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Date: Fri, 19 Jan 2018 13:26:15 +0100
From: Greg Kroah-Hartman <gregkh@linux-foundation.org>
To: David Woodhouse <dwmw2@infradead.org>
Cc: Razvan Ghitulete <rga@amazon.de>,
        Guenter Roeck <linux@roeck-us.net>, stable@vger.kernel.org
Subject: Re: Build errors in v4.4-stable-queue (i386)
Message-ID: <20180119122615.GA11701@kroah.com>
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On Fri, Jan 19, 2018 at 11:21:54AM +0100, David Woodhouse wrote:
> On Fri, 2018-01-19 at 10:34 +0100, David Woodhouse wrote:
> > On Thu, 2018-01-18 at 19:10 +0100, Greg Kroah-Hartman wrote:
> > > 
> > > On Thu, Jan 18, 2018 at 08:41:58AM -0800, Guenter Roeck wrote:
> > > > 
> > > > 
> > > > Building i386:defconfig ... failed
> > > > --------------
> > > > Error log:
> > > > arch/x86/entry/entry_32.S: Assembler messages:
> > > > arch/x86/entry/entry_32.S:230: Error: too many memory references
> > > > for `mov'
> > > Ick, no good, 0-day has pointed this out as well.
> > > 
> > > Razvan and David, any ideas?
> > 
> > 	CALL_NOSPEC PT_EBX(%esp)
> > 
> > That turns into a retpoline with
> > 
> > � � � � mov PT_EBX(%esp), 0(%esp)
> > 
> > Which is doubly wrong, because not only can't you have two memory
> > operands to a 'mov' but %esp has already *moved* by the time we get
> > here so we'd be using the wrong source anyway.
> > 
> > We need to pick a victim register and load PT_EBX(%esp) into it, then
> > CALL_NOSPEC %\reg.
> > 
> > We'll fix this and also the RSP-clobbering in context switch that you
> > just sent a "fails to apply" message for.
> 
> Try this. Not even build tested. I think we can have %edx here, as it
> would be the second argument to the kthread function, and clobbered by
> it too.
> 
> Signed-off-by-if-it-works: David Woodhouse <dwmw@amazon.co.uk>
> 
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -227,7 +227,8 @@ ENTRY(ret_from_kernel_thread)
> ��������pushl���$0x0202�������������������������# Reset kernel eflags
> ��������popfl
> ��������movl����PT_EBP(%esp), %eax
> -�������CALL_NOSPEC PT_EBX(%esp)
> +�������movl����PT_EBX(%esp), %edx
> +�������CALL_NOSPEC %edx
> ��������movl����$0, PT_EAX(%esp)
> �

I don't have a way to test this, I'll merge it into the existing patch
and push out a new tree to see how 0-day and Guenter's build-farm handle
it.

thanks,

greg k-h