My mac has 64-bit EFI, but it only boots with 32-bit kernel

64-bitbootkernel

I followed the guide at
http://macperformanceguide.com/SnowLeopard-64bit.html
to boot into 64-bit mode. I had no problems with the instructions and on the boot screen it says "PAE enabled, 64bit mode enabled" but when the system boots, both uname -a and System Profiler tell me that it has booted into 32-bit mode.

I really need to boot into the 64-bit kernel, what should I do?

System is MacBook Unibody (Early 2009, 6 GB RAM, 2.4 Intel CPU, 10.6.6)

Best Answer

64-bit Mac CPUs cannot boot 64-bit kernel due to one of the following reasons:

The machine has 32-bit EFI.
The machine’s model is prohibited from booting K64 through a hardcoded list within the boot loader. (The list excludes "non-Pro" machines.)

Both limitations are artificial and imposed by Apple, although the first one is important because if a 32-bit EFI were allowed to boot the kernel wouldn't be able to use firmware services.

IF you really, really, really want to boot these machines with a 64-bit kernel, you'll need to perform hackery on /System/Library/CoreServices/boot.efi. This is quite risky. More info:

http://osxbook.com/blog/2009/08/31/is-your-machine-good-enough-for-snow-leopard-k64/

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MacOS – How to know the kernel extensions are 64-bit ready

As far as I know, System Profiler won't display information for any .kext's that are being loaded and are located somewhere else besides the /System/Library/Extensions/ folder.

To get comprehensive information about the kernel extensions which are currently loaded and in use on your Mac, you can use the kextstat command line tool.

Open up the Terminal application (in the /Applications/Utilities/ folder), type the following at the prompt, and then hit return:

 kextstat

You will get a large list of all the loaded kernel extensions. You'll primarily want to focus on the bundle identifiers of the loaded .kexts. (That's the backwards domain name string such as "com.apple...."). You should be able to eliminate the ones that include "com.apple", as those will be Apple's and should have a K64 version. Once you've gotten rid of those, you'll then need to go over the remaining ones to make sure they are built as universal K32+K64 versions, or whether you may need to make sure you have the latest updates.

For example, after eliminating all the Apple kexts on the output I get, I have the following kexts listed. Since I switched to K64 a year or so ago, all of these are in order so everything is fine.

MacPro:~ mdouma46$ kextstat
Index Refs Address          Size   Wired  Name (Version) <Linked Against>
73  0 0xffffff7f8111a000 0x8000 0x8000  com.AmbrosiaSW.AudioSupport (3.2) <72 5 4 3 1>
81  0 0xffffff7f811bf000 0x9000 0x9000  jp.plentycom.driver.SteerMouse (4.0.2) <55 29 24 5 4 3>
105 0 0xffffff7f81499000 0x5000 0x5000  com.Cycling74.driver.Soundflower (1.5.2) <72 5 4 3>
115 0 0xffffff7f814bf000 0xd1000 0xd1000 com.vmware.kext.vmx86 (3.1.2) <7 5 4 3 1>
116 0 0xffffff7f81590000 0xc000 0xc000   com.vmware.kext.vmci (3.1.2) <5 4 3 1>
117 0 0xffffff7f8159c000 0x7000 0x7000  com.vmware.kext.vmioplug (3.1.2) <29 24 5 4 3 1>
118 0 0xffffff7f815a3000 0xa000 0xa000  com.vmware.kext.vmnet (3.1.2) <5 4 3 1>
119 0 0xffffff7f815ad000 0x2000 0x2000  com.nvidia.CUDA (1.1.0) <4 1>

MacBook – If I install more RAM should I boot into 64bit Kernel? Does it matter

According to this article at macperformanceguide.com, you will see performance gains (5-30%) by running graphics applications in 64-bit mode.

Note that you don't necessarily need to switch to a 64-bit Kernel, you just need to ensure that Lightroom runs in 64-bit mode.

Best Answer

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MacOS – How to know the kernel extensions are 64-bit ready

MacBook – If I install more RAM should I boot into 64bit Kernel? Does it matter

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