netdev - Re: [PATCH iproute2] ip xfrm: support 64bit kernel and 32bit userspace

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Date:	Sun, 30 Nov 2014 09:42:48 -0800
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	roy.qing.li@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH iproute2] ip xfrm: support 64bit kernel and 32bit
 userspace

On Sun, 30 Nov 2014 01:33:22 +0000
Ben Hutchings <ben@...adent.org.uk> wrote:

> On Fri, 2014-11-28 at 14:58 +0800, roy.qing.li@...il.com wrote:
> > From: Li RongQing <roy.qing.li@...il.com> 
> > 
> > The size of struct xfrm_userpolicy_info is 168 bytes for 64bit kernel, and
> > 164 bytes for 32bit userspace because of the different alignment.
> 
> I think it's specific to x86 as other architectures have the same type
> alignments for 32- and 64-bit variants.
> 
> > and lead to "ip xfrm" be unable to work.
> > 
> > add a pad in struct xfrm_userpolicy_info, and enable it by set
> > KERNEL_64_USERSPACE_32 to y
> [...]
> 
> This doesn't make sense.  32-bit compat needs to work like 32-bit native
> - no exceptions, no workarounds in userland.  And if you really want to
> work around this in userland you'll need a run-time, not compile-time,
> check.

I agree with Ben, this is not a good solution.
It creates a 3rd ABI (32, 64, and 32/64).

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