Messages in this thread | | | Date | Wed, 27 Jul 2016 12:38:00 +0100 | From | Dave Martin <> | Subject | Re: [PATCH v15 04/10] arm64: Kprobes with single stepping support |
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On Wed, Jul 27, 2016 at 12:19:59PM +0100, Daniel Thompson wrote:
[...]
> It is interesting to note that you force large_func() to stack its arguments > (by providing 8 dummy int arguments first) then the implicit > pass-by-reference behavior is still preserved even for a stacked argument; > large_func() ends up as: > > ~~~ > large_func: > ldr x0, [sp] > ldr x0, [x0] > ret > ~~~ > > Only thing is... I *still* haven't found anything in the AArch64 PCS which > describes this behavior. > > I'm coming to believe that this is a mistake and this information (and the > threshold at which implicit pass-by-reference kicks in) should be documented > in section 7.
Is that answered by this?
B.3. If the argument type is a Composite Type that is larger than 16 bytes, then the argument is copied to memory allocated by the caller and the argument is replaced by a pointer to the copy.
Experimenting with gcc's behaviour seems to back this up.
Cheers ---Dave
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