Bindgen assues wrong size for struct

[cbourjau]

I stumbled over an issue in bindgen today where the auto-generated test fails due to an unexpected size of the struct. The input header generated from creduce seems easy enough so it might also be that I am missing something? Is there any other information I could provide?

Input C Header

typedef struct {
  long double a
} max_align_t;

Bindgen Invocation

    let bindings = bindgen::Builder::default()
        .header("isolated-test-case.h")
        .generate()
        .expect("Unable to generate bindings");

Actual Results

-*- mode: compilation; default-directory: "~/repos/azure-iot-hub-sys/" -*-
Compilation started at Mon Feb 18 17:25:09

RUST_BACKTRACE=1 cargo t
    Blocking waiting for file lock on build directory
   Compiling azure-iot-hub-sys v0.1.0 (/home/christian/repos/azure-iot-hub-sys)
    Finished dev [unoptimized + debuginfo] target(s) in 1.74s
     Running target/debug/deps/azure_iot_hub_sys-6b0efcabc2d22f67

running 2 tests
test tests::it_works ... ok
test bindgen_test_layout_max_align_t ... FAILED

failures:

---- bindgen_test_layout_max_align_t stdout ----
thread 'bindgen_test_layout_max_align_t' panicked at 'assertion failed: `(left == right)`
  left: `8`,
 right: `16`: Size of: max_align_t', /home/christian/repos/azure-iot-hub-sys/target/debug/build/azure-iot-hub-sys-121d4cf2ab9da7ba/out/bindings.rs:10:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:59
             at src/libstd/panicking.rs:211
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:221
   4: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:491
   5: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:398
   6: std::panicking::begin_panic_fmt
             at src/libstd/panicking.rs:353
   7: azure_iot_hub_sys::bindgen_test_layout_max_align_t
             at ./target/debug/build/azure-iot-hub-sys-121d4cf2ab9da7ba/out/bindings.rs:10
   8: azure_iot_hub_sys::bindgen_test_layout_max_align_t::{{closure}}
             at ./target/debug/build/azure-iot-hub-sys-121d4cf2ab9da7ba/out/bindings.rs:9
   9: core::ops::function::FnOnce::call_once
             at /rustc/9fda7c2237db910e41d6a712e9a2139b352e558b/src/libcore/ops/function.rs:238
  10: <F as alloc::boxed::FnBox<A>>::call_box
             at src/libtest/lib.rs:1471
             at /rustc/9fda7c2237db910e41d6a712e9a2139b352e558b/src/libcore/ops/function.rs:238
             at /rustc/9fda7c2237db910e41d6a712e9a2139b352e558b/src/liballoc/boxed.rs:673
  11: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:102


failures:
    bindgen_test_layout_max_align_t

test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out

error: test failed, to rerun pass '--lib'

Compilation exited abnormally with code 101 at Mon Feb 18 17:25:11

and/or

/* automatically generated by rust-bindgen */

#[repr(C)]
#[derive(Debug, Copy, Clone)]
pub struct max_align_t {
    pub a: f64,
}
#[test]
fn bindgen_test_layout_max_align_t() {
    assert_eq!(
        ::std::mem::size_of::<max_align_t>(),
        16usize,
        concat!("Size of: ", stringify!(max_align_t))
    );
    assert_eq!(
        unsafe { &(*(::std::ptr::null::<max_align_t>())).a as *const _ as usize },
        0usize,
        concat!(
            "Offset of field: ",
            stringify!(max_align_t),
            "::",
            stringify!(a)
        )
    );
}

Expected Results

It seems strange to me that bindgen expected the struct to be 16 bytes wide.

[cbourjau]

Sorry, this is a duplicate of #1338; closing this in favor of that one.