Sergey Fedorov <serge.f...@gmail.com> writes:
> On 19/04/16 14:37, Alex Bennée wrote:
>> Sergey Fedorov <sergey.fedo...@linaro.org> writes:
> (snip)
>>> diff --git a/cpu-exec.c b/cpu-exec.c
>>> index bbfcbfb54385..065cc9159477 100644
>>> --- a/cpu-exec.c
>>> +++ b/cpu-exec.c
>>> @@ -508,11 +508,8 @@ int cpu_exec(CPUState *cpu)
>>> next_tb = 0;
>>> tcg_ctx.tb_ctx.tb_invalidated_flag = 0;
>>> }
>>> - /* see if we can patch the calling TB. When the TB
>>> - spans two pages, we cannot safely do a direct
>>> - jump. */
>>> - if (next_tb != 0 && tb->page_addr[1] == -1
>>> - && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
>>> + /* See if we can patch the calling TB. */
>>> + if (next_tb != 0 &&
>>> !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
>>> tb_add_jump((TranslationBlock *)(next_tb &
>>> ~TB_EXIT_MASK),
>>> next_tb & TB_EXIT_MASK, tb);
>>> }
>> We've already discussed on IRC the confusion of next_tb ;-)
>
> Yes, I'd rather add a patch to clean up 'next_tb' naming to "tcg: Misc
> clean-up patches" series. This series is to deal with direct block
> chaining only.
Yeah that makes sense.
>
>>> diff --git a/target-alpha/translate.c b/target-alpha/translate.c
>>> index 5b86992dd367..5fa66309ce2e 100644
>>> --- a/target-alpha/translate.c
>>> +++ b/target-alpha/translate.c
>>> @@ -464,7 +464,10 @@ static bool use_goto_tb(DisasContext *ctx, uint64_t
>>> dest)
>>> if (in_superpage(ctx, dest)) {
>>> return true;
>>> }
>>> - /* Check for the dest on the same page as the start of the TB. */
>>> + /* Direct jumps with goto_tb are only safe within the page this TB
>>> resides
>>> + * in because we don't take care of direct jumps when address mapping
>>> + * changes.
>>> + */
>> I'm all for harmonising the comments but I think for the common case we
>> could refer to a central location for the page linking rules and only
>> expand the comment for subtle differences between the front ends.
>
> You mean, it'd be better to put a detailed explanation in a comment for
> e.g. tlb_flush() and refer to it in every place like this?
Yes.
>
>
>>> return ((ctx->tb->pc ^ dest) & TARGET_PAGE_MASK) == 0;
>>> }
> (snip)
>>> diff --git a/target-arm/translate.c b/target-arm/translate.c
>>> index 940ec8d981d1..aeb3e84e8d40 100644
>>> --- a/target-arm/translate.c
>>> +++ b/target-arm/translate.c
>>> @@ -4054,7 +4054,12 @@ static inline void gen_goto_tb(DisasContext *s, int
>>> n, target_ulong dest)
>>> TranslationBlock *tb;
>>>
>>> tb = s->tb;
>>> - if ((tb->pc & TARGET_PAGE_MASK) == (dest & TARGET_PAGE_MASK)) {
>>> + /* Direct jumps with goto_tb are only safe within the pages this TB
>>> resides
>>> + * in because we don't take care of direct jumps when address mapping
>>> + * changes.
>>> + */
>>> + if ((tb->pc & TARGET_PAGE_MASK) == (dest & TARGET_PAGE_MASK) ||
>>> + ((s->pc - 1) & TARGET_PAGE_MASK) == (dest &
>>> TARGET_PAGE_MASK)) {
>> Isn't this check avoided by the fact the translate loop bails on end_of_page?
>
> A TB can straddle a page boundary in Thumb mode. A TB can begin with an
> T32 instruction straddling a page boundary, thus this check should be
> useful :)
OK.
>
> Kind regards,
> Sergey
--
Alex Bennée
