Re: [Qemu-devel] TCG register allocator

[Xin Tong <xerox.time.tech@gmail.com>]

The segfault is caused by jumping to the middle of an instruction. so
i want to know which TB jumps here.

Thanks

Xin


On Wed, Jan 25, 2012 at 10:54 AM, Xin Tong <xerox.time.tech@gmail.com> wrote:
> I have a bug, it segfaults when executing a translation blocks. when i
> disable block chaining, the bug disappears.  However, with block
> chaining, i do not know which translation block jumps to the code
> which caused the segfault. I want to reserve a register and use it to
> record the last translation block executed.  So at entry, i assign the
> translation blocks address to the register and when the segfault
> happens, I can get the last translation block executed.
>
> Thanks
>
>
>
> On Wed, Jan 25, 2012 at 10:49 AM, Peter Maydell
> <peter.maydell@linaro.org> wrote:
>> On 25 January 2012 15:42, Xin Tong <xerox.time.tech@gmail.com> wrote:
>>> I tried to reserve a register in target-i386 with this code
>>>
>>> target-i386/translate.c    tb_env = tcg_global_reg_new_ptr(TCG_AREG1, "env");
>>
>> Why do you want to define a second global which holds the environment
>> variable? Just use TCG_AREG0 for that.
>>
>>> i386/tcg-target.h         #define TCG_AREG1 TCG_REG_R13
>>>
>>> i386/tcg-target.c         tcg_out_movi(s, TCG_TYPE_PTR, TCG_AREG1, args[0]);
>>>
>>> But when i looked into the dynamically generated code, the place which
>>> i use TCG_AREG1 becomes RBP and RBP is not reserved either.
>>
>> If the reason you're trying to reserve a register is so you can use
>> it as a temporary in tcg-target.c's codegen, then reserve it in
>> tcg_target_init(). (But x86-32 is very short on registers as it is,
>> so really it would be much better not to...)
>>
>> -- PMM