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Re: Re: Problem with CYG_HAL_TABLES


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
> > 
> 
> -- 
> Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos
> and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss
> 
> 

-- 
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