linux-kernel - Re: [tip:x86/x32] x32: Fix alignment fail in struct compat

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Date:	Wed, 18 Apr 2012 11:21:08 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"H.J. Lu" <hjl.tools@...il.com>
CC:	mingo@...hat.com, linux-kernel@...r.kernel.org, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/x32] x32: Fix alignment fail in struct compat_siginfo

On 04/18/2012 11:15 AM, H.J. Lu wrote:
> 
> In x32 glibc, I have
> 
> # if compile for X32
> /* si_utime and si_stime must be 4 byte aligned for x32 to match the
>    kernel.  We align siginfo_t to 8 bytes so that si_utime and si_stime
>    are actually aligned to 8 bytes since their offsets are multiple of
>    8 bytes.  */
> typedef __clock_t __attribute__ ((__aligned__ (4))) __sigchld_clock_t;
> #  define __SI_ALIGNMENT __attribute__ ((__aligned__ (8)))
> # else
> typedef __clock_t __sigchld_clock_t;
> #  define __SI_ALIGNMENT
> # endif
> 
> typedef struct siginfo
>   {
> ...
> 	/* SIGCHLD.  */
> 	struct
> 	  {
> 	    __pid_t si_pid;	/* Which child.  */
> 	    __uid_t si_uid;	/* Real user ID of sending process.  */
> 	    int si_status;	/* Exit value or signal.  */
> 	    __sigchld_clock_t si_utime;
> 	    __sigchld_clock_t si_stime;
> 	  } _sigchld;
> ...
>   } siginfo_t __SI_ALIGNMENT;
> 

So in other words, a separate type just for this.  However, the question
still holds: could we simply change __kernel_clock_t for x32 and be done
with it?  It would affect the alignment of struct tms, I guess; it
wouldn't really affect the kernel directly since the kernel gets a
pointer straight from userspace for times(2), but it would kind of mess
up a userspace which uses __kernel_clock_t directly.

Urk, okay...

	-hpa
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