acpi_tables/
sdt.rs

1// Copyright 2020 The ChromiumOS Authors
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5use std::fs::File;
6use std::io::ErrorKind;
7use std::io::Read;
8use std::io::Result;
9use std::path::Path;
10
11use zerocopy::FromBytes;
12use zerocopy::Immutable;
13use zerocopy::IntoBytes;
14
15/// SDT represents for System Description Table. The structure SDT is a
16/// generic format for creating various ACPI tables like DSDT/FADT/MADT.
17#[derive(Clone)]
18pub struct SDT {
19    data: Vec<u8>,
20}
21
22pub const HEADER_LEN: u32 = 36;
23const LENGTH_OFFSET: usize = 4;
24const CHECKSUM_OFFSET: usize = 9;
25
26#[allow(clippy::len_without_is_empty)]
27impl SDT {
28    /// Set up the ACPI table header at the front of the SDT.
29    /// The arguments correspond to the elements in the ACPI
30    /// table headers.
31    pub fn new(
32        signature: [u8; 4],
33        length: u32,
34        revision: u8,
35        oem_id: [u8; 6],
36        oem_table: [u8; 8],
37        oem_revision: u32,
38    ) -> Self {
39        // The length represents for the length of the entire table
40        // which includes this header. And the header is 36 bytes, so
41        // lenght should be >= 36. For the case who gives a number less
42        // than the header len, use the header len directly.
43        let len: u32 = if length < HEADER_LEN {
44            HEADER_LEN
45        } else {
46            length
47        };
48        let mut data = Vec::with_capacity(length as usize);
49        data.extend_from_slice(&signature);
50        data.extend_from_slice(&len.to_le_bytes());
51        data.push(revision);
52        data.push(0); // checksum
53        data.extend_from_slice(&oem_id);
54        data.extend_from_slice(&oem_table);
55        data.extend_from_slice(&oem_revision.to_le_bytes());
56        data.extend_from_slice(b"CROS");
57        data.extend_from_slice(&0u32.to_le_bytes());
58
59        data.resize(length as usize, 0);
60        let mut sdt = SDT { data };
61
62        sdt.update_checksum();
63        sdt
64    }
65
66    /// Set up the ACPI table from file content. Verify file checksum.
67    pub fn from_file(path: &Path) -> Result<Self> {
68        let mut file = File::open(path)?;
69        let mut data = Vec::new();
70        file.read_to_end(&mut data)?;
71        let checksum = super::generate_checksum(data.as_slice());
72        if checksum == 0 {
73            Ok(SDT { data })
74        } else {
75            Err(ErrorKind::InvalidData.into())
76        }
77    }
78
79    pub fn is_signature(&self, signature: &[u8; 4]) -> bool {
80        self.data[0..4] == *signature
81    }
82
83    fn update_checksum(&mut self) {
84        self.data[CHECKSUM_OFFSET] = 0;
85        let checksum = super::generate_checksum(self.data.as_slice());
86        self.data[CHECKSUM_OFFSET] = checksum;
87    }
88
89    pub fn as_slice(&self) -> &[u8] {
90        self.data.as_slice()
91    }
92
93    pub fn append<T: IntoBytes + Immutable>(&mut self, value: T) {
94        self.data.extend_from_slice(value.as_bytes());
95        self.write(LENGTH_OFFSET, self.data.len() as u32);
96    }
97
98    pub fn append_slice(&mut self, value: &[u8]) {
99        self.data.extend_from_slice(value);
100        self.write(LENGTH_OFFSET, self.data.len() as u32);
101    }
102
103    /// Read a value at the given offset
104    pub fn read<T: FromBytes + Default>(&self, offset: usize) -> T {
105        self.as_slice()
106            .get(offset..)
107            .and_then(|bytes| {
108                let (val, _) = T::read_from_prefix(bytes).ok()?;
109                Some(val)
110            })
111            .unwrap_or_default()
112    }
113
114    /// Write a value at the given offset
115    pub fn write<T: IntoBytes + Immutable>(&mut self, offset: usize, value: T) {
116        let value_len = std::mem::size_of::<T>();
117        if (offset + value_len) > self.data.len() {
118            return;
119        }
120        self.data[offset..offset + value_len].copy_from_slice(value.as_bytes());
121        self.update_checksum();
122    }
123
124    pub fn len(&self) -> usize {
125        self.data.len()
126    }
127}
128
129#[cfg(test)]
130mod tests {
131    use std::io::Write;
132
133    use tempfile::NamedTempFile;
134
135    use super::SDT;
136
137    #[test]
138    fn test_sdt() {
139        let mut sdt = SDT::new(*b"TEST", 40, 1, *b"CROSVM", *b"TESTTEST", 1);
140        let sum: u8 = sdt
141            .as_slice()
142            .iter()
143            .fold(0u8, |acc, x| acc.wrapping_add(*x));
144        assert_eq!(sum, 0);
145        sdt.write(36, 0x12345678_u32);
146        let sum: u8 = sdt
147            .as_slice()
148            .iter()
149            .fold(0u8, |acc, x| acc.wrapping_add(*x));
150        assert_eq!(sum, 0);
151    }
152
153    #[test]
154    fn test_sdt_read_write() -> Result<(), std::io::Error> {
155        let temp_file = NamedTempFile::new()?;
156        let expected_sdt = SDT::new(*b"TEST", 40, 1, *b"CROSVM", *b"TESTTEST", 1);
157
158        // Write SDT to file.
159        {
160            let mut writer = temp_file.as_file();
161            writer.write_all(expected_sdt.as_slice())?;
162        }
163
164        // Read it back and verify.
165        let actual_sdt = SDT::from_file(temp_file.path())?;
166        assert!(actual_sdt.is_signature(b"TEST"));
167        assert_eq!(actual_sdt.as_slice(), expected_sdt.as_slice());
168        Ok(())
169    }
170}
acpi_tables/sdt.rs

acpi_tables/
sdt.rs
