Not that I’m aware of. The decoding of an instruction is complicated and also dependent on the current operating mode and a few other things. So, for an OS to pass those lengths before hand, it’d have to know everything about the current state of the processor at that instruction. For example, in 16 and 32 bit modes, opcodes 0x40 through 0x4F are single byte INC and DEC (one for each register). In 64 bit mode, those are the single byte REX prefixes; The actual opcode follows. See also: the halting problem.
As for why it became an issue, instruction sets need to be designed from the beginning to be forward expandable. Intel has historically not done that with x86. Take AVX for example. Originally, it was just 128 bit (XMM) vectors encoded as an opcode with various prefix bytes being used in ways they weren’t intended. Later, 256 bit vectors were needed. So they made the VEX prefix. But it only had 1 bit for vector length. This allowed 128 bit (XMM) and 256 bit (YMM) vectors, but nothing else. So when AVX-512 came along, Intel had to ditch it and create the EVEX prefix and allow both to be used. But EVEX only has 2 bits for vector length. So, should something past AVX-512 come out (AVX-768 or AVX-1024?), it’ll probably use the reserved bit pattern 11, and they’ll be stuck again if they want to go past that.
For an example of this being done right, ForwardCom[0] (started by the great Agner Fog) took the “forward compatibility” (hence the name) issue into mind and used 2 bits to signal the instruction length. It’ll probably never reach silicon, but it and RISC-V (which is in silicon form) are good examples of attempting to keep things forward compatible.
> Not that I’m aware of. The decoding of an instruction is complicated and also dependent on the current operating mode and a few other things. So, for an OS to pass those lengths before hand, it’d have to know everything about the current state of the processor at that instruction
The compiler would know the instruction boundaries. It could store that information in a read-only section in the executable. The OS would then just pass that section to the CPU somehow.
I don't think there is anything impossible about this. Would there be sufficient performance benefit to justify the added complexity? I don't know, quite possibly not.
I'm not sure why it would be. If the boundary information were wrong, the CPU instruction decode would fail, but that should just be an invalid instruction exception, which operating systems already know how to handle.
