3 ms·
No, that's done by the decoder. It actually does nothing.
by fluoridation 2mo ago
No, that's done by the decoder. It actually does nothing.
- russdill 2mo agoI mean....there are several architectures out there which has a nop that is a jump forward. Kind of a tree forest issue imho
- fluoridation 2mo agoI don't know about other architectures in as much detail. I know x86 NOP does nothing.
- loeg 2mo agoThe decoder is an implementation detail that is a subcomponent of NOP; GP was right, and your correction isn't.
- fluoridation 2mo agoIt'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".
- loeg 2mo agoADD does in fact do that.
- fluoridation 2mo agoI'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.
- dxdm 2mo agoLove 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.
- fluoridation 2mo agoInsightful and compelling. Tell me another one.
- dxdm 2mo agoWith pleasure. There was a boy A very strange, enchanted boy They say he wandered very far Very far, over land and sea A little shy and sad of eye But very wise was he. And then one day A magic day he passed my way And while we spoke of many things Fools and kings This he said to me: "The greatest thing you'll ever learn Is just to love and be loved in return."
- phire 2mo agoAs 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.
- amluto 2mo agoAs long as everyone is being outrageous pedantic: NOP, like all other non-faulting, non-control-transferring instructions, increments RIP by the length of the instruction, which may or may not be one. A prefixed NOP is still NOP.
- dlcarrier 2mo agoIt's still part of the instruction to increment it by one, as opposed to write a value or offset to it, as jump instructions do.
- fluoridation 2mo agoSee my sibling response.