Re: inline asm with sse problem

[wojtekb82_23 <wojtekb82_23 at o2 dot pl>]

Dnia 7 lutego 2008 2:29 Tom St Denis <tstdenis@ellipticsemi.com> napisaÅ(a):

> > I have the code [appendix 1] that I compile using [appendix 2] on system
> > [appendix 3].
> > I get a Segmentation fault at line:
> > 0x080487ca : movups (%esi),%xmm0
> > 0x080487cd : addps  (%ebx),%xmm0 
> > 0x080487d0 : movups %xmm0,(%ebx) 
> > What am I doing wrong?
> 
> What is the alignment of %ebx?  If it's not 16 byte aligned you're probably going to get a fault.
> 

Thanks, but I still get the same error with alignment:

#include <iostream>

using namespace std;

int main() {
	void* p;
	void* q;
	
	if (posix_memalign(&p, 16, 4*sizeof(float)) < 0) {
		cerr << "ERR" << endl;
		return 1;
	}
	
	float* dst = static_cast<float*>(p);
	
	if (posix_memalign(&q, 16, 4*sizeof(float)) < 0) {
		cerr << "ERR" << endl;
		return 1;
	}
	
	float* src = static_cast<float*>(q);
	
	
	for(int i = 0; i<4; i++)
	{
		dst[i] = 0;
		src[i] = 1;
	}
	
	cout << dst[0] << " " << dst[1] << " " << dst[2] << " " << dst[3] << endl;
	 
	asm ("movups 0(%[src]), %%xmm0\n\t"
		 "addps  0(%[dst]), %%xmm0\n\t"
	     "movups %%xmm0, 0(%[dst])\n\t"
	     : [dst] "=r" (dst)
	     : [src] "r" (src)
	     : "xmm0");


    cout << dst[0] << " " << dst[1] << " " << dst[2] << " " << dst[3] << endl;
    
	return 0;
}

And what about the "wrong" compilation when passing -O0?


Regards,
WB.