Re: [Qemu-devel] [PATCH v2 37/45] tcg: introduce **tcg_ctxs to keep track of all TCGContext's

[Richard Henderson]

On 07/16/2017 10:04 AM, Emilio G. Cota wrote:
> Groundwork for supporting multiple TCG contexts.
>
> Note that having n_tcg_ctxs is unnecessary. However, it is
> convenient to have it, since it will simplify iterating over the
> array: we'll have just a for loop instead of having to iterate
> over a NULL-terminated array (which would require n+1 elems)
> or having to check with ifdef's for usermode/softmmu.
>
> Signed-off-by: Emilio G. Cota <address@hidden>
> ---
>   tcg/tcg.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
>
> diff --git a/tcg/tcg.c b/tcg/tcg.c
> index f907c47..8094278 100644
> --- a/tcg/tcg.c
> +++ b/tcg/tcg.c
> @@ -115,6 +115,8 @@ static int tcg_target_const_match(tcg_target_long val, 
> TCGType type,
>   static void tcg_out_tb_init(TCGContext *s);
>   static bool tcg_out_tb_finalize(TCGContext *s);
>   
> +static TCGContext **tcg_ctxs;
> +static unsigned int n_tcg_ctxs;

I'm perfectly happy introducing these now, and converting stuff to use them.

> +static void tcg_ctxs_init(TCGContext *s)
> +{
> +    tcg_ctxs = g_new(TCGContext *, 1);
> +    tcg_ctxs[0] = s;
> +    n_tcg_ctxs = 1;
> +}

This was confusing to me, trying to figure out how this function would be 
extended for multi-threading.  But it turns out it isn't -- it just goes away.

> @@ -381,6 +390,7 @@ void tcg_context_init(TCGContext *s)
>           indirect_reg_alloc_order[i] = tcg_target_reg_alloc_order[i];
>       }
>   
> +    tcg_ctxs_init(s);
>       tcg_ctx = s;
>   }

Thus I think it would be simpler for the interim to do

    tcg_ctx = s;
    tcg_ctxs = &tcg_ctx;
    n_tcg_ctxs = 1;


r~