[U-Boot] [PATCH 5/5] lib: Enable private libgcc by default

[Sergey Kubushyn]

On Thu, 24 Mar 2016, Marek Vasut wrote:

> On 03/24/2016 12:47 AM, Sergey Kubushyn wrote:
>> On Thu, 24 Mar 2016, Marek Vasut wrote:
>>
>>> On 03/24/2016 12:08 AM, Tom Rini wrote:
>>>> On Wed, Mar 23, 2016 at 04:02:07PM -0700, Sergey Kubushyn wrote:
>>>>> On Wed, 23 Mar 2016, Tom Rini wrote:
>>>>>
>>>>>> On Wed, Mar 23, 2016 at 06:08:45PM +0100, Albert ARIBAUD wrote:
>>>>>>> Hello Tom,
>>>>>>>
>>>>>>> On Wed, 23 Mar 2016 09:22:38 -0400, Tom Rini <trini at konsulko.com>
>>>>>>> wrote:
>>>>>>>> On Wed, Mar 23, 2016 at 01:53:35PM +0100, Albert ARIBAUD wrote:
>>>>>>>>> Hello Marek,
>>>>>>>>>
>>>>>>>>> On Sun, 20 Mar 2016 17:15:34 +0100, Marek Vasut <marex at denx.de>
>>>>>>>>> wrote:
>>>>>>>>>> This patch decouples U-Boot binary from the toolchain on
>>>>>>>>>> systems where
>>>>>>>>>> private libgcc is available. Instead of pulling in functions
>>>>>>>>>> provided
>>>>>>>>>> by the libgcc from the toolchain, U-Boot will use it's own set
>>>>>>>>>> of libgcc
>>>>>>>>>> functions. These functions are usually imported from Linux
>>>>>>>>>> kernel, which
>>>>>>>>>> also uses it's own libgcc functions instead of the ones
>>>>>>>>>> provided by the
>>>>>>>>>> toolchain.
>>>>>>>>>>
>>>>>>>>>> This patch solves a rather common problem. The toolchain can
>>>>>>>>>> usually
>>>>>>>>>> generate code for many variants of target architecture and
>>>>>>>>>> often even
>>>>>>>>>> different endianness. The libgcc on the other hand is usually
>>>>>>>>>> compiled
>>>>>>>>>> for one particular configuration and the functions provided by
>>>>>>>>>> it may
>>>>>>>>>> or may not be suited for use in U-Boot. This can manifest in
>>>>>>>>>> two ways,
>>>>>>>>>> either the U-Boot fails to compile altogether and linker will
>>>>>>>>>> complain
>>>>>>>>>> or, in the much worse case, the resulting U-Boot will build,
>>>>>>>>>> but will
>>>>>>>>>> misbehave in very subtle and hard to debug ways.
>>>>>>>>>
>>>>>>>>> I don't think using private libgcc by default is a good idea.
>>>>>>>>>
>>>>>>>>> U-Boot's private libgcc is not a feature of U-Boot, but a fix
>>>>>>>>> for some
>>>>>>>>> cases where a target cannot properly link with the libgcc
>>>>>>>>> provided by
>>>>>>>>> the (specific release of the) GCC toolchain in use. Using
>>>>>>>>> private libgcc
>>>>>>>>> to other cases than these does not fix or improve anything; those
>>>>>>>>> other cases were working and did not require any fix in this
>>>>>>>>> respect.
>>>>>>>>
>>>>>>>> This isn't true, exactly.  If using clang for example everyone
>>>>>>>> needs to
>>>>>>>> enable this code.  We're also using -fno-builtin -ffreestanding
>>>>>>>> which
>>>>>>>> should limit the amount of interference from the toolchain.  And
>>>>>>>> we get
>>>>>>>> that.
>>>>>>>
>>>>>>> You mean clang does not produce self-sustained binaries?
>>>>>>
>>>>>> clang does not provide "libgcc", so there's no -lgcc providing all of
>>>>>> the functions that are (today) in:
>>>>>> _ashldi3.S _ashrdi3.S _divsi3.S  _lshrdi3.S _modsi3.S _udivsi3.S
>>>>>> _umodsi3.S div0.S  _uldivmod.S
>>>>>> which aside from __modsi3 and __umodsi3 are all __aeabi_xxx
>>>>>
>>>>> There is also _udivmoddi4 pulled from libgcc for 64-bit division
>>>>> since we
>>>>> switched to 64-bit all around ARM. It comes from clock calculations for
>>>>> video, e.g. from drivers/video/ipu_common.c for i.MX6.
>>>>
>>>> Well, this is an example of why we both don't want libgcc ever nor do we
>>>> want to overly expand what we do offer.  In this case isn't it an
>>>> example of something that should be using lldiv/do_div/etc?
>>>
>>> I haven't seen the _udivmoddi4 emitted in my tests. Linux's libgcc copy
>>> also doesn't implement the function. Which toolchain do you use and
>>> which target did you compile?
>>
>> I'm using my own armv7hl-linux-gnueabi toolchain built for hard float.
>> Linux
>> arm libgcc does have arch/arm/lib/div64.S file that provides __do_div64()
>> function that is used by do_div() from include/asm/div64.h for 32-bit ARM
>> platform. Sure, arm64 has neither div64.h nor div64.S. We _DO_ have div64.h
>> (that is totally different from what Linux provides) but no div64.S in
>> arch/arm/lib.
>
> In that case, we should just import div64.S from Linux on arm32 and be
> done with it ? Since we now have all the necessary macros thanks to the
> first four patches in this series, that should be trivial.
>
> What do you think? I can bake a patch real quick, so you can test it ?

Sure I'll test it, no problems. Just bake the patch :)

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