1 files changed, 66 insertions, 0 deletions
diff --git a/mirai.old/asm/context.zig b/mirai.old/asm/context.zig
new file mode 100644
index 0000000..ada6585
--- /dev/null
+++ b/mirai.old/asm/context.zig
@@ -0,0 +1,66 @@
+//! Context Switching Operations
+//! Low-level assembly for switching between Kata execution contexts
+
+const kata_mod = @import("../kata/kata.zig");
+
+/// Switch to a Kata's execution context
+/// This function never returns - it jumps to userspace via iretq
+pub fn switch_to_context(ctx: *const kata_mod.Context, page_table: u64, kernel_stack: u64) noreturn {
+    const ctx_addr = @intFromPtr(ctx);
+
+    asm volatile (
+    // Load context address and page table into registers
+        \\mov %[ctx_addr], %%rdi
+        \\mov %[pt], %%rsi
+        \\
+        // Switch to kata's higher-half kernel stack
+        \\mov %[kstack], %%rsp
+        \\
+        // Read iretq frame values from context struct
+        // Offsets based on Context struct layout:
+        //   rsp=56, rip=128, rflags=136, cs=144, ss=152
+        \\mov 152(%%rdi), %%r12
+        \\mov 56(%%rdi), %%r13
+        \\mov 136(%%rdi), %%r14
+        \\mov 144(%%rdi), %%r15
+        \\mov 128(%%rdi), %%rax
+        \\
+        // Build iretq frame (ss, rsp, rflags, cs, rip)
+        \\pushq %%r12
+        \\pushq %%r13
+        \\pushq %%r14
+        \\pushq %%r15
+        \\pushq %%rax
+        \\
+        // Switch to user page table
+        \\mov %%rsi, %%cr3
+        \\
+        // Restore registers from context (offsets from Context struct)
+        // rax=0, rbx=8, rcx=16, rdx=24, rsi=32, rdi=40, rbp=48
+        // r8=64, r9=72, r10=80, r11=88, r12=96, r13=104, r14=112, r15=120
+        \\mov 8(%%rdi), %%rbx
+        \\mov 16(%%rdi), %%rcx
+        \\mov 24(%%rdi), %%rdx
+        \\mov 32(%%rdi), %%rsi
+        \\mov 48(%%rdi), %%rbp
+        \\mov 64(%%rdi), %%r8
+        \\mov 72(%%rdi), %%r9
+        \\mov 80(%%rdi), %%r10
+        \\mov 88(%%rdi), %%r11
+        \\mov 96(%%rdi), %%r12
+        \\mov 104(%%rdi), %%r13
+        \\mov 112(%%rdi), %%r14
+        \\mov 120(%%rdi), %%r15
+        \\mov 0(%%rdi), %%rax
+        \\mov 40(%%rdi), %%rdi
+        \\
+        // Jump to userspace
+        \\iretq
+        :
+        : [ctx_addr] "r" (ctx_addr),
+          [pt] "r" (page_table),
+          [kstack] "r" (kernel_stack),
+        : .{ .memory = true }
+    );
+    unreachable;
+}