linux-kernel - Follow-up to remaining issue with alignment of __log

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Date:	Thu, 14 Jun 2012 21:19:31 +0200
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	swarren@...dia.com
Cc:	linux-kernel@...r.kernel.org, haojian.zhuang@...il.com,
	linux-arm-kernel@...ts.infradead.org, jic23@....ac.uk, kay@...y.org
Subject: Follow-up to remaining issue with alignment of __log_buf in printk.c


Hi Stephen and others,

I have a XScale PXA based board with has the alignement issue which makes the
kernel trap during its early stage.

I wonder what is the status now, is there a fix available ?

I have tracked what happens on PXA. The pxa is an ARM v5TE chip. The new printk
version you submitted is translated to the following assembly on the line :
        msg->ts_nsec = local_clock();
Into:
=> 0xc001bbe0 <log_store+496>:	strd	r0, [r4, r5]

In ARMv5, the "strd" assembly opcode expects the address to be 64bits aligned,
hence the bug.

Now the solutions I have seen so far in the mailing lists :
 - #define LOG_ALIGN (__alignof__(u64))
   Does always work.
 - #define LOG_ALIGN (__alignof__(struct log))
   Doesn't work with my toolchain, as __alignof__(struct log) is 4, not 8

What are you intending to do to solve the ARMv5 issue ? Are you waiting for
someone to submit a patch ?

Cheers.

-- 
Robert
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