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>

2 files changed, 78 insertions, 0 deletions

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.
+