Rust PDL backend (caa5be2f) · Commits · e / os / android_packages_modules_Bluetooth

tools/pdl/Android.bp

+41 −0

Original line number	Diff line number	Diff line
		@@ -289,3 +289,44 @@ python_test_host {
		":pypdl",
		],
		}

		// Defaults for the rust_noalloc backend
		genrule_defaults {
		name: "pdl_rust_noalloc_generator_defaults",
		cmd: "set -o pipefail;" +
		" $(location :pdl) --output-format rust_no_alloc $(in) \|" +
		" $(location :rustfmt) > $(out)",
		tools: [
		":pdl",
		":rustfmt",
		],
		}

		// Generate the rust_noalloc backend srcs against the little-endian test vectors
		genrule {
		name: "pdl_rust_noalloc_le_test_backend_srcs",
		defaults: ["pdl_rust_noalloc_generator_defaults"],
		srcs: ["tests/canonical/le_rust_noalloc_test_file.pdl"],
		out: ["_packets.rs"],
		}

		// Generate the rust_noalloc test harness srcs for the supplied test vectors
		genrule {
		name: "pdl_rust_noalloc_le_test_gen_harness",
		cmd: "set -o pipefail;" +
		" $(location :pdl) $(in) --output-format rust_no_alloc_test" +
		" > $(out)",
		srcs: ["tests/canonical/le_rust_noalloc_test_file.pdl"],
		out: ["test_rust_noalloc_parser.rs"],
		tools: [":pdl"],
		}

		// The test target for rust_noalloc
		rust_test_host {
		name: "pdl_rust_noalloc_le_test",
		srcs: [
		":pdl_rust_noalloc_le_test_gen_harness",
		":pdl_rust_noalloc_le_test_backend_srcs",
		],
		test_suites: ["general-tests"],
		}
		No newline at end of file

tools/pdl/src/ast.rs

+4 −0

Original line number	Diff line number	Diff line
		@@ -79,6 +79,8 @@ pub enum Field {
		Size { loc: SourceRange, field_id: String, width: usize },
		#[serde(rename = "count_field")]
		Count { loc: SourceRange, field_id: String, width: usize },
		#[serde(rename = "elementsize_field")]
		ElementSize { loc: SourceRange, field_id: String, width: usize },
		#[serde(rename = "body_field")]
		Body { loc: SourceRange },
		#[serde(rename = "payload_field")]
		@@ -260,6 +262,7 @@ impl Field {
		Field::Checksum { loc, .. }
		\| Field::Padding { loc, .. }
		\| Field::Size { loc, .. }
		\| Field::ElementSize { loc, .. }
		\| Field::Count { loc, .. }
		\| Field::Body { loc, .. }
		\| Field::Payload { loc, .. }
		@@ -277,6 +280,7 @@ impl Field {
		Field::Checksum { .. }
		\| Field::Padding { .. }
		\| Field::Size { .. }
		\| Field::ElementSize { .. }
		\| Field::Count { .. }
		\| Field::Body { .. }
		\| Field::Payload { .. }

tools/pdl/src/backends.rs

+2 −0

Original line number	Diff line number	Diff line
		//! Compiler backends.

		pub mod intermediate;
		pub mod json;
		pub mod rust;
		pub mod rust_no_allocation;

tools/pdl/src/backends/intermediate.rs

0 → 100644

+516 −0

Original line number	Diff line number	Diff line
		use std::collections::{hash_map::Entry, HashMap};

		use crate::ast;

		pub struct Schema<'a> {
		pub packets_and_structs: HashMap<&'a str, PacketOrStruct<'a>>,
		pub enums: HashMap<&'a str, Enum<'a>>,
		}

		pub struct PacketOrStruct<'a> {
		pub computed_offsets: HashMap<ComputedOffsetId<'a>, ComputedOffset<'a>>,
		pub computed_values: HashMap<ComputedValueId<'a>, ComputedValue<'a>>,
		/// whether the parse of this packet needs to know its length,
		/// or if the packet can determine its own length
		pub length: PacketOrStructLength,
		}

		pub enum PacketOrStructLength {
		Static(usize),
		Dynamic,
		NeedsExternal,
		}

		pub struct Enum<'a> {
		pub tags: &'a [ast::Tag],
		pub width: usize,
		}

		#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
		pub enum ComputedValueId<'a> {
		// needed for array fields + varlength structs - note that this is in OCTETS, not BITS
		// this always works since array entries are either structs (which are byte-aligned) or integer-octet-width scalars
		FieldSize(&'a str),

		// needed for arrays with fixed element size (otherwise codegen will loop!)
		FieldElementSize(&'a str), // note that this is in OCTETS, not BITS
		FieldCount(&'a str),

		Custom(u16),
		}

		#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
		pub enum ComputedOffsetId<'a> {
		// these quantities are known by the runtime
		HeaderStart,

		// if the packet needs its length, this will be supplied. otherwise it will be computed
		PacketEnd,

		// these quantities will be computed and stored in computed_values
		FieldOffset(&'a str), // needed for all fields, measured in BITS
		FieldEndOffset(&'a str), // needed only for Payload + Body fields, as well as variable-size structs (not arrays), measured in BITS
		Custom(u16),
		TrailerStart,
		}

		pub enum ComputedValue<'a> {
		Constant(usize),
		CountStructsUpToSize {
		base_id: ComputedOffsetId<'a>,
		size: ComputedValueId<'a>,
		struct_type: &'a str,
		},
		SizeOfNStructs {
		base_id: ComputedOffsetId<'a>,
		n: ComputedValueId<'a>,
		struct_type: &'a str,
		},
		Product(ComputedValueId<'a>, ComputedValueId<'a>),
		Divide(ComputedValueId<'a>, ComputedValueId<'a>),
		Difference(ComputedOffsetId<'a>, ComputedOffsetId<'a>),
		ValueAt {
		offset: ComputedOffsetId<'a>,
		width: usize,
		},
		}

		#[derive(Copy, Clone)]
		pub enum ComputedOffset<'a> {
		ConstantPlusOffsetInBits(ComputedOffsetId<'a>, i64),
		SumWithOctets(ComputedOffsetId<'a>, ComputedValueId<'a>),
		Alias(ComputedOffsetId<'a>),
		}

		pub fn generate(file: &ast::File) -> Result<Schema, String> {
		let mut schema = Schema { packets_and_structs: HashMap::new(), enums: HashMap::new() };
		match file.endianness.value {
		ast::EndiannessValue::LittleEndian => {}
		_ => unimplemented!("Only little_endian endianness supported"),
		};

		for decl in &file.declarations {
		process_decl(&mut schema, decl);
		}

		Ok(schema)
		}

		fn process_decl<'a>(schema: &mut Schema<'a>, decl: &'a ast::Decl) {
		match decl {
		ast::Decl::Enum { id, tags, width, .. } => process_enum(schema, id, tags, *width),
		ast::Decl::Packet { id, fields, .. } \| ast::Decl::Struct { id, fields, .. } => {
		process_packet_or_struct(schema, id, fields)
		}
		ast::Decl::Group { .. } => todo!(),
		_ => unimplemented!("type {decl:?} not supported"),
		}
		}

		fn process_enum<'a>(schema: &mut Schema<'a>, id: &'a str, tags: &'a [ast::Tag], width: usize) {
		schema.enums.insert(id, Enum { tags, width });
		schema.packets_and_structs.insert(
		id,
		PacketOrStruct {
		computed_offsets: HashMap::new(),
		computed_values: HashMap::new(),
		length: PacketOrStructLength::Static(width),
		},
		);
		}

		fn process_packet_or_struct<'a>(schema: &mut Schema<'a>, id: &'a str, fields: &'a [ast::Field]) {
		schema.packets_and_structs.insert(id, compute_getters(schema, fields));
		}

		fn compute_getters<'a>(schema: &Schema<'a>, fields: &'a [ast::Field]) -> PacketOrStruct<'a> {
		let mut prev_pos_id = None;
		let mut curr_pos_id = ComputedOffsetId::HeaderStart;
		let mut computed_values = HashMap::new();
		let mut computed_offsets = HashMap::new();

		let mut cnt = 0;

		let one_id = ComputedValueId::Custom(cnt);
		let one_val = ComputedValue::Constant(1);
		cnt += 1;
		computed_values.insert(one_id, one_val);

		let mut needs_length = false;

		for field in fields {
		// populate this only if we are an array with a knowable size
		let mut next_prev_pos_id = None;

		let next_pos = match field {
		ast::Field::Reserved { width, .. } => {
		ComputedOffset::ConstantPlusOffsetInBits(curr_pos_id, *width as i64)
		}
		ast::Field::Scalar { id, width, .. } => {
		computed_offsets
		.insert(ComputedOffsetId::FieldOffset(id), ComputedOffset::Alias(curr_pos_id));
		ComputedOffset::ConstantPlusOffsetInBits(curr_pos_id, *width as i64)
		}
		ast::Field::Fixed { width, enum_id, .. } => {
		let offset = match (width, enum_id) {
		(Some(width), _) => *width,
		(_, Some(enum_id)) => schema.enums[enum_id.as_str()].width,
		_ => unreachable!(),
		};
		ComputedOffset::ConstantPlusOffsetInBits(curr_pos_id, offset as i64)
		}
		ast::Field::Size { field_id, width, .. } => {
		computed_values.insert(
		ComputedValueId::FieldSize(field_id),
		ComputedValue::ValueAt { offset: curr_pos_id, width: *width },
		);
		ComputedOffset::ConstantPlusOffsetInBits(curr_pos_id, *width as i64)
		}
		ast::Field::Count { field_id, width, .. } => {
		computed_values.insert(
		ComputedValueId::FieldCount(field_id.as_str()),
		ComputedValue::ValueAt { offset: curr_pos_id, width: *width },
		);
		ComputedOffset::ConstantPlusOffsetInBits(curr_pos_id, *width as i64)
		}
		ast::Field::ElementSize { field_id, width, .. } => {
		computed_values.insert(
		ComputedValueId::FieldElementSize(field_id),
		ComputedValue::ValueAt { offset: curr_pos_id, width: *width },
		);
		ComputedOffset::ConstantPlusOffsetInBits(curr_pos_id, *width as i64)
		}
		ast::Field::Group { .. } => {
		unimplemented!("this should be removed by the linter...")
		}
		ast::Field::Checksum { .. } => unimplemented!("checksum not supported"),
		ast::Field::Body { .. } => {
		computed_offsets.insert(
		ComputedOffsetId::FieldOffset("_body_"),
		ComputedOffset::Alias(curr_pos_id),
		);
		let computed_size_id = ComputedValueId::FieldSize("_body_");
		let end_offset = if computed_values.contains_key(&computed_size_id) {
		ComputedOffset::SumWithOctets(curr_pos_id, computed_size_id)
		} else {
		if needs_length {
		panic!("only one variable-length field can exist")
		}
		needs_length = true;
		ComputedOffset::Alias(ComputedOffsetId::TrailerStart)
		};
		computed_offsets.insert(ComputedOffsetId::FieldEndOffset("_body_"), end_offset);
		end_offset
		}
		ast::Field::Payload { size_modifier, .. } => {
		if size_modifier.is_some() {
		unimplemented!("size modifiers not supported")
		}
		computed_offsets.insert(
		ComputedOffsetId::FieldOffset("_payload_"),
		ComputedOffset::Alias(curr_pos_id),
		);
		let computed_size_id = ComputedValueId::FieldSize("_payload_");
		let end_offset = if computed_values.contains_key(&computed_size_id) {
		ComputedOffset::SumWithOctets(curr_pos_id, computed_size_id)
		} else {
		if needs_length {
		panic!("only one variable-length field can exist")
		}
		needs_length = true;
		ComputedOffset::Alias(ComputedOffsetId::TrailerStart)
		};
		computed_offsets.insert(ComputedOffsetId::FieldEndOffset("_payload_"), end_offset);
		end_offset
		}
		ast::Field::Array {
		id,
		width,
		type_id,
		size_modifier,
		size: statically_known_count,
		..
		} => {
		if size_modifier.is_some() {
		unimplemented!("size modifiers not supported")
		}

		computed_offsets
		.insert(ComputedOffsetId::FieldOffset(id), ComputedOffset::Alias(curr_pos_id));

		// there are a few parameters to consider when parsing arrays
		// 1: the count of elements
		// 2: the total byte size (possibly by subtracting out the len of the trailer)
		// 3: whether the structs know their own lengths
		// parsing is possible if we know (1 OR 2) AND 3

		if let Some(count) = statically_known_count {
		computed_values
		.insert(ComputedValueId::FieldCount(id), ComputedValue::Constant(*count));
		}

		let statically_known_width_in_bits = if let Some(type_id) = type_id {
		if let PacketOrStructLength::Static(len) =
		schema.packets_and_structs[type_id.as_str()].length
		{
		Some(len)
		} else {
		None
		}
		} else if let Some(width) = width {
		Some(*width)
		} else {
		unreachable!()
		};

		// whether the count is known prior to parsing the field
		let is_count_known = computed_values.contains_key(&ComputedValueId::FieldCount(id));
		// whether the total field size is explicitly specified
		let is_total_size_known =
		computed_values.contains_key(&ComputedValueId::FieldSize(id));

		let element_size = if let Some(type_id) = type_id {
		match schema.packets_and_structs[type_id.as_str()].length {
		PacketOrStructLength::Static(width) => {
		assert!(width % 8 == 0);
		Some(width / 8)
		}
		PacketOrStructLength::Dynamic => None,
		PacketOrStructLength::NeedsExternal => None,
		}
		} else if let Some(width) = width {
		assert!(width % 8 == 0);
		Some(width / 8)
		} else {
		unreachable!()
		};
		if let Some(element_size) = element_size {
		computed_values.insert(
		ComputedValueId::FieldElementSize(id),
		ComputedValue::Constant(element_size),
		);
		}

		// whether we can know the length of each element in the array by greedy parsing,
		let structs_know_length = if let Some(type_id) = type_id {
		match schema.packets_and_structs[type_id.as_str()].length {
		PacketOrStructLength::Static(_) => true,
		PacketOrStructLength::Dynamic => true,
		PacketOrStructLength::NeedsExternal => {
		computed_values.contains_key(&ComputedValueId::FieldElementSize(id))
		}
		}
		} else {
		width.is_some()
		};

		if !structs_know_length {
		panic!("structs need to know their own length, if they live in an array")
		}

		let mut out = None;
		if let Some(count) = statically_known_count {
		if let Some(width) = statically_known_width_in_bits {
		// the fast path, if the count and width are statically known, is to just immediately multiply
		// otherwise this becomes a dynamic computation
		assert!(width % 8 == 0);
		computed_values.insert(
		ComputedValueId::FieldSize(id),
		ComputedValue::Constant(count * width / 8),
		);
		out = Some(ComputedOffset::ConstantPlusOffsetInBits(
		curr_pos_id,
		(count * width) as i64,
		));
		}
		}

		// note: this introduces a forward dependency with the total_size_id
		// however, the FieldSize(id) only depends on the FieldElementSize(id) if FieldCount() == true
		// thus, there will never be an infinite loop, since the FieldElementSize(id) only depends on the
		// FieldSize() if the FieldCount() is not unknown
		if !is_count_known {
		// the count is not known statically, or from earlier in the packet
		// thus, we must compute it from the total size of the field, known either explicitly or implicitly via the trailer
		// the fast path is to do a divide, but otherwise we need to loop over the TLVs
		computed_values.insert(
		ComputedValueId::FieldCount(id),
		if computed_values.contains_key(&ComputedValueId::FieldElementSize(id)) {
		ComputedValue::Divide(
		ComputedValueId::FieldSize(id),
		ComputedValueId::FieldElementSize(id),
		)
		} else {
		ComputedValue::CountStructsUpToSize {
		base_id: curr_pos_id,
		size: ComputedValueId::FieldSize(id),
		struct_type: type_id.as_ref().unwrap(),
		}
		},
		);
		}

		if let Some(out) = out {
		// we are paddable if the total size is known
		next_prev_pos_id = Some(curr_pos_id);
		out
		} else if is_total_size_known {
		// we are paddable if the total size is known
		next_prev_pos_id = Some(curr_pos_id);
		ComputedOffset::SumWithOctets(curr_pos_id, ComputedValueId::FieldSize(id))
		} else if is_count_known {
		// we are paddable if the total count is known, since structs know their lengths
		next_prev_pos_id = Some(curr_pos_id);

		computed_values.insert(
		ComputedValueId::FieldSize(id),
		if computed_values.contains_key(&ComputedValueId::FieldElementSize(id)) {
		ComputedValue::Product(
		ComputedValueId::FieldCount(id),
		ComputedValueId::FieldElementSize(id),
		)
		} else {
		ComputedValue::SizeOfNStructs {
		base_id: curr_pos_id,
		n: ComputedValueId::FieldCount(id),
		struct_type: type_id.as_ref().unwrap(),
		}
		},
		);
		ComputedOffset::SumWithOctets(curr_pos_id, ComputedValueId::FieldSize(id))
		} else {
		// we can try to infer the total size if we are still in the header
		// however, we are not paddable in this case
		next_prev_pos_id = None;

		if needs_length {
		panic!("either the total size, or the count of elements in an array, must be known")
		}
		// now we are in the trailer
		computed_values.insert(
		ComputedValueId::FieldSize(id),
		ComputedValue::Difference(ComputedOffsetId::TrailerStart, curr_pos_id),
		);
		needs_length = true;
		ComputedOffset::Alias(ComputedOffsetId::TrailerStart)
		}
		}
		ast::Field::Padding { size, .. } => {
		if let Some(prev_pos_id) = prev_pos_id {
		ComputedOffset::ConstantPlusOffsetInBits(prev_pos_id, *size as i64)
		} else {
		panic!("padding must follow array field with known total size")
		}
		}
		ast::Field::Typedef { id, type_id, .. } => {
		computed_offsets
		.insert(ComputedOffsetId::FieldOffset(id), ComputedOffset::Alias(curr_pos_id));

		match schema.packets_and_structs[type_id.as_str()].length {
		PacketOrStructLength::Static(len) => {
		ComputedOffset::ConstantPlusOffsetInBits(curr_pos_id, len as i64)
		}
		PacketOrStructLength::Dynamic => {
		computed_values.insert(
		ComputedValueId::FieldSize(id),
		ComputedValue::SizeOfNStructs {
		base_id: curr_pos_id,
		n: one_id,
		struct_type: type_id,
		},
		);
		ComputedOffset::SumWithOctets(curr_pos_id, ComputedValueId::FieldSize(id))
		}
		PacketOrStructLength::NeedsExternal => {
		let end_offset = if let Entry::Vacant(entry) =
		computed_values.entry(ComputedValueId::FieldSize(id))
		{
		// its size is presently unknown
		if needs_length {
		panic!(
		"cannot have multiple variable-length fields in a single packet/struct"
		)
		}
		// we are now in the trailer
		entry.insert(ComputedValue::Difference(
		ComputedOffsetId::TrailerStart,
		curr_pos_id,
		));
		needs_length = true;
		ComputedOffset::Alias(ComputedOffsetId::TrailerStart)
		} else {
		ComputedOffset::SumWithOctets(
		curr_pos_id,
		ComputedValueId::FieldSize(id),
		)
		};
		computed_offsets.insert(ComputedOffsetId::FieldEndOffset(id), end_offset);
		end_offset
		}
		}

		// it is possible to size a struct in this variant of PDL, even though the linter doesn't allow it
		}
		};

		prev_pos_id = next_prev_pos_id;
		curr_pos_id = ComputedOffsetId::Custom(cnt);
		cnt += 1;
		computed_offsets.insert(curr_pos_id, next_pos);
		}

		// TODO(aryarahul): simplify compute graph to improve trailer resolution?

		// we are now at the end of the packet
		let length = if needs_length {
		// if we needed the length, use the PacketEnd and length to reconstruct the TrailerStart
		let trailer_length =
		compute_length_to_goal(&computed_offsets, curr_pos_id, ComputedOffsetId::TrailerStart)
		.expect("trailers should have deterministic length");
		computed_offsets.insert(
		ComputedOffsetId::TrailerStart,
		ComputedOffset::ConstantPlusOffsetInBits(ComputedOffsetId::PacketEnd, -trailer_length),
		);
		PacketOrStructLength::NeedsExternal
		} else {
		// otherwise, try to reconstruct the full length, if possible
		let full_length =
		compute_length_to_goal(&computed_offsets, curr_pos_id, ComputedOffsetId::HeaderStart);
		if let Some(full_length) = full_length {
		computed_offsets.insert(
		ComputedOffsetId::PacketEnd,
		ComputedOffset::ConstantPlusOffsetInBits(
		ComputedOffsetId::HeaderStart,
		full_length,
		),
		);
		PacketOrStructLength::Static(full_length as usize)
		} else {
		computed_offsets
		.insert(ComputedOffsetId::PacketEnd, ComputedOffset::Alias(curr_pos_id));
		PacketOrStructLength::Dynamic
		}
		};

		PacketOrStruct { computed_values, computed_offsets, length }
		}

		fn compute_length_to_goal(
		computed_offsets: &HashMap<ComputedOffsetId, ComputedOffset>,
		start: ComputedOffsetId,
		goal: ComputedOffsetId,
		) -> Option<i64> {
		let mut out = 0;
		let mut pos = start;
		while pos != goal {
		match computed_offsets.get(&pos).ok_or_else(\|\| format!("key {pos:?} not found")).unwrap() {
		ComputedOffset::ConstantPlusOffsetInBits(base_id, offset) => {
		out += offset;
		pos = *base_id;
		}
		ComputedOffset::Alias(alias) => pos = *alias,
		ComputedOffset::SumWithOctets { .. } => return None,
		}
		}
		Some(out)
		}