1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
#![no_std]
#![warn(box_pointers, missing_copy_implementations, missing_debug_implementations)]
#![warn(unused_extern_crates, unused_import_braces, unused_qualifications, unused_results)]
#![warn(variant_size_differences)]

// TODO move to a module
macro_rules! check {
    ($e:expr) => {
        if !$e {
            return Err("");
        }
    };
    ($e:expr, $msg: expr) => {
        if !$e {
            return Err($msg);
        }
    };
}

#[cfg(feature = "compression")]
extern crate std;
#[cfg(feature = "compression")]
extern crate flate2;

extern crate zero;

pub mod header;
pub mod sections;
pub mod program;
pub mod symbol_table;
pub mod dynamic;
pub mod hash;

use header::Header;
use sections::{SectionHeader, SectionIter};
use program::{ProgramHeader, ProgramIter};
use zero::{read, read_str};

pub type P32 = u32;
pub type P64 = u64;

#[derive(Debug)]
pub struct ElfFile<'a> {
    pub input: &'a [u8],
    pub header: Header<'a>,
}

impl<'a> ElfFile<'a> {
    pub fn new(input: &'a [u8]) -> Result<ElfFile<'a>, &'static str> {
        header::parse_header(input).map(|header| ElfFile {input, header})
    }

    pub fn section_header(&self, index: u16) -> Result<SectionHeader<'a>, &'static str> {
        sections::parse_section_header(self.input, self.header, index)
    }

    pub fn section_iter(&self) -> impl Iterator<Item = SectionHeader<'a>> + '_ {
        SectionIter {
            file: self,
            next_index: 0,
        }
    }

    pub fn program_header(&self, index: u16) -> Result<ProgramHeader<'a>, &'static str> {
        program::parse_program_header(self.input, self.header, index)
    }

    pub fn program_iter(&self) -> impl Iterator<Item = ProgramHeader<'a>> + '_ {
        ProgramIter {
            file: self,
            next_index: 0,
        }
    }

    pub fn get_shstr(&self, index: u32) -> Result<&'a str, &'static str> {
        self.get_shstr_table().map(|shstr_table| read_str(&shstr_table[(index as usize)..]))
    }

    pub fn get_string(&self, index: u32) -> Result<&'a str, &'static str> {
        let header = self.find_section_by_name(".strtab").ok_or("no .strtab section")?;
        if header.get_type()? != sections::ShType::StrTab {
            return Err("expected .strtab to be StrTab");
        }
        Ok(read_str(&header.raw_data(self)[(index as usize)..]))
    }

    pub fn get_dyn_string(&self, index: u32) -> Result<&'a str, &'static str> {
        let header = self.find_section_by_name(".dynstr").ok_or("no .dynstr section")?;
        Ok(read_str(&header.raw_data(self)[(index as usize)..]))
    }

    // This is really, stupidly slow. Not sure how to fix that, perhaps keeping
    // a HashTable mapping names to section header indices?
    pub fn find_section_by_name(&self, name: &str) -> Option<SectionHeader<'a>> {
        for sect in self.section_iter() {
            if let Ok(sect_name) = sect.get_name(self) {
                if sect_name == name {
                    return Some(sect);
                }
            }
        }

        None
    }

    fn get_shstr_table(&self) -> Result<&'a [u8], &'static str> {
        // TODO cache this?
        let header = self.section_header(self.header.pt2.sh_str_index());
        header.map(|h| &self.input[(h.offset() as usize)..])
    }
}

/// A trait for things that are common ELF conventions but not part of the ELF
/// specification.
pub trait Extensions<'a> {
    /// Parse and return the value of the .note.gnu.build-id section, if it
    /// exists and is well-formed.
    fn get_gnu_buildid(&self) -> Option<&'a [u8]>;

    /// Parse and return the value of the .gnu_debuglink section, if it
    /// exists and is well-formed.
    fn get_gnu_debuglink(&self) -> Option<(&'a str, u32)>;

    /// Parse and return the value of the .gnu_debugaltlink section, if it
    /// exists and is well-formed.
    fn get_gnu_debugaltlink(&self) -> Option<(&'a str, &'a [u8])>;
}

impl<'a> Extensions<'a> for ElfFile<'a> {
    fn get_gnu_buildid(&self) -> Option<&'a [u8]> {
        self.find_section_by_name(".note.gnu.build-id")
            .and_then(|header| header.get_data(self).ok())
            .and_then(|data| match data {
                // Handle Note32 if it's ever implemented!
                sections::SectionData::Note64(header, data) => Some((header, data)),
                _ => None,
            })
            .and_then(|(header, data)| {
                // Check for NT_GNU_BUILD_ID
                if header.type_() != 0x3 {
                    return None;
                }

                if header.name(data) != "GNU" {
                    return None;
                }

                Some(header.desc(data))
            })
    }

    fn get_gnu_debuglink(&self) -> Option<(&'a str, u32)> {
        self.find_section_by_name(".gnu_debuglink")
            .and_then(|header| {
                let data = header.raw_data(self);
                let file = read_str(data);
                // Round up to the nearest multiple of 4.
                let checksum_pos = ((file.len() + 4) / 4) * 4;
                if checksum_pos + 4 <= data.len() {
                    let checksum: u32 = *read(&data[checksum_pos..]);
                    Some((file, checksum))
                } else {
                    None
                }
            })
    }

    fn get_gnu_debugaltlink(&self) -> Option<(&'a str, &'a [u8])> {
        self.find_section_by_name(".gnu_debugaltlink")
            .map(|header| header.raw_data(self))
            .and_then(|data| {
                let file = read_str(data);
                // The rest of the data is a SHA1 checksum of the debuginfo, no alignment
                let checksum_pos = file.len() + 1;
                if checksum_pos <= data.len() {
                    Some((file, &data[checksum_pos..]))
                } else {
                    None
                }
            })
    }
}

#[cfg(test)]
#[macro_use]
extern crate std;

#[cfg(test)]
mod test {
    use std::prelude::v1::*;

    use std::mem;

    use super::*;
    use header::{HeaderPt1, HeaderPt2_};

    fn mk_elf_header(class: u8) -> Vec<u8> {
        let header_size = mem::size_of::<HeaderPt1>() +
                          match class {
            1 => mem::size_of::<HeaderPt2_<P32>>(),
            2 => mem::size_of::<HeaderPt2_<P64>>(),
            _ => 0,
        };
        let mut header = vec![0x7f, 'E' as u8, 'L' as u8, 'F' as u8];
        let data = 1u8;
        let version = 1u8;
        header.extend_from_slice(&[class, data, version]);
        header.resize(header_size, 0);
        header
    }

    #[test]
    fn interpret_class() {
        assert!(ElfFile::new(&mk_elf_header(0)).is_err());
        assert!(ElfFile::new(&mk_elf_header(1)).is_ok());
        assert!(ElfFile::new(&mk_elf_header(2)).is_ok());
        assert!(ElfFile::new(&mk_elf_header(42u8)).is_err());
    }
}