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Add patchAPIC conversion guide #26

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1 change: 1 addition & 0 deletions .vuepress/config.js
Original file line number Diff line number Diff line change
Expand Up @@ -239,6 +239,7 @@ module.exports = {
},
['/Universal/irq', 'IRQ Fix'],
['/Universal/spoof', 'GPU Spoof'],
['/Universal/apic', 'APIC Patching'],
]
},
{
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71 changes: 71 additions & 0 deletions Universal/apic.md
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# Patching the APIC table

An odd issue some HEDT users may experience is a kernel panic relating to more cores defined in APIC than actually present:

```
panic(cpu 0 caller 0x......): "x86_validate topology() 32 threads but 33 registered from MADT~0/...
```

The reason for this kernel panic is due to macOS's assumption that the first CPU in ACPI is always enabled, which on servers and HEDT systems may not always true.
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To get around this, we want to patch our APIC table to point the first CPU entry to an active CPU.


## Dumping your DSDT and APIC tables

Dumping your DSDT and APIC table is quite easy, however some of the methods mentioned in [Getting a copy of our DSDT](../Manual/dumpmd) may not provide you will all the needed files. Methods that will provide a full dump:
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* acpidump.exe
* Just run the program, don't give any specific arguments
* Clover's F4
* UEFI Shell using acpidump.efi
* OpenCore's SysReport quirk

And don't forget to follow the decompile guide as well: [Compiling and decompiling ACPI Tables](../Manual/compile.md)


## Examining our ACPI table

So lets take a look at our APIC table first:

![](../images/Universal/apic-md/apic-table.png)

Here we can see a list of all the CPU threads, and info about each one. Lets look at the first `[Processor Local APIC]` entry:

```
[02Ch 0044 1] Subtable Type : 00 [Processor Local APIC]
[02Dh 0045 1] Length : 08
[02Eh 0046 1] Processor ID : 00
[02Fh 0047 1] Local Apic ID : 02
[030h 0048 4] Flags (decoded below) : 00000001
Processor Enabled : 1
Runtime Online Capable : 0
```

Here we're given some important info, but the most important part:
```
Processor ID : 00
```

This value is what matches up the APIC's table entry to your DSDT, and is passed to macOS to determine the first CPU entry. And here we get a glimpse into what might be causing our kernel panic.

Next open your DSDT and search for `Processor`:

![](../images/Universal/apic-md/dsdt-processor-entry.png)

Here we're given some important info regarding the first CPU:

```
Processor (C000, 0x80, 0x00000410, 0x06)
```

If we check the [ACPI Spec](https://uefi.org/sites/default/files/resources/ACPI_6_3_final_Jan30.pdf), section 19.6.108, we see the info is parsed as follows:

```
Processor (ProcessorName, ProcessorID, PBlockAddress, PblockLength)
```


Now if we look at the `ProcessorID` section, we notice it's `0x80`, but this doesn't match up with the first entry in our APIC table(`00`). Now we can get a clearer idea of what's wrong with out APIC table and why it kernel panics.
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## Patching the APIC table
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