linux-kernel - Re: SYSV IPC broken for no-legacy syscall kernels (was Re: [RFC PATCH v1 26/31] ARC: Build system: Makefiles, Kconfig, Linker script)

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Date:	Mon, 11 Mar 2013 12:44:54 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
CC:	Arnd Bergmann <arnd@...db.de>, <linux-arch@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Markos <markos.chandras@...tec.com>
Subject: Re: SYSV IPC broken for no-legacy syscall kernels (was Re: [RFC PATCH
 v1 26/31] ARC: Build system: Makefiles, Kconfig, Linker script)

Hi Vineet,

On 11/03/13 12:29, Vineet Gupta wrote:
> On Wednesday 07 November 2012 07:43 PM, Arnd Bergmann wrote:
>> On Wednesday 07 November 2012, Vineet Gupta wrote:
>>
>>> +
>>> +config ARC
>>> +	def_bool y
>>> +	select ARCH_WANT_IPC_PARSE_VERSION
>>> +	# ARC Busybox based initramfs absolutely relies on DEVTMPFS for /dev
>>> +	# DEVTMPS in turn needs HOTPLUG
>>> +	select DEVTMPFS if !INITRAMFS_SOURCE=""
>>> +	select GENERIC_ATOMIC64
>>> +	select GENERIC_CLOCKEVENTS
>>> +	select GENERIC_FIND_FIRST_BIT
>>> +	# for now, we don't need GENERIC_IRQ_PROBE, CONFIG_GENERIC_IRQ_CHIP
>>> +	select GENERIC_IRQ_SHOW
>>> +	select GENERIC_PENDING_IRQ if SMP
>>> +	select GENERIC_SMP_IDLE_THREAD
>>> +	select HAVE_GENERIC_HARDIRQS
>>> +	select HOTPLUG if !INITRAMFS_SOURCE=""
>>> +	select MODULES_USE_ELF_RELA
>> You should not need ARCH_WANT_IPC_PARSE_VERSION
> 
> It seems, we have a small bug in sysV IPC.
> A lot of LTP tests have started failing on ARC 3.9-rc1 kernel due to absence of
> ARCH_WANT_IPC_PARSE_VERSION.
> 
> I'm assuming that for newer arches, msgctl(2) and friends need to have  need to
> have @cmd of type 0x01nn where 0x0100 is IPC_64.
> However for ! ARCH_WANT_IPC_PARSE_VERSION, ipc/util.h seems to be defining a dummy
> version of ipc_parse_version(), which doesn't strip out the 0x0100 from @cmds,
> causing the code to not enter the switch block in SYSCALL_DEFINE3(msgctl) making
> it fail.
> Adding the above item to arch/arc/Kconfig obviously fixes the breakage.
> 
> It seems there is some bogosity in the way ipc_parse_version() is defined. Given
> the way it is used, to strip out the 0x0100 bit, it seems we always need the
> function variant - the IA-64 ish comment in there seems to be bit-rot.
> 
> What do you think ?

FYI, for metag we assumed this was intentional and that IPC_64 shouldn't
be passed since it is the default behaviour for new arches.
You may find the following uClibc commit relevant:
http://git.uclibc.org/uClibc/commit/?id=6c2fa3451f35f8d78a31689044b2d19efa4eaca2

Cheers
James

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