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

-----Original Message-----
From: Bruce Richardson <redacted>
Sent: Friday, January 29, 2021 3:42 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 02:36:58PM +0000, Juraj Linkeš wrote:

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-----Original Message-----
From: Bruce Richardson <redacted>
Sent: Friday, January 29, 2021 2:51 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 12:33:06PM +0000, Juraj Linkeš wrote:

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-----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:

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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.

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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 +++++++++++++++++++++++++++++---

-

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 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-

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compiling')

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

when

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cross-compiling')

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+	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

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array

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

'.format(element)

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

@0@'.format(cross_compiler))

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+		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.

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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.

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On top of that, this would save lines and wouldn't need as many
code

comments. I'll change it.

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+		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".

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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>'

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(not necessarily to 'kernel_dir', as the user may change that) and
only for native builds, right?

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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?

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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.

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So what do you specify as the "kernel_dir" for the cross compile?

The place where I cloned (and cross-compiled) linux sources: $HOME/linux.

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

If possible, that would be great.

Ok, I'll look into it.

/Bruce