Indeed, the register variable syntax is necessary for many of the registers; there are only so many of them that have been stuffed into the one-letter constrain

Indeed, the register variable syntax is necessary for many of the registers; there are only so many of them that have been stuffed into the one-letter constraint. I've used it before for making raw x86-64 Linux syscalls (which can use r10, r8, and r9) without going through errno, as part of a silly little project ([0]) to read from a file descriptor without writing to process memory. [0] https://pastebin.com/mepsedCC https://pastebin.com/mepsedCC