root: Add basic internal syscall helper

1 files changed, 32 insertions, 8 deletions

diff --git a/src/root.zig b/src/root.zig
index 636452c..7a8ce3a 100644
--- a/src/root.zig
+++ b/src/root.zig
@@ -1,14 +1,38 @@
-// SPDX-FileCopyrightText: Zig contributors
+// SPDX-FileCopyrightText: 2024 Himbeer <himbeer@disroot.org>
 //
-// SPDX-License-Identifier: MIT
+// SPDX-License-Identifier: AGPL-3.0-or-later
 
 const std = @import("std");
-const testing = std.testing;
 
-export fn add(a: i32, b: i32) i32 {
-    return a + b;
-}
+pub const max_args = 6;
+
+const Result = struct {
+    value: usize,
+    error_code: usize,
+};
+
+fn ecall(number: usize, args: anytype) Result {
+    comptime var registers = [max_args]usize{0};
+    inline for (args, 0..) |arg, i| {
+        if (i >= max_args) @compileError("Too many arguments to system call");
+        registers[i] = @bitCast(arg);
+    }
 
-test "basic add functionality" {
-    try testing.expect(add(3, 7) == 10);
+    var result: Result = undefined;
+    asm volatile (
+        \\ ecall
+        \\ sw a0, 0(%[value])
+        \\ sw a1, 0(%[error_code])
+        :
+        : [value] "r" (&result.value),
+          [error_code] "r" (&result.error_code),
+          [a0] "{a0}" (registers[0]),
+          [a1] "{a1}" (registers[1]),
+          [a2] "{a2}" (registers[2]),
+          [a3] "{a3}" (registers[3]),
+          [a4] "{a4}" (registers[4]),
+          [a5] "{a5}" (registers[5]),
+          [number] "{a7}" (number),
+    );
+    return result;
 }