Re: [PATCH 07/10] tcg: implement bulletproof JIT

[Richard Henderson]

On 10/14/20 9:03 AM, Joelle van Dyne wrote:
>>> static int encode_search(TranslationBlock *tb, uint8_t *block)
>>> {
>>> -    uint8_t *highwater = tcg_ctx->code_gen_highwater;
>>> -    uint8_t *p = block;
>>> +    uint8_t *highwater;
>>> +    uint8_t *p;
>>>     int i, j, n;
>>>
>>> +    highwater = (uint8_t *)TCG_CODE_PTR_RW(tcg_ctx,
>>> +                                           tcg_ctx->code_gen_highwater);
>>> +    p = (uint8_t *)TCG_CODE_PTR_RW(tcg_ctx, block);
>>
>> Why do you need explicit casts here? Can this be avoided by using
>> appropriate type or within the macro (I haven't checked this at all just
>> dislike casts as they can hide problems otherwise caught by the compiler).
> There's the choice between tcg_insn_unit * and uint8_t *. Since it's
> used much more widely in tcg-target.inc.c, it seemed like
> tcg_insn_unit * was a better choice.

False choice.  This is why tcg_ctx->code_gen_highwater is void*.

>>> +#if defined(CONFIG_IOS_JIT)
>>> +# define TCG_CODE_PTR_RW(s, code_ptr) \
>>> +    (tcg_insn_unit *)((uintptr_t)(code_ptr) + (s)->code_rw_mirror_diff)

Better as

static inline void *tcg_code_ptr_rw(TCGContext *s, void *rx)
{
#ifdef CONFIG_IOS_JIT
    return rx + s->code_rw_mirror_diff;
#else
    return rx;
#endif
}


r~