cfg_if! { if#[cfg(all(libc_int128, target_arch = "aarch64", not(target_os = "windows")))] { // This introduces partial support for FFI with __int128 and // equivalent types on platforms where Rust's definition is validated // to match the standard C ABI of that platform. // // Rust does not guarantee u128/i128 are sound for FFI, and its // definitions are in fact known to be incompatible. [0] // // However these problems aren't fundamental, and are just platform // inconsistencies. Specifically at the time of this writing: // // * For x64 SysV ABIs (everything but Windows), the types are underaligned. // * For all Windows ABIs, Microsoft doesn't actually officially define __int128, // and as a result different implementations don't actually agree on its ABI. // // But on the other major aarch64 platforms (android, linux, ios, macos) we have // validated that rustc has the right ABI for these types. This is important because // aarch64 uses these types in some fundamental OS types like user_fpsimd_struct, // which represents saved simd registers. // // Any API which uses these types will need to `#[ignore(improper_ctypes)]` // until the upstream rust issue is resolved, but this at least lets us make // progress on platforms where this type is important. // // The list of supported architectures and OSes is intentionally very restricted, // as careful work needs to be done to verify that a particular platform // has a conformant ABI. // // [0]: https://github.com/rust-lang/rust/issues/54341
/// C `__int128` (a GCC extension that's part of many ABIs) pubtype __int128 = i128; /// C `unsigned __int128` (a GCC extension that's part of many ABIs) pubtype __uint128 = u128; /// C __int128_t (alternate name for [__int128][]) pubtype __int128_t = i128; /// C __uint128_t (alternate name for [__uint128][]) pubtype __uint128_t = u128;
// NOTE: if you add more platforms to here, you may need to cfg // these consts. They should always match the platform's values // for `sizeof(__int128)` and `_Alignof(__int128)`. const _SIZE_128: usize = 16; const _ALIGN_128: usize = 16;
// Since Rust doesn't officially guarantee that these types // have compatible ABIs, we const assert that these values have the // known size/align of the target platform's libc. If rustc ever // tries to regress things, it will cause a compilation error. // // This isn't a bullet-proof solution because e.g. it doesn't // catch the fact that llvm and gcc disagree on how x64 __int128 // is actually *passed* on the stack (clang underaligns it for // the same reason that rustc *never* properly aligns it).
static_assert_eq!(core::mem::size_of::<__int128>(), _SIZE_128);
static_assert_eq!(core::mem::align_of::<__int128>(), _ALIGN_128);
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