Use C for syscalls

Cargo.toml

@@ -12,3 +12,6 @@ lto = "thin"
 
 [dependencies]
 cstr_core = { version = "0.2.4", default-features = false, features = ["nightly"] }
+
+[build-dependencies]
+cc = "1.0.72"

build.rs

@@ -0,0 +1,8 @@
+fn main() {
+    println!("cargo:rerun-if-changed=src/syscalls.c");
+    cc::Build::new()
+        .file("src/syscalls.c")
+        .flag("-fno-PIC") // for some reason `pic(false)` doesn't work
+        .static_flag(true)
+        .compile("syscalls");
+}

src/lib.rs

@@ -1,22 +1,8 @@
-#![feature(asm)]
 #![no_std]
 
-macro_rules! syscall {
-    ($fn_no:literal) => {{
-        let mut res: i32 = $fn_no;
+mod sys;
 
-        asm!("int 0x40", inout("eax") res);
-        res
-    }};
-    ($fn_no:literal, $($reg:tt)*) => {{
-        let mut res: i32 = $fn_no;
-        asm!("int 0x40",
-            $($reg)*,
-            inout("eax") res,
-        );
-        res
-    }}
-}
+pub use sys::*;
 
 #[derive(Clone, Copy)]
 pub struct Color(u8, u8, u8);
@@ -29,9 +15,11 @@ impl Color {
     pub fn r(&self) -> u8 {
         self.0
     }
+
     pub fn g(&self) -> u8 {
         self.1
     }
+
     pub fn b(&self) -> u8 {
         self.2
     }
@@ -41,11 +29,6 @@ impl Color {
     }
 }
 
-#[inline]
-pub unsafe fn start_window_draw() {
-    syscall!(12, in("ebx") 1);
-}
-
 pub struct Dot {
     pub x: u32,
     pub y: u32,
@@ -66,17 +49,21 @@ pub struct WindowParams<'a> {
     pub title: Option<&'a cstr_core::CStr>,
 }
 
-#[inline]
-pub unsafe fn define_window(start: Dot, width: u32, height: u32, params: WindowParams<'_>) {
+pub fn define_window(start: Dot, width: u32, height: u32, params: WindowParams<'_>) {
     const RELATIVE_FLAG: u32 = 0x20;
-    syscall!(
-        0,
-        in("ebx") start.x * 65536 + width,
-        in("ecx") start.y * 65536 + height,
-        in("edx") params.color.as_rgb_val() |
-            (RELATIVE_FLAG | (params.title.is_some() as u32) << 4 | params.kind as u32) << 24,
-        in("edi") params.title.map(|s| s.as_ptr()).unwrap_or_else(core::ptr::null)
-    );
+
+    unsafe {
+        sys::define_window(
+            start.x * 65536 + width,
+            start.y * 65536 + height,
+            params.color.as_rgb_val()
+                | (RELATIVE_FLAG | (params.title.is_some() as u32) << 4 | params.kind as u32) << 24,
+            params
+                .title
+                .map(|s| s.as_ptr())
+                .unwrap_or_else(core::ptr::null) as u32,
+        );
+    }
 }
 
 pub struct WindowTextParams<'a> {
@@ -85,30 +72,23 @@ pub struct WindowTextParams<'a> {
     pub bg_color: Option<Color>,
 }
 
-#[inline]
-pub unsafe fn display_message(start: Dot, params: WindowTextParams<'_>) {
+pub fn display_message(start: Dot, params: WindowTextParams<'_>) {
     const UTF8_FLAG: u32 = 0b0011_0000 << 24;
     const BG_FLAG: u32 = 0b0100_0000 << 24;
-    // XXX: llvm uses esi internally for x86-32
-    //      hope we're lucky enough so it won't be overwritten.
-    asm!("mov esi, {}", in(reg) params.text.len());
-    syscall!(
-        4,
-        in("ebx") start.x * 65536 + start.y,
-        in("ecx") params.color.as_rgb_val() | BG_FLAG * params.bg_color.is_some() as u32 | UTF8_FLAG,
-        in("edx") params.text.as_ptr()
-    );
-}
 
-#[inline]
-pub unsafe fn end_window_draw() {
-    syscall!(12, in("ebx") 2);
+    unsafe {
+        sys::display_message(
+            start.x * 65536 + start.y,
+            params.color.as_rgb_val() | BG_FLAG * params.bg_color.is_some() as u32 | UTF8_FLAG,
+            params.text.as_ptr() as u32,
+            0,
+            params.text.len() as u32,
+        );
+    }
 }
 
 pub fn exit() -> ! {
-    unsafe { syscall!(-1) };
-
-    unsafe { core::hint::unreachable_unchecked() }
+    unsafe { sys::exit() }
 }
 
 #[panic_handler]
@@ -122,18 +102,16 @@ pub enum Event {
     KeyPress,
 }
 
-#[inline]
 pub fn fetch_event() -> Option<Event> {
-    match unsafe { syscall!(10) } {
+    match unsafe { sys::wait_event() } {
         1 => Some(Event::Redraw),
         2 => Some(Event::KeyPress),
         _ => None,
     }
 }
 
-#[inline]
 pub fn fetch_key() -> Option<u8> {
-    let res = unsafe { syscall!(2) };
+    let res = unsafe { sys::pressed_key() };
     if res == 1 {
         None
     } else {

src/main.rs

@@ -1,4 +1,3 @@
-#![feature(asm)]
 #![no_std]
 #![no_main]
 

src/sys.rs

@@ -0,0 +1,16 @@
+#[link(name = "syscalls")]
+extern "C" {
+    pub fn start_window_draw();
+
+    pub fn end_window_draw();
+
+    #[link_name = "exit0"]
+    pub fn exit() -> !;
+
+    pub fn define_window(ebx: u32, ecx: u32, edx: u32, edi: u32);
+    pub fn display_message(ebx: u32, ecx: u32, edx: u32, edi: u32, esi: u32);
+
+    pub fn wait_event() -> u32;
+
+    pub fn pressed_key() -> u32;
+}

src/syscalls.c

@@ -0,0 +1,54 @@
+void start_window_draw() {
+    __asm__ volatile (
+        "int $0x40;"
+        :: "a"(12), "b"(1)
+    );
+}
+
+void end_window_draw() {
+    __asm__ volatile (
+        "int $0x40;"
+        :: "a"(12), "b"(2)
+    );
+}
+
+void exit0() {
+    __asm__ volatile (
+        "int $0x40;"
+        :: "a"(-1)
+    );
+}
+
+void define_window(unsigned ebx, unsigned ecx, unsigned edx, unsigned edi) {
+    __asm__ volatile (
+        "int $0x40;"
+        :: "a"(0), "b"(ebx), "c"(ecx), "d"(edx), "D"(edi)
+        : "memory"
+    );
+}
+
+void display_message(unsigned ebx, unsigned ecx, unsigned edx, unsigned edi, unsigned esi) {
+    __asm__ volatile (
+        "int $0x40;"
+        :: "a"(4), "b"(ebx), "c"(ecx), "d"(edx), "D"(edi), "S"(esi)
+        : "memory"
+    );
+}
+
+unsigned wait_event() {
+    unsigned res;
+    __asm__ volatile (
+        "int $0x40;"
+        : "=r"(res) : "a"(10)
+    );
+    return res;
+}
+
+unsigned pressed_key() {
+    unsigned res;
+    __asm__ volatile (
+        "int $0x40;"
+        : "=r"(res) : "a"(2)
+    );
+    return res;
+}