Epiphany - Alignment question (double word)

[Joel Sherrill]

On November 26, 2014 10:34:16 AM CST, Hesham Moustafa <heshamelmatary at gmail.com> wrote:
>Hi,
>
>
>On Tue, Nov 25, 2014 at 8:21 PM, Gedare Bloom <gedare at gwu.edu> wrote:
>
>I'm pretty sure STACK_ALIGNMENT just does the initial stack align for
>the start of the stack. The compiler is responsible for laying out the
>frames after that, and for generating aligned entries in the stack
>itself. Probably the compiler is being too lax. Check for some
>compiler flags for the target that might be used to increase the
>alignment, for example if there is a strict alignment flag. Check with
>the epiphany / parallela boards too, ask about compiler flags for
>alignment problems.
>
>I checked their GCC port, and I think they define the proper macros for
>stack alignments to 8 bytes. However, when debugging on real HW
>(Parallella), I can see that some structures are allocated on non
>8-bytes boundaries, and also structures passed as function arguments
>are not aligned.

So the stack is correctly aligned when the task is started but allocation of variables is misaligned? If so, that's a GCC bug.

If these are malloced, then it is an issue for the heap configuration for this port.

>-Gedare
>
>
>On Tue, Nov 25, 2014 at 2:06 PM, Hesham Moustafa
><heshamelmatary at gmail.com> wrote:
>> Hi all,
>>
>> I came across an issue with alignment when I am porting RTEMS to
>Epiphany
>> now. The reference manual says that stores should be aligned
>according to
>> the store instruction type (half word, word, double word). For
>example strd
>> instruction should get an address aligned to 8 bytes. Although I set
>> CPU_ALIGNMENT and Stack aliment macros to 8 in cpu.h, I still get
>some
>> automatic variables not aligned to 8 bytes, which causes an exception
>when
>> executing relevant (double) store/load instructions.
>>
>> I had to apply a brute-force solution to get over this problem. For
>example
>> I add alignment's attribute to "CORE_mutex_Attributes attr
>__attribute__
>> ((aligned (8)));" and I set "#define
>CPU_TIMESTAMP_USE_STRUCT_TIMESPEC TRUE"
>> instead of using CPU_TIMESTAMP_USE_INT64
>>
>> Is there any other good solution for such a problem?
>>
>> Regards,
>> Hesham
>>
>
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