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Re: [PATCH 4/8] gdb/s390: Fill gen_return_address hook.


On 11/03/16 16:31, Andreas Arnez wrote:
On Fri, Mar 11 2016, Marcin KoÅcielnicki wrote:

We can always error() in there (and KFAIL the testcase in gdb.trace
that exercises it).  However, returning garbage here doesn't result in
garbage backtrace - this only collects data, if the unwinder actually
doing the work later determines it should look for the return address
on the stack, it'll just ignore our collected $r14 and consider the
return address unavailable (unless another collect rule happened to
match it).

Well, from that test case it appears that `$_ret' is generally not
expected to work very reliably.  Since r14 usually does work near
function entry, this may be sufficient for now.

So I'm OK with the patch.  Please add a small comment stating that this
is a best-can-do approach that usually works near function entry and may
yield wrong results otherwise.


Thanks, pushed with this comment:

/* The "gen_return_address" gdbarch method.  Since this is supposed to be
   just a best-effort method, and we don't really have the means to run
   the full unwinder here, just collect the link register.  */


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