On Thu, Oct 10, 2024 at 9:21 PM Yonghong Song <yonghong.song@xxxxxxxxx> wrote:
>
>
> On 10/10/24 1:53 PM, Alexei Starovoitov wrote:
> > On Thu, Oct 10, 2024 at 10:59 AM Yonghong Song <yonghong.song@xxxxxxxxx> wrote:
> >> static void emit_priv_frame_ptr(u8 **pprog, struct bpf_prog *bpf_prog,
> >> - enum bpf_priv_stack_mode priv_stack_mode)
> >> + enum bpf_priv_stack_mode priv_stack_mode,
> >> + bool is_subprog, u8 *image, u8 *temp)
> >> {
> >> u32 orig_stack_depth = round_up(bpf_prog->aux->stack_depth, 8);
> >> u8 *prog = *pprog;
> >>
> >> - if (priv_stack_mode == PRIV_STACK_ROOT_PROG)
> >> - emit_root_priv_frame_ptr(&prog, bpf_prog, orig_stack_depth);
> >> - else if (priv_stack_mode == PRIV_STACK_SUB_PROG && orig_stack_depth)
> >> + if (priv_stack_mode == PRIV_STACK_ROOT_PROG) {
> >> + int offs;
> >> + u8 *func;
> >> +
> >> + if (!bpf_prog->aux->has_prog_call) {
> >> + emit_root_priv_frame_ptr(&prog, bpf_prog, orig_stack_depth);
> >> + } else {
> >> + EMIT1(0x57); /* push rdi */
> >> + if (is_subprog) {
> >> + /* subprog may have up to 5 arguments */
> >> + EMIT1(0x56); /* push rsi */
> >> + EMIT1(0x52); /* push rdx */
> >> + EMIT1(0x51); /* push rcx */
> >> + EMIT2(0x41, 0x50); /* push r8 */
> >> + }
> >> + emit_mov_imm64(&prog, BPF_REG_1, (long) bpf_prog >> 32,
> >> + (u32) (long) bpf_prog);
> >> + func = (u8 *)__bpf_prog_enter_recur_limited;
> >> + offs = prog - temp;
> >> + offs += x86_call_depth_emit_accounting(&prog, func, image + offs);
> >> + emit_call(&prog, func, image + offs);
> >> + if (is_subprog) {
> >> + EMIT2(0x41, 0x58); /* pop r8 */
> >> + EMIT1(0x59); /* pop rcx */
> >> + EMIT1(0x5a); /* pop rdx */
> >> + EMIT1(0x5e); /* pop rsi */
> >> + }
> >> + EMIT1(0x5f); /* pop rdi */
> >> +
> >> + EMIT4(0x48, 0x83, 0xf8, 0x0); /* cmp rax,0x0 */
> >> + EMIT2(X86_JNE, num_bytes_of_emit_return() + 1);
> >> +
> >> + /* return if stack recursion has been reached */
> >> + EMIT1(0xC9); /* leave */
> >> + emit_return(&prog, image + (prog - temp));
> >> +
> >> + /* cnt -= 1 */
> >> + emit_alu_helper_1(&prog, BPF_ALU64 | BPF_SUB | BPF_K,
> >> + BPF_REG_0, 1);
> >> +
> >> + /* accum_stack_depth = cnt * subtree_stack_depth */
> >> + emit_alu_helper_3(&prog, BPF_ALU64 | BPF_MUL | BPF_K, BPF_REG_0,
> >> + bpf_prog->aux->subtree_stack_depth);
> >> +
> >> + emit_root_priv_frame_ptr(&prog, bpf_prog, orig_stack_depth);
> >> +
> >> + /* r9 += accum_stack_depth */
> >> + emit_alu_helper_2(&prog, BPF_ALU64 | BPF_ADD | BPF_X, X86_REG_R9,
> >> + BPF_REG_0);
> > That's way too much asm for logic that can stay in C.
> >
> > bpf_trampoline_enter() should select __bpf_prog_enter_recur_limited()
> > for appropriate prog_type/attach_type/etc.
>
> The above jit code not just for the main prog, but also for callback fn's
> since callback fn could call bpf prog as well. So putting in bpf trampoline
> not enough.
callback can call the prog only if bpf_call_prog() kfunc exists
and that's one more reason to avoid going that direction.
