Wrong expected union size with Rust union

[tmfink]

This issue can be reproduced by adding --unstable-union to tests/headers/16-byte-alignment.h.

Input C/C++ Header

typedef unsigned char uint8_t;
typedef unsigned short uint16_t;
typedef unsigned int uint32_t;

struct rte_ipv4_tuple {
    uint32_t src_addr;
    uint32_t dst_addr;
    union {
        struct {
            uint16_t dport;
            uint16_t sport;
        };
        uint32_t sctp_tag;
    };
};

struct rte_ipv6_tuple {
    uint8_t src_addr[16];
    uint8_t dst_addr[16];
    union {
        struct {
            uint16_t dport;
            uint16_t sport;
        };
        uint32_t    sctp_tag;
    };
};

union rte_thash_tuple {
    struct rte_ipv4_tuple   v4;
    struct rte_ipv6_tuple   v6;
} __attribute__((aligned(16)));

Bindgen Invocation

$ bindgen input.h --with-derive-hash --unstable-rust

Actual Results

Bindgen generates:

/* automatically generated by rust-bindgen */

#[repr(C)]
#[derive(Copy)]
pub struct rte_ipv4_tuple {
    pub src_addr: u32,
    pub dst_addr: u32,
    pub __bindgen_anon_1: rte_ipv4_tuple__bindgen_ty_1,
}
#[repr(C)]
#[derive(Copy)]
pub union rte_ipv4_tuple__bindgen_ty_1 {
    pub __bindgen_anon_1: rte_ipv4_tuple__bindgen_ty_1__bindgen_ty_1,
    pub sctp_tag: u32,
}
#[repr(C)]
#[derive(Debug, Copy, Hash)]
pub struct rte_ipv4_tuple__bindgen_ty_1__bindgen_ty_1 {
    pub dport: u16,
    pub sport: u16,
}
#[test]
fn bindgen_test_layout_rte_ipv4_tuple__bindgen_ty_1__bindgen_ty_1() {
    assert_eq!(::std::mem::size_of::<rte_ipv4_tuple__bindgen_ty_1__bindgen_ty_1>()
               , 4usize , concat ! (
               "Size of: " , stringify ! (
               rte_ipv4_tuple__bindgen_ty_1__bindgen_ty_1 ) ));
    assert_eq! (::std::mem::align_of::<rte_ipv4_tuple__bindgen_ty_1__bindgen_ty_1>()
                , 2usize , concat ! (
                "Alignment of " , stringify ! (
                rte_ipv4_tuple__bindgen_ty_1__bindgen_ty_1 ) ));
    assert_eq! (unsafe {
                & (
                * ( 0 as * const rte_ipv4_tuple__bindgen_ty_1__bindgen_ty_1 )
                ) . dport as * const _ as usize } , 0usize , concat ! (
                "Alignment of field: " , stringify ! (
                rte_ipv4_tuple__bindgen_ty_1__bindgen_ty_1 ) , "::" ,
                stringify ! ( dport ) ));
    assert_eq! (unsafe {
                & (
                * ( 0 as * const rte_ipv4_tuple__bindgen_ty_1__bindgen_ty_1 )
                ) . sport as * const _ as usize } , 2usize , concat ! (
                "Alignment of field: " , stringify ! (
                rte_ipv4_tuple__bindgen_ty_1__bindgen_ty_1 ) , "::" ,
                stringify ! ( sport ) ));
}
impl Clone for rte_ipv4_tuple__bindgen_ty_1__bindgen_ty_1 {
    fn clone(&self) -> Self { *self }
}
#[test]
fn bindgen_test_layout_rte_ipv4_tuple__bindgen_ty_1() {
    assert_eq!(::std::mem::size_of::<rte_ipv4_tuple__bindgen_ty_1>() , 4usize
               , concat ! (
               "Size of: " , stringify ! ( rte_ipv4_tuple__bindgen_ty_1 ) ));
    assert_eq! (::std::mem::align_of::<rte_ipv4_tuple__bindgen_ty_1>() ,
                4usize , concat ! (
                "Alignment of " , stringify ! ( rte_ipv4_tuple__bindgen_ty_1 )
                ));
    assert_eq! (unsafe {
                & ( * ( 0 as * const rte_ipv4_tuple__bindgen_ty_1 ) ) .
                sctp_tag as * const _ as usize } , 0usize , concat ! (
                "Alignment of field: " , stringify ! (
                rte_ipv4_tuple__bindgen_ty_1 ) , "::" , stringify ! ( sctp_tag
                ) ));
}
impl Clone for rte_ipv4_tuple__bindgen_ty_1 {
    fn clone(&self) -> Self { *self }
}
#[test]
fn bindgen_test_layout_rte_ipv4_tuple() {
    assert_eq!(::std::mem::size_of::<rte_ipv4_tuple>() , 12usize , concat ! (
               "Size of: " , stringify ! ( rte_ipv4_tuple ) ));
    assert_eq! (::std::mem::align_of::<rte_ipv4_tuple>() , 4usize , concat ! (
                "Alignment of " , stringify ! ( rte_ipv4_tuple ) ));
    assert_eq! (unsafe {
                & ( * ( 0 as * const rte_ipv4_tuple ) ) . src_addr as * const
                _ as usize } , 0usize , concat ! (
                "Alignment of field: " , stringify ! ( rte_ipv4_tuple ) , "::"
                , stringify ! ( src_addr ) ));
    assert_eq! (unsafe {
                & ( * ( 0 as * const rte_ipv4_tuple ) ) . dst_addr as * const
                _ as usize } , 4usize , concat ! (
                "Alignment of field: " , stringify ! ( rte_ipv4_tuple ) , "::"
                , stringify ! ( dst_addr ) ));
}
impl Clone for rte_ipv4_tuple {
    fn clone(&self) -> Self { *self }
}
#[repr(C)]
#[derive(Copy)]
pub struct rte_ipv6_tuple {
    pub src_addr: [u8; 16usize],
    pub dst_addr: [u8; 16usize],
    pub __bindgen_anon_1: rte_ipv6_tuple__bindgen_ty_1,
}
#[repr(C)]
#[derive(Copy)]
pub union rte_ipv6_tuple__bindgen_ty_1 {
    pub __bindgen_anon_1: rte_ipv6_tuple__bindgen_ty_1__bindgen_ty_1,
    pub sctp_tag: u32,
}
#[repr(C)]
#[derive(Debug, Copy, Hash)]
pub struct rte_ipv6_tuple__bindgen_ty_1__bindgen_ty_1 {
    pub dport: u16,
    pub sport: u16,
}
#[test]
fn bindgen_test_layout_rte_ipv6_tuple__bindgen_ty_1__bindgen_ty_1() {
    assert_eq!(::std::mem::size_of::<rte_ipv6_tuple__bindgen_ty_1__bindgen_ty_1>()
               , 4usize , concat ! (
               "Size of: " , stringify ! (
               rte_ipv6_tuple__bindgen_ty_1__bindgen_ty_1 ) ));
    assert_eq! (::std::mem::align_of::<rte_ipv6_tuple__bindgen_ty_1__bindgen_ty_1>()
                , 2usize , concat ! (
                "Alignment of " , stringify ! (
                rte_ipv6_tuple__bindgen_ty_1__bindgen_ty_1 ) ));
    assert_eq! (unsafe {
                & (
                * ( 0 as * const rte_ipv6_tuple__bindgen_ty_1__bindgen_ty_1 )
                ) . dport as * const _ as usize } , 0usize , concat ! (
                "Alignment of field: " , stringify ! (
                rte_ipv6_tuple__bindgen_ty_1__bindgen_ty_1 ) , "::" ,
                stringify ! ( dport ) ));
    assert_eq! (unsafe {
                & (
                * ( 0 as * const rte_ipv6_tuple__bindgen_ty_1__bindgen_ty_1 )
                ) . sport as * const _ as usize } , 2usize , concat ! (
                "Alignment of field: " , stringify ! (
                rte_ipv6_tuple__bindgen_ty_1__bindgen_ty_1 ) , "::" ,
                stringify ! ( sport ) ));
}
impl Clone for rte_ipv6_tuple__bindgen_ty_1__bindgen_ty_1 {
    fn clone(&self) -> Self { *self }
}
#[test]
fn bindgen_test_layout_rte_ipv6_tuple__bindgen_ty_1() {
    assert_eq!(::std::mem::size_of::<rte_ipv6_tuple__bindgen_ty_1>() , 4usize
               , concat ! (
               "Size of: " , stringify ! ( rte_ipv6_tuple__bindgen_ty_1 ) ));
    assert_eq! (::std::mem::align_of::<rte_ipv6_tuple__bindgen_ty_1>() ,
                4usize , concat ! (
                "Alignment of " , stringify ! ( rte_ipv6_tuple__bindgen_ty_1 )
                ));
    assert_eq! (unsafe {
                & ( * ( 0 as * const rte_ipv6_tuple__bindgen_ty_1 ) ) .
                sctp_tag as * const _ as usize } , 0usize , concat ! (
                "Alignment of field: " , stringify ! (
                rte_ipv6_tuple__bindgen_ty_1 ) , "::" , stringify ! ( sctp_tag
                ) ));
}
impl Clone for rte_ipv6_tuple__bindgen_ty_1 {
    fn clone(&self) -> Self { *self }
}
#[test]
fn bindgen_test_layout_rte_ipv6_tuple() {
    assert_eq!(::std::mem::size_of::<rte_ipv6_tuple>() , 36usize , concat ! (
               "Size of: " , stringify ! ( rte_ipv6_tuple ) ));
    assert_eq! (::std::mem::align_of::<rte_ipv6_tuple>() , 4usize , concat ! (
                "Alignment of " , stringify ! ( rte_ipv6_tuple ) ));
    assert_eq! (unsafe {
                & ( * ( 0 as * const rte_ipv6_tuple ) ) . src_addr as * const
                _ as usize } , 0usize , concat ! (
                "Alignment of field: " , stringify ! ( rte_ipv6_tuple ) , "::"
                , stringify ! ( src_addr ) ));
    assert_eq! (unsafe {
                & ( * ( 0 as * const rte_ipv6_tuple ) ) . dst_addr as * const
                _ as usize } , 16usize , concat ! (
                "Alignment of field: " , stringify ! ( rte_ipv6_tuple ) , "::"
                , stringify ! ( dst_addr ) ));
}
impl Clone for rte_ipv6_tuple {
    fn clone(&self) -> Self { *self }
}
#[repr(C)]
#[derive(Copy)]
pub union rte_thash_tuple {
    pub v4: rte_ipv4_tuple,
    pub v6: rte_ipv6_tuple,
}
#[test]
fn bindgen_test_layout_rte_thash_tuple() {
    assert_eq!(::std::mem::size_of::<rte_thash_tuple>() , 48usize , concat ! (
               "Size of: " , stringify ! ( rte_thash_tuple ) ));
    assert_eq! (unsafe {
                & ( * ( 0 as * const rte_thash_tuple ) ) . v4 as * const _ as
                usize } , 0usize , concat ! (
                "Alignment of field: " , stringify ! ( rte_thash_tuple ) ,
                "::" , stringify ! ( v4 ) ));
    assert_eq! (unsafe {
                & ( * ( 0 as * const rte_thash_tuple ) ) . v6 as * const _ as
                usize } , 0usize , concat ! (
                "Alignment of field: " , stringify ! ( rte_thash_tuple ) ,
                "::" , stringify ! ( v6 ) ));
}
impl Clone for rte_thash_tuple {
    fn clone(&self) -> Self { *self }
}

Compiling bindings (after adding a main function) leads to:

$ rustc --test test.rs -o test  # build test harness
...
$ ./test
running 7 tests
test bindgen_test_layout_rte_ipv4_tuple__bindgen_ty_1 ... ok
test bindgen_test_layout_rte_ipv6_tuple ... ok
test bindgen_test_layout_rte_ipv6_tuple__bindgen_ty_1 ... ok
test bindgen_test_layout_rte_ipv4_tuple ... ok
test bindgen_test_layout_rte_ipv4_tuple__bindgen_ty_1__bindgen_ty_1 ... ok
test bindgen_test_layout_rte_ipv6_tuple__bindgen_ty_1__bindgen_ty_1 ... ok
test bindgen_test_layout_rte_thash_tuple ... FAILED

failures:

---- bindgen_test_layout_rte_thash_tuple stdout ----
        thread 'bindgen_test_layout_rte_thash_tuple' panicked at 'assertion failed: `(left == right)` (left: `36`, right: `48`): Size of: rte_thash_tuple', tests/16-byte-alignment.rs:199
note: Run with `RUST_BACKTRACE=1` for a backtrace.

Expected Results

Predicted and actual union sizes match.