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

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Message-ID: <CAMe9rOq7LduF4aLPe9qatedxps4WPCgOHTD=E_Lje4_tu6tyZw@mail.gmail.com>
Date:	Wed, 18 Apr 2012 11:15:57 -0700
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	"H. Peter Anvin" <hpa@...or.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 Wed, Apr 18, 2012 at 11:10 AM, H. Peter Anvin <hpa@...or.com> wrote:
> On 04/18/2012 11:01 AM, H.J. Lu wrote:
>> On Wed, Apr 18, 2012 at 10:47 AM, H. Peter Anvin <hpa@...or.com> wrote:
>>> On 04/18/2012 10:38 AM, H.J. Lu wrote:
>>>>
>>>> It doesn't match struct siginfo in include/asm-generic/siginfo.h for
>>>> x32.
>>>>
>>>
>>> What is missing (from either)?
>>>
>>
>> include/asm-generic/siginfo.h has
>>
>>                 /* SIGCHLD */
>>                 struct {
>>                         __kernel_pid_t _pid;    /* which child */
>>                         __ARCH_SI_UID_T _uid;   /* sender's uid */
>>                         int _status;            /* exit code */
>>                         __kernel_clock_t _utime;
>>                         __kernel_clock_t _stime;
>>                 } _sigchld;
>>
>>
>> Although x32 __kernel_clock_t is s64 with 64bit alignment, in
>> _sigchld, it must be compat_s64 with 32bit alignment.
>>
>
> What would you suggest?  Change __kernel_clock_t?  It would somewhat
> stink to have to muck with things here.
>
> The problem here of course is that this is a phony misalignment...
>
>        -hpa
>

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;


-- 
H.J.
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