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SubjectRe: [PATCH 4.4 05/53] x86/asm: Use register variable to get stack pointer value
El Tue, Feb 06, 2018 at 02:37:06PM -0800 Greg Kroah-Hartman ha dit:

> On Tue, Feb 06, 2018 at 01:59:41PM -0800, Matthias Kaehlcke wrote:
> > Hi Greg,
> >
> > El Mon, Jan 22, 2018 at 09:39:57AM +0100 Greg Kroah-Hartman ha dit:
> >
> > > 4.4-stable review patch. If anyone has any objections, please let me know.
> > >
> > > ------------------
> > >
> > > From: Andrey Ryabinin <aryabinin@virtuozzo.com>
> > >
> > > commit 196bd485ee4f03ce4c690bfcf38138abfcd0a4bc upstream.
> > >
> > > Currently we use current_stack_pointer() function to get the value
> > > of the stack pointer register. Since commit:
> > >
> > > f5caf621ee35 ("x86/asm: Fix inline asm call constraints for Clang")
> > >
> > > ... we have a stack register variable declared. It can be used instead of
> > > current_stack_pointer() function which allows to optimize away some
> > > excessive "mov %rsp, %<dst>" instructions:
> > >
> > > -mov %rsp,%rdx
> > > -sub %rdx,%rax
> > > -cmp $0x3fff,%rax
> > > -ja ffffffff810722fd <ist_begin_non_atomic+0x2d>
> > >
> > > +sub %rsp,%rax
> > > +cmp $0x3fff,%rax
> > > +ja ffffffff810722fa <ist_begin_non_atomic+0x2a>
> > >
> > > Remove current_stack_pointer(), rename __asm_call_sp to current_stack_pointer
> > > and use it instead of the removed function.
> > >
> > > Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> > > Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
> > > Cc: Andy Lutomirski <luto@kernel.org>
> > > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > > Cc: Peter Zijlstra <peterz@infradead.org>
> > > Cc: Thomas Gleixner <tglx@linutronix.de>
> > > Link: http://lkml.kernel.org/r/20170929141537.29167-1-aryabinin@virtuozzo.com
> > > Signed-off-by: Ingo Molnar <mingo@kernel.org>
> > > [dwmw2: We want ASM_CALL_CONSTRAINT for retpoline]
> > > Signed-off-by: David Woodhouse <dwmw@amazon.co.ku>
> > > Signed-off-by: Razvan Ghitulete <rga@amazon.de>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> >
> > We recently merged this patch to the Chrome OS kernel tree and it
> > broke our x86 builds with clang:
> >
> > arch/x86/include/asm/asm.h:116:50: error: register 'rsp' unsuitable for global register variables on this target
> > register unsigned long current_stack_pointer asm(_ASM_SP);
> > ^
> > arch/x86/include/asm/asm.h:41:18: note: expanded from macro '_ASM_SP'
> > #define _ASM_SP __ASM_REG(sp)
> > ^
> > arch/x86/include/asm/asm.h:24:32: note: expanded from macro '__ASM_REG'
> > #define __ASM_REG(reg) __ASM_SEL_RAW(e##reg, r##reg)
> > ^
> > arch/x86/include/asm/asm.h:19:29: note: expanded from macro '__ASM_SEL_RAW'
> > # define __ASM_SEL_RAW(a,b) __ASM_FORM_RAW(b)
> > ^
> > arch/x86/include/asm/asm.h:10:32: note: expanded from macro '__ASM_FORM_RAW'
> > # define __ASM_FORM_RAW(x) #x
> > ^
> > <scratch space>:4:1: note: expanded from here
> > "rsp"
> > ^
> > 1 error generated.
> >
> >
> > This can be fixed by also integrating the following patch:
> >
> > commit 520a13c530aeb5f63e011d668c42db1af19ed349
> > Author: Josh Poimboeuf <jpoimboe@redhat.com>
> > Date: Thu Sep 28 16:58:26 2017 -0500
> >
> > x86/asm: Fix inline asm call constraints for GCC 4.4
> >
> >
> > Admittedly a v4.4 kernel built with clang + LTS merges is a very
> > special case and we can fix this in Chrome OS by integrating the above
> > patch locally. Still it would be good to get it into stable to avoid
> > others from running into this, especially since the fix is very
> > simple.
> >
> > Actually I just noticed that the patch also isn't in v4.9, which could
> > extend the number of affected 'users' significantly, so I think we
> > almost certainly want Josh's patch in stable.
>
> That patch doesn't apply cleanly to the 4.4.y or 4.9.y trees anymore.
> It seems that only one hunk of it is really needed, the #ifndef change,
> right? If so, I'll be glad to apply that portion.

Indeed, only the #ifndef change is needed.

Thanks!

m.

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