[APIC Driver] Kernel Crashes with Memory > 1024M

[candiedoperation]

Issue Description

On APIC Initialization, Kernel Crashes when the available memory is above 1024M

Troubleshooting

• Source of problem traces back to Apic::Initialize(); at interrupt.cpp
• The function calls AcpiDef::GetTableBySignature(ACPI_SIG_MADT, AcpiProvider::Xsdt, &MadtAddr);
• However, in the cases when the memory is above 1024M, the subsequent routine (u32 SdtEntries = ((Xsdt->Header.Length - sizeof(Xsdt->Header)) / 8);) that dereferences the required pointers fails and causes a triple fault
• Debugging the Rsdp->XsdtAddress using printf statements in acpipvdr.cpp indicated that the memory address of XSDT when memory < 1024M is 0x3fff0030 whereas, when memory > 1024M is 0x7fff0030

Memory < 1024M Debugging	Memory > 1024M Debugging

[candiedoperation]

Commit 3759444 prevents a triple fault by reorganizing fault code to occur after interrupts are completely initialized. Though this prevents the triple fault, the PAGE FAULT exception persists.

[candiedoperation]

That took a long time! The troubleshooting steps above make sense. The Page Table setup and identity mapping stuff in commit 3759444 were really preliminary and allowed virtual memory access only up-to 1024M. However, all IO/APIC addresses are way above that range.

Commit 9aa791d fixes this issue as it introduces a bootstrap memory manager (bootmem.cpp) and a WIP physical and virtual memory manager. Closing this issue finally (after two months) 🥳