packed type cannot transitively contain a `#[repr(align)]` type

[ic3man5]

Input C/C++ Header

#include <stdint.h>

#pragma pack(push, 2)

typedef struct _UART_SETTINGS
{
	uint16_t Baudrate;
	uint16_t spbrg;
	uint16_t brgh;
	uint16_t parity;
	uint16_t stop_bits;
	uint8_t flow_control; /* 0- off, 1 - Simple CTS RTS */
	uint8_t reserved_1;
	union {
		uint32_t bOptions;
		struct
		{
			unsigned invert_tx : 1;
			unsigned invert_rx : 1;
			unsigned half_duplex : 1;
			unsigned reserved_bits : 13;
			unsigned reserved_bits2 : 16;
		} opts;
	} options;
} UART_SETTINGS;

#pragma pack(pop)

Bindgen Invocation

$ bindgen test.h >> test.rs

Actual Results

error[E0588]: packed type cannot transitively contain a `#[repr(align)]` type
   --> src\main.rs:149:1
    |
149 | / pub union _UART_SETTINGS__bindgen_ty_1 {
150 | |     pub bOptions: u32,
151 | |     pub opts: _UART_SETTINGS__bindgen_ty_1__bindgen_ty_1,
152 | | }
    | |_^
    |
note: `_UART_SETTINGS__bindgen_ty_1__bindgen_ty_1` has a `#[repr(align)]` attribute
   --> src\main.rs:156:1
    |
156 | / pub struct _UART_SETTINGS__bindgen_ty_1__bindgen_ty_1 {
157 | |     pub _bitfield_align_1: [u8; 0],
158 | |     pub _bitfield_1: __BindgenBitfieldUnit<[u8; 4usize]>,
159 | | }
    | |_^

Expected Results

compile successfully. If bitfields are removed and or packed is removed this work.

[kpishere]

I'm getting a similar error when trying to build https://github.com/nviennot/tinyusb-sys-rs.git

I'm building with: cargo build --verbose --features device,cdc,rp2040 --target thumbv6m-none-eabi

I get these errors

Running `rustc --crate-name tinyusb_sys --edition=2021 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type lib --emit=dep-info,metadata,link -C embed-bitcode=no -C debuginfo=2 --cfg 'feature="cdc"' --cfg 'feature="device"' --cfg 'feature="rp2040"' -C metadata=222396e23cc7c407 -C extra-filename=-222396e23cc7c407 --out-dir /Users/kevinpeck/Desktop/RepRap-RatRigVCore3/tinyusb-sys-rs/target/thumbv6m-none-eabi/debug/deps --target thumbv6m-none-eabi -C incremental=/Users/kevinpeck/Desktop/RepRap-RatRigVCore3/tinyusb-sys-rs/target/thumbv6m-none-eabi/debug/incremental -L dependency=/Users/kevinpeck/Desktop/RepRap-RatRigVCore3/tinyusb-sys-rs/target/thumbv6m-none-eabi/debug/deps -L dependency=/Users/kevinpeck/Desktop/RepRap-RatRigVCore3/tinyusb-sys-rs/target/debug/deps --extern cty=/Users/kevinpeck/Desktop/RepRap-RatRigVCore3/tinyusb-sys-rs/target/thumbv6m-none-eabi/debug/deps/libcty-539500295d24c90b.rmeta -L native=/Users/kevinpeck/Desktop/RepRap-RatRigVCore3/tinyusb-sys-rs/target/thumbv6m-none-eabi/debug/build/tinyusb-sys-d484e22ceeda2732/out -l static=tinyusb`
error[E0588]: packed type cannot transitively contain a `#[repr(align)]` type
    --> /Users/kevinpeck/Desktop/RepRap-RatRigVCore3/tinyusb-sys-rs/target/thumbv6m-none-eabi/debug/build/tinyusb-sys-d484e22ceeda2732/out/bindings.rs:3910:1
     |
3910 | / pub struct cdc_desc_func_telephone_call_state_reporting_capabilities_t {
3911 | |     #[doc = "< Size of this descriptor in bytes."]
3912 | |     pub bLength: u8,
3913 | |     #[doc = "< Descriptor Type, must be Class-Specific"]
...    |
3917 | |     pub bmCapabilities: cdc_desc_func_telephone_call_state_reporting_capabilities_t__bindgen_ty_1,
3918 | | }
     | |_^
     |
note: `cdc_desc_func_telephone_call_state_reporting_capabilities_t__bindgen_ty_1` has a `#[repr(align)]` attribute
    --> /Users/kevinpeck/Desktop/RepRap-RatRigVCore3/tinyusb-sys-rs/target/thumbv6m-none-eabi/debug/build/tinyusb-sys-d484e22ceeda2732/out/bindings.rs:3922:1
     |
3922 | / pub struct cdc_desc_func_telephone_call_state_reporting_capabilities_t__bindgen_ty_1 {
3923 | |     pub _bitfield_align_1: [u32; 0],
3924 | |     pub _bitfield_1: __BindgenBitfieldUnit<[u8; 4usize]>,
3925 | | }
     | |_^

For more information about this error, try `rustc --explain E0588`.
error: could not compile `tinyusb-sys` due to previous error

Caused by:
  process didn't exit successfully: `rustc --crate-name tinyusb_sys --edition=2021 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type lib --emit=dep-info,metadata,link -C embed-bitcode=no -C debuginfo=2 --cfg 'feature="cdc"' --cfg 'feature="device"' --cfg 'feature="rp2040"' -C metadata=222396e23cc7c407 -C extra-filename=-222396e23cc7c407 --out-dir /Users/kevinpeck/Desktop/RepRap-RatRigVCore3/tinyusb-sys-rs/target/thumbv6m-none-eabi/debug/deps --target thumbv6m-none-eabi -C incremental=/Users/kevinpeck/Desktop/RepRap-RatRigVCore3/tinyusb-sys-rs/target/thumbv6m-none-eabi/debug/incremental -L dependency=/Users/kevinpeck/Desktop/RepRap-RatRigVCore3/tinyusb-sys-rs/target/thumbv6m-none-eabi/debug/deps -L dependency=/Users/kevinpeck/Desktop/RepRap-RatRigVCore3/tinyusb-sys-rs/target/debug/deps --extern cty=/Users/kevinpeck/Desktop/RepRap-RatRigVCore3/tinyusb-sys-rs/target/thumbv6m-none-eabi/debug/deps/libcty-539500295d24c90b.rmeta -L native=/Users/kevinpeck/Desktop/RepRap-RatRigVCore3/tinyusb-sys-rs/target/thumbv6m-none-eabi/debug/build/tinyusb-sys-d484e22ceeda2732/out -l static=tinyusb` (exit status: 1)

Where the source looks like

/// \brief Telephone Call and Line State Reporting Capabilities Descriptor
/// \details The Telephone Call and Line State Reporting Capabilities functional descriptor describes the abilities of a
/// telephone device to report optional call and line states.
typedef struct TU_ATTR_PACKED
{
  uint8_t bLength            ; ///< Size of this descriptor in bytes.
  uint8_t bDescriptorType    ; ///< Descriptor Type, must be Class-Specific
  uint8_t bDescriptorSubType ; ///< Descriptor SubType one of above CDC_FUCN_DESC_
  struct {
    uint32_t interrupted_dialtone   : 1; ///< 0 : Reports only dialtone (does not differentiate between normal and interrupted dialtone). 1 : R
eports interrupted dialtone in addition to normal dialtone
    uint32_t ringback_busy_fastbusy : 1; ///< 0 : Reports only dialing state. 1 : Reports ringback, busy, and fast busy states.
    uint32_t caller_id              : 1; ///< 0 : Does not report caller ID. 1 : Reports caller ID information.
    uint32_t incoming_distinctive   : 1; ///< 0 : Reports only incoming ringing. 1 : Reports incoming distinctive ringing patterns.
    uint32_t dual_tone_multi_freq   : 1; ///< 0 : Cannot report dual tone multi-frequency (DTMF) digits input remotely over the telephone line.
 1 : Can report DTMF digits input remotely over the telephone line.
    uint32_t line_state_change      : 1; ///< 0 : Does not support line state change notification. 1 : Does support line state change notificat
ion
    uint32_t TU_RESERVED            : 26;
  } bmCapabilities;
}cdc_desc_func_telephone_call_state_reporting_capabilities_t;

[ojeda]

Seen by the kernel as well at: https://lore.kernel.org/all/[email protected]/

struct alt_instr {
	s32 instr_offset;	/* original instruction */
	s32 repl_offset;	/* offset to replacement instruction */

	union {
		struct {
			u32 cpuid: 16;	/* CPUID bit set for replacement */
			u32 flags: 16;	/* patching control flags */
		};
		u32 ft_flgs;
	};

	u8  instrlen;		/* length of original instruction */
	u8  replacementlen;	/* length of new instruction */
} __packed;

[0x5459]

Encountered the same problem when binding spdk.

#include <stdint.h>

struct __attribute__((packed)) spdk_nvme_sgl_descriptor {
	uint64_t address;
	union {
		struct {
			uint8_t reserved[7];
			uint8_t subtype	: 4;
			uint8_t type	: 4;
		} generic;

		struct {
			uint32_t length;
			uint8_t reserved[3];
			uint8_t subtype	: 4;
			uint8_t type	: 4;
		} unkeyed;

		struct {
			uint64_t length		: 24;
			uint64_t key		: 32;
			uint64_t subtype	: 4;
			uint64_t type		: 4;
		} keyed;
	};
};

[tomDev5]

Any solution?

[ic3man5]

Here is a simple breakdown of the actual issue at hand. It looks the rust compiler can't align and pack at the same time which is causing the issue.

#[derive(Debug, Clone, Copy)]
#[repr(C, packed(2))]
struct PackedAlignedTest {
    a: u32,
    b: u16,
    inner: PackedAlignedInnerTest,
}

#[derive(Debug, Clone, Copy)]
#[repr(C, align(2))]
struct PackedAlignedInnerTest {
    c: u32,
    d: u16,
}

fn main() {
    let packed_aligned_test = PackedAlignedTest { 
        a: 0, 
        b: 1, 
        inner: PackedAlignedInnerTest { 
            c: 2, 
            d: 3 
        }
    };
    println!("{packed_aligned_test:#?}");
}

error[E0588]: packed type cannot transitively contain a `#[repr(align)]` type
  --> src/main.rs:3:1
   |
3  | struct PackedAlignedTest {
   | ^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: `PackedAlignedInnerTest` has a `#[repr(align)]` attribute
  --> src/main.rs:11:1
   |
11 | struct PackedAlignedInnerTest {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0588`.
error: could not compile `playground` (bin "playground") due to previous error

From what I can tell there was an oversight in this issue: https://github.com/rust-lang/rust/issues/33158

Currently #[repr(packed())] structs cannot transitively contain #[repr(align())] structs due to differing behavior between msvc and gcc. Do we want to keep this a hard error, pick one behavior over the other, or provide some way to choose which behavior is desired?

This was never resolved and missed in review.