Add read-no-alloc feature gate

.github/workflows/rust.yml

@@ -103,6 +103,8 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - run: cargo test --no-default-features
+      # Ensure gimli can be built without alloc.
+      - run: cargo check --no-default-features --feature read-no-alloc
       - run: cargo test --no-default-features --features read
       - run: cargo test --no-default-features --features read,fallible-iterator
       - run: cargo test --no-default-features --features read,std

Cargo.toml

@@ -38,8 +38,9 @@ test-assembler = "0.1.3"
 typed-arena = "2"
 
 [features]
-read = []
-endian-reader = ["stable_deref_trait"]
+read-no-alloc = []
+read = ["read-no-alloc"]
+endian-reader = ["read", "stable_deref_trait"]
 write = ["indexmap"]
 std = ["fallible-iterator/std", "stable_deref_trait/std"]
 default = ["read", "write", "std", "fallible-iterator", "endian-reader"]

src/constants.rs

@@ -81,9 +81,9 @@ macro_rules! dw {
                 if let Some(s) = self.static_string() {
                     f.pad(s)
                 } else {
-                    f.pad(&format!("Unknown {}: {}",
+                    write!(f, "Unknown {}: {}",
                                    stringify!($struct_name),
-                                   self.0))
+                                   self.0)
                 }
             }
         }

src/leb128.rs

@@ -45,7 +45,7 @@
 //! ```
 
 const CONTINUATION_BIT: u8 = 1 << 7;
-#[cfg(feature = "read")]
+#[cfg(feature = "read-no-alloc")]
 const SIGN_BIT: u8 = 1 << 6;
 
 #[inline]
@@ -62,7 +62,7 @@ fn low_bits_of_u64(val: u64) -> u8 {
 
 /// A module for reading signed and unsigned integers that have been LEB128
 /// encoded.
-#[cfg(feature = "read")]
+#[cfg(feature = "read-no-alloc")]
 pub mod read {
     use super::{low_bits_of_byte, CONTINUATION_BIT, SIGN_BIT};
     use crate::read::{Error, Reader, Result};

src/lib.rs

@@ -37,6 +37,7 @@
 #![no_std]
 
 #[allow(unused_imports)]
+#[cfg(any(feature = "read", feature = "write"))]
 #[macro_use]
 extern crate alloc;
 
@@ -62,10 +63,10 @@ pub use crate::endianity::{BigEndian, Endianity, LittleEndian, NativeEndian, Run
 
 pub mod leb128;
 
-#[cfg(feature = "read")]
+#[cfg(feature = "read-no-alloc")]
 pub mod read;
 // For backwards compat.
-#[cfg(feature = "read")]
+#[cfg(feature = "read-no-alloc")]
 pub use crate::read::*;
 
 #[cfg(feature = "write")]

src/read/cfi.rs

@@ -1,3 +1,4 @@
+#[cfg(feature = "read")]
 use alloc::vec::Vec;
 
 use core::cmp::{Ord, Ordering};
@@ -10,9 +11,9 @@ use super::util::{ArrayLike, ArrayVec};
 use crate::common::{DebugFrameOffset, EhFrameOffset, Encoding, Format, Register, SectionId};
 use crate::constants::{self, DwEhPe};
 use crate::endianity::Endianity;
-use crate::read::{
-    EndianSlice, Error, Expression, Reader, ReaderOffset, Result, Section, StoreOnHeap,
-};
+#[cfg(feature = "read")]
+use crate::read::StoreOnHeap;
+use crate::read::{EndianSlice, Error, Expression, Reader, ReaderOffset, Result, Section};
 
 /// `DebugFrame` contains the `.debug_frame` section's frame unwinding
 /// information required to unwind to and recover registers from older frames on
@@ -1738,8 +1739,10 @@ impl<R: Reader> FrameDescriptionEntry<R> {
 
 /// Specification of what storage should be used for [`UnwindContext`].
 ///
-/// Normally you would only need to use [`StoreOnHeap`], which places the stack
-/// on the heap using [`Vec`]. This is the default storage type parameter for [`UnwindContext`].
+#[cfg_attr(feature = "read", doc = "
+Normally you would only need to use [`StoreOnHeap`], which places the stack
+on the heap using [`Vec`]. This is the default storage type parameter for [`UnwindContext`].
+")]
 ///
 /// If you need to avoid [`UnwindContext`] from allocating memory, e.g. for signal safety,
 /// you can provide you own storage specification:
@@ -1780,8 +1783,10 @@ pub trait UnwindContextStorage<R: Reader>: Sized {
     type Stack: ArrayLike<Item = UnwindTableRow<R, Self>>;
 }
 
+#[cfg(feature = "read")]
 const MAX_RULES: usize = 192;
 
+#[cfg(feature = "read")]
 impl<R: Reader> UnwindContextStorage<R> for StoreOnHeap {
     type Rules = [(Register, RegisterRule<R>); MAX_RULES];
     type Stack = Vec<UnwindTableRow<R, Self>>;
@@ -1814,7 +1819,11 @@ impl<R: Reader> UnwindContextStorage<R> for StoreOnHeap {
 /// # }
 /// ```
 #[derive(Clone, PartialEq, Eq)]
-pub struct UnwindContext<R: Reader, A: UnwindContextStorage<R> = StoreOnHeap> {
+pub struct UnwindContext<
+    R: Reader,
+    #[cfg(not(feature = "read"))] A: UnwindContextStorage<R>,
+    #[cfg(feature = "read")] A: UnwindContextStorage<R> = StoreOnHeap,
+> {
     // Stack of rows. The last row is the row currently being built by the
     // program. There is always at least one row. The vast majority of CFI
     // programs will only ever have one row on the stack.
@@ -1849,6 +1858,7 @@ impl<R: Reader, A: UnwindContextStorage<R>> Default for UnwindContext<R, A> {
     }
 }
 
+#[cfg(feature = "read")]
 impl<R: Reader> UnwindContext<R> {
     /// Construct a new call frame unwinding context.
     pub fn new() -> Self {
@@ -2036,7 +2046,13 @@ impl<R: Reader, A: UnwindContextStorage<R>> UnwindContext<R, A> {
 /// > recording just the differences starting at the beginning address of each
 /// > subroutine in the program.
 #[derive(Debug)]
-pub struct UnwindTable<'a, 'ctx, R: Reader, A: UnwindContextStorage<R> = StoreOnHeap> {
+pub struct UnwindTable<
+    'a,
+    'ctx,
+    R: Reader,
+    #[cfg(not(feature = "read"))] A: UnwindContextStorage<R>,
+    #[cfg(feature = "read")] A: UnwindContextStorage<R> = StoreOnHeap,
+> {
     code_alignment_factor: Wrapping<u64>,
     data_alignment_factor: Wrapping<i64>,
     next_start_address: u64,
@@ -2347,7 +2363,11 @@ impl<'a, 'ctx, R: Reader, A: UnwindContextStorage<R>> UnwindTable<'a, 'ctx, R, A
 // - https://github.com/libunwind/libunwind/blob/11fd461095ea98f4b3e3a361f5a8a558519363fa/include/tdep-aarch64/dwarf-config.h#L32
 // - https://github.com/libunwind/libunwind/blob/11fd461095ea98f4b3e3a361f5a8a558519363fa/include/tdep-arm/dwarf-config.h#L31
 // - https://github.com/libunwind/libunwind/blob/11fd461095ea98f4b3e3a361f5a8a558519363fa/include/tdep-mips/dwarf-config.h#L31
-struct RegisterRuleMap<R: Reader, S: UnwindContextStorage<R> = StoreOnHeap> {
+struct RegisterRuleMap<
+    R: Reader,
+    #[cfg(not(feature = "read"))] S: UnwindContextStorage<R>,
+    #[cfg(feature = "read")] S: UnwindContextStorage<R> = StoreOnHeap,
+> {
     rules: ArrayVec<S::Rules>,
 }
 
@@ -2490,7 +2510,11 @@ impl<'iter, R: Reader> Iterator for RegisterRuleIter<'iter, R> {
 /// A row in the virtual unwind table that describes how to find the values of
 /// the registers in the *previous* frame for a range of PC addresses.
 #[derive(PartialEq, Eq)]
-pub struct UnwindTableRow<R: Reader, S: UnwindContextStorage<R> = StoreOnHeap> {
+pub struct UnwindTableRow<
+    R: Reader,
+    #[cfg(not(feature = "read"))] S: UnwindContextStorage<R>,
+    #[cfg(feature = "read")] S: UnwindContextStorage<R> = StoreOnHeap,
+> {
     start_address: u64,
     end_address: u64,
     saved_args_size: u64,

src/read/endian_slice.rs

@@ -1,6 +1,8 @@
 //! Working with byte slices that have an associated endianity.
 
+#[cfg(feature = "read")]
 use alloc::borrow::Cow;
+#[cfg(feature = "read")]
 use alloc::string::String;
 use core::ops::{Deref, Index, Range, RangeFrom, RangeTo};
 use core::str;
@@ -82,6 +84,7 @@ where
 
     /// Converts the slice to a string, including invalid characters,
     /// using `String::from_utf8_lossy`.
+    #[cfg(feature = "read")]
     #[inline]
     pub fn to_string_lossy(&self) -> Cow<'input, str> {
         String::from_utf8_lossy(self.slice)
@@ -284,11 +287,18 @@ where
         Ok(EndianSlice::new(slice, self.endian))
     }
 
+    #[cfg(not(feature = "read"))]
+    fn cannot_implement() -> super::reader::seal_if_no_alloc::Sealed {
+        super::reader::seal_if_no_alloc::Sealed
+    }
+
+    #[cfg(feature = "read")]
     #[inline]
     fn to_slice(&self) -> Result<Cow<[u8]>> {
         Ok(self.slice.into())
     }
 
+    #[cfg(feature = "read")]
     #[inline]
     fn to_string(&self) -> Result<Cow<str>> {
         match str::from_utf8(self.slice) {
@@ -297,6 +307,7 @@ where
         }
     }
 
+    #[cfg(feature = "read")]
     #[inline]
     fn to_string_lossy(&self) -> Result<Cow<str>> {
         Ok(String::from_utf8_lossy(self.slice))

src/read/mod.rs

@@ -186,7 +186,9 @@ pub use self::addr::*;
 mod cfi;
 pub use self::cfi::*;
 
+#[cfg(feature = "read")]
 mod dwarf;
+#[cfg(feature = "read")]
 pub use self::dwarf::*;
 
 mod endian_slice;
@@ -200,7 +202,9 @@ pub use self::endian_reader::*;
 mod reader;
 pub use self::reader::*;
 
+#[cfg(feature = "read")]
 mod abbrev;
+#[cfg(feature = "read")]
 pub use self::abbrev::*;
 
 mod aranges;
@@ -209,7 +213,9 @@ pub use self::aranges::*;
 mod index;
 pub use self::index::*;
 
+#[cfg(feature = "read")]
 mod line;
+#[cfg(feature = "read")]
 pub use self::line::*;
 
 mod lists;

src/read/op.rs

@@ -1,12 +1,15 @@
 //! Functions for parsing and evaluating DWARF expressions.
 
+#[cfg(feature = "read")]
 use alloc::vec::Vec;
 use core::mem;
 
 use super::util::{ArrayLike, ArrayVec};
 use crate::common::{DebugAddrIndex, DebugInfoOffset, Encoding, Register};
 use crate::constants;
-use crate::read::{Error, Reader, ReaderOffset, Result, StoreOnHeap, UnitOffset, Value, ValueType};
+#[cfg(feature = "read")]
+use crate::read::StoreOnHeap;
+use crate::read::{Error, Reader, ReaderOffset, Result, UnitOffset, Value, ValueType};
 
 /// A reference to a DIE, either relative to the current CU or
 /// relative to the section.
@@ -938,6 +941,7 @@ impl<R: Reader> Expression<R> {
     /// let mut eval = expression.evaluation(unit.encoding());
     /// let mut result = eval.evaluate().unwrap();
     /// ```
+    #[cfg(feature = "read")]
     #[inline]
     pub fn evaluation(self, encoding: Encoding) -> Evaluation<R> {
         Evaluation::new(self.0, encoding)
@@ -982,8 +986,10 @@ impl<R: Reader> OperationIter<R> {
 
 /// Specification of what storage should be used for [`Evaluation`].
 ///
-/// Normally you would only need to use [`StoreOnHeap`], which places the stacks and the results
-/// on the heap using [`Vec`]. This is the default storage type parameter for [`Evaluation`].
+#[cfg_attr(feature = "read", doc = "
+Normally you would only need to use [`StoreOnHeap`], which places the stacks and the results
+on the heap using [`Vec`]. This is the default storage type parameter for [`Evaluation`].
+")]
 ///
 /// If you need to avoid [`Evaluation`] from allocating memory, e.g. for signal safety,
 /// you can provide you own storage specification:
@@ -1030,6 +1036,7 @@ pub trait EvaluationStorage<R: Reader> {
     type Result: ArrayLike<Item = Piece<R>>;
 }
 
+#[cfg(feature = "read")]
 impl<R: Reader> EvaluationStorage<R> for StoreOnHeap {
     type Stack = Vec<Value>;
     type ExpressionStack = Vec<(R, R)>;
@@ -1082,7 +1089,11 @@ impl<R: Reader> EvaluationStorage<R> for StoreOnHeap {
 /// println!("{:?}", result);
 /// ```
 #[derive(Debug)]
-pub struct Evaluation<R: Reader, S: EvaluationStorage<R> = StoreOnHeap> {
+pub struct Evaluation<
+    R: Reader,
+    #[cfg(not(feature = "read"))] S: EvaluationStorage<R>,
+    #[cfg(feature = "read")] S: EvaluationStorage<R> = StoreOnHeap,
+> {
     bytecode: R,
     encoding: Encoding,
     object_address: Option<u64>,
@@ -1108,6 +1119,7 @@ pub struct Evaluation<R: Reader, S: EvaluationStorage<R> = StoreOnHeap> {
     result: ArrayVec<S::Result>,
 }
 
+#[cfg(feature = "read")]
 impl<R: Reader> Evaluation<R> {
     /// Create a new DWARF expression evaluator.
     ///
@@ -1116,6 +1128,19 @@ impl<R: Reader> Evaluation<R> {
     pub fn new(bytecode: R, encoding: Encoding) -> Self {
         Self::new_in(bytecode, encoding)
     }
+
+    /// Get the result of this `Evaluation`.
+    ///
+    /// # Panics
+    /// Panics if this `Evaluation` has not been driven to completion.
+    pub fn result(self) -> Vec<Piece<R>> {
+        match self.state {
+            EvaluationState::Complete => self.result.into_vec(),
+            _ => {
+                panic!("Called `Evaluation::result` on an `Evaluation` that has not been completed")
+            }
+        }
+    }
 }
 
 impl<R: Reader, S: EvaluationStorage<R>> Evaluation<R, S> {
@@ -1956,21 +1981,6 @@ impl<R: Reader, S: EvaluationStorage<R>> Evaluation<R, S> {
     }
 }
 
-impl<R: Reader> Evaluation<R, StoreOnHeap> {
-    /// Get the result of this `Evaluation`.
-    ///
-    /// # Panics
-    /// Panics if this `Evaluation` has not been driven to completion.
-    pub fn result(self) -> Vec<Piece<R>> {
-        match self.state {
-            EvaluationState::Complete => self.result.into_vec(),
-            _ => {
-                panic!("Called `Evaluation::result` on an `Evaluation` that has not been completed")
-            }
-        }
-    }
-}
-
 #[cfg(test)]
 // Tests require leb128::write.
 #[cfg(feature = "write")]