Re: [RFC/TileGX 1/6] fix args alignment bug

Joel Brobecker
2013-01-18T13:14:12Z

> gdb/ChangeLog:
>
> * tilegx-tdep.c (tilegx_push_dummy_call): args pushed on stack
> should be aligned to 64bit.

Some questions below...

> - /* Loop backwards through arguments to determine stack alignment. */
> - alignlen = 0;
> -
> - for (j = nargs - 1; j >= i; j--)
> - {
> - typelen = TYPE_LENGTH (value_enclosing_type (args[j]));
> - alignlen += (typelen + 3) & (~3);
> - }
> -
> - if (alignlen & 0x4)
> - stack_dest -= 4;

Do you have any hint as to why this code was written the way it was?
It doesn't seem like the type of code that would be added by accident.
Did Jeff (the apparent author) misunderstand the ABI?

> typelen = TYPE_LENGTH (value_enclosing_type (args[j]));
> - slacklen = ((typelen + 3) & (~3)) - typelen;
> + slacklen = ((typelen + 7) & (~7)) - typelen;

This is a detail, but can you use utils.c:align_up, in this case?
(I find those midly more readable than these incantations, but
it's OK if you prefer the code to stay as is).

> /* Add 2 words for linkage space to the stack. */
> - stack_dest = stack_dest - 8;
> - write_memory (stack_dest, two_zero_words, 8);
> + stack_dest = stack_dest - 16;
> + write_memory (stack_dest, four_zero_words, 16);

It looks like you need to adjust the comment as well.

--
Joel