Re: [Qemu-devel] [RFC] tcg: workaround branch instruction overflow in tcg_out_qemu_ld/st

[Laurent Vivier]

On 27/04/2018 14:17, Laurent Vivier wrote:
> ppc64 uses a BC instruction to call the tcg_out_qemu_ld/st
> slow path. BC instruction uses a relative address encoded
> on 14 bits.
> 
> The slow path functions are added at the end of the generated
> instructions buffer, in the reverse order of the callers.
> So more we have slow path functions more the distance between
> the caller (BC) and the function increases.
> 
> This patch changes the behavior to generate the functions in
> the same order of the callers.
> 
> Fixes: 15fa08f845 ("tcg: Dynamically allocate TCGOps")
> Signed-off-by: Laurent Vivier <address@hidden>
> ---
> 
> Notes:
>     This is an RFC for several reasons:
>     - it doens't really fix the overflow problem
>       only avoids the case
>     - it uses a recursive function to revert the slow path
>       functions order (and we can have a stack overflow...),

I think the number of slow path functions cannot be greater than
TCG_MAX_INSNS (i.e. 512): is it enough to overflow the stack?

Thanks,
Laurent