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

[Sergey Fedorov]

On 24/03/16 18:40, Alex Bennée wrote:
> 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.

The other way around: 'tb->jmp_reset_offset[n]' are reset before calling
tcg_gen_code() and are set during tcg_gen_code() execution.

Kind regards,
Sergey