[Bug 1780] New: [ARM] Change CPU_PARTITION_ALIGNMENT to 4

[bugzilla-daemon at rtems.org]

https://www.rtems.org/bugzilla/show_bug.cgi?id=1780

           Summary: [ARM] Change CPU_PARTITION_ALIGNMENT to 4
           Product: RTEMS
           Version: HEAD
          Platform: All
        OS/Version: RTEMS
            Status: NEW
          Severity: normal
          Priority: P3
         Component: cpukit
        AssignedTo: joel.sherrill at oarcorp.com
        ReportedBy: sebastian.huber at embedded-brains.de


On 04/12/2011 08:52 AM, Sebastian Huber wrote:
> On 04/12/2011 04:39 AM, Kirspel, Kevin wrote:
>> The CPU_PARTITION_ALIGNMENT for ARM has been changed from 4 to 8 bytes
>> in the latest 4.10 release.
> 
> http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042d/IHI0042D_aapcs.pdf
> 
> Yes, this is in accordance to AAPCS section 5.2.1.2
> "Stack constraints at a public interface".
> 
> The constraint for the CPU_ALIGNMENT and CPU_HEAP_ALIGNMENT is section 4.1
> "Fundamental Data Types" table 1, e.g. a double *d = malloc(sizeof(double))
> must be possible.
> 
>> When creating a partition , the buffer size
>> must be a multiple of this value.  The GCC compiler does not generate
>> structures sizes that are multiples of 8.
> 
> This is all right.
> 
>> The following call fails with RTEMS_INVALID_SIZE due to the multiple of
>> 8 requirement.  In the example, sizeof(state_event_t) is 12 bytes:
>>
>> rtems_partition_create(name, starting_addr, sizeof( state_event_t ) *
>> 4096, sizeof( state_event_t ), RTEMS_LOCAL, &id );
>>
>>  
>>
>> The CPU_STACK_ALIGNMENT for ARM should be set to 8 but I am not sure
>> about the others: CPU_ALIGNMENT, CPU_HEAP_ALIGNMENT, and
>> CPU_PARTITION_ALIGNMENT.  The call above should be allowed.
> 
> In of section 4.3.1 "Aggregates" we have:
> 
>  o The alignment of an aggregate shall be the alignment of its most-aligned
>    component.
> 
>  o The size of an aggregate shall be the smallest multiple of its alignment
>    that is sufficient to hold all of its members when they are laid out
>    according to these rules.
> 
> Thus it should be sufficient to set CPU_PARTITION_ALIGNMENT to 4 (we need 4 due
> to implementation constraints).

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