[PATCH V3] arm: fix get_user BE behavior for target variable with size of 8 bytes

Russell King - ARM Linux linux at arm.linux.org.uk
Sat Sep 13 01:16:42 PDT 2014

On Thu, Aug 28, 2014 at 10:51:06PM -0700, Victor Kamensky wrote:
> e38361d 'ARM: 8091/2: add get_user() support for 8 byte types' commit
> broke V7 BE get_user call when target var size is 64 bit, but '*ptr' size
> is 32 bit or smaller. e38361d changed type of __r2 from 'register
> unsigned long' to 'register typeof(x) __r2 asm("r2")' i.e before the change
> even when target variable size was 64 bit, __r2 was still 32 bit.
> But after e38361d commit, for target var of 64 bit size, __r2 became 64
> bit and now it should occupy 2 registers r2, and r3. The issue in BE case
> that r3 register is least significant word of __r2 and r2 register is most
> significant word of __r2. But __get_user_4 still copies result into r2 (most
> significant word of __r2). Subsequent code copies from __r2 into x, but
> for situation described it will pick up only garbage from r3 register.
> Special __get_user_64t_(124) functions are introduced. They are similar to
> corresponding __get_user_(124) function but result stored in r3 register
> (lsw in case of 64 bit __r2 in BE image). Those function are used by
> get_user macro in case of BE and target var size is 64bit.
> Also changed __get_user_lo8 name into __get_user_32t_8 to get consistent
> naming accross all cases.
> Signed-off-by: Victor Kamensky <victor.kamensky at linaro.org>
> Suggested-by: Daniel Thompson <daniel.thompson at linaro.org>
> Reviewed-by: Daniel Thompson <daniel.thompson at linaro.org>

This patch isn't quite right, since it causes compile regressions:

ERROR: "__get_user_64t_4" [fs/ext4/ext4.ko] undefined!
ERROR: "__get_user_64t_4" [fs/cifs/cifs.ko] undefined!

This was noticed by Olof's builder, with his allmodconfig.  I don't
have the configuration to reproduce these failures.

Could you look into these please?

FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up
according to speedtest.net.

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