On 02/21/2014 02:06 PM, Cody Rigney wrote: > On Fri, Feb 21, 2014 at 4:53 AM, Andrew Haley <aph@xxxxxxxxxx> wrote: >> >> You can use a memory operand as an output, as in "=m"(*a) or simply >> add "memory" to the clobber list. And you must add all clobbered >> registers to the clobber list. Then it should work. >> > I added all the registers and "memory" to clobber and it worked! > Since I think it's more efficient to specify which memory is changing, > I'm going to give the "=m" (*a) a shot. So even though you > dereference the pointer, gcc will know the length of the memory(say 2 > bytes) that changes? Or do you have to specify each index of the > memory(e.g. char a[2]; ..... asm ... "=m" (*a), "=m" (*(a+1)))? It's hard for me to give a 100% answer to that one, but GCC has an idea what memory is reachable from every pointer. So, this won't clobber memory that's unreachable or has a different type from that pointer. It probably doesn't matter. Andrew. P.S. Please don't top-post on GCC lists. :-)
