From 80af2e88528d9d0ca8dc7a9bae48639307cefedd Mon Sep 17 00:00:00 2001
From: Matthew Leach <dev@mattleach.net>
Date: Thu, 30 Apr 2026 20:43:51 +0100
Subject: [PATCH] libkernel: pg_offset: decouple from `VirtualMemory` trait

Since the only requirement for a `PageOffsetTranslator` is a constant
offset, pass that in as a generic parameter, allowing it to be decoupled
from the `VirtualMemory` trait.
---
 libkernel/src/memory/proc_vm/address_space.rs |  3 ---
 libkernel/src/memory/proc_vm/pg_offset.rs     | 18 +++++++-----------
 src/arch/arm64/mod.rs                         |  4 ++--
 src/arch/mod.rs                               |  3 +++
 src/drivers/virtio_hal.rs                     |  3 +--
 src/memory/mod.rs                             |  4 ++--
 6 files changed, 15 insertions(+), 20 deletions(-)

diff --git a/libkernel/src/memory/proc_vm/address_space.rs b/libkernel/src/memory/proc_vm/address_space.rs
index 68d80d9..813d2d2 100644
--- a/libkernel/src/memory/proc_vm/address_space.rs
+++ b/libkernel/src/memory/proc_vm/address_space.rs
@@ -208,9 +208,6 @@ pub trait VirtualMemory: CpuOps + Sized {
     /// The address space type used for the kernel.
     type KernelAddressSpace: KernAddressSpace;
 
-    /// The starting address for the logical mapping of all physical ram.
-    const PAGE_OFFSET: usize;
-
     /// Obtain a reference to the kernel's address space.
     fn kern_address_space() -> &'static SpinLockIrq<Self::KernelAddressSpace, Self>;
 }
diff --git a/libkernel/src/memory/proc_vm/pg_offset.rs b/libkernel/src/memory/proc_vm/pg_offset.rs
index e7fce19..ba876ee 100644
--- a/libkernel/src/memory/proc_vm/pg_offset.rs
+++ b/libkernel/src/memory/proc_vm/pg_offset.rs
@@ -1,22 +1,18 @@
 //! Page-offset arithmetic helpers.
 
-use super::address_space::VirtualMemory;
-use crate::memory::address::{AddressTranslator, TPA, TVA};
-use core::marker::PhantomData;
+pub(crate) use crate::memory::address::{AddressTranslator, TPA, TVA};
 
 /// Translates between physical and virtual addresses using a fixed page-offset mapping.
-pub struct PageOffsetTranslator<VM: VirtualMemory> {
-    _phantom: PhantomData<VM>,
-}
+pub struct PageOffsetTranslator<const OFFSET: usize>;
 
-unsafe impl<VM: VirtualMemory> Send for PageOffsetTranslator<VM> {}
-unsafe impl<VM: VirtualMemory> Sync for PageOffsetTranslator<VM> {}
+unsafe impl<const OFFSET: usize> Send for PageOffsetTranslator<OFFSET> {}
+unsafe impl<const OFFSET: usize> Sync for PageOffsetTranslator<OFFSET> {}
 
-impl<T, VM: VirtualMemory> AddressTranslator<T> for PageOffsetTranslator<VM> {
+impl<T, const OFFSET: usize> AddressTranslator<T> for PageOffsetTranslator<OFFSET> {
     fn virt_to_phys(va: TVA<T>) -> TPA<T> {
         let mut v = va.value();
 
-        v -= VM::PAGE_OFFSET;
+        v -= OFFSET;
 
         TPA::from_value(v)
     }
@@ -24,7 +20,7 @@ impl<T, VM: VirtualMemory> AddressTranslator<T> for PageOffsetTranslator<VM> {
     fn phys_to_virt(pa: TPA<T>) -> TVA<T> {
         let mut v = pa.value();
 
-        v += VM::PAGE_OFFSET;
+        v += OFFSET;
 
         TVA::from_value(v)
     }
diff --git a/src/arch/arm64/mod.rs b/src/arch/arm64/mod.rs
index e01c8a2..6711c66 100644
--- a/src/arch/arm64/mod.rs
+++ b/src/arch/arm64/mod.rs
@@ -78,8 +78,6 @@ impl VirtualMemory for Aarch64 {
     type ProcessAddressSpace = Arm64ProcessAddressSpace;
     type KernelAddressSpace = Arm64KernelAddressSpace;
 
-    const PAGE_OFFSET: usize = PAGE_OFFSET;
-
     fn kern_address_space() -> &'static SpinLock<Self::KernelAddressSpace> {
         KERN_ADDR_SPC.get().unwrap()
     }
@@ -89,6 +87,8 @@ impl Arch for Aarch64 {
     type UserContext = ExceptionState;
     type PTraceGpRegs = Arm64PtraceGPRegs;
 
+    const PAGE_OFFSET: usize = PAGE_OFFSET;
+
     fn new_user_context(entry_point: VA, stack_top: VA) -> Self::UserContext {
         ExceptionState {
             x: [0; 31],
diff --git a/src/arch/mod.rs b/src/arch/mod.rs
index b026af1..750e3df 100644
--- a/src/arch/mod.rs
+++ b/src/arch/mod.rs
@@ -37,6 +37,9 @@ pub trait Arch: CpuOps + VirtualMemory {
     /// The type for GP regs copied via `PTRACE_GETREGSET`.
     type PTraceGpRegs: UserCopyable + for<'a> From<&'a Self::UserContext>;
 
+    /// The starting address for the logical mapping of all physical ram.
+    const PAGE_OFFSET: usize;
+
     fn name() -> &'static str;
 
     fn cpu_count() -> usize;
diff --git a/src/drivers/virtio_hal.rs b/src/drivers/virtio_hal.rs
index 55c0b92..cbb59ae 100644
--- a/src/drivers/virtio_hal.rs
+++ b/src/drivers/virtio_hal.rs
@@ -1,9 +1,8 @@
-use crate::arch::ArchImpl;
+use crate::arch::{Arch, ArchImpl};
 use crate::memory::PageOffsetTranslator;
 use core::ptr::NonNull;
 use libkernel::memory::PAGE_SIZE;
 use libkernel::memory::address::{PA, TPA};
-use libkernel::memory::proc_vm::address_space::VirtualMemory;
 use libkernel::memory::region::PhysMemoryRegion;
 use log::trace;
 use virtio_drivers::{BufferDirection, Hal, PhysAddr};
diff --git a/src/memory/mod.rs b/src/memory/mod.rs
index 7fbd663..4d5fb02 100644
--- a/src/memory/mod.rs
+++ b/src/memory/mod.rs
@@ -1,5 +1,5 @@
 use crate::{
-    arch::ArchImpl,
+    arch::{Arch, ArchImpl},
     sync::{OnceLock, SpinLock},
 };
 use libkernel::memory::{
@@ -19,7 +19,7 @@ pub mod process_vm;
 pub mod uaccess;
 
 pub type PageOffsetTranslator =
-    libkernel::memory::proc_vm::pg_offset::PageOffsetTranslator<ArchImpl>;
+    libkernel::memory::proc_vm::pg_offset::PageOffsetTranslator<{ ArchImpl::PAGE_OFFSET }>;
 
 // Initial memory allocator. Used for initial memory setup.
 const STATIC_REGION_COUNT: usize = 128;