linux-kernel - Re: [PATCH v2] signals, pkeys: make si

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Date:	Mon, 29 Feb 2016 08:57:32 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Stephen Rothwell <sfr@...b.auug.org.au>
Cc:	"H. Peter Anvin" <hpa@...or.com>, tglx@...utronix.de,
	peterz@...radead.org, Dave Hansen <dave@...1.net>,
	linux-kernel@...r.kernel.org, dave.hansen@...ux.intel.com,
	akpm@...ux-foundation.org, mingo@...e.hu,
	linux-next@...r.kernel.org, deller@....de
Subject: Re: [PATCH v2] signals, pkeys: make si_pkey 32 bits


* Stephen Rothwell <sfr@...b.auug.org.au> wrote:

> In order to prevent a change of alignment of the _sifields union in the
> siginfo structure on (some) 32 bit platforms and an ABI breakage, we
> change the type of _pkey to unsigned int.  If more bits are needed in
> the future, a second unsigned int could be added.
> 
> Fixes: cd0ea35ff551 ("signals, pkeys: Notify userspace about protection key faults")
> Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: Stephen Rothwell <sfr@...b.auug.org.au>
> ---
>  arch/ia64/include/uapi/asm/siginfo.h | 2 +-
>  arch/mips/include/uapi/asm/siginfo.h | 2 +-
>  include/uapi/asm-generic/siginfo.h   | 2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/ia64/include/uapi/asm/siginfo.h b/arch/ia64/include/uapi/asm/siginfo.h
> index 0151cfab929d..19e7db0c9453 100644
> --- a/arch/ia64/include/uapi/asm/siginfo.h
> +++ b/arch/ia64/include/uapi/asm/siginfo.h
> @@ -70,7 +70,7 @@ typedef struct siginfo {
>  					void __user *_upper;
>  				} _addr_bnd;
>  				/* used when si_code=SEGV_PKUERR */
> -				u64 _pkey;
> +				unsigned int _pkey;
>  			};
>  		} _sigfault;
>  
> diff --git a/arch/mips/include/uapi/asm/siginfo.h b/arch/mips/include/uapi/asm/siginfo.h
> index 6f4edf0d794c..3cc14f4a5936 100644
> --- a/arch/mips/include/uapi/asm/siginfo.h
> +++ b/arch/mips/include/uapi/asm/siginfo.h
> @@ -93,7 +93,7 @@ typedef struct siginfo {
>  					void __user *_upper;
>  				} _addr_bnd;
>  				/* used when si_code=SEGV_PKUERR */
> -				u64 _pkey;
> +				unsigned int _pkey;
>  			};
>  		} _sigfault;
>  
> diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
> index 90384d55225b..f4459dc3d31b 100644
> --- a/include/uapi/asm-generic/siginfo.h
> +++ b/include/uapi/asm-generic/siginfo.h
> @@ -98,7 +98,7 @@ typedef struct siginfo {
>  					void __user *_upper;
>  				} _addr_bnd;
>  				/* used when si_code=SEGV_PKUERR */
> -				u64 _pkey;
> +				unsigned int _pkey;
>  			};
>  		} _sigfault;
>  

Please use the standard ABI integer type pattern: __u32.

The advantage of only using __[su][8|16|32|64] integer types is that it's 
"obvious" at a glance that an ABI is bitness-invariant.

For example include/uapi/linux/perf_event.h only uses such ABI-safe types, and 
arch/x86/include/uapi is using these types 95%+ of the time.

( The various struct siginfo definitions should probably be harmonized as well, 
  but in a separate patch. )

Thanks,

	Ingo