On Wed, Mar 31, 2021 at 02:44:56PM +0900, Masami Hiramatsu wrote:
> +#ifdef CONFIG_UNWINDER_ORC
> +unsigned long recover_optprobe_trampoline(unsigned long addr, unsigned long *sp)
> +{
> + unsigned long offset, entry, probe_addr;
> + struct optimized_kprobe *op;
> + struct orc_entry *orc;
> +
> + entry = find_kprobe_optinsn_slot_entry(addr);
> + if (!entry)
> + return addr;
> +
> + offset = addr - entry;
> +
> + /* Decode arg1 and get the optprobe */
> + op = (void *)extract_set_arg1((void *)(entry + TMPL_MOVE_IDX));
> + if (!op)
> + return addr;
> +
> + probe_addr = (unsigned long)op->kp.addr;
> +
> + if (offset < TMPL_END_IDX) {
> + orc = orc_find((unsigned long)optprobe_template_func + offset);
> + if (!orc || orc->sp_reg != ORC_REG_SP)
> + return addr;
> + /*
> + * Since optprobe trampoline doesn't push caller on the stack,
> + * need to decrement 1 stack entry size
> + */
> + *sp += orc->sp_offset - sizeof(long);
> + return probe_addr;
> + } else {
> + return probe_addr + offset - TMPL_END_IDX;
> + }
> +}
> +#endif
Hm, I'd like to avoid intertwining kprobes and ORC like this.
ORC unwinds other generated code by assuming the generated code uses a
frame pointer. Could we do that here?
With CONFIG_FRAME_POINTER, unwinding works because SAVE_REGS_STRING has
ENCODE_FRAME_POINTER, but that's not going to work for ORC.
Instead of these patches, can we 'push %rbp; mov %rsp, %rbp' at the
beginning of the template and 'pop %rbp' at the end?
I guess SAVE_REGS_STRING would need to be smart enough to push the
original saved version of %rbp. Of course then that breaks the
kretprobe_trampoline() usage, so it may need to be a separate macro.
[ Or make the same change to kretprobe_trampoline(). Then the other
patch set wouldn't be needed either ;-) ]
Of course the downside is, when you get an interrupt during the frame
pointer setup, unwinding is broken. But I think that's acceptable for
generated code. We've lived with that limitation for all code, with
CONFIG_FRAME_POINTER, for many years.
Eventually we may want to have a way to register generated code (and the
ORC for it).
--
Josh
