inline ASM: SSE

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Article #165

#165

From: Christoph Brunner
Date: Sun, 25 May 2003 18:59

38 lines
2716 bytes

Hi,

I'm currently trying to get into extended inline ASM in gcc (gcc version 
3.2.2, gas 2.13.90.0.18).
However, I'm having some trouble: The following code, using SSE 
instructions, segfaults, and I don't really know why.

Perhaps someone could give me a hint?

void add_asm(float *a, float *b, float *c, int n)
{
    // a,b,c properly aligned; (n % 4) = 0
    int iter = 0;
	
    __asm__ __volatile__
    (
	"calc:\n"
	"subl $4, %%ecx\n"
		
	// perform package load/addition/store
	"movaps (%3), %%xmm0\n"
	"addps (%4), %%xmm0\n"
	"movaps %%xmm0, (%0)\n"
	// increment number of iterations
	"addl $1, %1\n"
	// advance pointers
	// removing the following lines prevents the segfault
	"addl $16, %3\n"
	"addl $16, %4\n"
	"addl $16, %0\n"

	"jnz calc\n"

	: "+r"(c), "+r"(iter), "+c" (n)
	: "r"(a), "r"(b)
    );
    printf("iter:%d\n", iter); // STRANGE: always prints "0"
}

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From: Christoph Brunner <cb100@gmx.net>
Newsgroups: comp.lang.asm.x86,gnu.gcc.help
Subject: inline ASM: SSE
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