stage1: support 32-bit registers for BIOS calls

stage1/src/asm/int.s

@@ -9,7 +9,7 @@
  */
 /* fn __do_bios_int(regs: &mut BiosIntRegs) -> u8 */
 GLOBL __do_bios_int
-	pushal						// '1 v
+	pushal						// '1 (4 -> 36)
 
 	/*
 	 * Move the `regs` parameter into %ebp.  `call` pushes one longword
@@ -18,21 +18,24 @@ GLOBL __do_bios_int
 	 */
 	mov	36(%esp), %ebp
 	/* now load all registers with their desired values */
-	mov	(%ebp), %ax
+	mov	24(%ebp), %eax
-	mov	2(%ebp), %cx
+	push	%eax		/* %ds and %es */	//  '2 (36 -> 40)
-	mov	4(%ebp), %dx
+	mov	(%ebp), %eax
-	mov	6(%ebp), %bx
+	mov	4(%ebp), %ecx
-	mov	8(%ebp), %si
+	mov	8(%ebp), %edx
-	mov	10(%ebp), %di
+	mov	12(%ebp), %ebx
+	mov	16(%ebp), %esi
+	mov	20(%ebp), %edi
 
-	push	%ebp					//  '2 v
+	push	%eax					//   '3 (40 -> 44)
-
+	push	%edx					//    '4 (44 -> 48)
-	push	%eax					//   '3 v
-	push	%edx					//    '4 v
 	call	prot_to_real
 	.code16
-	pop	%edx					//    '4 ^
+	pop	%edx					//    '4 (44 <- 48)
-	pop	%eax					//   '3 ^
+	pop	%eax					//   '3 (40 <- 44)
+
+	pop	%es					//  '2 (38 <- 40)
+	pop	%ds					//  '2 (36 <- 38)
 
 	/* call that polymorphism! */
 	.byte 0xcd	/* opcode for `int imm8` */
@@ -41,27 +44,34 @@ GLOBL __bios_int_number, object
 
 	/* be careful not to touch EFLAGS now because that's our return value */
 
-	push	%eax					//   '3 v
+	push	%ds					//  '2 (36 -> 38)
-	push	%edx					//    '4 v
+	push	%es					//  '2 (38 -> 40)
-	pushfl						//     '5 v
+
+	push	%eax					//   '3 (40 -> 44)
+	push	%edx					//    '4 (44 -> 48)
+	pushfl						//     '5 (48 -> 52)
 	call	real_to_prot
 	.code32
-	popfl						//     '5 ^
+	popfl						//     '5 (48 <- 52)
-	pop	%edx					//    '4 ^
+	pop	%edx					//    '4 (44 <- 48)
-	pop	%eax					//   '3 ^
+	pop	%eax					//   '3 (40 <- 44)
 
-	pop	%ebp					//  '2 ^
+	/* the BIOS call might have trashed %ebp, restore it */
+	mov	40(%esp), %ebp
 
-	mov	%ax, (%ebp)
+	mov	%eax, (%ebp)
-	mov	%cx, 2(%ebp)
+	pop	%eax					//  '2 (36 <- 40)
-	mov	%dx, 4(%ebp)
+	mov	%eax, 24(%ebp)
-	mov	%bx, 6(%ebp)
+	mov	%ecx, 4(%ebp)
-	mov	%si, 8(%ebp)
+	mov	%edx, 8(%ebp)
-	mov	%di, 10(%ebp)
+	mov	%ebx, 12(%ebp)
+	mov	%esi, 16(%ebp)
+	mov	%edi, 20(%ebp)
 
-	popal						// '1 ^
+	popal						// '1 (4 <- 36)
 	setc	%al
 	/* this is not really required, but just in case */
 	movzbl	%al, %eax
-	ret
+
+	ret						//'0 (0 <- 4)
 END __do_bios_int

stage1/src/asm/mod.rs

@@ -18,11 +18,6 @@ include_asm!("common.s");
 
 // stage1 header containing its magic, size, checksum, and entry point
 include_asm!("header.s");
-extern "C" {
-    pub static _stage1_magic: u16;
-    pub static _stage1_len: u16;
-    pub static _stage1_csum: u32;
-}
 
 // main bootstrap routine that calls the rust entry point
 include_asm!("boot.s");
@@ -53,21 +48,22 @@ extern "C" {
 #[repr(C)]
 #[derive(Copy, Clone, Default)]
 pub struct BiosIntRegs {
-    pub ax: u16,
+    pub eax: u32,
-    pub cx: u16,
+    pub ecx: u32,
-    pub dx: u16,
+    pub edx: u32,
-    pub bx: u16,
+    pub ebx: u32,
-    pub si: u16,
+    pub esi: u32,
-    pub di: u16,
+    pub edi: u32,
+    pub ds: u16,
+    pub es: u16,
 }
 
 pub type BiosResult = Result<BiosIntRegs, BiosIntRegs>;
 
 /// Temporarily return to Real Mode and do a BIOS interrupt with the
-/// specified register values.  Returns `Ok` if the carry flag was
+/// specified register values.  Returns `Ok` if the carry flag was clear
-/// clear after the interrupt, and `Err` if it was set.  In either
+/// after the interrupt, and `Err` if it was set.  In either case, the
-/// case, the wrapped value contains the state of the registers after
+/// wrapped value contains the state of the registers after the interrupt.
-/// the interrupt.
 ///
 /// ## Safety
 ///