On Fri, Apr 27, 2012 at 02:27:29PM -0700, Roland McGrath wrote:
> The expectation was that every arch would eventually switch on
> CORE_DUMP_USE_REGSET. (Looks like so far 12 do and so ~16 don't.)
> Certainly avoiding the overhead of user_regset for core dumping is not
> worth any new code complexity or extra arch hooks, since that overhead
> even on the worst-case arch (ia64) has got to be marginal in comparison
> to all the memory-copying and i/o going on. For imagined potential
> tracing/fancier-debugging cases that might be used in high-throughput
> ways the question would be different, but such uses still remain to be
> implemented.
BTW, speaking of tracehook - you do realize that there are some
architectures where check for user_mode() in do_signal() is not
useless? I.e. there do_notify_resume() _can_ be called when
returning to kernel mode. And that'll get you tracehook_notify_resume()
called when you probably wouldn't want it to be; key_replace_session_keyring()
call is not desirable in that situation and the stuff Oleg wants
to add in tracehook_notify_resume() won't be happy with that either...
I think all such architectures need that check lifted to do_notify_resume()
(and the rest needs it killed, of course). Including x86, by the look
of it - we _probably_ can't get there with TIF_NOTIFY_RESUME and
!user_mode(regs), but I'm not entirely sure of that. arm is in about the
same situation; alpha, ppc{32,64}, sparc{32,64} and m68k really can't get
there like that (they all check it in the asm glue). mips probably might,
unless I'm misreading their ret_from_fork()... Fun.
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