parse header

elven-parser/src/lib.rs

@@ -1 +1 @@
-pub fn yeet() {}
+pub mod raw;

elven-parser/src/raw.rs

@@ -0,0 +1,114 @@
+//! Structures and parsers for ELF64. ELF32 can knock itself out.
+
+use std::mem;
+
+#[derive(Debug)]
+pub struct Addr(u64);
+#[derive(Debug)]
+pub struct Offset(u64);
+#[derive(Debug)]
+pub struct Section(u16);
+#[derive(Debug)]
+pub struct Versym(u16);
+
+#[derive(Debug, Clone, thiserror::Error)]
+pub enum ElfParseError {
+    #[error("The file is too small. Expected at least {0} bytes, found {1} bytes")]
+    FileTooSmall(usize, usize),
+    #[error("The input is not aligned in memory. Expected align {0}, found align {1}")]
+    UnalignedInput(usize, usize),
+    #[error("The magic of the file did not match. Maybe it's not an ELF file?. Found {0:x?}")]
+    WrongMagic([u8; 4]),
+}
+
+/// A raw ELF. Does not come with cute ears for now.
+#[derive(Debug)]
+pub struct Elf<'a> {
+    pub header: &'a ElfHeader,
+}
+
+#[derive(Debug)]
+#[repr(C)]
+pub struct ElfHeader {
+    pub ident: [u8; 16],
+    pub r#type: u16,
+    pub machine: u16,
+    pub version: u32,
+    pub entry: Addr,
+    pub phoff: Offset,
+    pub shoff: Offset,
+    pub flags: u32,
+    pub ehsize: u16,
+    pub phentsize: u16,
+    pub phnum: u16,
+    pub shentsize: u16,
+    pub shnum: u16,
+    pub shstrndex: u16,
+}
+
+impl<'a> Elf<'a> {
+    pub fn parse(input: &'a [u8]) -> Result<Self, ElfParseError> {
+        const HEADER_SIZE: usize = mem::size_of::<ElfHeader>();
+        const HEADER_ALIGN: usize = mem::align_of::<ElfHeader>();
+
+        if input.len() < HEADER_SIZE {
+            return Err(ElfParseError::FileTooSmall(HEADER_SIZE, input.len()));
+        }
+
+        let input_ptr = input as *const [u8];
+
+        let input_addr = input_ptr as *const u8 as usize;
+        let align = input_addr.trailing_zeros() as usize;
+
+        if align < HEADER_ALIGN {
+            return Err(ElfParseError::UnalignedInput(HEADER_ALIGN, align));
+        }
+
+        let header = input_ptr as *const ElfHeader;
+        // SAFETY: We checked that the size is enough. We checked that the alignment matches.
+        // ElfHeader is POD.
+        let header = unsafe { &*header };
+
+        let magic = header.ident[..4].try_into().unwrap();
+
+        if magic != [0x7f, b'E', b'L', b'F'] {
+            return Err(ElfParseError::WrongMagic(magic));
+        }
+
+        Ok(Elf { header })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::{fs, path::Path};
+
+    use memmap2::Mmap;
+
+    use super::*;
+
+    fn load_test_file(file_name: impl AsRef<Path>) -> Mmap {
+        let name = file_name.as_ref();
+        let this_file_path = Path::new(env!("CARGO_MANIFEST_DIR")).join(file!());
+        let double_this_crate = this_file_path.parent().unwrap().parent().unwrap();
+        let workspace_root = double_this_crate.parent().unwrap().parent().unwrap();
+
+        let file_path = workspace_root.join("test_data").join("out").join(name);
+
+        let file = fs::File::open(&file_path).expect(&format!(
+            "Failed to open test file {} at path {}. Consider running `test_data/create_test_data.sh` to create the test data files",
+            name.display(),
+            file_path.display()
+        ));
+
+        unsafe { Mmap::map(&file).unwrap() }
+    }
+
+    #[test]
+    fn rust_hello_world_bin() {
+        let file = load_test_file("hello_world");
+        let elf = Elf::parse(&file).unwrap();
+        dbg!(elf);
+        panic!()
+    }
+}