Messages in this thread | | | From | Andi Kleen <> | Subject | Re: [RFC PATCH 0/2] kpatch: dynamic kernel patching | Date | Thu, 01 May 2014 13:45:33 -0700 |
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Josh Poimboeuf <jpoimboe@redhat.com> writes: > > kpatch checks the backtraces of all tasks in stop_machine() to ensure > that no instances of the old function are running when the new function > is applied.
How does that work for tail calls?
call foo foo: ... jmp bar
bar: ... code executing ...
When you backtrace you will see foo, but you are running in bar.
Note that tail calls can be indirect, so they cannot be resolved statically.
CONFIG_DEBUG_INFO usually disables tail calls, but not supporting it would seem like a large limitation, as the cost can be high.
It wouldn't surprise me if there are some similar special cases that can even happen with them disabled.
In theory you could read LBRs, but even that may miss some extreme cases.
-Andi
-- ak@linux.intel.com -- Speaking for myself only
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