As specified by the spec, it arguably increments RIP by one.
The actual typical hardware implementation just fetches the next 16-32 bytes from icache, shifts it to the correct alignment, and slams it into a bunch of parallel decoders which each attempts to decode one x86 instruction per byte.
The next cycle, the first 1-6 non-overlapping valid instructions are accepted into a queue for further decoding. The NOP almost certainly takes up space in this queue.
At no point does RIP get incremented by one. There isn't even a single physical RIP register to increment, the CPU is "executing" dozens or even hundreds of RIPs in parallel.
It's not an implementation detail, because the decoder runs before the execution of every instruction. If we're going to say that NOP increments IP by one, then we should also say that ADD "stores in dst the addition of src and dst, as well as incrementing IP by the length of the instruction", and JMP imm "increments JMP by imm + the length of the instruction".
I'm not disputing the total effect. I'm asking if you'd rather describe ADD and JMP in this manner, in order to say that NOP does not in fact do nothing.
Love the pedantry here. I'm currently at: no op code does anything, it's all fancy effects in the hardware that can be described in arbitrary detail, which somehow allows me to cause these letters to appear on your screen.
As specified by the spec, it arguably increments RIP by one.
The actual typical hardware implementation just fetches the next 16-32 bytes from icache, shifts it to the correct alignment, and slams it into a bunch of parallel decoders which each attempts to decode one x86 instruction per byte.
The next cycle, the first 1-6 non-overlapping valid instructions are accepted into a queue for further decoding. The NOP almost certainly takes up space in this queue.
At no point does RIP get incremented by one. There isn't even a single physical RIP register to increment, the CPU is "executing" dozens or even hundreds of RIPs in parallel.
It's not an implementation detail, because the decoder runs before the execution of every instruction. If we're going to say that NOP increments IP by one, then we should also say that ADD "stores in dst the addition of src and dst, as well as incrementing IP by the length of the instruction", and JMP imm "increments JMP by imm + the length of the instruction".
ADD does in fact do that.
I'm not disputing the total effect. I'm asking if you'd rather describe ADD and JMP in this manner, in order to say that NOP does not in fact do nothing.
Love the pedantry here. I'm currently at: no op code does anything, it's all fancy effects in the hardware that can be described in arbitrary detail, which somehow allows me to cause these letters to appear on your screen.