Simplify 32-bit x86 assembly

src/i686.asm

@@ -1,42 +0,0 @@
-BITS 32
-
-section .text
-
-global ustart
-extern start
-
-ustart:
-  ; Setup a stack.
-  mov eax, 0x21000384 ; SYS_CLASS_FILE+SYS_ARG_SLICE+SYS_MMAP
-  mov ebx, 0xFFFFFFFF ; dummy `fd`, indicates anonymous map
-  mov ecx, map ; pointer to Map struct
-  mov edx, map_size ; size of Map struct
-  int 0x80
-
-  ; Test for success (nonzero value).
-  cmp eax, 0
-  jg .continue
-  ; (failure)
-  ud2
-.continue:
-  ; Subtract 16 since all instructions seem to hate non-canonical ESP values :)
-  lea esp, [eax+size-16]
-  mov ebp, esp
-
-  ; Stack has the same alignment as `size`.
-  call start
-  ; `start` must never return.
-  ud2
-
-section .rodata
-map:
-  dd 0 ; offset (unused)
-  dd size
-  dd flags
-  dd address - size
-
-map_size equ $ - map
-
-size equ 65536 ; 64 KiB
-address equ 0x80000000 ; highest possible (normal) user address, why not
-flags equ 0x0006000E ; PROT_READ+PROT_WRITE, MAP_PRIVATE+MAP_FIXED_NOREPLACE

src/i686.rs

@@ -0,0 +1,53 @@
+use core::mem;
+use syscall::{
+    data::Map,
+    flag::MapFlags,
+    number::SYS_FMAP,
+};
+
+const STACK_SIZE: usize = 64 * 1024; // 64 KiB
+static MAP: Map = Map {
+    offset: 0,
+    size: STACK_SIZE,
+    flags: MapFlags::PROT_READ
+            .union(MapFlags::PROT_WRITE)
+            .union(MapFlags::MAP_PRIVATE)
+            .union(MapFlags::MAP_FIXED_NOREPLACE),
+    address: 0x8000_0000 - STACK_SIZE, // highest possible user address
+};
+
+#[naked]
+#[no_mangle]
+pub unsafe extern "C" fn ustart() {
+    core::arch::asm!(
+        "
+        # Setup a stack.
+        mov eax, {number}
+        mov ebx, {fd}
+        lea ecx, {map} # pointer to Map struct
+        mov edx, {map_size} # size of Map struct
+        int 0x80
+
+        # Test for success (nonzero value).
+        cmp eax, 0
+        jg 1f
+        # (failure)
+        ud2
+        1:
+        # Subtract 16 since all instructions seem to hate non-canonical ESP values :)
+        lea esp, [eax+{stack_size}-16]
+        mov ebp, esp
+
+        # Stack has the same alignment as `size`.
+        call start
+        # `start` must never return.
+        ud2
+        ",
+        fd = const usize::MAX, // dummy fd indicates anonymous map
+        map = sym MAP,
+        map_size = const mem::size_of::<Map>(),
+        number = const SYS_FMAP,
+        stack_size = const STACK_SIZE,
+        options(noreturn),
+    );
+}