repc-impl 0.1.1

// SPDX-License-Identifier: MIT OR Apache-2.0
use crate::builder::common::{
    ignore_non_zero_sized_bitfield_type_alignment, ignore_zero_sized_bitfield_type_alignmont,
    min_zero_width_bitfield_alignment, unnamed_field_affects_record_alignment,
};
use crate::builder::sysv_like::{Dialect, RecordLayoutBuilder};
use crate::layout::{FieldLayout, RecordField, RecordKind, Type, TypeLayout};
use crate::result::{err, ErrorType, Result};
use crate::target::{system_compiler, Compiler, Target};
use crate::util::{
    align_to, annotation_alignment, is_attr_packed, size_add, MaxAssign, MinAssign, MinExt,
    BITS_PER_BYTE,
};

pub(crate) fn compute_layout(target: Target, ty: &Type<()>) -> Result<Type<TypeLayout>> {
    super::compute_layout(target, ty, Dialect::Sysv)
}

pub(super) fn layout_fields(
    rlb: &mut RecordLayoutBuilder,
    fields: &[RecordField<()>],
) -> Result<()> {
    for f in fields {
        layout_field(rlb, f)?;
    }
    Ok(())
}

fn layout_field(rlb: &mut RecordLayoutBuilder, field: &RecordField<()>) -> Result<()> {
    let ty = super::compute_layout(rlb.target, &field.ty, Dialect::Sysv)?;
    let layout = match field.bit_width {
        Some(size_bits) => layout_bit_field(
            rlb,
            ty.layout.size_bits,
            ty.layout.field_alignment_bits,
            field,
            size_bits,
        ),
        None => layout_regular_field(rlb, ty.layout, field),
    }?;
    rlb.record_fields.push(RecordField {
        layout,
        annotations: field.annotations.clone(),
        named: field.named,
        bit_width: field.bit_width,
        ty,
    });
    Ok(())
}

fn layout_bit_field(
    rlb: &mut RecordLayoutBuilder,
    ty_size_bits: u64,
    mut ty_field_alignment_bits: u64,
    field: &RecordField<()>,
    width: u64,
) -> Result<Option<FieldLayout>> {
    if width > 0 {
        if width > ty_size_bits {
            return Err(err(ErrorType::OversizedBitfield));
        }
        // Some targets ignore the alignment of the underlying type when laying out
        // non-zero-sized bit-fields. See test case 0072. On such targets, bit-fields never
        // cross a storage boundary. See test case 0081.
        if ignore_non_zero_sized_bitfield_type_alignment(rlb.target) {
            ty_field_alignment_bits = 1;
        }
    } else {
        // Some targets ignore the alignment of the underlying type when laying out
        // zero-sized bit-fields. See test case 0073.
        if ignore_zero_sized_bitfield_type_alignmont(rlb.target) {
            ty_field_alignment_bits = 1;
        }
        // Some targets have a minimum alignment of zero-sized bit-fields. See test case
        // 0074.
        ty_field_alignment_bits.assign_max(min_zero_width_bitfield_alignment(rlb.target));
    }
    // __attribute__((packed)) on the record is identical to __attribute__((packed)) on each
    // field. See test case 0067.
    let attr_packed = rlb.attr_packed || is_attr_packed(&field.annotations);
    let has_packing_annotations = attr_packed || rlb.max_field_alignment_bits.is_some();
    let annotation_alignment = annotation_alignment(rlb.target, &field.annotations).unwrap_or(1);
    let first_unused_bit = match rlb.kind {
        RecordKind::Union => 0,
        RecordKind::Struct => rlb.size_bits,
    };
    let mut field_alignment_bits = 1;
    if width == 0 {
        // A zero-sized bit-field aligns the starting position for subsequent fields
        // to the field alignment of the type unless it was explicitly increased.
        // __attribute__((packed)) and #pragma pack are ignored. See test case 0082.
        field_alignment_bits = ty_field_alignment_bits.max(annotation_alignment);
    } else if system_compiler(rlb.target) == Compiler::Gcc {
        // On GCC, the field alignment is at least the alignment requested by annotations
        // except as restricted by #pragma pack. See test case 0083.
        field_alignment_bits = annotation_alignment.min2(rlb.max_field_alignment_bits);
        // On GCC, if there are no packing annotations and
        // - the field would otherwise start at an offset such that it would cross a
        //   storage boundary or
        // - the alignment of the type is larger than its size,
        // then it is aligned to the type's field alignment. See test case 0083.
        if !has_packing_annotations {
            let start_bit = align_to(first_unused_bit, field_alignment_bits)?;
            let field_crosses_storage_boundary =
                start_bit % ty_field_alignment_bits + width > ty_size_bits;
            if ty_field_alignment_bits > ty_size_bits || field_crosses_storage_boundary {
                field_alignment_bits.assign_max(ty_field_alignment_bits);
            }
        }
    } else {
        assert_eq!(system_compiler(rlb.target), Compiler::Clang);
        // On Clang, the alignment requested by annotations is not respected if it is
        // larger than the value of #pragma pack. See test case 0083.
        if annotation_alignment <= rlb.max_field_alignment_bits.unwrap_or(u64::MAX) {
            field_alignment_bits.assign_max(annotation_alignment);
        }
        // On Clang, if there are no packing annotations and the field would cross a
        // storage boundary if it were positioned at the first unused bit in the record,
        // it is aligned to the type's field alignment. See test case 0083.
        if !has_packing_annotations {
            let field_crosses_storage_boundary =
                first_unused_bit % ty_field_alignment_bits + width > ty_size_bits;
            if field_crosses_storage_boundary {
                field_alignment_bits.assign_max(ty_field_alignment_bits);
            }
        }
    }
    let offset_bits = align_to(first_unused_bit, field_alignment_bits)?;
    rlb.size_bits.assign_max(size_add(offset_bits, width)?);
    // Unnamed fields do not contribute to the record alignment except on a few targets.
    // See test case 0079.
    if field.named || unnamed_field_affects_record_alignment(rlb.target) {
        let inherited_alignment_bits;
        if width == 0 {
            // If the width is 0, #pragma pack and __attribute__((packed)) are ignored.
            // See test case 0075.
            inherited_alignment_bits = ty_field_alignment_bits.max(annotation_alignment);
        } else if let Some(max_field_alignment_bits) = rlb.max_field_alignment_bits {
            // Otherwise, if a #pragma pack is in effect, __attribute__((packed)) on the field or
            // record is ignored. See test case 0076.
            inherited_alignment_bits = ty_field_alignment_bits
                .max(annotation_alignment)
                .min(max_field_alignment_bits);
        } else if attr_packed {
            // Otherwise, if the field or the record is packed, the field alignment is 1 bit unless
            // it is explicitly increased with __attribute__((aligned)). See test case 0077.
            inherited_alignment_bits = annotation_alignment;
        } else {
            // Otherwise, the field alignment is the field alignment of the underlying type unless
            // it is explicitly increased with __attribute__((aligned)). See test case 0078.
            inherited_alignment_bits = ty_field_alignment_bits.max(annotation_alignment);
        }
        rlb.alignment_bits.assign_max(inherited_alignment_bits);
    }
    match field.named {
        true => Ok(Some(FieldLayout {
            offset_bits,
            size_bits: width,
        })),
        false => Ok(None),
    }
}

fn layout_regular_field(
    rlb: &mut RecordLayoutBuilder,
    type_layout: TypeLayout,
    field: &RecordField<()>,
) -> Result<Option<FieldLayout>> {
    let mut field_alignment_bits = type_layout.field_alignment_bits;
    // If the struct or the field is packed, then the alignment of the underlying type is
    // ignored. See test case 0084.
    if rlb.attr_packed || is_attr_packed(&field.annotations) {
        field_alignment_bits = BITS_PER_BYTE;
    }
    // The field alignment can be increased by __attribute__((aligned)) annotations on the
    // field. See test case 0085.
    field_alignment_bits.assign_max(annotation_alignment(rlb.target, &field.annotations));
    // #pragma pack takes precedence over all other attributes. See test cases 0084 and
    // 0085.
    field_alignment_bits.assign_min(rlb.max_field_alignment_bits);
    let offset_bits = match rlb.kind {
        // A struct field starts at the next offset in the struct that is properly
        // aligned with respect to the start of the struct.
        RecordKind::Struct => align_to(rlb.size_bits, field_alignment_bits)?,
        // A union field always starts at offset 0.
        RecordKind::Union => 0,
    };
    let size_bits = type_layout.size_bits;
    rlb.size_bits.assign_max(size_add(offset_bits, size_bits)?);
    // The alignment of a record is the maximum of its field alignments. See test cases
    // 0084, 0085, 0086.
    rlb.alignment_bits.assign_max(field_alignment_bits);
    Ok(Some(FieldLayout {
        offset_bits,
        size_bits,
    }))
}