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Re: [RFC]: MD_FALLBACK_FRAME_STATE_FOR macro for darwin PPC
David Daney writes:
> Andreas Tobler wrote:
> > David Daney wrote:
> >> I know next to nothing about PPC ABIs, but are any of these floating
> >> point registers?
> > There are, yes.
> >> Are there any call saved FP registers in this ABI? and if so are you
> >> restoring them. Although I don't think that the unwinder uses
> >> floating point, it seems that restoring call saved FP registers is a
> >> good idea if you are not already doing it.
> > Well, here I expect the advise from the experts, I have floats around
> > and I may try to restore them.
> > But, I need some guidance here.
> When I did the MD_FALLBACK_FRAME_STATE_FOR for mips/linux I did not
> handle floating point either as the problem did not occur to me until
> after I checked in the code.
> However after thinking about it and posting:
> I learned that this is a real issue.
> I may be about ready to do some more mips/linux work soon and may
> revisit MD_FALLBACK_FRAME_STATE_FOR. Because in its current state it
> seems to be incomplete.
You only need to restore what has been saved. Looking at
/usr/src/linux-2.4/arch/mips/kernel/signal.c, it seems that there is a
call to save_fp_context(). However, this is only executed if
(current->used_math) is set; you mustn't restore any fp registers if
the process hasn't saved the fp state.
There is a field called sc_used_math in the sigcontext struct. I
think this tells you what you need to know. But I am not a kernel