On Fri, Mar 29, 2024 at 11:47 AM Andrii Nakryiko <andrii@xxxxxxxxxx> wrote:
>
> Add two new BPF instructions for dealing with per-CPU memory.
>
> One, BPF_LDX | BPF_ADDR_PERCPU | BPF_DW (where BPF_ADD_PERCPU is unused
> 0xe0 opcode),
ADD or ADDR ?
> I also added BPF_LDX | BPF_MEM_PERCPU | BPF_{B,H,W,DW} (BPF_MEM_PERCPU using
> another unused 0xc0 opcode), which can be considered an optimization
> instruction, which allows to *read* per-CPU data up to 8 bytes in one
> instruction, without having to first resolve the address and then
> dereferencing the memory. This one is used in inlining of
> bpf_get_smp_processor_id(), but it would be fine to implement the latter with
> BPF_ADD_PERCPU, followed by normal BPF_LDX | BPF_MEM, so I'm fine dropping
ADD or ADDR ?
Looking at the rest is probably ADDR.
Feels weird for BPF_LDX to mean dst = src + percpu_off.
Should it be on BPF_ALU64 side? Like a flavor of BPF_MOV ?
We have several of such flavors:
off = 1 -> arena
off = 8, 16, 32 - swaps
off = 2 - might be nop_of_goto
