Re: arm-elf-gcc : change default data alignement depending on ARM/THUMB

[Yves Rutschle <y dot rutschle at indigovision dot com>]

On Thu, Aug 21, 2003 at 09:48:47AM -0500, Bill Gatliff
wrote:
> As you've seen, structure implementations can change in
> response to changes in compiler settings and versions---
> but the hardware doesn't!

Hey. Get your hardware developer to make hardware that can
read the software's mind as it should. :-)

> Oh, and I left the "volatile" keyword out of all of the above, but you 
> absolutely, positively need it as well when you're touching hardware.  

Linus Torvalds said somewhere he didn't like volatile
because it never did what people expected. Linux people
usually use a macro as follows:

#define barrier()   __asm__ __volatile__("": : :"memory")

which invalidates all assumption on memory: it forces things
to be pushed to the hardware.

E.g:

    int i;
    i = 0;
    i = 5;

will typically compile as one memory set (and if i is used
a few lines later, no memory access at all), whereas:

    int i;
    i = 0;
    barrier();
    i = 5;

will perform garantee a write instruction will be issued
(then you hope someone switched off the cache, but that's
another story entirely).

/Y

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