what is the order of source operands in AT&T syntax compared to Intel syntax?
The Intel ISA reference documentation for this instruction is clear:
VPBLENDVB xmm1, xmm2, xmm3/m128, xmm4
Select byte values from
xmm2
andxmm3/m128
using mask bits in the specified mask register,xmm4
, and store the values intoxmm1
.
xmm1
is the destination,xmm2/3/4
are source operands
So what does this become using AT&T syntax? We know that the destination register must be last, but what is the order of source operands?
vpblendvb $xmm2, $xmm3, $xmm4, $xmm1
or
vpblendvb $xmm4, $xmm3, $xmm2, $xmm1
or something else?
Assembling (note GAS uses %
instead of $
to denote registers) the following:
vpblendvb %xmm4, %xmm3, %xmm2, %xmm1
with the GNU assembler (version 2.21.0.20110327 on x86_64 2.6.38 linux) and then disassembling yields:
$ objdump -d a.out
0: c4 e3 69 4c cb 40 vpblendvb %xmm4,%xmm3,%xmm2,%xmm1
in intel syntax (as the manual shows):
$ objdump -d -M intel a.out
0: c4 e3 69 4c cb 40 vpblendvb xmm1,xmm2,xmm3,xmm4
So it looks like the order of all the arguments is reversed.