Re: FFI + JIT alignment limit
- From: Mike Pall <mike-1301@xxxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Fri, 18 Jan 2013 01:35:34 +0100
Simon Cooke wrote:
> According to the manual JIT compilation fails currently for:
>
> * Allocations of C types with a size > 128 bytes or an alignment > 8 bytes.
>
> Is the alignment constraint a fundamental limitation of the
> implementation, or would it be possible to extend JIT support to
> include 16-byte alignment?
The current memory allocator only guarantees 8 byte alignment.
That necessitates some contorted code for aligning cdata types and
their headers to make the GC happy (compare lj_cdata_newv with the
inlined lj_cdata_new). I haven't added the messy code required to
do this from JIT-compiled code. It'll be all much simpler with the
new GC, which offers 16 byte alignment right away.
A temporary workaround for you would be to get a chunk of memory
plus 16 extra bytes, compute an aligned pointer to it and then use
that for passing data to the library.
BTW: Passing or returning structs by value isn't compiled, either.
--Mike
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