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// Copyright 2020 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
use data_model::DataInit;
/// SDT represents for System Description Table. The structure SDT is a
/// generic format for creating various ACPI tables like DSDT/FADT/MADT.
pub struct SDT {
data: Vec<u8>,
}
const HEADER_LEN: u32 = 36;
const LENGTH_OFFSET: usize = 4;
const CHECKSUM_OFFSET: usize = 9;
#[allow(clippy::len_without_is_empty)]
impl SDT {
/// Set up the ACPI table header at the front of the SDT.
/// The arguments correspond to the elements in the ACPI
/// table headers.
pub fn new(
signature: [u8; 4],
length: u32,
revision: u8,
oem_id: [u8; 6],
oem_table: [u8; 8],
oem_revision: u32,
) -> Self {
// The length represents for the length of the entire table
// which includes this header. And the header is 36 bytes, so
// lenght should be >= 36. For the case who gives a number less
// than the header len, use the header len directly.
let len: u32 = if length < HEADER_LEN {
HEADER_LEN
} else {
length
};
let mut data = Vec::with_capacity(length as usize);
data.extend_from_slice(&signature);
data.extend_from_slice(&len.to_le_bytes());
data.push(revision);
data.push(0); // checksum
data.extend_from_slice(&oem_id);
data.extend_from_slice(&oem_table);
data.extend_from_slice(&oem_revision.to_le_bytes());
data.extend_from_slice(b"CROS");
data.extend_from_slice(&0u32.to_le_bytes());
data.resize(length as usize, 0);
let mut sdt = SDT { data };
sdt.update_checksum();
sdt
}
fn update_checksum(&mut self) {
self.data[CHECKSUM_OFFSET] = 0;
let checksum = super::generate_checksum(self.data.as_slice());
self.data[CHECKSUM_OFFSET] = checksum;
}
pub fn as_slice(&self) -> &[u8] {
&self.data.as_slice()
}
pub fn append<T: DataInit>(&mut self, value: T) {
self.data.extend_from_slice(value.as_slice());
self.write(LENGTH_OFFSET, self.data.len() as u32);
}
/// Write a value at the given offset
pub fn write<T: DataInit>(&mut self, offset: usize, value: T) {
let value_len = std::mem::size_of::<T>();
if (offset + value_len) > self.data.len() {
return;
}
self.data[offset..offset + value_len].copy_from_slice(&value.as_slice());
self.update_checksum();
}
pub fn len(&self) -> usize {
self.data.len()
}
}
#[cfg(test)]
mod tests {
use super::SDT;
#[test]
fn test_sdt() {
let mut sdt = SDT::new(*b"TEST", 40, 1, *b"CROSVM", *b"TESTTEST", 1);
let sum: u8 = sdt
.as_slice()
.iter()
.fold(0u8, |acc, x| acc.wrapping_add(*x));
assert_eq!(sum, 0);
sdt.write(36, 0x12345678 as u32);
let sum: u8 = sdt
.as_slice()
.iter()
.fold(0u8, |acc, x| acc.wrapping_add(*x));
assert_eq!(sum, 0);
}
}
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