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

[Sergey Fedorov <serge.fdrv@gmail.com>]

On 24/03/16 18:11, Alex Bennée wrote:
> sergey.fedorov@linaro.org writes:
>> From: Sergey Fedorov <serge.fdrv@gmail.com>
>>
>> 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]'.

Kind regards,
Sergey