From: swarren@wwwdotorg•org (Stephen Warren)
To: linux-arm-kernel@lists•infradead.org
Subject: arm: Remaining issue with alignment of __log_buf in printk.c
Date: Sun, 27 May 2012 10:03:20 -0600 [thread overview]
Message-ID: <4FC25048.109@wwwdotorg.org> (raw)
In-Reply-To: <4FC22098.3070803@kernel.org>
On 05/27/2012 06:39 AM, Jonathan Cameron wrote:
> Hi All,
>
> My stargate 2 board refused to start and after bisection I ended
> up at the same patch that Stephen found an alignment issue in.
> Unfortunately Stephen's patch doesn't seem to have fixed the
> issue for me.
> https://lkml.org/lkml/2012/5/10/510 is the thread. Patch from
> Stephen is : f8450fca6ecdea38b5a882fdf6cd097e3ec8651c
>
> Increasing the alignement for 32 bit systems to 8 seems to do the
> job but I can't immediately think why...
>
> System is a pxa27x strong arm.
The first element in the structure type that's actually stored in the
__log_buf array is a u64; see struct log in kernel/printk.c. Depending
on alignment rules, a u64 and a struct containing it might require a
4-byte or 8-byte alignment. The following link implies this might have
changed over time:
http://wiki.debian.org/ArmEabiPort#Struct_packing_and_alignment
(see "64-bit data type alignment" a little below that anchor). I'm not
sure what ABI the kernel expects to use internally, or your compiler;
perhaps you need the new EABI 8-byte alignment requirement for a u64 and
hence the struct as a whole, but Tegra (or my toolchain?) is OK with the
older 4-byte alignment for a u64 or struct?
Further, I'm not sure if the following alignment selection logic:
> #if !defined(CONFIG_64BIT) || defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
> #define LOG_ALIGN 4
> #else
> #define LOG_ALIGN 8
> #endif
... uses the CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS for its intended
purpose?
Russell, can you please comment here. Thanks.
next prev parent reply other threads:[~2012-05-27 16:03 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-27 12:39 arm: Remaining issue with alignment of __log_buf in printk.c Jonathan Cameron
2012-05-27 16:03 ` Stephen Warren [this message]
2012-05-27 16:14 ` Russell King - ARM Linux
2012-05-27 17:01 ` Jonathan Cameron
2012-05-29 16:14 ` Stephen Warren
2012-05-29 16:32 ` Kay Sievers
2012-05-29 17:13 ` Stephen Warren
-- strict thread matches above, loose matches on Subject: below --
2012-05-27 12:39 Jonathan Cameron
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