Re: FAILED: patch "[PATCH] ARC: mm: fix build breakage with STRICT_MM_TYPECHECKS" failed to apply to 4.4-stable tree

["gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>]

On Tue, Sep 06, 2016 at 10:24:29AM -0700, Vineet Gupta wrote:
> On 09/05/2016 06:05 AM, gregkh@linuxfoundation.org wrote:
> > The patch below does not apply to the 4.4-stable tree.
> > If someone wants it applied there, or to any other stable or longterm
> > tree, then please email the backport, including the original git commit
> > id to <stable@vger.kernel.org>.
> >
> > thanks,
> >
> > greg k-h
> 
> There were 2 commits after 4.4 which prevent a clean backport.
> Reworked patch below. Please apply.
> 
> ---------------->
> rom 54607da05b9c3d4c5ee23ce0f21d7f91b83b6c34 Mon Sep 17 00:00:00 2001
> From: Vineet Gupta <vgupta@synopsys.com>
> Date: Tue, 16 Aug 2016 18:27:07 -0700
> Subject: [PATCH] ARC: mm: fix build breakage with STRICT_MM_TYPECHECKS
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
> 
> |  CC      mm/memory.o
> | In file included from ../mm/memory.c:53:0:
> | ../include/linux/pfn_t.h: In function ‘pfn_t_pte’:
> | ../include/linux/pfn_t.h:78:2: error: conversion to non-scalar type requested
> |  return pfn_pte(pfn_t_to_pfn(pfn), pgprot);
> 
> With STRICT_MM_TYPECHECKS pte_t is a struct and the offending code
> forces a cast which ends up shifting a struct and hence the gcc warning.
> 
> Note that in recent past some of the arches (aarch64, s390) made
> STRICT_MM_TYPECHECKS default, but we don't for ARC as this leads to slightly
> worse generated code, given ARC ABI definition of returning structs
> (which pte_t would become)
> 
> Quoting from ARC ABI...
> 
>   "Results of type struct are returned in a caller-supplied temporary
>   variable whose address is passed in r0.
>   For such functions, the arguments are shifted so that they are
>   passed in r1 and up."
> 
> So
>  - struct to be returned would be allocated on stack requiring extra
>    code at call sites
>  - callee updates stack memory to facilitate the return (vs. simple
>    MOV into return reg r0)
> 
> Hence STRICT_MM_TYPECHECKS is not enabled by default for ARC
> 
> Cc: <stable@vger.kernel.org>   #4.4+
> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
> ---
>  arch/arc/include/asm/pgtable.h | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/arc/include/asm/pgtable.h b/arch/arc/include/asm/pgtable.h
> index 3cab04255ae0..e5fec320f158 100644
> --- a/arch/arc/include/asm/pgtable.h
> +++ b/arch/arc/include/asm/pgtable.h
> @@ -277,8 +277,7 @@ static inline void pmd_set(pmd_t *pmdp, pte_t *ptep)
>  
>  #define mk_pte(page, prot)    pfn_pte(page_to_pfn(page), prot)
>  #define pte_pfn(pte)        (pte_val(pte) >> PAGE_SHIFT)
> -#define pfn_pte(pfn, prot)    (__pte(((pte_t)(pfn) << PAGE_SHIFT) | \
> -                 pgprot_val(prot)))
> +#define pfn_pte(pfn, prot)    (__pte(((pfn) << PAGE_SHIFT) | pgprot_val(prot)))
>  #define __pte_index(addr)    (((addr) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1))
>  
>  /*

This doesn't apply either :(