Add libmemoffset to com.android.virt apex

This is a new dependency in newer crosvm.

Bug: 174797066
Test: m
Change-Id: I03032d4d80d2e89e5766dd0d5feca1577c3231a9
2 files changed
tree: 1fe928a093ae07f172447eb103ce48f5325895ab
  1. .cargo_vcs_info.json
  2. .gitignore
  3. .travis.yml
  4. Android.bp
  5. Cargo.toml
  6. Cargo.toml.orig
  7. LICENSE
  8. METADATA
  9. MODULE_LICENSE_MIT
  10. OWNERS
  11. README.md
  12. TEST_MAPPING
  13. build.rs
  14. ci/
  15. patches/
  16. src/
README.md

memoffset

C-Like offset_of functionality for Rust structs.

Introduces the following macros:

  • offset_of! for obtaining the offset of a member of a struct.
  • offset_of_tuple! for obtaining the offset of a member of a tuple. (Requires Rust 1.20+)
  • span_of! for obtaining the range that a field, or fields, span.

memoffset works under no_std environments.

Usage

Add the following dependency to your Cargo.toml:

[dependencies]
memoffset = "0.6"

These versions will compile fine with rustc versions greater or equal to 1.19.

Add the following lines at the top of your main.rs or lib.rs files.

#[macro_use]
extern crate memoffset;

Examples

#[macro_use]
extern crate memoffset;

#[repr(C, packed)]
struct Foo {
    a: u32,
    b: u32,
    c: [u8; 5],
    d: u32,
}

fn main() {
    assert_eq!(offset_of!(Foo, b), 4);
    assert_eq!(offset_of!(Foo, d), 4+4+5);

    assert_eq!(span_of!(Foo, a),        0..4);
    assert_eq!(span_of!(Foo, a ..  c),  0..8);
    assert_eq!(span_of!(Foo, a ..= c),  0..13);
    assert_eq!(span_of!(Foo, ..= d),    0..17);
    assert_eq!(span_of!(Foo, b ..),     4..17);
}

Feature flags

Usage in constants

memoffset has experimental support for compile-time offset_of! on a nightly compiler.

In order to use it, you must enable the unstable_const crate feature and several compiler features.

Cargo.toml:

[dependencies.memoffset]
version = "0.6"
features = ["unstable_const"]

Your crate root: (lib.rs/main.rs)

#![feature(ptr_offset_from, const_ptr_offset_from, const_maybe_uninit_as_ptr, const_raw_ptr_deref)]

If you intend to use offset_of! inside a const fn, also add the const_fn compiler feature.

Raw references

Recent nightlies support a way to create raw pointers that avoids creating intermediate safe references. memoffset can make use of that feature to avoid what is technically Undefined Behavior. Use the unstable_raw feature to enable this.