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gringo
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Joined: 27 Apr 2003
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 Posted: Mon Nov 17, 2008 9:39 am Post subject: CONFIG_x86_64=y set but 32 bit kernel ? |
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hi all,
hopefully someone can sched some light : we all know about the in-kernel merge some time ago between both i386/x86_64 resulting in only one arch, x86.
That´s all fine and cool, but why do i get a 32 bit kernel even if i have CONFIG_X86_64=y set ?
| Code: | -->ls -la arch/x86_64/boot
total 8
drwxr-xr-x 2 root root 4096 oct 5 14:36 .
drwxr-xr-x 3 root root 4096 oct 5 14:36 ..
lrwxrwxrwx 1 root root 22 oct 5 14:36 bzImage -> ../../x86/boot/bzImage |
| Code: | -->file arch/x86/boot/bzImage
arch/x86/boot/bzImage: Linux kernel x86 boot executable RO-rootFS, root_dev 0x906, swap_dev 0x1, Normal VGA |
The vmlinux image created in the root directory is 64bit btw.
Is this expected ? I have been searching and looking around a bit but i don´t see anything that explains this behaviour and yes, this happens with gentoo-sources and with current git.
I guess the Kernel section is better suited for this thread than the amd64 one, even if it apparently is x86_64 related. More kernel gurus will read this here.
TIA
( this question came up in a thread in the spanish section of this forums -> https://forums.gentoo.org/viewtopic-t-714420.html)
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jw5801
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Joined: 12 Jun 2008
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Location: Melbourne, Australia
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| Posted: Mon Nov 17, 2008 12:58 pm Post subject: |
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This is expected I believe. I know I definitely have a 64-bit kernel, yet it still gets compiled into the x86 directory and symlinked. Try booting into the kernel and checking with:
Should tell you it's x86_64. `uname -a' will give you a bunch of other info about your kernel too. |
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gringo
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| Posted: Mon Nov 17, 2008 1:40 pm Post subject: |
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yeah, i know, uname says it´s a x86_64 system of course but i was wondering why the kernel image is 32bits, at least the compressed kernel image is.
cheers
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jw5801
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Location: Melbourne, Australia
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| Posted: Mon Nov 17, 2008 1:49 pm Post subject: |
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| I think most bootloaders can only load 32-bit executables, therefore the compressed image is 32-bit but actually unloads the 64-bit kernel. That's just an educated guess though. |
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gringo
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| Posted: Mon Nov 17, 2008 2:19 pm Post subject: |
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thanks, that´s what i was guessing too.
I´ve read somewhere the kernel is responsible to switch to long mode once executed, but my thought was this was only because of a grub ( paging) limitation and that´s why i was a bit confused after seeing the default generated kernel was 32bit only. I assumed lilo could boot such a beast.
thanks for your input 
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gimpel
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Location: Munich, Bavaria
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| Posted: Mon Nov 17, 2008 2:23 pm Post subject: |
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They just merged i386 and x86_64 tree into x86 in the kernel, as both is x86 after all.
http://lwn.net/Articles/243704/
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gringo
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| Posted: Mon Nov 17, 2008 2:26 pm Post subject: |
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| Quote: | | If you end up with a symlink in arch/x86_64/boot then your kernel is 64bit. |
no, it´s not, check yourself.
Apparently it will switch to long mode once run but file says it isn´t a 64bit executable.
cheers
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gimpel
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| Posted: Mon Nov 17, 2008 2:28 pm Post subject: |
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Ah, I thought you were just wondering why the bzImage ends up in arch/x86
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