On 2018-11-11, Masami Hiramatsu mhiramat@kernel.org wrote:
addr = kretprobe_ret_addr(current, addr, stack_addr(regs));But since kretprobe will be an event, which can kick the stackdump. BTW, from kretprobe, regs->ip should always be the trampoline handler, see arch/x86/kernel/kprobes/core.c:772 :-) So it must be fixed always.
Right, but kretprobe_ret_addr() is returning the *original* return address (and we need to do an (addr == kretprobe_trampoline)). The real problem is that stack_addr(regs) isn't the same as it is during kretprobe setup (but kretprobe_ret_addr() works everywhere else).
I think stack_addr(regs) should be same when this is called from kretprobe handler context. Otherwise, yes, it is not same, but in that case, regs->ip is not kretprobe_trampoline too.
I figured it out.
It should be (regs->sp - 1) (just like it is inside the relevant unwinder function for ORC). I now have a prototype which works under the frame unwinder[*] -- however under ORC you can only see the top-most function (the unwinder doesn't see the other function calls). I'm playing with ORC hints with kretprobe_trampoline to try to improve things but it's still a bit screwy.
[*]: However, I've noticed that the stack traces between the two traces no longer match. On kprobe you get function_name+1, but on kretprobe you get function_caller+foo. Obviously it's working but the return address results in slightly different stack traces. This means that stack trace aggregation between kprobe and kretprobe won't work anymore -- at least not like it did in my original patch. So I'm really not sure where to go from here.
I can send around another patchset to illustrate the problem if you like (as well as show how the current unwinding code works).