On 10 Mar 2014, at 19:10, Mathias Bauer <[email protected]> wrote:
> Hi dear list,
>
> the code in libobjc2 that implements imp_ImplementationWithBlock does not
> work on at least some ARM platforms.
>
> At least on boards using an Exynos CPU I see random crashes when using
> imp_ImplementationWithBlock for dynamically provided implementations for
> property getters and setters.
>
> The crash always happens at an address that is a page boundary - it's the
> boundary of the current page for trampolines. So it seems that at the memory
> of the IMP there is no trampoline code, instead of that this memory area
> behaves like a playgound slide that finally lets the IP move to the page
> boundary.
>
> The trampoline and its two addresses are written to this memory through a
> pointer memory-mapped to a file handle with PROT_WRITE, while another pointer
> memory-mapped to the same file handle with PROT_READ|PROT_EXEC is used to
> read and execute the data later.
>
> It seems that on the architecture that experiences the crashes there is a
> time lag between writing the data and the availability of the bytes as
> executable code, because the crash goes away if I add some delay after
> writing the data.
>
> It seems that we somehow need to make sure that what was written can be
> executed immediately after that.
I think on ARM we need an instruction memory barrier there. We probably do on
MIPS too.
Can you try adding this at the end of the imp_ImplementationWithBlock function
and see if it fixes it on ARM?
volatile __asm__ ("imb")
David
-- Sent from my brain
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