x86_64_defconfig and i386_defconfig: What is the difference?

Post by Rajat Jain
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?

I wouldn't run either one on an actual machine. Defconfigs are *example*
configs, only useful as a template for customizing for actual hardware.

Paul Bolle

2014-09-09 14:19:54 UTC

Post by V***@vt.edu

Post by Rajat Jain
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?

I wouldn't run either one on an actual machine. Defconfigs are *example*
configs, only useful as a template for customizing for actual hardware.

It is probably easiest to take the .config file of the latest kernel of
the distribution you are using as a starting point. In that case you
know that this starting point at least works on your machine.

(I remember seeing tutorials that show you how to generate a .config
from scratch. I wonder whether anyone actually does that. It should be
quite a bit of work for an uncertain outcome. Ie, you might end up
trying quite a few configurations before hitting one that works
reasonably for your machine.)

Hope this helps,

Paul Bolle

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V***@vt.edu

2014-09-09 14:26:27 UTC

Post by Paul Bolle
(I remember seeing tutorials that show you how to generate a .config
from scratch. I wonder whether anyone actually does that.

Distros did that originally. Now they just keep delta'ing their
known-working config. The pain involved was part of why localmodconfig
and friends were created....

Matthias Brugger

2014-09-09 14:06:07 UTC

Post by Rajat Jain
Hi,
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.

Cheers,
Matthias

[0] http://kernelnewbies.org/FAQ/KernelCrossCompilation

Post by Rajat Jain
Thanks,
Rajat
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V***@vt.edu

2014-09-09 14:27:53 UTC

Post by Rajat Jain
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.

Abreu, Ian

2014-09-09 14:34:43 UTC

To add to this, if you're trying to compile a kernel to work for a specific
platform or board and it's not working, 'make menuconfig' is your friend for
taking a bare bones kernel .config and making it your own.

-----Original Message-----
From: linux-newbie-***@vger.kernel.org
[mailto:linux-newbie-***@vger.kernel.org] On Behalf Of
***@vt.edu
Sent: Tuesday, September 09, 2014 10:28 AM
To: Matthias Brugger
Cc: Rajat Jain; linux-***@vger.kernel.org; kernelnewbies
Subject: Re: x86_64_defconfig and i386_defconfig: What is the difference?

Post by Rajat Jain
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?

Post by Matthias Brugger
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.

Rajat Jain

2014-09-09 15:11:00 UTC

Hi,

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
#
# 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"
...
#
# 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-----
Sent: Tuesday, September 09, 2014 7:28 AM
To: Matthias Brugger
Subject: Re: x86_64_defconfig and i386_defconfig: What is the difference?

Post by Rajat Jain
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.

Hubert CHAUMETTE

2014-09-09 15:28:36 UTC

Post by Rajat Jain
Hi,

Hello Rajat,
Indeed, the i386 is for 32bits kernels, and x86_64 for 64 bits ones.=

If you

generate the configurations using "make ARCH=3Dx86 defconfig" and "m=

ake

ARCH=3Di386 defconfig", you can easily compare the resulting configu=
#
# Automatically generated file; DO NOT EDIT.
# Linux/i386 3.17.0-rc1 Kernel Configuration # # CONFIG_64BIT is not=

set

CONFIG_X86_32=3Dy CONFIG_X86=3Dy CONFIG_INSTRUCTION_DECODER=3Dy
CONFIG_OUTPUT_FORMAT=3D"elf32-i386"
CONFIG_ARCH_DEFCONFIG=3D"arch/x86/configs/i386_defconfig"
...
#
# Automatically generated file; DO NOT EDIT.
# Linux/x86 3.17.0-rc1 Kernel Configuration # CONFIG_64BIT=3Dy
CONFIG_X86_64=3Dy CONFIG_X86=3Dy CONFIG_INSTRUCTION_DECODER=3Dy
CONFIG_OUTPUT_FORMAT=3D"elf64-x86-64"
CONFIG_ARCH_DEFCONFIG=3D"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-----
Sent: Tuesday, September 09, 2014 7:28 AM
To: Matthias Brugger
Subject: Re: x86_64_defconfig and i386_defconfig: What is the differ=

ence?

Post by Rajat Jain
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=

=2E

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 targe=

t machine,

which is what I think Rajat was asking about.
A defconfig is usually only known verified to boot on a few (possibl=

y one)

examples of that architecture hardware. For embedded ARM, it may be=

one

specific development board or hardware device. For x86, I think the=

y try to

keep it "will probably kind of sort of boot on generic PC hardware w=

ith a

common distro, but anything fancylike a webcam or better graphics th=

an "vga

tty emulation" may not work".
A defconfig is pretty much just a proof of concept starting point fo=

r an actual

working config for a given hardware system.

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e" in

Post by Rajat Jain
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.linux-learn.org/faqs

Sorry, I mistakenly replied only to the OP.
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Rajat Jain

2014-09-09 17:51:43 UTC

Hi,

Post by Abreu, Ian
-----Original Message-----
Sent: Tuesday, September 09, 2014 7:28 AM
To: Matthias Brugger
Subject: Re: x86_64_defconfig and i386_defconfig: What is the difference?

Post by Rajat Jain
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.

Right.

I'm trying to generate x86 images for someone else to test, who's going to test it on a standard / generic x86 machine:

https://lkml.org/lkml/2014/9/9/35

What I was not sure is that which config should I use to generate an image for a "standard x86 machine". Now I do understand (I provided him 2 images - 1 for the 32 bit (using i386_defconfig) and another for 64 bit (using x86_64_defconfig).

Thanks,

Rajat

Post by Abreu, Ian
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.

Peter Teoh

2014-09-13 01:10:28 UTC

Post by Rajat Jain
Hi,
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?

i386 or 32-bit machines? i think it don't exists anymore, but what likely
is correct: i386-compatible machine.

The i386 config is for 32-bit OS, ie, the entire binaries must be build for
32-bit architecture.

So choose the correct config provided u have the correct userspace
files/libraries to support it.

Post by Rajat Jain
Thanks,
Rajat
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Regards,
Peter Teoh

Rajat Jain

2014-09-13 03:44:43 UTC