stage1: fix more mode switching bugs
BIOS calls from Rust should work now.
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2585C2DC6D79B485
6 changed files with 79 additions and 62 deletions
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@ -15,7 +15,7 @@ repository = "https://git.bsd.gay/fef/bussy"
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[profile.dev]
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panic = "abort"
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opt-level = "s"
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opt-level = 0
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lto = false
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codegen-units = 1
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debug = true
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@ -77,14 +77,18 @@ GLOBL _boot
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a20_enabled:
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/* int13/00 RESET DISK SYSTEM */
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mov $0, %ah
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mov boot_drive, %dl
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int $0x13
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/* make absolutely sure that %sp is aligned */
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and $0xfffc, %sp
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and $0xfffc, %esp
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/* make real_to_prot return directly to rust */
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pushw $main
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jmp real_to_prot
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call real_to_prot
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.code32
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/* initialize an empty stack frame */
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xor %ebp, %ebp
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jmp main
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.code16
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err_no_a20:
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mov $msg_err_no_a20, %ax
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@ -7,12 +7,17 @@
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* goes back to Protected Mode again. Furthermore, the interrupt
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* number is written ahead of time by the callee.
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*/
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/* fn __do_bios_int(regs: &mut BiosIntRegs) -> u8 */
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GLOBL __do_bios_int
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push %ebp /* '1 v */
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mov %esp, %ebp
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pushal /* '2 v */
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pushal // '1 v
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mov 8(%ebp), %ebp
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/*
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* Move the `regs` parameter into %ebp. `call` pushes one longword
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* (4 bytes) for the return address, then the `pushal` above pushes
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* 8 longwords (32 bytes), so the pointer is at offset 36.
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*/
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mov 36(%esp), %ebp
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/* now load all registers with their desired values */
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mov (%ebp), %ax
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mov 2(%ebp), %cx
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mov 4(%ebp), %dx
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@ -20,30 +25,32 @@ GLOBL __do_bios_int
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mov 8(%ebp), %si
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mov 10(%ebp), %di
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push %ebp /* '3 v */
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push %ebp // '2 v
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push %eax /* '4 v */
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push %edx /* '5 v */
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push %eax // '3 v
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push %edx // '4 v
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call prot_to_real
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.code16
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pop %edx /* '5 ^ */
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pop %eax /* '4 ^ */
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pop %edx // '4 ^
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pop %eax // '3 ^
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/* call that polymorphism! */
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.byte 0xcd /* opcode for `int imm8` */
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GLOBL __bios_int_number, object
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.byte 0x18 /* this is the imm8 */
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.byte 0x18 /* this is the imm8 (overwritten by caller) */
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push %eax /* '4 v */
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push %edx /* '5 v */
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pushfl /* '6 v */
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/* be careful not to touch EFLAGS now because that's our return value */
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push %eax // '3 v
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push %edx // '4 v
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pushfl // '5 v
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call real_to_prot
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.code32
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popfl /* '6 ^ */
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pop %edx /* '5 ^ */
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pop %eax /* '4 ^ */
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popfl // '5 ^
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pop %edx // '4 ^
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pop %eax // '3 ^
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pop %ebp /* '3 ^ */
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pop %ebp // '2 ^
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mov %ax, (%ebp)
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mov %cx, 2(%ebp)
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@ -51,11 +58,10 @@ GLOBL __bios_int_number, object
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mov %bx, 6(%ebp)
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mov %si, 8(%ebp)
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mov %di, 10(%ebp)
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mov %al, 12(%ebp)
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popal /* '2 ^ */
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popal // '1 ^
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setc %al
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/* this is not really required, but just in case */
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movzbl %al, %eax
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pop %ebx /* '1 ^ */
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ret
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END __do_bios_int
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@ -1,7 +1,11 @@
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use core::ptr::write_volatile;
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// XXX This doesn't emit proper debug symbols for assembly sources
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macro_rules! include_asm {
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($name:literal) => {
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::core::arch::global_asm!(
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::core::concat!(".file \"", $name, "\""), // for better debugging
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::core::concat!(".file \"", $name, "\""),
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::core::include_str!($name),
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::core::concat!(".file \"", ::core::file!(), "\""),
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options(raw, att_syntax),
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@ -9,7 +13,7 @@ macro_rules! include_asm {
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};
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}
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// common macros for the other assembly files, keep at the beginning
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// common macros for the other assembly files, keep this at the beginning
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include_asm!("common.s");
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// stage1 header containing its magic, size, checksum, and entry point
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@ -20,15 +24,17 @@ extern "C" {
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pub static _stage1_csum: u32;
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}
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// main bootstrap routine that calls the rust entry point
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include_asm!("boot.s");
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// switch between real and protected mode
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include_asm!("pmode.s");
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// do bios interrupts from protected mode
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include_asm!("int.s");
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extern "C" {
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/// Temporarily return to Real Mode and do a BIOS interrupt with the
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/// specified register values. Returns the value of the carry flag
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/// (`true` if CF=1, `false` if CF=0).
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/// specified register values. Returns the value of the carry flag.
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///
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/// ## Safety
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///
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@ -62,9 +68,13 @@ pub type BiosResult = Result<BiosIntRegs, BiosIntRegs>;
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/// clear after the interrupt, and `Err` if it was set. In either
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/// case, the wrapped value contains the state of the registers after
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/// the interrupt.
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///
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/// ## Safety
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///
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/// This is horrendously unsafe and there is nothing you can do about it.
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pub unsafe fn do_bios_int(number: u8, mut regs: BiosIntRegs) -> BiosResult {
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// this might be mildly unsafe
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__bios_int_number = number;
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write_volatile(&mut __bios_int_number, number);
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let cf = __do_bios_int(&mut regs);
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if cf == 0 {
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Ok(regs)
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@ -6,13 +6,17 @@
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* Intel(R) 64 and IA-32 Architectures Software Developer's Manual
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* vol. 3A, chapter 9.9.1. Lines prefixed with '>' are direct quotes.
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* Annotations within those lines are enclosed in [square brackets].
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* Must be called in Real Mode, returns in Protected Mode.
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*
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* ATTENTION: This messes with the stack! Before calling this, you
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* MUST ensure that the stack pointer is aligned to 4 bytes (that is,
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* *before* the call to this subroutine pushes the return address).
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* ATTENTION: This messes with the stack! Before calling this function,
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* you MUST ensure that %sp is aligned to 4 bytes. The stack pointer
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* will be automatically translated to its linear address equivalent
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* (i.e. %esp = %ss * 0x10 + %sp), however, it DOES NOT touch %ebp.
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*
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* ATTENTION: This trashes registers %ax and %dx, as well as EFLAGS.
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* ATTENTION: You MUST call this from real mode (.code16), and any code
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* following the call MUST be for 32-bit protected mode (.code32).
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*
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* ATTENTION: This trashes %eax, %edx, eflags, and ALL segment registers.
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* Furthermore, it clears the IF flag (i.e. it disables interrupts).
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*
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> Intel 64 and IA-32 processors have slightly different requirements
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> for switching to protected mode. To ensure upwards and downwards
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@ -64,11 +68,10 @@ GLOBL real_to_prot
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> jump or call to the next instruction in the instruction stram.)
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*/
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ljmpl $0x08, $1f
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.code32
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1: .code32
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/* recompute the (now linear) stack address */
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1: xor %eax, %eax
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xor %eax, %eax
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mov %ss, %ax
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shl $4, %eax
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add %eax, %esp
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@ -87,20 +90,11 @@ GLOBL real_to_prot
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> 7. If a local descriptor table is going to be used [...]
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*
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* No.
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*/
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/*
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> 8. Execute the LTR instruction to load the task register with
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> a segment selector to the initial protected-mode task or to
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> a writable area of memory that can be used to store TSS
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> information on a task switch.
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*
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* If you insist ...
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*/
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//mov $0x28, %ax
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//ltr %ax /* offset 0x28 into GDT, 32-bit TSS */
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/*
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> 8. Execute the LTR instruction [...]
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*
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* We don't do tasks here
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*
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> 9. After entering protected mode, the segment registers continue
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> to hold the contents they had in real-address mode.
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> The JMP or CALL instruction in step 4 resets the CS register.
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@ -252,8 +246,9 @@ GLOBL prot_to_real
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out %al, $0x70
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in $0x71, %al
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jmpw *%dx
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jmp *%dx
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END prot_to_real
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.code32
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.data
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@ -265,7 +260,8 @@ END gdtr
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/*
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* This figure is based on the Intel SDM vol. 3A, fig. 5-1.
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* Reordered so that the structure matches the definition below.
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* Reordered so that the structure matches the definition below, i.e.
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* little endian byte order (bits WITHIN the bytes are big endian).
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*
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* | 0 1 | 2 3 |
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* +-------------------------------+-------------------------------+
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@ -322,23 +318,18 @@ END gdt
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.section .bss
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/* dummy IDT Register value (0 entries) */
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/* dummy IDT Register value (0 entries) */
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LOCAL prot_idtr
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.word 0
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.long 0
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END prot_idtr
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/* this is where we store the Real Mode IDT for later BIOS calls */
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/* this is where we store the Real Mode IDT for later BIOS calls */
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LOCAL real_idtr
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.word 0
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.long 0
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END real_idtr
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/* stores whether real mode sp was aligned */
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LOCAL real_sp_offset
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.word 0
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END real_sp_offset
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LOCAL real_ss
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.word 0
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END real_ss
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@ -1,11 +1,13 @@
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#![no_std]
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#![no_main]
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use crate::asm::{do_bios_int, BiosIntRegs};
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use core::arch::asm;
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use core::panic::PanicInfo;
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mod asm;
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/// Collection of all assembly sources and symbols they expose
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pub mod asm;
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use asm::{do_bios_int, BiosIntRegs};
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#[no_mangle]
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pub extern "C" fn main() -> ! {
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@ -25,6 +27,10 @@ pub fn rust_panic(_info: &PanicInfo) -> ! {
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pub fn print(s: &str) {
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for b in s.bytes() {
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if b == b'\0' {
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break;
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}
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let regs = BiosIntRegs {
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ax: 0x0e00 | b as u16,
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bx: 0x0001,
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