boot: Add structures for Info, E820, and Params

To support multiple boot protocols, we need a common abstraction for
the information given in a boot protocol. This is the Info trait. This
also requires adding a common E820Entry structure, so we can get the
memory map.

We also add a boot::Params structure (i.e. the Linux Zeropage) to make
reading/writing the structure easier. This will let us avoid needing to
hardcode struct offsets.

The layout for these structures is taken from the Kernel's
    arch/x86/include/uapi/asm/bootparam.h

Signed-off-by: Joe Richey <joerichey@google.com>

Author: josephlr

src/boot.rs

@@ -0,0 +1,187 @@
+use core::mem;
+
+use crate::common;
+
+// Common data needed for all boot paths
+pub trait Info {
+    // Starting address of the Root System Descriptor Pointer
+    fn rsdp_addr(&self) -> u64;
+    // The kernel command line (not including null terminator)
+    fn cmdline(&self) -> &[u8];
+    // Methods to access the E820 Memory map
+    fn num_entries(&self) -> u8;
+    fn entry(&self, idx: u8) -> E820Entry;
+}
+
+#[derive(Clone, Copy, Debug)]
+#[repr(C, packed)]
+pub struct E820Entry {
+    pub addr: u64,
+    pub size: u64,
+    pub entry_type: u32,
+}
+
+impl E820Entry {
+    pub const RAM_TYPE: u32 = 1;
+}
+
+// The so-called "zeropage"
+#[derive(Clone, Copy)]
+#[repr(C, packed)]
+pub struct Params {
+    screen_info: ScreenInfo,        // 0x000
+    apm_bios_info: ApmBiosInfo,     // 0x040
+    _pad2: [u8; 4],                 // 0x054
+    tboot_addr: u64,                // 0x058
+    ist_info: IstInfo,              // 0x060
+    pub acpi_rsdp_addr: u64,        // 0x070
+    _pad3: [u8; 8],                 // 0x078
+    hd0_info: HdInfo,               // 0x080 - obsolete
+    hd1_info: HdInfo,               // 0x090 - obsolete
+    sys_desc_table: SysDescTable,   // 0x0a0 - obsolete
+    olpc_ofw_header: OlpcOfwHeader, // 0x0b0
+    ext_ramdisk_image: u32,         // 0x0c0
+    ext_ramdisk_size: u32,          // 0x0c4
+    ext_cmd_line_ptr: u32,          // 0x0c8
+    _pad4: [u8; 0x74],              // 0x0cc
+    edd_info: EdidInfo,             // 0x140
+    efi_info: EfiInfo,              // 0x1c0
+    alt_mem_k: u32,                 // 0x1e0
+    scratch: u32,                   // 0x1e4
+    e820_entries: u8,               // 0x1e8
+    eddbuf_entries: u8,             // 0x1e9
+    edd_mbr_sig_buf_entries: u8,    // 0x1ea
+    kbd_status: u8,                 // 0x1eb
+    secure_boot: u8,                // 0x1ec
+    _pad5: [u8; 2],                 // 0x1ed
+    sentinel: u8,                   // 0x1ef
+    _pad6: [u8; 1],                 // 0x1f0
+    pub hdr: Header,                // 0x1f1
+    _pad7: [u8; 0x290 - HEADER_END],
+    edd_mbr_sig_buffer: [u32; 16], // 0x290
+    e820_table: [E820Entry; 128],  // 0x2d0
+    _pad8: [u8; 0x30],             // 0xcd0
+    eddbuf: [EddInfo; 6],          // 0xd00
+    _pad9: [u8; 0x114],            // 0xeec
+}
+
+impl Default for Params {
+    fn default() -> Self {
+        // SAFETY: Struct consists entirely of primitive integral types.
+        unsafe { mem::zeroed() }
+    }
+}
+
+impl Params {
+    pub fn set_entries(&mut self, info: &dyn Info) {
+        self.e820_entries = info.num_entries();
+        for i in 0..self.e820_entries {
+            self.e820_table[i as usize] = info.entry(i);
+        }
+    }
+}
+
+impl Info for Params {
+    fn rsdp_addr(&self) -> u64 {
+        self.acpi_rsdp_addr
+    }
+    fn cmdline(&self) -> &[u8] {
+        unsafe { common::from_cstring(self.hdr.cmd_line_ptr as u64) }
+    }
+    fn num_entries(&self) -> u8 {
+        self.e820_entries
+    }
+    fn entry(&self, idx: u8) -> E820Entry {
+        assert!(idx < self.num_entries());
+        self.e820_table[idx as usize]
+    }
+}
+
+const HEADER_START: usize = 0x1f1;
+const HEADER_END: usize = HEADER_START + mem::size_of::<Header>();
+
+#[derive(Clone, Copy, Debug)]
+#[repr(C, packed)]
+pub struct Header {
+    pub setup_sects: u8,
+    pub root_flags: u16,
+    pub syssize: u32,
+    pub ram_size: u16,
+    pub vid_mode: u16,
+    pub root_dev: u16,
+    pub boot_flag: u16,
+    pub jump: u16,
+    pub header: [u8; 4],
+    pub version: u16,
+    pub realmode_swtch: u32,
+    pub start_sys_seg: u16,
+    pub kernel_version: u16,
+    pub type_of_loader: u8,
+    pub loadflags: u8,
+    pub setup_move_size: u16,
+    pub code32_start: u32,
+    pub ramdisk_image: u32,
+    pub ramdisk_size: u32,
+    pub bootsect_kludge: u32,
+    pub heap_end_ptr: u16,
+    pub ext_loader_ver: u8,
+    pub ext_loader_type: u8,
+    pub cmd_line_ptr: u32,
+    pub initrd_addr_max: u32,
+    pub kernel_alignment: u32,
+    pub relocatable_kernel: u8,
+    pub min_alignment: u8,
+    pub xloadflags: u16,
+    pub cmdline_size: u32,
+    pub hardware_subarch: u32,
+    pub hardware_subarch_data: u64,
+    pub payload_offset: u32,
+    pub payload_length: u32,
+    pub setup_data: u64,
+    pub pref_address: u64,
+    pub init_size: u32,
+    pub handover_offset: u32,
+}
+
+// Right now the stucts below are unused, so we only need them to be the correct
+// size. Update test_size_and_offset if a struct's real definition is added.
+#[derive(Clone, Copy)]
+#[repr(C, packed)]
+struct ScreenInfo([u8; 0x40]);
+#[derive(Clone, Copy)]
+#[repr(C, packed)]
+struct ApmBiosInfo([u8; 0x14]);
+#[derive(Clone, Copy)]
+#[repr(C, packed)]
+struct IstInfo([u8; 0x10]);
+#[derive(Clone, Copy)]
+#[repr(C, packed)]
+struct HdInfo([u8; 0x10]);
+#[derive(Clone, Copy)]
+#[repr(C, packed)]
+struct SysDescTable([u8; 0x10]);
+#[derive(Clone, Copy)]
+#[repr(C, packed)]
+struct OlpcOfwHeader([u8; 0x10]);
+#[derive(Clone, Copy)]
+#[repr(C, packed)]
+struct EdidInfo([u8; 0x80]);
+#[derive(Clone, Copy)]
+#[repr(C, packed)]
+struct EfiInfo([u8; 0x20]);
+#[derive(Clone, Copy)]
+#[repr(C, packed)]
+struct EddInfo([u8; 0x52]);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_size_and_offset() {
+        assert_eq!(mem::size_of::<Header>(), 119);
+        assert_eq!(mem::size_of::<E820Entry>(), 20);
+        assert_eq!(mem::size_of::<Params>(), 4096);
+
+        assert_eq!(offset_of!(Params, hdr), HEADER_START);
+    }
+}

src/main.rs

@@ -34,6 +34,7 @@ mod common;
 #[cfg(not(test))]
 mod asm;
 mod block;
+mod boot;
 mod bzimage;
 mod efi;
 mod fat;