linux_bzimage_builder/
lib.rs

1// SPDX-License-Identifier: MPL-2.0
2
3//! The linux bzImage builder.
4//!
5//! This crate is responsible for building the bzImage. It contains methods to build
6//! the setup binary (with source provided in another crate) and methods to build the
7//! bzImage from the setup binary and the kernel ELF.
8//!
9//! We should build the asterinas kernel as an ELF file, and feed it to the builder to
10//! generate the bzImage. The builder will generate the PE/COFF header for the setup
11//! code and concatenate it to the ELF file to make the bzImage.
12//!
13//! The setup code should be built into the ELF target and we convert it to a flat binary
14//! in the builder.
15
16pub mod encoder;
17mod mapping;
18mod pe_header;
19
20use std::{
21    fs::File,
22    io::{Read, Seek, SeekFrom, Write},
23    path::Path,
24};
25
26use align_ext::AlignExt;
27pub use encoder::{encode_kernel, PayloadEncoding};
28use mapping::{SetupFileOffset, SetupVA};
29use xmas_elf::{program::SegmentData, sections::SectionData};
30
31/// The type of the bzImage that we are building through `make_bzimage`.
32///
33/// Currently, Legacy32 and Efi64 are mutually exclusive.
34pub enum BzImageType {
35    Legacy32,
36    Efi64,
37}
38
39/// Making a bzImage given the kernel ELF and setup source.
40///
41/// Explanations for the arguments:
42///  - `target_image_path`: The path to the target bzImage;
43///  - `image_type`: The type of the bzImage that we are building;
44///  - `setup_elf_path`: The path to the setup ELF;
45///
46pub fn make_bzimage(target_image_path: &Path, image_type: BzImageType, setup_elf_path: &Path) {
47    let mut setup_elf = Vec::new();
48    File::open(setup_elf_path)
49        .unwrap()
50        .read_to_end(&mut setup_elf)
51        .unwrap();
52    let mut setup = to_flat_binary(&setup_elf);
53    // Align the flat binary to `SECTION_ALIGNMENT`.
54    setup.resize(setup.len().align_up(pe_header::SECTION_ALIGNMENT), 0x00);
55
56    let mut kernel_image = File::create(target_image_path).unwrap();
57    kernel_image.write_all(&setup).unwrap();
58
59    if matches!(image_type, BzImageType::Efi64) {
60        assert_elf64_reloc_supported(&setup_elf);
61
62        // Write the PE/COFF header to the start of the file.
63        // Since the Linux boot header starts at 0x1f1, we can write the PE/COFF header directly to the
64        // start of the file without overwriting the Linux boot header.
65        let pe_header = pe_header::make_pe_coff_header(&setup_elf);
66        assert!(pe_header.len() <= 0x1f1, "PE/COFF header is too large");
67
68        kernel_image.seek(SeekFrom::Start(0)).unwrap();
69        kernel_image.write_all(&pe_header).unwrap();
70    }
71}
72
73/// To build the legacy32 bzImage setup header, the OSDK should use this target.
74pub fn legacy32_rust_target_json() -> &'static str {
75    include_str!("x86_64-i386_pm-none.json")
76}
77
78/// We need a flat binary which satisfies PA delta == File offset delta,
79/// and objcopy does not satisfy us well, so we should parse the ELF and
80/// do our own objcopy job.
81///
82/// Interestingly, the resulting binary should be the same as the memory
83/// dump of the kernel setup header when it's loaded by the bootloader.
84fn to_flat_binary(elf_file: &[u8]) -> Vec<u8> {
85    let elf = xmas_elf::ElfFile::new(elf_file).unwrap();
86    let mut bin = Vec::<u8>::new();
87
88    for program in elf.program_iter() {
89        if program.get_type().unwrap() == xmas_elf::program::Type::Load {
90            let SegmentData::Undefined(header_data) = program.get_data(&elf).unwrap() else {
91                panic!("Unexpected segment data type");
92            };
93            let dst_file_offset = usize::from(SetupFileOffset::from(SetupVA::from(
94                program.virtual_addr() as usize,
95            )));
96
97            // Note that `mem_size` can be greater than `file_size`. The remaining part must be
98            // filled with zeros.
99            let mem_length = program.mem_size() as usize;
100            if bin.len() < dst_file_offset + mem_length {
101                bin.resize(dst_file_offset + mem_length, 0);
102            }
103
104            // Copy the bytes in the `file_size` part.
105            let file_length = program.file_size() as usize;
106            let dest_slice = bin[dst_file_offset..dst_file_offset + file_length].as_mut();
107            dest_slice.copy_from_slice(header_data);
108        }
109    }
110
111    bin
112}
113
114fn assert_elf64_reloc_supported(elf_file: &[u8]) {
115    const R_X86_64_RELATIVE: u32 = 8;
116
117    let elf = xmas_elf::ElfFile::new(elf_file).unwrap();
118
119    let SectionData::Rela64(rela64) = elf
120        .find_section_by_name(".rela")
121        .unwrap()
122        .get_data(&elf)
123        .unwrap()
124    else {
125        panic!("the ELF64 relocation data is not of the correct type");
126    };
127
128    rela64.iter().for_each(|r| {
129        assert_eq!(
130            r.get_type(),
131            R_X86_64_RELATIVE,
132            "the ELF64 relocation type is not supported"
133        )
134    });
135}
linux_bzimage_builder/lib.rs

linux_bzimage_builder/
lib.rs
