multiboot: basic support for multiboot info

well, it's not trivial to use bios function because thanks to grub +
multiboot, we are already in protected mode when the startup code takes
control. Also the MB info is easier to play with than BIOS (or ACPI)

Signed-off-by: Tianhao Wang <shrik3@mailbox.org>

7 files changed, 150 insertions, 7 deletions

diff --git a/boot/startup-x86_64.s b/boot/startup-x86_64.s
index 448576a..6392d0f 100644
--- a/boot/startup-x86_64.s
+++ b/boot/startup-x86_64.s
@@ -11,7 +11,8 @@ MAX_MEM: equ 512
 [GLOBAL startup]
 [GLOBAL pml4]
 [GLOBAL pdp]
-
+[GLOBAL mb_magic]
+[GLOBAL mb_info_addr]
 ; functions from other parts of rustubs
 [EXTERN vectors_start]
 [EXTERN idt]
@@ -28,6 +29,12 @@ MAX_MEM: equ 512
 startup:
 	cld
 	cli
+	; with multiboot specs, grub initialzes the registers:
+	; EAX: magic value 0x2BADB002
+	; EBX: 32-bit physical address of the multiboot information struct
+	; we store them in global variables for future uses in rust code.
+	mov	   dword [mb_magic], eax
+	mov	   dword [mb_info_addr], ebx
 	; setup GDT by loading GDT descriptor
 	; see docs/x86_gdt.txt
 	lgdt   [gdt_80]
@@ -156,6 +163,11 @@ gdt_80:
 	dw	4*8 - 1   ; GDT limit=24, 4 GDT entries - 1
 	dq	gdt		  ; GDT address
 
+; multiboot info
+mb_magic:
+	dd 	0x00000000
+mb_info_addr:
+	dd 	0x00000000
 
 [SECTION .bss]
 
diff --git a/defs/x86_64-linker.ld b/defs/x86_64-linker.ld
index caecb48..39d8876 100644
--- a/defs/x86_64-linker.ld
+++ b/defs/x86_64-linker.ld
@@ -1,5 +1,10 @@
 /* defs for Multiboot headers */
+/* https://www.gnu.org/software/grub/manual/multiboot/multiboot.txt */
 MB_MAGIC = 0x1badb002;
+/* bit 0
+ * all boot modules loaded along with the operating system must be
+ * aligned on page (4KB) bit 1 must include mem_* structures
+ */
 MB_FLAGS = 0x3;
 MB_CHKSUM = 0x100000000 - (MB_MAGIC + MB_FLAGS);
 
@@ -9,7 +14,8 @@ SECTIONS
 
 	.boot :
 	{
-		header_start = .; LONG(MB_MAGIC)
+		header_start = .;
+		LONG(MB_MAGIC)
 		LONG(MB_FLAGS)
 		LONG(MB_CHKSUM)
 		LONG(0)
diff --git a/docs/multiboot.txt b/docs/multiboot.txt
new file mode 100644
index 0000000..4762e45
--- /dev/null
+++ b/docs/multiboot.txt
@@ -0,0 +1,45 @@
+https://www.gnu.org/software/grub/manual/multiboot/multiboot.txt
+
+        +-------------------+
+0       | flags             |    (required)
+        +-------------------+
+4       | mem_lower         |    (present if flags[0] is set)
+8       | mem_upper         |    (present if flags[0] is set)
+        +-------------------+
+12      | boot_device       |    (present if flags[1] is set)
+        +-------------------+
+16      | cmdline           |    (present if flags[2] is set)
+        +-------------------+
+20      | mods_count        |    (present if flags[3] is set)
+24      | mods_addr         |    (present if flags[3] is set)
+        +-------------------+
+28 - 40 | syms              |    (present if flags[4] or
+        |                   |                flags[5] is set)
+        +-------------------+
+44      | mmap_length       |    (present if flags[6] is set)
+48      | mmap_addr         |    (present if flags[6] is set)
+        +-------------------+
+52      | drives_length     |    (present if flags[7] is set)
+56      | drives_addr       |    (present if flags[7] is set)
+        +-------------------+
+60      | config_table      |    (present if flags[8] is set)
+        +-------------------+
+64      | boot_loader_name  |    (present if flags[9] is set)
+        +-------------------+
+68      | apm_table         |    (present if flags[10] is set)
+        +-------------------+
+72      | vbe_control_info  |    (present if flags[11] is set)
+76      | vbe_mode_info     |
+80      | vbe_mode          |
+82      | vbe_interface_seg |
+84      | vbe_interface_off |
+86      | vbe_interface_len |
+        +-------------------+
+88      | framebuffer_addr  |    (present if flags[12] is set)
+96      | framebuffer_pitch |
+100     | framebuffer_width |
+104     | framebuffer_height|
+108     | framebuffer_bpp   |
+109     | framebuffer_type  |
+110-115 | color_info        |
+        +-------------------+
diff --git a/src/arch/x86_64/asm/e820.s b/src/arch/x86_64/asm/e820.s
deleted file mode 100644
index 59c672a..0000000
--- a/src/arch/x86_64/asm/e820.s
+++ /dev/null
@@ -1,2 +0,0 @@
-; getting an E820 memory map, code from osdev wiki.
-; this only works in real mode ... how to do it in long mode?
diff --git a/src/lib.rs b/src/lib.rs
index 759c7c0..3651a81 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -8,13 +8,13 @@ mod ds;
 mod io;
 mod machine;
 mod mm;
+use crate::machine::key::Modifiers;
 use arch::x86_64::interrupt;
 use arch::x86_64::interrupt::pic_8259;
 use arch::x86_64::interrupt::pic_8259::PicDeviceInt;
 use core::panic::PanicInfo;
 use machine::cgascr::CGAScreen;
-
-use crate::machine::key::Modifiers;
+use machine::multiboot;
 
 #[cfg(not(test))]
 #[panic_handler]
@@ -28,14 +28,18 @@ pub extern "C" fn _entry() -> ! {
 	// init code
 	io::set_attr(0x1f);
 	io::clear_screen();
+	assert!(multiboot::check_magic(), "bad multiboot magic!");
+	let mbi = multiboot::get_mb_info().expect("bad multiboot info flags");
+	println!("MB INFO: {:#X?}", mbi);
 	interrupt::init();
 	pic_8259::allow(PicDeviceInt::KEYBOARD);
 	interrupt::interrupt_enable();
-	io::print_welcome();
 	let mut framemap = mm::pma::FMap::new();
 	framemap.init();
 	println!("Bitmap starting from : {:p}", framemap.bm.as_ptr());
 	println!("Skip first {} bytes", framemap.skip_byte);
+	println!("system init .. done!");
+	// io::print_welcome();
 
 	// busy loop query keyboard
 	loop {
diff --git a/src/machine/mod.rs b/src/machine/mod.rs
index 46ca961..a2cf730 100644
--- a/src/machine/mod.rs
+++ b/src/machine/mod.rs
@@ -4,5 +4,6 @@ pub mod interrupt;
 pub mod key;
 pub mod keyctrl;
 pub mod mem;
+pub mod multiboot;
 
 // TODO: this module *should* be arch independent.
diff --git a/src/machine/multiboot.rs b/src/machine/multiboot.rs
new file mode 100644
index 0000000..3056db3
--- /dev/null
+++ b/src/machine/multiboot.rs
@@ -0,0 +1,77 @@
+use crate::io::*;
+// provide functions to parse information provided by grub multiboot
+// see docs/multiboot.txt
+extern "C" {
+	static mb_magic: u32;
+	static mb_info_addr: u32;
+}
+
+#[repr(C)]
+#[repr(packed)]
+#[derive(Debug)]
+pub struct MultibootMmap {
+	pub size: u32,
+	pub addr: u64,
+	pub len: u64,
+	pub mtype: u32,
+}
+
+#[repr(C)]
+#[repr(packed)]
+#[derive(Debug, Clone, Copy)]
+pub struct MultibootInfo {
+	pub flags: MultibootInfoFlags,
+	pub mem_lower: u32,
+	pub mem_upper: u32,
+}
+
+use bitflags::bitflags;
+bitflags! {
+	/// the MultibootInfoFlags indicate which fields are valid in the MultibootInfo
+	/// atm we only need the MEM and MMAP flags for memory management info.
+	#[derive(Copy, Clone, Debug)]
+	pub struct MultibootInfoFlags: u32 {
+		const MEM           = 1 << 0;
+		const BOOT_DEVICE   = 1 << 1;
+		const CMDLINE       = 1 << 2;
+		const MODS          = 1 << 3;
+		const SYM_TBL       = 1 << 4;
+		const SHDR          = 1 << 5;
+		const MMAP          = 1 << 6;
+		const DRIVES        = 1 << 7;
+		const CONF_TBL      = 1 << 8;
+		const BL_NAME       = 1 << 9;
+		const APM_TBL       = 1 << 10;
+		const VBE_TBL       = 1 << 11;
+		const FRAMEBUFFER   = 1 << 12;
+	}
+}
+
+impl MultibootInfoFlags {
+	/// only 13 bits of the MB info flags are defined. The other flag bits must
+	/// be zero for the info block to be valie.
+	const VALID_MASK: u32 = 0x1FFF;
+
+	pub fn check_valid(&self) -> bool {
+		return self.bits() <= Self::VALID_MASK;
+	}
+}
+
+pub fn check_magic() -> bool {
+	return unsafe { mb_magic == 0x2BADB002 };
+}
+
+pub fn get_mb_info() -> Option<MultibootInfo> {
+	if !check_magic() {
+		return None;
+	}
+	let mbi = unsafe { *(mb_info_addr as *mut MultibootInfo) };
+	let flags = mbi.flags;
+	if !flags.check_valid() {
+		return None;
+	}
+	return Some(mbi);
+}
+
+// TODO: expand MultibootInfo struct defs if needed.
+