linux-kernel - Re: samples/kdbus/kdbus-workers.c and cross compiling MIPS

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Date:	Thu, 30 Jul 2015 16:23:52 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:	David Herrmann <dh.herrmann@...glemail.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Daniel Mack <daniel@...que.org>,
	Djalal Harouni <tixxdz@...ndz.org>, linux-mips@...ux-mips.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>
Subject: Re: samples/kdbus/kdbus-workers.c and cross compiling MIPS

Hi

On Thu, Jul 30, 2015 at 3:50 PM, Paul Gortmaker
<paul.gortmaker@...driver.com> wrote:
> On 2015-07-29 12:31 PM, David Herrmann wrote:
>> Hi
>>
>> On Wed, Jul 29, 2015 at 6:19 PM, Paul Gortmaker
>> <paul.gortmaker@...driver.com> wrote:
>>> Hi David,
>>>
>>> Does it make sense to build this sample when cross compiling?
>>>
>>> The reason I ask is that it has been breaking the linux-next build of
>>> allmodconfig for a while now, with:
>>>
>>>   HOSTCC  samples/kdbus/kdbus-workers
>>> samples/kdbus/kdbus-workers.c: In function ‘prime_new’:
>>> samples/kdbus/kdbus-workers.c:934:18: error: ‘__NR_memfd_create’ undeclared (first use in this function)
>>>   p->fd = syscall(__NR_memfd_create, "prime-area", MFD_CLOEXEC);
>>>                   ^
>>> samples/kdbus/kdbus-workers.c:934:18: note: each undeclared identifier is reported only once for each function it appears in
>>> scripts/Makefile.host:91: recipe for target 'samples/kdbus/kdbus-workers' failed
>>> make[2]: *** [samples/kdbus/kdbus-workers] Error 1
>>
>> mips does have this syscall, so I assume the problem is out-of-date
>> kernel headers. You can fix this by running:
>>
>>     $ make headers_install
>
> No, let me try and clarify. Please note the emphasis on cross compiling
> and automated build coverage, i.e. there is no place for manual steps.

User-space samples in ./samples/ are compiled with HOSTCC, which is
the compiler for the _local_ machine. Regardless of cross-compiling
the same local compiler is used. So I cannot understand why this is
even remotely related to cross compiling. Please elaborate.
Please note that this is HOSTCC running, so it does *NOT* require the
toolchain for your cross-compiled architecture.

Also, please tell me why your system has "linux/memfd.h" available,
but __NR_memfd_create is undefined?

Anyway, patch is attached. Can you verify it works?
David

diff --git a/samples/kdbus/Makefile b/samples/kdbus/Makefile
index 137f842..dbd9de8 100644
--- a/samples/kdbus/Makefile
+++ b/samples/kdbus/Makefile
@@ -1,9 +1,13 @@
 # kbuild trick to avoid linker error. Can be omitted if a module is built.
 obj- := dummy.o

+ifndef CROSS_COMPILE
+
 hostprogs-$(CONFIG_SAMPLE_KDBUS) += kdbus-workers

 always := $(hostprogs-y)

 HOSTCFLAGS_kdbus-workers.o += -I$(objtree)/usr/include
 HOSTLOADLIBES_kdbus-workers := -lrt
+
+endif
--
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