From 3b749153b84425f6077b05af8d7fd891dc86ca6e Mon Sep 17 00:00:00 2001
From: Imbus <>
Date: Sat, 27 Dec 2025 02:08:36 +0100
Subject: [PATCH] riscv vm stuff

---
 riscv-vm.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 riscv-vm.c

diff --git a/riscv-vm.c b/riscv-vm.c
new file mode 100644
index 0000000..d3f9eec
--- /dev/null
+++ b/riscv-vm.c
@@ -0,0 +1,66 @@
+#include <assert.h>
+#include <stdint.h>
+#include <stdio.h>
+
+#define PPN_MASK    (UINT64_MAX >> 20)
+
+#define PPN_TO_PA(PPN) ((PPN & PPN_MASK) << 12)
+#define PA_TO_PPN(PA)  (PA >> 12)
+
+#define ALIGN_UP(n, align)   (((n) + (align) - 1) & ~((align) - 1))
+#define ALIGN_DOWN(n, align) ((n) & ~((align) - 1))
+
+#define IS_ALIGNED(x, align)     (((uintptr_t)(x) & ((uintptr_t)(align) - 1)) == 0)
+#define IS_ALIGNED_ANY(x, align) (((uintptr_t)(x) % (uintptr_t)(align)) == 0)
+
+#define IS_POWER_OF_TWO(x) (((x) != 0) && (((x) & ((x) - 1)) == 0))
+#define IS_ALIGNED_POW2(x, align)                                                                                      \
+    (assert(IS_POWER_OF_TWO((uintptr_t)(align))), (((uintptr_t)(x) & ((uintptr_t)(align) - 1)) == 0))
+
+#define VM_MODE_SV39 (2 << 64)
+
+#define PTE_V (1 << 0)
+#define PTE_R (1 << 1)
+#define PTE_W (1 << 2)
+#define PTE_X (1 << 3)
+/* And so on... */
+
+#define IS_LEAF(PTE) ((PTE & (PTE_R | PTE_W | PTE_X)) != 0)
+
+#define PTE_PPN(PTE, LEVEL) (((PTE) >> (10 + ((LEVEL) * 9)) & 0x1FF))
+
+int main(void) {
+    assert(IS_ALIGNED(0, 1));
+    assert(IS_ALIGNED(8, 8));
+    assert(IS_ALIGNED(12, 4));
+    assert(!IS_ALIGNED(66, 16));
+    assert(!IS_ALIGNED(234, 4096));
+    assert(!IS_ALIGNED(4099, 4096));
+
+    assert(PPN_MASK == 0b11111111111111111111111111111111111111111111);
+    assert(PPN_MASK == 17592186044415);
+    assert(PPN_MASK == 0xFFFFFFFFFFF);
+
+    printf("%lu", PPN_TO_PA(0xAAAAAA));
+    assert(IS_ALIGNED(PPN_TO_PA(0xAAAAAAAAAAAA), 4096));
+
+    uint64_t pte = 0b11111111110000000001111111110000000001111111111;
+
+    assert(pte & PTE_V);
+    assert(pte & PTE_R);
+    assert(pte & PTE_W);
+    assert(pte & PTE_X);
+
+    assert(IS_LEAF(pte));
+
+    assert(PTE_PPN(pte, 0) == 0);
+    assert(PTE_PPN(pte, 1) == 0b111111111);
+    assert(PTE_PPN(pte, 2) == 0);
+    pte <<= 9;
+    assert(PTE_PPN(pte, 0) == 0b111111111);
+    assert(PTE_PPN(pte, 1) == 0);
+    assert(PTE_PPN(pte, 2) == 0b111111111);
+
+    assert(!IS_LEAF(pte)); // Rightmost bits are now shifted out
+
+}