Re: [RFC PATCH 21/23] powerpc64 is not necessarily BigEndian anymore! :)

["Vladimir 'φ-coder/phcoder' Serbinenko" <phcoder@gmail.com>]

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On 03.04.2014 21:54, Andrey Borzenkov wrote:
> В Thu, 3 Apr 2014 12:26:57 -0700
> Ram Pai <linuxram@us.ibm.com> пишет:
> 
>>>>>
>>>>>> Well. that is the issue.  Various distros have varied support for
>>>>>> cross-compilation (multi-arch support). If the distro does not 
>>>>>> have 32bit BE libraries natively installed (out-of-the-box), they
>>>>>> wont be able to generate a 32bit BE grub loader.
>>>>>
>>>>> We speak only about target code that runs at boot time. This code does
>>>>> not use any library. 
>>>>
>>>> I am not a compiler/toolchain expert. But dont we need all the necessary
>>>> tools and libraries in /lib/<arch>-<dist>-linux/ directory for cross
>>>> compilation; even to generate static executables?
>>>>
>>>>> It only needs compiler support. GRUB does not
>>>>> support anything besides gcc and recently some clang support was added.
>>>>> Do you have real life example of distribution which does not support
>>>>> -mbig gcc option to produce big-endian *code*?
>>>>
>>>> This is ideally what I want too. But it is not possible
>>>> **out-of-the-box** on any distro for power arch.  I am told
>>>> that debian has a new multi-arch support added which makes this
>>>> work out-of-the-box, but it is still in early stages to work
>>>> seemlessly **out-of-the-box**. I may be wrong.
>>>>
>>>
>>> If distribution is capable of building Linux kernel, it should be
>>> capable of compiling 32 bit big-endian code. Linux startup code on
>>> PowerPC is built as 32 bit big-endian:
>>>
>>> BOOTCFLAGS    := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
>>>                  -fno-strict-aliasing -Os -msoft-float -pipe \
>>>                  -fomit-frame-pointer -fno-builtin -fPIC -nostdinc \
>>>                  -isystem $(shell $(CROSS32CC) -print-file-name=include) \
>>>                  -mbig-endian
>>
>>
>> But that is different though. Yes it is possible to cross compile for
>> any target on any arch.  But the key is that the environment needs to be
>> setup to do so.  
>>
>> We are talking about generating crosscompiled grub boot loader by an
>> uninitiated/not-so-expert adminstrator. If the distribution makes it
>> easy for that administrator to be able to cross-compile, than life is
>> easy.  But that is not generally the case though.
> 
> E-h-h ... could you be more specific? You need exactly the same tool
> set to compile 32 bit big-endian grub as to compile Linux kernel. So
> it follows that generally it is impossible to compile Linux kernel on
> distributions for ppc64le. Is it what you mean?
> 
>>                                                   The administrator has
>> to scramble around to find the right cross-compilation setup installed
>> on her system to achieve the end result.
>>
> 
> I try to understand what exactly is required beyond what is needed to
> compile Linux kernel? I do not consider need to install a couple of
> RPMs as high burden.
> 
> Here is what grub2 on SUSE needs:
> 
> %ifarch x86_64 ppc64
> BuildRequires:  gcc-32bit
> BuildRequires:  glibc-32bit
> BuildRequires:  glibc-devel-32bit
> %else
> BuildRequires:  gcc
> BuildRequires:  glibc-devel
> %ifarch s390x
> BuildRequires:  glibc-static
> %endif
> %endif
> 
> See https://build.opensuse.org/package/show/Base:System/grub2

I see you have some outdated patches like btrfs ones, you shouldn't need
them now (didn't really look in them).
As for eliminating libgcc dependency I created branch phcoder/no-libgcc.
For ppc only ucmpdi2 was needed actually.
> for
> details. It simply forces -m32 -big-endian for powerpc. It also includes
> brute-force patche to work around libgcc issue that probably may be
> done differently, but otherwise it is amazingly small change.
> 



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