ASM Community

Hi there,

I'm trying to educate myself about the operation of some of the AVX instructions and to that end cobble together small apps to step through in GDB. I usually write assembler for Linux, but since the VM in which I run it (on my Sandybridge laptop) doesn't support AVX instructions, I've had to put it together in Windows instead. I've been using GAS since I started learning assembler, and have persisted with this approach on Windows. I'm running a 64-bit Windows 7 OS.

Unfortunately, even though I've been staring at the code for a good few hours, I still seem to be getting something wrong. When I step over the VGATHER instruction in GDB, I get a SIGILL signal; when I execute the binary from the command line, Windows tells me that the app has "stopped working" and that its searching for a solution (good luck with that).

The code looks like this:

.section .data
	.align 0x10
values:
	.double	10.0, 20.0, 30.0, 40.0
mask:
	.quad	-1, -1, -1, -1
vindices:
	.quad	0, 1, 2, 3

.section .text
	.globl	main
main:
	nop
	subq	$0x40, %rsp

	call	__main

	vmovdqa      mask, %ymm3
	vmovdqa      vindices, %ymm4
	movq         $values, %r13
	vgatherqpd   %ymm3, (%r13,%ymm4,8), %ymm5

	addq	$0x40, %rsp
	movq	$0x00, %rax
	ret

My "make.bat" script looks like this:

@echo off
gcc -gstabs -o avxmul.exe -m64 avxmul.s

gcc -v emits the slightly shortened output:

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=c:/users/michaelg/applications/mingw64/bin/../libexec/gcc/x86_64-w64-mingw32/4.6.3/lto-wrapper.exe
Target: x86_64-w64-mingw32
...
Thread model: posix
gcc version 4.6.3 20111208 (prerelease) (GCC)

If anyone can spot an obvious issue, please let me know. I've not yet written a CPUID test, but will do that after as soon as I hit "post" (and put the curry in the microwave). It's a Sandybridge CPU (4-core, 2.7GHz i7-2620M), so AVX (and AVX2) should be supported, right?

Cheers guys,

Michael