sylveos

commit a0e84bf32460b7868e293d9aa2daf5a9879b3cd3
parent ab2d3ee79f760a36c0bb12ca2ceb8b44c01d84a4
Author: Sylvia Ivory <git@sivory.net>
Date:   Fri, 23 Jan 2026 20:17:55 -0800

Add syscall-2 (new root needed)

Diffstat:
M
pi/cpsr.zig
 | 
15
++++++++++++++-
M
pi/interrupts.zig
 | 
8
++++----
A
src/labs/4-syscall-2.zig
 | 
80
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
M
src/main.zig
 | 
2
+-

4 files changed, 99 insertions(+), 6 deletions(-)
diff --git a/pi/cpsr.zig b/pi/cpsr.zig
@@ -33,13 +33,26 @@ pub inline fn get() CPSR {
     );
 }
 
+pub inline fn get_s() CPSR {
+    return asm volatile ("MRS %[result], spsr"
+        : [result] "=r" (-> CPSR),
+    );
+}
+
 pub inline fn set(cpsr: CPSR) void {
-    return asm volatile ("MSR cpsr_c, %[value]"
+    return asm volatile ("MSR cpsr_cxsf, %[value]"
         :
         : [value] "r" (@as(u32, @bitCast(cpsr))),
         : .{ .cpsr = true });
 }
 
+pub inline fn set_s(cpsr: CPSR) CPSR {
+    return asm volatile ("MRS spsr_cxsf, %[value]"
+        :
+        : [value] "r" (cpsr),
+        : .{ .cpsr = true });
+}
+
 pub inline fn enable_interrupts() void {
     var cpsr = get();
     cpsr.i = true;
diff --git a/pi/interrupts.zig b/pi/interrupts.zig
@@ -102,13 +102,13 @@ comptime {
         \\ .global software_interrupt;
         \\ .type software_interrupt, %function;
         \\ software_interrupt:
-        \\   push {r0-r2, lr}
-        \\   mov  r1, r0
+        \\   push {r0-r12, lr}
         \\   sub  lr, lr, #4
+        \\   mov  r1, r0
         \\   mov  r0, lr
         \\   bl syscall_handler
-        \\   pop {r0-r2, lr}
-        \\   subs pc, lr, #0
+        \\   pop {r0-r12, lr}
+        \\   movs pc, lr
     );
 }
 extern fn software_interrupt() void;
diff --git a/src/labs/4-syscall-2.zig b/src/labs/4-syscall-2.zig
@@ -0,0 +1,80 @@
+const pi = @import("pi");
+
+const uart = @import("devices/mini-uart.zig");
+
+comptime {
+    asm (
+        \\ .global syscall_hello;
+        \\ .type syscall_hello, %function;
+        \\ syscall_hello:
+        \\   push {lr}
+        \\   swi 1
+        \\   pop {lr}
+        \\   bx lr
+        \\
+        \\ .global syscall_illegal;
+        \\ .type syscall_illegal, %function;
+        \\ syscall_illegal:
+        \\   push {lr}
+        \\   swi 2
+        \\   pop {lr}
+        \\   bx lr
+    );
+}
+
+extern fn syscall_hello(msg: *const u8) i32;
+extern fn syscall_illegal() i32;
+
+const Syscall = packed struct(u32) {
+    num: u24,
+    _: u4,
+    cond: u4,
+};
+
+export fn syscall_handler(pc: u32, r0: u32) i32 {
+    const syscall: Syscall = @bitCast(pi.mem.get_u32(@ptrFromInt(pc)));
+
+    uart.writer.print("instruction=0x{X}, number={d}\n", .{ @as(u32, @bitCast(syscall)), syscall.num }) catch {};
+
+    const spsr = pi.cpsr.get_s();
+    uart.writer.print("saved spsr mode = {t}\n", .{spsr.mode}) catch {};
+
+    switch (syscall.num) {
+        1 => {
+            uart.write_slice("syscall: ");
+            const str: [*]const u8 = @ptrFromInt(r0);
+            var i: usize = 0;
+
+            while (str[i] != 0) {
+                uart.write_byte(str[i]);
+                i += 1;
+            }
+
+            syscall_return(0);
+            return 0;
+        },
+        else => {
+            uart.writer.print("illegal system call: {d}!\n", .{syscall.num}) catch {};
+            syscall_return(-1);
+            return -1;
+        },
+    }
+}
+
+pub fn main() !void {
+    // Switch to user
+    var cpsr = pi.cpsr.get();
+    cpsr.mode = .User;
+    pi.cpsr.set(cpsr);
+
+    try uart.writer.print("current stack pointer = 0x{x}\n", .{pi.get_sp()});
+    try uart.writer.print("current cpsr mode = {t}\n", .{cpsr.mode});
+
+    try uart.writer.print("running syscall hello\n", .{});
+    const res_hello = syscall_hello(@ptrCast("hello world!\n"));
+    try uart.writer.print("result of calling syscall: {d}\n", .{res_hello});
+
+    try uart.writer.print("running illegal call\n", .{});
+    const res_illegal = syscall_illegal();
+    try uart.writer.print("result of illegal syscall: {d}\n", .{res_illegal});
+}
diff --git a/src/main.zig b/src/main.zig
@@ -1 +1 @@
-pub fn main() !void {}
+fn main() !void {}