stage1: implement bios disk access
parent
68f56352ad
commit
4c8a00abc4
@ -0,0 +1,19 @@
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.section .bss
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.align 8
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GLOBL dap
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.skip 0x10
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END dap
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.align 8
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GLOBL drive_parms
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.skip 0x1a
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END drive_parms
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/*
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* According to the GRUB:
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* <http://git.savannah.gnu.org/cgit/grub.git/tree/include/grub/i386/pc/biosdisk.h?h=grub-2.06#n76>
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* the ThinkPad X20 BIOS ignores the `size` member and writes
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* garbage data out of bounds on the drive parameter structure
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*/
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.skip 0x10
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@ -0,0 +1,107 @@
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use core::mem::size_of;
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use core::ptr::{read_volatile, write_volatile};
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use core::sync::atomic::{compiler_fence, Ordering};
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use crate::asm::{dap, do_bios_int, drive_parms, BiosIntRegs};
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#[repr(C, packed)]
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pub struct DriveParams {
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size: u16,
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flags: u16,
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cylinders: u32,
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heads: u32,
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sectors_per_track: u32,
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total_sectors: u64,
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sector_size: u16,
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}
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pub fn get_sector_size(drive_number: u8) -> Option<u16> {
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// rustc whines about unaligned members due to repr(packed)
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// but we know FOR SURE that everything is aligned properly
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unsafe {
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let drive_params_ptr = (&mut drive_parms) as *mut DriveParams;
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write_volatile(
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drive_params_ptr as *mut u16,
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size_of::<DriveParams>() as u16,
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);
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let regs = do_bios_int(
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0x13,
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BiosIntRegs {
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eax: 0x4800,
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edx: drive_number as u32,
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esi: drive_params_ptr as u32,
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..Default::default()
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},
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)
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.ok()?;
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if regs.eax & 0xff00 == 0 {
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Some(read_volatile(
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(drive_params_ptr as *const u8).add(16) as *const u16
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))
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} else {
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None
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}
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}
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}
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#[repr(C, packed)]
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pub struct DiskAddressPacket {
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size: u8,
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_rsvd: u8,
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sector_count: u16,
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buffer_offset: u16,
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buffer_segment: u16,
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lba: u64,
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}
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/// Read one logical sector from a disk using BIOS int13/42.
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///
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/// ## Safety
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///
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/// Since this uses a BIOS call, there is no real safety here.
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/// The best approximation to safety requires the following:
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///
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/// - `dest` MUST have capacity for at least the size of a sector.
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/// - If the sector size is a power of 2, `dest` MUST be aligned to a sector size.
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/// - If the sector size is not a power of 2, `dest` MUST be aligned to the next
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/// power of 2 greater than the sector size.
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/// - `dest` SHOULD be aligned to at least 64 K.
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/// - `dest` MUST be in low memory (i.e. below 1 M).
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/// - `drive_number` MUST be a valid BIOS drive number.
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/// - `lba` SHOULD fit into 48 bits.
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pub unsafe fn read_lba(dest: *mut u8, drive_number: u8, lba: u64) -> Result<(), u8> {
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debug_assert!((dest as usize) >= (1 << 16));
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debug_assert!((dest as usize) < (1 << 20));
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let dap_ptr = (&mut dap) as *mut DiskAddressPacket;
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dap = DiskAddressPacket {
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size: size_of::<DiskAddressPacket>() as u8,
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_rsvd: 0,
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sector_count: 1,
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buffer_offset: ((dest as usize) & 0xf) as u16,
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buffer_segment: ((dest as usize) >> 4) as u16,
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lba,
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};
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compiler_fence(Ordering::SeqCst);
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let ah = do_bios_int(
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0x13,
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BiosIntRegs {
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eax: 0x4200,
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edx: drive_number as u32,
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esi: dap_ptr as u32,
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..Default::default()
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},
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)
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.map(|regs| (regs.eax >> 8) as u8)
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.map_err(|regs| (regs.eax >> 8) as u8)?;
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if ah == 0 {
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Ok(())
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} else {
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Err(ah)
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}
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}
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