build: support KNI cross-compilation

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.

Signed-off-by: Juraj Linkeš <juraj.linkes@pantheon.tech>
Reviewed-by: Bruce Richardson <bruce.richardson@intel.com>

2 files changed, 81 insertions, 17 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..b434706796 100644
--- a/kernel/linux/meson.build
+++ b/kernel/linux/meson.build
@@ -3,25 +3,89 @@
 
 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')
-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
+		# backward compatibility:
+		# the headers could still be in the 'build' subdir
+		if not kernel_build_dir.endswith('build') and not kernel_build_dir.endswith('build/')
+			kernel_build_dir = join_paths(kernel_build_dir, 'build')
+			make_returncode = run_command('make', '-sC', kernel_build_dir,
+					'kernelversion').returncode()
+		endif
+	endif
+
+	if make_returncode != 0
+		error('Cannot compile kernel modules as requested - are kernel headers installed?')
+	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?')
+# 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)