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List:       linux-ia64
Subject:    [Linux-ia64] FW: incorrect misalignment handling
From:       "Zach, Yoav" <yoav.zach () intel ! com>
Date:       2001-08-12 7:46:24
[Download RAW message or body]

the attachment did not get by. here it is:

-------------------------------------- start code
--------------------------------------
#include <stdio.h>

char buff[20]
/* uncomment the next line to see how it is done in hw */
// __attribute__ ((aligned (16)))
;
int main()
{
    int i;

    for (i = 0; i< 10; i++)
        buff[i] = 'a';
    for (i = 10; i < 20; i++)
        buff[i] = 'A';
    __asm__ ("
        movl r2 = buff;;
        fmerge.s f10 = f0, f1;;
        stfe [r2] = f10;;
    ");
    printf("buff[10] = %c\n", buff[10]);
    return 0;
} 
-------------------------------------- end code
----------------------------------------

>  -----Original Message-----
> From: 	Zach, Yoav  
> Sent:	Sunday, August 12, 2001 9:59 AM
> To:	'linux-ia64@linuxia64.org'
> Cc:	Luck, Tony
> Subject:	incorrect misalignment handling
> 
> We encountered a problem with the handling of misaligned operations. When
> handling a misaligned 'stfX' instruction, the kernel uses the function
> emulate_store_float( ), which practically copies the source to destination
> byte by byte. The length of the operation is determined according to the
> instruction's fsz completer, using the float_fsz table:
> 
> static const unsigned char float_fsz[4]={
> 	16, /* extended precision (e) */
> 	8,  /* integer (8)            */
> 	4,  /* single precision (s)   */
> 	8   /* double precision (d)   */
> }
> 
> The problem is that fsz==e means the operation length is 10 bytes, and not
> 16 bytes as in the implementation. Attached is a small test case that
> demonstrates this problem.
> 
> My questions are:
> *	Is there a rationale behind this implementation, or is it just a
> mistake ?
> *	If it is a mistake, was it corrected in kernel versions later than
> 2.4.3 ? 
> 
>  <<mis64.c>> 
> TIA,
> Yoav.
> 
> Yoav Zach
> Mail:        yoav.zach@intel.com
> 

["mis64.c" (application/octet-stream)]

#include <stdio.h>

char buff[20]
/* uncomment the next line to see how it is done in hw */
// __attribute__ ((aligned (16)))
;
int main()
{
    int i;

    for (i = 0; i< 10; i++)
        buff[i] = 'a';
    for (i = 10; i < 20; i++)
        buff[i] = 'A';
    __asm__ ("
        movl r2 = buff;;
        fmerge.s f10 = f0, f1;;
        stfe [r2] = f10;;
    ");
    printf("buff[10] = %c\n", buff[10]);
    return 0;
} 


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