[Sablevm-user] Re: 64 bit alignment

[Etienne M. G. <eg...@j-...>]

Hi Mr. Li,

[I would rather have this discussion on the sablevm-user mailing list,
as it gets automatically archived.  So, I am CC'ing my reply there.]

See answer below:

xli wrote:
> ...
> I have a question about 64-bit alignment for double and long values.
> For example, when we load a double value, such as 0.0, to the stack,
> the following code will be executed:
> 
> DCONST_0:
>   {
>     *((jdouble *) &stack[frame->stack_size]) = 0.0;
>     frame->stack_size += 2;
>   }
>   goto *((frame->pc++)->addr);
> 
> How do we know that the current stack address is 64-bit alligned?

It will be probably aligned, because of the definition of "stack":

_svmt_stack_frame_entry *volatile stack = NULL;

where

typedef union _svmt_stack_frame_entry_union _svmt_stack_frame_entry;

and

union _svmt_stack_frame_entry_union
{
  jint jint;
  jfloat jfloat;
  void *addr;
};


On a 64 bit platform, sizeof(void *)  will be 64 bits.  All we have to
do, now, is make sure the remaining of the stack is aligned (which I
have to double check).  

This is an important point to check.  I will need a lot of feedback from
people like you to make sure SableVM is easily portable to various
systems with a minimal effort.


-- 
----------------------------------------------------------------------
Etienne M. Gagnon, M.Sc.                     e-mail: eg...@j-...
Author of SableCC:                 http://www.sable.mcgill.ca/sablecc/
and SableVM:                                   http://www.sablevm.org/
----------------------------------------------------------------------