Remove access to unaligned refs from bzImage tests

[AlexandruCihodaru]

Summary of the PR

Replace access to unaligned reference in bzImage tests with std::ptr::addr_of macro and read_unaligned method.
Fixes: #123

Requirements

Before submitting your PR, please make sure you addressed the following
requirements:

• All commits in this PR are signed (with git commit -s), and the commit
  message has max 60 characters for the summary and max 75 characters for each
  description line.
• [] All added/changed functionality has a corresponding unit/integration
  test.
• All added/changed public-facing functionality has entries in the "Upcoming
  Release" section of CHANGELOG.md (if no such section exists, please create one).
• [] Any newly added unsafe code is properly documented.

[rbradford]

Whoops, looks like I forgot to send this comment as it was part of a review.

[rbradford]

This comment is a bit ambiguous. Rust allows you to read the contents of fields in an struct even if they are not aligned if that type is Copy. What you can't do is safely deference references to unaligned members.

Here is a little example:

#[repr(packed)]
struct Foo {
    a: u8,
    b: u64
}

// This won't compile due to unaligned access as the members are referenced
//fn bad(foo: &Foo) {
//    println!("{} {}", foo.a, foo.b)
//}

// This version is fine as we can copy the values from the struct
fn good(foo: &Foo) {
    let (a, b) = (foo.a, foo.b);
    println!("{} {}", a, b)
}

fn main() {
    let foo = Foo {a: 1, b: 2};
    good(&foo)
}

I would therefore advise against using the word "reading" here. Alternatively if the values setup_header are just copied to the stack then all this could be simplfied to:

        let setup_header = loader_result.setup_header.unwrap();
        let header = setup_header.header; 
        assert_eq!(header, 0x53726448);

I hope this is helpful as I went through the same journey to understand the details of this error.

[andreeaflorescu]

@AlexandruCihodaru do you mind sending an update with the suggestion from @rbradford? This is a good catch!

[AlexandruCihodaru]

Sure thing. Will create a new PR this week.