[ECOS] Re: Problem with CYG_HAL_TABLES

[Jay Foster]

I think that I have identified the issue for me.  The last member of 
MY_TYPE is a thread stack storage.  It is declared as:

    /* Thread stack */
     cyg_uint8 stack[TASK_STK_SIZE] __attribute__((aligned(16)));

This apparently causes gcc to give the entire MY_TYPE object the same 
alignment, even though only that one member of MY_TYPE needs it.  I 
worked around this by defining my own CYG_HAL_TABLE_BEGIN and 
CYG_HAL_TABLE_END macros with the alignment changed to 
CYGARC_ALIGNMENT.  CYGARC_ALIGNMENT is 4, which is equivalent to 
__attribute__((aligned(16))).

Although not the cause of my issue, I think that CYG_HAL_TABLE_BEGIN, 
CYG_HAL_TABLE_END, and CYG_HAL_TABLE_TYPE should all use the same 
alignment.

Jay

On 1/25/2011 6:02 AM, Sergei Gavrikov wrote:
> Hi Jay,
>
> On Thu, 20 Jan 2011, Jay Foster wrote:
>
>> Looking at the definition of CYG_HAL_TABLE_TYPE and
>> CYG_HAL_TABLE_BEGIN, I see that the CYG_HAL_TABLE_BEGIN uses an
>> alignment of CYGARC_P2ALIGNMENT and the CYG_HAL_TABLE_TYPE uses an
>> alignment of CYGARC_ALIGNMENT.
>>
>> For the ARM architecture, these are defined to be different
>> (CYGARC_P2ALIGNMENT is 2 and CYGARC_ALIGNMENT is 4).  This would
>> result in the table label being 4 byte aligned and the elements 16
>> byte aligned.
> It seemed for me "P2" stands for "power of 2", so 2^2 == 4 and that is
> okay ~ http://sourceware.org/binutils/docs/as/P2align.html
>
> For example for i386 architecture they defined
>
> # define CYGARC_ALIGNMENT 32
> # define CYGARC_P2ALIGNMENT 5
>
> i.e. 2^5 == 32
>
>> The question is why has this not caused me problems before this?
> Jay, I tried your example 'as is' for a few ARM targets (LE/BE) (well I
> could only guess what MY_TYPE is) and couldn't reproduce such a miss-
> alignment for _MY_LABEL_.
>
> I just use GDB to test your example for ARM targets
>
> ## .gdbinit --
> set output-radix 16
> target sim
> print&(_MY_LABEL_)
> print&(my_instance1)
> detach
> quit
>
> This did print always the same addresses. Hm, puzzle. Just a guess, may
> be you use some -falign-* GCC option? However, TAB macros written in
> asm. And how did you declare the labels? Hope, that is something like
>
> extern MY_TYPE  _MY_LABEL_[],
>                  _MY_LABEL_END_;
>
>
>
> Is it possible to reproduce the issue if you will provide more
> information?
>
>
> Sergei
>
>> On 1/20/2011 9:30 AM, Jay Foster wrote:
>>> I have used the CYG_HAL_TABLE mechanism before with success, but I am now
>>> running into an alignment problem with a new application.  This is on an ARM
>>> architecture.
>>>
>>> I have an object defined as:
>>>
>>> typedef struct
>>> {
>>>   ....
>>> } CYG_HAL_TABLE_TYPE MY_TYPE;
>>>
>>> I then declare the HAL table array as:
>>>
>>> CYG_HAL_TABLE_BEGIN( _MY_LABEL_, _my_name_ );
>>> CYG_HAL_TABLE_END( _MY_LABEL_END_, _my_name_ );
>>>
>>> I then place two instances of the object into the HAL table array:
>>>
>>> MY_TYPE  my_instance1 CYG_HAL_TABLE_QUALIFIED_ENTRY(_my_name_, 2) =
>>> {
>>>      ....
>>> };
>>>
>>> MY_TYPE  my_instance2 CYG_HAL_TABLE_QUALIFIED_ENTRY(_my_name_, 3) =
>>> {
>>>      ....
>>> };
>>>
>>> I then iterate the table using:
>>>
>>>     MY_TYPE *p;
>>>
>>>      for (p=&(_MY_LABEL_[0]); p!=&(_MY_LABEL_END_); p++)
>>>      {
>>>      }
>>>
>>> This fails due to alignment issues:
>>>
>>>      The _MY_LABEL_ is not at the same address as the first element in the
>>> array (my_instance1) due to alignment issues.  The iteration then fails.
>>> _MY_LABEL_ is aligned on a 4 byte boundary and the array elements are
>>> aligned on 16 byte boundaries.  Is there any way to make this work?
>>>
>>> Jay
>>>
>> -- 
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>>
>>

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