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Does anyone have any info on why the actual macOS installation isn't bootable by both architectures? I seem to have lots of different universal and x86_64 binar

Does anyone have any info on why the actual macOS installation isn't bootable by both architectures? I seem to have lots of different universal and x86_64 binaries and kexts on my M1 machine. Also the kernel (that I thought was the actual kernel in use) in /System/Library/Kernels reports "Mach-O 64-bit executable x86_64" so I'm kinda confused about all this. I'd appreciate any pointers.

pram 6y ago
I presume it’s because the M1 variant doesn’t use EFI to boot.
- Toutouxc 6y ago
  That's what I'm expecting to learn, but I wonder what's going on inside regarding the kernel and dylibs (and other stuff I don't understand yet).
my123 6y ago
On your M1 machine, the used kernel is /System/Library/Kernels/kernel.release.t8101. (for T810x processors, A14 is T8101 and M1 is T8103, both share the same kernel) The installation should be bootable by both, but not sure that the flow to bless an install done on another machine to be bootable on an other M1 one is done/fully functional yet. (on M1 machines, you need to bless external volumes before booting from them) Booting an install done on an M1 on an x86 Mac should work already though.
- marcan_42 6y ago
  That's not the kernel. I mean, it's the kernel, but not the kernel that the machine boots from. The built-in bootloader actually boots iBoot2 from /System/Volumes/Preboot/(UUID)/boot/(long hash)/usr/standalone/firmware/iBoot.img4, and that then loads the Darwin kernel from /System/Volumes/Preboot/(UUID)/boot/(long hash)/System/Library/Caches/com.apple.kernelcaches/kernelcache. However, the system firmware can only boot this from the internal SSD, not from any external storage. When you choose an external disk to boot from (the "bless" thing), those files get copied to the internal SSD, and it boots from that instead.
  - mrkstu 6y ago
    So you literally cannot boot an M1 Mac with a nonfunctional internal drive, even if you’re successfully ’booting’ from an external drive before it fails? The SSD is integral to its functioning?
    - my123 6y ago
      Yes.
      - mrkstu 6y ago
        Good to know- glad I got a terabyte drive then, since it will less likely suffer a wear failure in its usable lifetime, but sad that a wear part guarantees a finite lifetime for a machine with no moving parts.
  - my123 6y ago
    That's the immutable kernelcache shipped by the machine, and isn't only the kernel but also includes the kexts. You can then rebuild your own kernel cache from /System/Library/Extensions and /System/Library/Kernels. (eventually with a recompiled kernel)
  - comex 6y ago
    But note that Intel Macs use a similar but completely different system, also redone in Big Sur, with a set of "kext collection" files in a different location and format. Because that makes so much sense.

pram 6y ago

I presume it’s because the M1 variant doesn’t use EFI to boot.

Toutouxc 6y ago
That's what I'm expecting to learn, but I wonder what's going on inside regarding the kernel and dylibs (and other stuff I don't understand yet).

my123 6y ago

On your M1 machine, the used kernel is /System/Library/Kernels/kernel.release.t8101. (for T810x processors, A14 is T8101 and M1 is T8103, both share the same kernel) The installation should be bootable by both, but not sure that the flow to bless an install done on another machine to be bootable on an other M1 one is done/fully functional yet. (on M1 machines, you need to bless external volumes before booting from them) Booting an install done on an M1 on an x86 Mac should work already though.

marcan_42 6y ago
That's not the kernel. I mean, it's the kernel, but not the kernel that the machine boots from. The built-in bootloader actually boots iBoot2 from /System/Volumes/Preboot/(UUID)/boot/(long hash)/usr/standalone/firmware/iBoot.img4, and that then loads the Darwin kernel from /System/Volumes/Preboot/(UUID)/boot/(long hash)/System/Library/Caches/com.apple.kernelcaches/kernelcache. However, the system firmware can only boot this from the internal SSD, not from any external storage. When you choose an external disk to boot from (the "bless" thing), those files get copied to the internal SSD, and it boots from that instead.
- mrkstu 6y ago
  So you literally cannot boot an M1 Mac with a nonfunctional internal drive, even if you’re successfully ’booting’ from an external drive before it fails? The SSD is integral to its functioning?
  - my123 6y ago
    Yes.
    - mrkstu 6y ago
      Good to know- glad I got a terabyte drive then, since it will less likely suffer a wear failure in its usable lifetime, but sad that a wear part guarantees a finite lifetime for a machine with no moving parts.
- my123 6y ago
  That's the immutable kernelcache shipped by the machine, and isn't only the kernel but also includes the kexts. You can then rebuild your own kernel cache from /System/Library/Extensions and /System/Library/Kernels. (eventually with a recompiled kernel)
- comex 6y ago
  But note that Intel Macs use a similar but completely different system, also redone in Big Sur, with a set of "kext collection" files in a different location and format. Because that makes so much sense.