[U-Boot] [PATCH v2] x86: lib: Implement standalone __udivdi3 etc instead of libgcc ones

[Stefan Roese]

Hi Bin,

On 29.11.2017 13:31, Bin Meng wrote:
> Hi Stefan,
> 
> On Wed, Nov 29, 2017 at 6:01 PM, Stefan Roese <sr at denx.de> wrote:
>> Hi Bin,
>>
>>
>> On 29.11.2017 10:23, Bin Meng wrote:
>>>
>>> On Wed, Nov 29, 2017 at 4:42 PM, Stefan Roese <sr at denx.de> wrote:
>>>>
>>>> Hi Bin,
>>>>
>>>> On 29.11.2017 09:30, Bin Meng wrote:
>>>>
>>>> <snip>
>>>>
>>>>>>> I wrote some codes soemthing like:
>>>>>>>
>>>>>>> s64 a, b, c;
>>>>>>> c = a/b;
>>>>>>>
>>>>>>> The compiler will generate codes to call __divdi3. This works before
>>>>>>> your
>>>>>>> patch.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> Yes, I understand this. But right now, we don't have any code
>>>>>> generating this error. And if this will happen at some time, I would
>>>>>> prefer to investigate this code sequence introducing this division, to
>>>>>> use the division functions / macros available in U-Boot (as mentioned
>>>>>> above) and in the kernel instead.
>>>>>>
>>>>>> Here a short explanation, why this new version is preferred to the
>>>>>> currently available functions pulled from libgcc: We are fixing an
>>>>>> "ugly" Yocto build problem with this patch, related to 32bit binaries
>>>>>> with 64bit toolchains (multilib) building by not relying on anything
>>>>>> from libgcc. Please see this thread for some more details:
>>>>>>
>>>>>> https://www.mail-archive.com/yocto@yoctoproject.org/msg36721.html
>>>>>>
>>>>>> I hope this helps a bit to understand the motivation behind this patch.
>>>>>>
>>>>>
>>>>> Thanks for the background. I am not familiar with yocto project, but
>>>>> is the build broken due to the gcc on the build host does not ship
>>>>> with multilib?
>>>>
>>>>
>>>>
>>>> Please take a look at the email thread mentioned above for a detailed
>>>> explanation. Especially this post should answer your questions:
>>>>
>>>> https://www.mail-archive.com/yocto@yoctoproject.org/msg36748.html
>>>
>>>
>>> Now I see. Thank you.
>>>
>>>>
>>>>> I am using a 64-bit host with gcc multilib, and there is no such build
>>>>> error observed.
>>>>
>>>>
>>>>
>>>> Right. This issue is only seen on Yocto builds (AFAIK). But again,
>>>> I would really like to see U-Boot x86 being self-contained without
>>>> any host libgcc dependencies as on other architectures as well.
>>>
>>>
>>> So to completely resolve such issue to make U-Boot self-contained, we
>>> should remove the reference to the host libgcc.a in
>>> arch/x86/lib/Makefile, and use CONFIG_USE_PRIVATE_GCC to include the
>>> build for div64.o. Thoughts?
>>
>>
>> I was under the impression, that I already removed the host libgcc
>> reference completely for x86 with my patch. But you are correct - there
>> still is a reference in this Makefile which is used by the standalone
>> code, AFAICT.
>>
>> Any quick idea on how to rid of this one as well?
>>
> 
> I believe we need change
> 
> obj-y  += div64.o
> 
> to
> 
> lib-$(CONFIG_USE_PRIVATE_LIBGCC) += div64.o
> 
> To remove the libgcc dependency completely.

Yep. Thanks.

I've posted v3 with this additional removal.

Thanks,
Stefan