unsafe xmas_elf::ElfFile::new_from_ptr(ptr: *const u8) constructor

[krh]

Sometimes they don't give you the length 😢

Parses header and scans program header, section header and sections for largest offset. Creates a slice from raw parts and calls ::new...

[krh]

// xmas_elf wants a slice, not a pointer, so we have to try to figure out how
// big the ELF data is from just the pointer.  We do this by first creating a
// slice for just the Elf64 header size.  From that we can see where the
// section headers end and extend the slice to cover those.  Since ELF doesn't
// guaranetee any ordering of section header vs sections, we scan the section
// headers to see where the last section ends, and if that's past the section
// headers, we further extend the slice and recreate the ELF one last time.
unsafe fn elf_from_ptr<'a>(image: *const c_void) -> Result<xmas_elf::ElfFile<'a>, &'static str> {
    let image = image.cast::<u8>();
    const ELF64_HEADER_SIZE: usize = 64;
    let slice = unsafe { std::slice::from_raw_parts(image, ELF64_HEADER_SIZE) };
    let elf = xmas_elf::ElfFile::new(slice)?;

    let section_header_end = elf.header.pt2.sh_offset() as usize
        + elf.header.pt2.sh_count() as usize * elf.header.pt2.sh_entry_size() as usize;

    let slice = unsafe { std::slice::from_raw_parts(image, section_header_end) };
    let elf = xmas_elf::ElfFile::new(slice)?;

    let last_section_end = elf
        .section_iter()
        .map(|s| s.offset() + s.size())
        .max()
        .ok_or(Err("no sections in ELF"))? as usize;
    if sh_end > end {
        let slice = unsafe { std::slice::from_raw_parts(image, std::cmp::max(end, last_section_end)) };
        xmas_elf::ElfFile::new(slice)
    } else {
        Ok(elf)
    }
}