From f57fd485c5637ac4bc6bf5fdb9e0e43b5ba7fa50 Mon Sep 17 00:00:00 2001
From: Mark Poliakov <mark@alnyan.me>
Date: Wed, 26 Mar 2025 14:22:33 +0200
Subject: [PATCH] WIP: Allow userspace to use stack

---
 src/arch/aarch64/vmm.zig |  8 ++++++--
 src/arch/riscv64/vmm.zig |  8 ++++++--
 src/kernel.zig           | 12 ++++++++++--
 src/thread.zig           | 19 +++++++++++++------
 4 files changed, 35 insertions(+), 12 deletions(-)

diff --git a/src/arch/aarch64/vmm.zig b/src/arch/aarch64/vmm.zig
index def4634..dea1441 100644
--- a/src/arch/aarch64/vmm.zig
+++ b/src/arch/aarch64/vmm.zig
@@ -155,6 +155,10 @@ pub fn Table(comptime Level: type) type {
             return table;
         }
 
+        pub fn from_physical_address(physical: PhysicalAddress) *@This() {
+            return @ptrFromInt(physical.virtualize());
+        }
+
         pub inline fn entry(self: *@This(), index: usize) *Entry {
             return &self.entries[index];
         }
@@ -167,7 +171,7 @@ pub fn Table(comptime Level: type) type {
             pub fn get_next_level(self: *Table(Level), index: usize) ?*Table(NextLevel) {
                 const ent = self.entry(index);
                 if (ent.raw.V and !ent.raw.P) {
-                    @panic("TODO: translate existing table");
+                    return Table(NextLevel).from_physical_address(ent.address());
                 }
                 return null;
             }
@@ -180,7 +184,7 @@ pub fn Table(comptime Level: type) type {
                     }
 
                     // Entry is a table
-                    @panic("TODO: translate existing table");
+                    return Table(NextLevel).from_physical_address(ent.address());
                 } else {
                     const table = try Table(NextLevel).allocate_empty();
                     const physical = table.physical_address();
diff --git a/src/arch/riscv64/vmm.zig b/src/arch/riscv64/vmm.zig
index 3799c01..f9eb6ca 100644
--- a/src/arch/riscv64/vmm.zig
+++ b/src/arch/riscv64/vmm.zig
@@ -115,6 +115,10 @@ pub fn Table(comptime Level: type) type {
             return .{ .entries = [_]Entry{.INVALID} ** 512 };
         }
 
+        pub fn from_physical_address(physical: PhysicalAddress) *@This() {
+            return @ptrFromInt(physical.virtualize());
+        }
+
         pub fn allocate_empty() Error!*@This() {
             const page = mem.phys.alloc_page() orelse return error.out_of_pages;
             const table = @as(*@This(), @ptrFromInt(page.virtualize()));
@@ -136,7 +140,7 @@ pub fn Table(comptime Level: type) type {
             pub fn get_next_level(self: *Table(Level), index: usize) ?*Table(NextLevel) {
                 const ent = self.entry(index);
                 if (ent.raw.v and ent.raw.is_table()) {
-                    @panic("TODO: translate existing table");
+                    return Table(NextLevel).from_physical_address(ent.address());
                 }
                 return null;
             }
@@ -150,7 +154,7 @@ pub fn Table(comptime Level: type) type {
                         @panic("TODO: handle mixed hugepages and tables");
                     }
                     // It is a table
-                    @panic("TODO: translate existing table");
+                    return Table(NextLevel).from_physical_address(ent.address());
                 } else {
                     // Allocate a new entry
                     const table = try Table(NextLevel).allocate_empty();
diff --git a/src/kernel.zig b/src/kernel.zig
index d7e8b64..df5d777 100644
--- a/src/kernel.zig
+++ b/src/kernel.zig
@@ -40,9 +40,17 @@ pub export fn kernel_main() callconv(.C) noreturn {
     const t0 = thread.Thread.create_kernel(&a, &f0, 1234);
 
     const code = switch (comptime arch.cpu) {
-        .riscv64 => &[_]u8{ 0x6F, 0x00, 0x00, 0x00 },
+        .riscv64 => &[_]u8{
+            0x93, 0x02, 0xB0, 0x07, // li t0, 123
+            0x13, 0x01, 0x81, 0xFF, // addi sp, sp, -8
+            0x23, 0x30, 0x51, 0x00, // sd t0, (sp)
+            0x6F, 0x00, 0x00, 0x00, // j .
+        },
         .aarch64 => &[_]u8{
-            0x00, 0x00, 0x00, 0x14,
+            0x60, 0x0F, 0x80, 0xD2, // mov x0, #123
+            0xFF, 0x23, 0x00, 0xD1, // sub sp, sp, #8
+            0xE0, 0x03, 0x00, 0xF9, // str x0, [sp]
+            0x00, 0x00, 0x00, 0x14, // b .
         },
     };
     const t1 = thread.test_create_user_from_code(&a, code) catch @panic("Could not create test thread");
diff --git a/src/thread.zig b/src/thread.zig
index 9f21473..a906cdf 100644
--- a/src/thread.zig
+++ b/src/thread.zig
@@ -217,17 +217,24 @@ pub fn test_create_user_from_code(a: *arena.Arena, code: []const u8) Thread.Erro
         address_space.clear();
     }
 
-    // Map 0x200000
-    const page = mem.phys.alloc_page() orelse return error.out_of_memory;
+    // @ 0x200000
+    const code_page = mem.phys.alloc_page() orelse return error.out_of_memory;
     errdefer {
-        mem.phys.free_page(page);
+        mem.phys.free_page(code_page);
+    }
+    // @ 0x201000
+    const stack_page = mem.phys.alloc_page() orelse return error.out_of_memory;
+    errdefer {
+        mem.phys.free_page(stack_page);
     }
-    try address_space.map_single_page(0x200000, page);
 
-    const page_data = @as([*]u8, @ptrFromInt(page.virtualize()))[0..code.len];
+    try address_space.map_single_page(0x200000, code_page);
+    try address_space.map_single_page(0x201000, stack_page);
+
+    const page_data = @as([*]u8, @ptrFromInt(code_page.virtualize()))[0..code.len];
     @memcpy(page_data, code);
 
-    const thread = Thread.create_user(a, address_space, 0x200000, 0, 0);
+    const thread = Thread.create_user(a, address_space, 0x200000, 0x201000, 0);
 
     return thread;
 }