Re: [PATCH 15/19] x86/dumpstack: convert show_trace_log_lvl() to the new unwinder
From: Byungchul Park
Date: Thu Jul 21 2016 - 17:51:11 EST
On Thu, Jul 21, 2016 at 04:21:52PM -0500, Josh Poimboeuf wrote:
> Convert show_trace_log_lvl() to the new unwinder. dump_trace() has been
> show_trace_log_lvl() is special compared to other users of the unwinder.
> It's the only place where both reliable *and* unreliable addresses are
> needed. With frame pointers enabled, most stack walking code doesn't
> want to know about unreliable addresses. But in this case, when we're
> dumping the stack to the console because something presumably went
> wrong, the unreliable addresses are useful:
> - They show stale data on the stack which can provide useful clues.
> - If something goes wrong with the unwinder, or if frame pointers are
> corrupt or missing, all the stack addresses still get shown.
> So in order to show all addresses on the stack, and at the same time
> figure out which addresses are reliable, we have to do the scanning and
> the unwinding in parallel.
> The scanning is done with the help of get_stack_info() to traverse the
> stacks. The unwinding is done separately by the new unwinder.
> In theory we could simplify show_trace_log_lvl() by instead pushing some
> of this logic into the unwind code. But then we would need some kind of
> "fake" frame logic in the unwinder which would add a lot of complexity
> and wouldn't be worth it in order to support only one user.
> Another benefit of this approach is that once we have a DWARF unwinder,
> we should be able to just plug it in with minimal impact to this code.
> Another change here is that callers of show_trace_log_lvl() don't need
> to provide the 'bp' argument. The unwinder already finds the relevant
> frame pointer by unwinding until it reaches the first frame after the
> provided stack pointer.
You seem to have changed a lot of code with which I dealt in another patch.
I might be supposed to wait until yours will be done. I need to check yours
at first anyway.