wasmparser: add RelocSectionReader (#1511)

Co-authored-by: Andy Li <andylizi666@gmail.com>

crates/wasmparser/src/readers/core.rs

@@ -15,6 +15,7 @@ mod memories;
 mod names;
 mod operators;
 mod producers;
+mod reloc;
 mod tables;
 mod tags;
 mod types;
@@ -36,6 +37,7 @@ pub use self::memories::*;
 pub use self::names::*;
 pub use self::operators::*;
 pub use self::producers::*;
+pub use self::reloc::*;
 pub use self::tables::*;
 pub use self::tags::*;
 pub use self::types::*;

crates/wasmparser/src/readers/core/reloc.rs

@@ -0,0 +1,302 @@
+use std::ops::Range;
+
+use crate::{BinaryReader, FromReader, Result, SectionLimited};
+
+/// Reader for relocation entries within a `reloc.*` section.
+pub type RelocationEntryReader<'a> = SectionLimited<'a, RelocationEntry>;
+
+/// Reader for reloc.* sections as defined by
+/// https://github.com/WebAssembly/tool-conventions/blob/main/Linking.md#relocation-sections.
+#[derive(Debug, Clone)]
+pub struct RelocSectionReader<'a> {
+    section: u32,
+    range: Range<usize>,
+    entries: SectionLimited<'a, RelocationEntry>,
+}
+
+impl<'a> RelocSectionReader<'a> {
+    /// Creates a new reader for a `reloc.*` section starting at
+    /// `original_position` within the wasm file.
+    pub fn new(data: &'a [u8], original_position: usize) -> Result<Self> {
+        let mut reader = BinaryReader::new_with_offset(data, original_position);
+        let range = reader.range().clone();
+        let section = reader.read_var_u32()?;
+        Ok(Self {
+            section,
+            range,
+            entries: SectionLimited::new(reader.remaining_buffer(), reader.original_position())?,
+        })
+    }
+
+    /// Index of section to which the relocations apply.
+    pub fn section_index(&self) -> u32 {
+        self.section
+    }
+
+    /// The byte range of the entire section.
+    pub fn range(&self) -> Range<usize> {
+        self.range.clone()
+    }
+
+    /// The relocation entries.
+    pub fn entries(&self) -> SectionLimited<'a, RelocationEntry> {
+        self.entries.clone()
+    }
+}
+
+macro_rules! back_to_enum {
+    ($(#[$meta:meta])+ $vis:vis enum $name:ident {
+        $($(#[$vmeta:meta])* $vname:ident $(= $val:expr)?,)*
+    }) => {
+        $(#[$meta])*
+        $vis enum $name {
+            $($(#[$vmeta])* $vname $(= $val)?,)*
+        }
+
+        impl std::convert::TryFrom<u8> for $name {
+            type Error = ();
+
+            fn try_from(v: u8) -> Result<Self, Self::Error> {
+                match v {
+                    $(x if x == $name::$vname as u8 => Ok($name::$vname),)*
+                    _ => Err(()),
+                }
+            }
+        }
+    }
+}
+
+back_to_enum! {
+
+    /// Relocation entry type. Each entry type corresponds to one of the
+    /// `R_WASM_*` constants defined at
+    /// https://github.com/llvm/llvm-project/blob/main/llvm/include/llvm/BinaryFormat/WasmRelocs.def
+    /// and
+    /// https://github.com/WebAssembly/tool-conventions/blob/main/Linking.md#relocation-sections.
+    #[derive(Debug, PartialEq, Eq, Hash, Clone, Copy)]
+    #[repr(u8)]
+    pub enum RelocationType {
+        /// A function index encoded as a 5-byte varuint32. Used for the
+        /// immediate argument of a call instruction. (since LLVM 10.0)
+        FunctionIndexLeb = 0,
+
+        /// A function table index encoded as a 5-byte varint32. Used to refer
+        /// to the immediate argument of a i32.const instruction, e.g. taking
+        /// the address of a function. (since LLVM 10.0)
+        TableIndexSleb = 1,
+
+        /// A function table index encoded as a uint32, e.g. taking the address
+        /// of a function in a static data initializer. (since LLVM 10.0)
+        TableIndexI32 = 2,
+
+        /// A linear memory index encoded as a 5-byte varuint32. Used for the
+        /// immediate argument of a load or store instruction, e.g. directly
+        /// loading from or storing to a C++ global. (since LLVM 10.0)
+        MemoryAddrLeb = 3,
+
+        /// A linear memory index encoded as a 5-byte varint32. Used for the
+        /// immediate argument of a i32.const instruction, e.g. taking the
+        /// address of a C++ global. (since LLVM 10.0)
+        MemoryAddrSleb = 4,
+
+        /// A linear memory index encoded as a uint32, e.g. taking the address
+        /// of a C++ global in a static data initializer. (since LLVM 10.0)
+        MemoryAddrI32 = 5,
+
+        /// A type index encoded as a 5-byte varuint32, e.g. the type immediate
+        /// in a call_indirect. (since LLVM 10.0)
+        TypeIndexLeb = 6,
+
+        /// A global index encoded as a 5-byte varuint32, e.g. the index
+        /// immediate in a get_global. (since LLVM 10.0)
+        GlobalIndexLeb = 7,
+
+        /// A byte offset within code section for the specific function encoded
+        /// as a uint32. The offsets start at the actual function code excluding
+        /// its size field. (since LLVM 10.0)
+        FunctionOffsetI32 = 8,
+
+        /// A byte offset from start of the specified section encoded as a
+        /// uint32. (since LLVM 10.0)
+        SectionOffsetI32 = 9,
+
+        /// An event index encoded as a 5-byte varuint32. Used for the immediate
+        /// argument of a throw and if_except instruction. (since LLVM 10.0)
+        EventIndexLeb = 10,
+
+        /// A memory address relative to the __memory_base wasm global. Used in
+        /// position independent code (-fPIC) where absolute memory addresses
+        /// are not known at link time.
+        MemoryAddrRelSleb = 11,
+
+        /// A function address (table index) relative to the __table_base wasm
+        /// global. Used in position indepenent code (-fPIC) where absolute
+        /// function addresses are not known at link time.
+        TableIndexRelSleb = 12,
+
+        /// A global index encoded as uint32. (since LLVM 11.0)
+        GlobalIndexI32 = 13,
+
+        /// The 64-bit counterpart of `MemoryAddrLeb`. A 64-bit linear memory
+        /// index encoded as a 10-byte varuint64, Used for the immediate
+        /// argument of a load or store instruction on a 64-bit linear memory
+        /// array. (since LLVM 11.0)
+        MemoryAddrLeb64 = 14,
+
+        /// The 64-bit counterpart of `MemoryAddrSleb`. A 64-bit linear memory
+        /// index encoded as a 10-byte varint64. Used for the immediate argument
+        /// of a i64.const instruction. (since LLVM 11.0)
+        MemoryAddrSleb64 = 15,
+
+        /// The 64-bit counterpart of `MemoryAddrI32`. A 64-bit linear memory
+        /// index encoded as a uint64, e.g. taking the 64-bit address of a C++
+        /// global in a static data initializer. (since LLVM 11.0)
+        MemoryAddrI64 = 16,
+
+        /// The 64-bit counterpart of `MemoryAddrRelSleb`.
+        MemoryAddrRelSleb64 = 17,
+
+        /// The 64-bit counterpart of `TableIndexSleb`. A function table index
+        /// encoded as a 10-byte varint64. Used to refer to the immediate
+        /// argument of a i64.const instruction, e.g. taking the address of a
+        /// function in Wasm64. (in LLVM 12.0)
+        TableIndexSleb64 = 18,
+
+        /// The 64-bit counterpart of `TableIndexI32`. A function table index
+        /// encoded as a uint64, e.g. taking the address of a function in a
+        /// static data initializer. (in LLVM 12.0)
+        TableIndexI64 = 19,
+
+        /// A table number encoded as a 5-byte varuint32. Used for the table
+        /// immediate argument in the table.* instructions. (in LLVM 12.0)
+        TableNumberLeb = 20,
+
+        /// An offset from the __tls_base symbol encoded as a 5-byte [varint32].
+        /// Used for PIC case to avoid absolute relocation. (in LLVM 12.0)
+        MemoryAddrTlsSleb = 21,
+
+        /// The 64-bit counterpart of `FunctionOffsetI32`. A byte offset within
+        /// code section for the specific function encoded as a uint64. (in LLVM
+        /// 12.0)
+        FunctionOffsetI64 = 22,
+
+        /// A byte offset between the relocating address and a linear memory
+        /// index encoded as a uint32. Used for pointer-relative addressing. (in
+        /// LLVM 13.0)
+        MemoryAddrLocrelI32 = 23,
+
+        /// The 64-bit counterpart of `TableIndexRelSleb`. A function table
+        /// index encoded as a 10-byte varint64. (in LLVM 13.0)
+        TableIndexRelSleb64 = 24,
+
+        /// The 64-bit counterpart of `MemoryAddrTlsSleb`. (in LLVM 13.0)
+        MemoryAddrTlsSleb64 = 25,
+
+        /// A function index encoded as a uint32. Used in custom sections for
+        /// function annotations (__attribute__((annotate(<name>))) (in LLVM
+        /// 17.0)
+        FunctionIndexI32 = 26,
+    }
+
+}
+
+impl<'a> FromReader<'a> for RelocationType {
+    fn from_reader(reader: &mut BinaryReader<'a>) -> Result<Self> {
+        let num = reader.read_u8()?;
+        num.try_into().or_else(|_| {
+            Err(BinaryReader::invalid_leading_byte_error(
+                num,
+                "RelocEntryType",
+                reader.original_position() - 1,
+            ))
+        })
+    }
+}
+
+/// Indicates the kind of addend that applies to a relocation entry.
+#[derive(Debug, PartialEq, Eq, Hash, Clone, Copy)]
+pub enum RelocAddendKind {
+    /// Relocation entry does not include an addend.
+    None,
+    /// Relocation entry includes a 32-bit addend.
+    Addend32,
+    /// Relocation entry includes a 64-bit addend.
+    Addend64,
+}
+
+/// Single relocation entry within a `reloc.*` section, as defined at
+/// https://github.com/WebAssembly/tool-conventions/blob/main/Linking.md#relocation-sections.
+#[derive(Debug, PartialEq, Eq, Hash, Clone, Copy)]
+pub struct RelocationEntry {
+    /// Relocation entry type.
+    pub ty: RelocationType,
+    /// Offset in bytes from the start of the section indicated by
+    /// `RelocSectionReader::section` targetted by this relocation.
+    pub offset: u32,
+    /// Index in the symbol table contained in the linking section that
+    /// corresponds to the value at `offset`.
+    pub index: u32,
+    /// Addend to add to the address, or `0` if not applicable. The value must
+    /// be consistent with the `self.ty.addend_kind()`.
+    pub addend: i64,
+}
+
+impl RelocationEntry {
+    /// Byte range relative to the start of the section indicated by
+    /// `RelocSectionReader::section` targetted by this relocation.
+    pub fn relocation_range(&self) -> Range<usize> {
+        (self.offset as usize)..(self.offset as usize + self.ty.extent())
+    }
+}
+
+impl RelocationType {
+    /// Indicates if this relocation type has an associated `RelocEntry::addend`.
+    pub const fn addend_kind(self: Self) -> RelocAddendKind {
+        use RelocationType::*;
+        match self {
+            MemoryAddrLeb | MemoryAddrSleb | MemoryAddrI32 | FunctionOffsetI32
+            | SectionOffsetI32 | MemoryAddrLocrelI32 | MemoryAddrRelSleb | MemoryAddrTlsSleb => {
+                RelocAddendKind::Addend32
+            }
+            MemoryAddrRelSleb64 | MemoryAddrTlsSleb64 | MemoryAddrLeb64 | MemoryAddrSleb64
+            | MemoryAddrI64 | FunctionOffsetI64 => RelocAddendKind::Addend64,
+            _ => RelocAddendKind::None,
+        }
+    }
+
+    /// Indicates the number of bytes that this relocation type targets.
+    pub const fn extent(self) -> usize {
+        use RelocationType::*;
+        match self {
+            FunctionIndexLeb | TableIndexSleb | MemoryAddrLeb | MemoryAddrSleb | TypeIndexLeb
+            | GlobalIndexLeb | EventIndexLeb | MemoryAddrRelSleb | TableIndexRelSleb
+            | TableNumberLeb | MemoryAddrTlsSleb => 5,
+            MemoryAddrLeb64 | MemoryAddrSleb64 | TableIndexSleb64 | TableIndexRelSleb64
+            | MemoryAddrRelSleb64 | MemoryAddrTlsSleb64 => 10,
+
+            TableIndexI32 | MemoryAddrI32 | FunctionOffsetI32 | SectionOffsetI32
+            | GlobalIndexI32 | MemoryAddrLocrelI32 | FunctionIndexI32 => 4,
+
+            MemoryAddrI64 | TableIndexI64 | FunctionOffsetI64 => 8,
+        }
+    }
+}
+
+impl<'a> FromReader<'a> for RelocationEntry {
+    fn from_reader(reader: &mut BinaryReader<'a>) -> Result<Self> {
+        let ty = RelocationType::from_reader(reader)?;
+        let offset = reader.read_var_u32()?;
+        let index = reader.read_var_u32()?;
+        let addend = match ty.addend_kind() {
+            RelocAddendKind::None => 0,
+            RelocAddendKind::Addend32 => reader.read_var_i32()? as i64,
+            RelocAddendKind::Addend64 => reader.read_var_i64()?,
+        };
+        Ok(RelocationEntry {
+            ty,
+            offset,
+            index,
+            addend,
+        })
+    }
+}