Re: [Qemu-devel] [PATCH 4/8] tcg: Init TB's direct jumps before making it visible

[Alex Bennée]

Sergey Fedorov <address@hidden> writes:

> On 24/03/16 18:11, Alex Bennée wrote:
>> address@hidden writes:
>>> From: Sergey Fedorov <address@hidden>
>>>
>>> diff --git a/translate-all.c b/translate-all.c
>>> index ca01dd325b8d..f68716e1819f 100644
>>> --- a/translate-all.c
>>> +++ b/translate-all.c
>>> @@ -1131,19 +1131,6 @@ static void tb_link_page(TranslationBlock *tb, 
>>> tb_page_addr_t phys_pc,
>>>          tb->page_addr[1] = -1;
>>>      }
>>>
>>> -    assert(((uintptr_t)tb & 3) == 0);
>>> -    tb->jmp_list_first = (uintptr_t)tb | 2;
>>> -    tb->jmp_list_next[0] = (uintptr_t)NULL;
>>> -    tb->jmp_list_next[1] = (uintptr_t)NULL;
>>> -
>>> -    /* init original jump addresses */
>>> -    if (tb->jmp_reset_offset[0] != TB_JMP_RESET_OFFSET_INVALID) {
>>> -        tb_reset_jump(tb, 0);
>>> -    }
>>> -    if (tb->jmp_reset_offset[1] != TB_JMP_RESET_OFFSET_INVALID) {
>>> -        tb_reset_jump(tb, 1);
>>> -    }
>>> -
>>>  #ifdef DEBUG_TB_CHECK
>>>      tb_page_check();
>>>  #endif
>>> @@ -1251,6 +1238,20 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>>>          ROUND_UP((uintptr_t)gen_code_buf + gen_code_size + search_size,
>>>                   CODE_GEN_ALIGN);
>>>
>>> +    /* init jump list */
>>> +    assert(((uintptr_t)tb & 3) == 0);
>>> +    tb->jmp_list_first = (uintptr_t)tb | 2;
>>> +    tb->jmp_list_next[0] = (uintptr_t)NULL;
>>> +    tb->jmp_list_next[1] = (uintptr_t)NULL;
>> maybe these should be further up the function with the other jmp setting 
>> code?
>
> I meant to keep them together with the following lines.
>
>>
>>> +
>>> +    /* init original jump addresses */
>>> +    if (tb->jmp_reset_offset[0] != TB_JMP_RESET_OFFSET_INVALID) {
>>> +        tb_reset_jump(tb, 0);
>>> +    }
>>> +    if (tb->jmp_reset_offset[1] != TB_JMP_RESET_OFFSET_INVALID) {
>>> +        tb_reset_jump(tb, 1);
>>> +    }
>> Why would tb->jmp_reset_offset[0] == TB_JMP_RESET_OFFSET_INVALID not be
>> the case as it is set a few lines further up.
>
> Because tcg_gen_code() gets called in between and it is passed
> '&tcg_ctx' which holds a pointer to 'tb->jmp_reset_offset'. tcg_out_op()
> is called from tcg_gen_code() and sets 'tb->jmp_reset_offset[n]'
> indirectly, as well as 'tb->jmp_insn_offset[n]'.

OK a quick addition to the comment: "these may have been reset in
tcg_gen_code" would be helpful here.

>
> Kind regards,
> Sergey


--
Alex Bennée