Re: x86_64_defconfig and i386_defconfig: What is the difference?

[Hubert CHAUMETTE <hubert.chaumette@wanadoo.fr>]

Le 09/09/2014 17:11, Rajat Jain a écrit :
> Hi,
>
> Thank you all for your responses. I got the answer I was looking for:
>
>> Hello Rajat,
>>
>> Indeed, the i386 is for 32bits kernels, and x86_64 for 64 bits ones. If you
>> generate the configurations using "make ARCH=x86 defconfig" and "make
>> ARCH=i386 defconfig", you can easily compare the resulting configurations :
>>
>> .config from i386_defconfig :
>> #
>> # Automatically generated file; DO NOT EDIT.
>> # Linux/i386 3.17.0-rc1 Kernel Configuration # # CONFIG_64BIT is not set
>> CONFIG_X86_32=y CONFIG_X86=y CONFIG_INSTRUCTION_DECODER=y
>> CONFIG_OUTPUT_FORMAT="elf32-i386"
>> CONFIG_ARCH_DEFCONFIG="arch/x86/configs/i386_defconfig"
>> ...
>>
>> .config from x86_64_defconfig :
>> #
>> # Automatically generated file; DO NOT EDIT.
>> # Linux/x86 3.17.0-rc1 Kernel Configuration # CONFIG_64BIT=y
>> CONFIG_X86_64=y CONFIG_X86=y CONFIG_INSTRUCTION_DECODER=y
>> CONFIG_OUTPUT_FORMAT="elf64-x86-64"
>> CONFIG_ARCH_DEFCONFIG="arch/x86/configs/x86_64_defconfig"
>> ...
>>
>> As you can see, i386 is the 32 bits variant of the x86 architecture. There are of
>> course many more differences between these two configurations.
>>
>> Regards,
>>
>> Hubert
> Thanks all again,
>
> Rajat
>
>
>> -----Original Message-----
>> From: Valdis.Kletnieks@vt.edu [mailto:Valdis.Kletnieks@vt.edu]
>> Sent: Tuesday, September 09, 2014 7:28 AM
>> To: Matthias Brugger
>> Cc: Rajat Jain; linux-newbie@vger.kernel.org; kernelnewbies
>> Subject: Re: x86_64_defconfig and i386_defconfig: What is the difference?
>>
>> On Tue, 09 Sep 2014 16:06:07 +0200, Matthias Brugger said:
>>
>>>> Can someone tell me if the i386 one is to be used when we want to
>>>> build for a 32bit machine and the x86_64 is to be used for 64 bit machine?
>>> You can build the kernel with any architecture for any architecture.
>>> This is called cross-compiling. The homepage [0] should explain you
>>> how to do that.
>> Right, but you still need to use a .config appropriate for the target machine,
>> which is what I think Rajat was asking about.
>>
>> A defconfig is usually only known verified to boot on a few (possibly one)
>> examples of that architecture hardware.  For embedded ARM, it may be one
>> specific development board or hardware device.  For x86, I think they try to
>> keep it "will probably kind of sort of boot on generic PC hardware with a
>> common distro, but anything fancylike a webcam or better graphics than "vga
>> tty emulation" may not work".
>>
>> A defconfig is pretty much just a proof of concept starting point for an actual
>> working config for a given hardware system.
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Sorry, I mistakenly replied only to the OP.
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