Error compiling in Assembly Code for cmpxchg16b - c++

Question

I am working on a project that requires a double-width-compare-and-swap operation (cmpxchg16b). I found the following code by luke h, however when I compile it with "g++-4.7 -g -DDEBUG=1 -std=c++0x dwcas2.c -o dwcas2.o" I get the following error:
Error:
g++-4.7 -g -DDEBUG=1 -m64 -std=c++0x dwcas2.c -o dwcas2.o
dwcas2.c: Assembler messages:
dwcas2.c:29: Error: junk `ptr ' after expression
Any ideas why?, I feel like it is something small and easy to fix, I just can not see it.
Computer Specs:
64-core ThinkMate RAX QS5-4410 server running Ubuntu 12.04 LTS. It is a NUMA system with four AMD Opteron 6272 CPUs (16 cores per chip #2.1 GHz) and 314 GB of shared memory.
Code:
#include <stdint.h>
namespace types
{
struct uint128_t
{
uint64_t lo;
uint64_t hi;
}
__attribute__ (( __aligned__( 16 ) ));
}
template< class T > inline bool cas( volatile T * src, T cmp, T with );
template<> inline bool cas( volatile types::uint128_t * src, types::uint128_t cmp, types::uint128_t with )
{
bool result;
__asm__ __volatile__
(
"lock cmpxchg16b oword ptr %1\n\t"
"setz %0"
: "=q" ( result )
, "+m" ( *src )
, "+d" ( cmp.hi )
, "+a" ( cmp.lo )
: "c" ( with.hi )
, "b" ( with.lo )
: "cc"
);
return result;
}
int main()
{
using namespace types;
uint128_t test = { 0xdecafbad, 0xfeedbeef };
uint128_t cmp = test;
uint128_t with = { 0x55555555, 0xaaaaaaaa };
return ! cas( & test, cmp, with );
}

Answer 1

On x86 GCC defaults to using AT&T syntax assembly, but your source is in Intel syntax. You probably also need "memory" in the clobber list.