x86 weirdness

Sascha Hauer s.hauer at pengutronix.de
Tue Jul 31 09:13:19 EDT 2012

Hi Erwin,

On Tue, Jul 31, 2012 at 12:49:29PM +0200, Erwin Rol wrote:
> Hey x86-asm-experts,

Surely you do not mean me ;)

> On 31-7-2012 0:36, Erwin Rol wrote:
> So when I use the memset code the asm looks like this below. As you
> can see the memset gets its 3 parameters from the stack (see
> comments below in the asm src). But when you look at the location
> when memset is called it looks like the caller tries to pass the
> parameters in registers. After looking into the Makefile I noticed
> the arch/x86/boot/* sources get compiled with -mregparm=3, but the
> other sources use normal calling convention. This means code from
> arch/x86/boot/* can not call any other barebox functions when they
> are not of type void f(void). The file arch/x86/boot/regs.c also
> calls memset but it seems the compiler notices that regs.c is 16bit
> code and so it inlines a 16bit memset version (I at least don't see
> a call function).
> Is there any GCC or LD magic we can use to prevent error like this?
> Wouldn't it be better to _not_ change the calling convention in the
> Makefile, but mark the functions that need it with __attribute__ ?

Maybe it's easier and more straight forward to just use a for-loop here
instead of playing magic games with attributes and or flags? Are there
more functions affected or is it just memset?


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