On Wed, 2024-02-21 at 17:25 +0100, Benjamin Tissoires wrote:
> This is still a WIP, but I think this can be dropped as we never
> get to this instruction. So what should we do here?
As Alexei replied in a separate sub-thread you probably want this
for sleepable timers. Here is full source code block:
if (insn->imm == BPF_FUNC_timer_set_callback ||
is_bpf_timer_set_sleepable_cb_kfunc(insn->imm)) {
...
struct bpf_insn ld_addrs[2] = {
BPF_LD_IMM64(BPF_REG_3, (long)prog->aux),
};
insn_buf[0] = ld_addrs[0];
insn_buf[1] = ld_addrs[1];
insn_buf[2] = *insn;
cnt = 3;
new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
...
}
Effectively, it sets up third function call parameter (R3)
for timer_set_callback() to be prog->aux.
E.g. before bpf_patch_insn_data():
r1 = ... timer ...
r2 = ... callback address ...
call timer_set_callback
After bpf_patch_insn_data():
r1 = ... timer ...
r2 = ... callback address ...
r3 = prog->aux ll
call timer_set_callback
This way it won't be necessary to walk stack in search for ctx.aux
in bpf_timer_set_sleepable_cb().
