link_arg.split('=')[1]
+		endif
+	endforeach
+	cross_args += ['CC=@0@'.format(cross_compiler),
+'LD=ld.@0@'.format(linker)] else
+	error('Unsupported cross compiler: @0@'.format(cross_compiler))
 endif

+cross_arch = host_machine.cpu_family() if host_machine.cpu_family()
+== 'aarch64'
+	cross_arch = 'arm64'
+endif
+
+cross_args += ['ARCH=@0@'.format(cross_arch),
+	'CROSS_COMPILE=@0@'.format(cross_prefix)]
+
 # DO ACTUAL MODULE BUILDING
 foreach d:subdirs
 	subdir(d)

diff --git a/meson_options.txt b/meson_options.txt index

6eff62e47d..de44d17c02 100644

--- a/meson_options.txt
+++ b/meson_options.txt

@@ -19,7 +19,7 @@ option('ibverbs_link', type: 'combo', choices :

['static', 'shared', 'dlopen'],  option('include_subdir_arch', type: 'string', value:

'',

quoted

 	description: 'subdirectory where to install arch-dependent headers')
option('kernel_dir', type: 'string', value: '',
-	description: 'Path to the kernel for building kernel modules. Headers

must be in $kernel_dir/build. Modules will be installed in
$DEST_DIR/$kernel_dir/extra/dpdk.')

quoted

+	description: 'Path to the kernel for building kernel modules.
+Headers must be in $kernel_dir. Modules will be installed in
+/lib/modules/$(uname -r)/extra/dpdk for native builds.')

While correct, the last sentence isn't really relevant to the build option, it's more
an additional note, and it seems a bit awkward. Maybe it can be shortened by
referencing "/lib/modules" rather than giving the full path.
Alternatively, maybe just putting the details in the documentation is a better
plan, and leaving the comment here as just "path to the kernel for building
kernel modules".

Having it in docs would be better, but where exactly? I tried looking, but didn't find a suitable place.

quoted

 option('machine', type: 'string', value: 'native',
 	description: 'set the target machine type')  option('max_ethports',
type: 'integer', value: 32,
--
2.20.1