Re: [PATCH] ARC: mm: fix build breakage with STRICT_MM_TYPECHECKS

["gregkh]

On Mon, Sep 12, 2016 at 09:32:55AM -0700, Vineet Gupta wrote:
> |  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))
>  
>  /*
> -- 
> 2.7.4

Whitespace is correct this time, thanks.  You can't cut-and-paste in a
web email client...

But, you forgot to say what the git commit id is for this patch :(

Can you resend it with that info?

thanks,

greg k-h