Add AlignType and use it for buffer allocations

src/context.rs

@@ -7,6 +7,21 @@ use Secp256k1;
 #[cfg(feature = "std")]
 pub use self::std_only::*;
 
+
+
+/// A type that represents the type with the biggest alignment we can get in rust.
+/// Trying to match what `malloc` does in C, this should be aligned enough to contain pointers too.
+/// This type can have different size/alignment depending on the architecture.
+#[cfg(any(target_pointer_width = "32", target_pointer_width = "16", target_pointer_wid = "8"))]
+pub type AlignType = u64;
+
+/// A type that represents the type with the biggest alignment we can get in rust.
+/// Trying to match what `malloc` does in C, this should be aligned enough to contain pointers too.
+/// This type can have different size/alignment depending on the architecture.
+#[cfg(not(any(target_pointer_width = "32", target_pointer_width = "16", target_pointer_wid = "8")))]
+pub type AlignType = usize;
+
+
 /// A trait for all kinds of Context's that Lets you define the exact flags and a function to deallocate memory.
 /// * DO NOT * implement it for your own types.
 pub unsafe trait Context {
@@ -15,7 +30,7 @@ pub unsafe trait Context {
     /// A constant description of the context.
     const DESCRIPTION: &'static str;
     /// A function to deallocate the memory when the context is dropped.
-    fn deallocate(ptr: *mut [u8]);
+    fn deallocate(ptr: *mut [AlignType]);
 }
 
 /// Marker trait for indicating that an instance of `Secp256k1` can be used for signing.
@@ -62,7 +77,7 @@ mod std_only {
         const FLAGS: c_uint = ffi::SECP256K1_START_SIGN;
         const DESCRIPTION: &'static str = "signing only";
 
-        fn deallocate(ptr: *mut [u8]) {
+        fn deallocate(ptr: *mut [AlignType]) {
             let _ = unsafe { Box::from_raw(ptr) };
         }
     }
@@ -71,7 +86,7 @@ mod std_only {
         const FLAGS: c_uint = ffi::SECP256K1_START_VERIFY;
         const DESCRIPTION: &'static str = "verification only";
 
-        fn deallocate(ptr: *mut [u8]) {
+        fn deallocate(ptr: *mut [AlignType]) {
             let _ = unsafe { Box::from_raw(ptr) };
         }
     }
@@ -80,15 +95,15 @@ mod std_only {
         const FLAGS: c_uint = VerifyOnly::FLAGS | SignOnly::FLAGS;
         const DESCRIPTION: &'static str = "all capabilities";
 
-        fn deallocate(ptr: *mut [u8]) {
+        fn deallocate(ptr: *mut [AlignType]) {
             let _ = unsafe { Box::from_raw(ptr) };
         }
     }
 
     impl<C: Context> Secp256k1<C> {
         /// Lets you create a context in a generic manner(sign/verify/all)
         pub fn gen_new() -> Secp256k1<C> {
-            let buf = vec![0u8; Self::preallocate_size_gen()].into_boxed_slice();
+            let buf = vec![0 as AlignType; Self::preallocate_size_gen()].into_boxed_slice();
             let ptr = Box::into_raw(buf);
             Secp256k1 {
                 ctx: unsafe { ffi::secp256k1_context_preallocated_create(ptr as *mut c_void, C::FLAGS) },
@@ -128,7 +143,7 @@ mod std_only {
     impl<C: Context> Clone for Secp256k1<C> {
         fn clone(&self) -> Secp256k1<C> {
             let clone_size = unsafe {ffi::secp256k1_context_preallocated_clone_size(self.ctx)};
-            let ptr_buf = Box::into_raw(vec![0u8; clone_size].into_boxed_slice());
+            let ptr_buf = Box::into_raw(vec![0 as AlignType; clone_size].into_boxed_slice());
             Secp256k1 {
                 ctx: unsafe { ffi::secp256k1_context_preallocated_clone(self.ctx, ptr_buf as *mut c_void) },
                 phantom: PhantomData,
@@ -149,7 +164,7 @@ unsafe impl<'buf> Context for SignOnlyPreallocated<'buf> {
     const FLAGS: c_uint = ffi::SECP256K1_START_SIGN;
     const DESCRIPTION: &'static str = "signing only";
 
-    fn deallocate(_ptr: *mut [u8]) {
+    fn deallocate(_ptr: *mut [AlignType]) {
         // Allocated by the user
     }
 }
@@ -158,7 +173,7 @@ unsafe impl<'buf> Context for VerifyOnlyPreallocated<'buf> {
     const FLAGS: c_uint = ffi::SECP256K1_START_VERIFY;
     const DESCRIPTION: &'static str = "verification only";
 
-    fn deallocate(_ptr: *mut [u8]) {
+    fn deallocate(_ptr: *mut [AlignType]) {
         // Allocated by the user
     }
 }
@@ -167,14 +182,14 @@ unsafe impl<'buf> Context for AllPreallocated<'buf> {
     const FLAGS: c_uint = SignOnlyPreallocated::FLAGS | VerifyOnlyPreallocated::FLAGS;
     const DESCRIPTION: &'static str = "all capabilities";
 
-    fn deallocate(_ptr: *mut [u8]) {
+    fn deallocate(_ptr: *mut [AlignType]) {
         // Allocated by the user
     }
 }
 
 impl<'buf, C: Context + 'buf> Secp256k1<C> {
     /// Lets you create a context with preallocated buffer in a generic manner(sign/verify/all)
-    pub fn preallocated_gen_new(buf: &'buf mut [u8]) -> Result<Secp256k1<C>, Error> {
+    pub fn preallocated_gen_new(buf: &'buf mut [AlignType]) -> Result<Secp256k1<C>, Error> {
         if buf.len() < Self::preallocate_size_gen() {
             return Err(Error::NotEnoughMemory);
         }
@@ -185,14 +200,14 @@ impl<'buf, C: Context + 'buf> Secp256k1<C> {
                     C::FLAGS)
             },
             phantom: PhantomData,
-            buf: buf as *mut [u8],
+            buf: buf as *mut [AlignType],
         })
     }
 }
 
 impl<'buf> Secp256k1<AllPreallocated<'buf>> {
     /// Creates a new Secp256k1 context with all capabilities
-    pub fn preallocated_new(buf: &'buf mut [u8]) -> Result<Secp256k1<AllPreallocated<'buf>>, Error> {
+    pub fn preallocated_new(buf: &'buf mut [AlignType]) -> Result<Secp256k1<AllPreallocated<'buf>>, Error> {
         Secp256k1::preallocated_gen_new(buf)
     }
     /// Uses the ffi `secp256k1_context_preallocated_size` to check the memory size needed for a context
@@ -203,7 +218,7 @@ impl<'buf> Secp256k1<AllPreallocated<'buf>> {
 
 impl<'buf> Secp256k1<SignOnlyPreallocated<'buf>> {
     /// Creates a new Secp256k1 context that can only be used for signing
-    pub fn preallocated_signing_only(buf: &'buf mut [u8]) -> Result<Secp256k1<SignOnlyPreallocated<'buf>>, Error> {
+    pub fn preallocated_signing_only(buf: &'buf mut [AlignType]) -> Result<Secp256k1<SignOnlyPreallocated<'buf>>, Error> {
         Secp256k1::preallocated_gen_new(buf)
     }
 
@@ -216,7 +231,7 @@ impl<'buf> Secp256k1<SignOnlyPreallocated<'buf>> {
 
 impl<'buf> Secp256k1<VerifyOnlyPreallocated<'buf>> {
     /// Creates a new Secp256k1 context that can only be used for verification
-    pub fn preallocated_verification_only(buf: &'buf mut [u8]) -> Result<Secp256k1<VerifyOnlyPreallocated<'buf>>, Error> {
+    pub fn preallocated_verification_only(buf: &'buf mut [AlignType]) -> Result<Secp256k1<VerifyOnlyPreallocated<'buf>>, Error> {
         Secp256k1::preallocated_gen_new(buf)
     }
 

src/ffi.rs

@@ -18,6 +18,7 @@
 //! not be needed for most users.
 use core::{mem, hash, slice};
 use types::*;
+use context::AlignType;
 
 /// Flag for context to enable no precomputation
 pub const SECP256K1_START_NONE: c_uint = 1;
@@ -271,16 +272,18 @@ extern "C" {
 // Returns: a newly created context object.
 //  In:      flags: which parts of the context to initialize.
 pub unsafe extern "C" fn secp256k1_context_create(flags: c_uint) -> *mut Context {
-    assert!(mem::align_of::<usize>() >= mem::align_of::<u8>());
-    assert_eq!(mem::size_of::<usize>(), mem::size_of::<&usize>());
+    assert!(mem::align_of::<AlignType>() >= mem::align_of::<u8>());
+    assert!(mem::align_of::<AlignType>() >= mem::align_of::<usize>());
+    assert!(mem::size_of::<AlignType>() >= mem::size_of::<usize>());
+    assert_eq!(mem::size_of::<AlignType>(), mem::size_of::<&AlignType>());
 
-    let word_size = mem::size_of::<usize>();
+    let word_size = mem::size_of::<AlignType>();
     let n_words = (secp256k1_context_preallocated_size(flags) + word_size - 1) / word_size;
 
-    let buf = vec![0usize; n_words + 1].into_boxed_slice();
-    let ptr = Box::into_raw(buf) as *mut usize;
-    ::core::ptr::write(ptr, n_words);
-    let ptr: *mut usize = ptr.offset(1);
+    let buf = vec![0 as AlignType; n_words + 1].into_boxed_slice();
+    let ptr = Box::into_raw(buf) as *mut AlignType;
+    ::core::ptr::write(ptr, n_words as AlignType);
+    let ptr: *mut AlignType = ptr.offset(1);
 
     secp256k1_context_preallocated_create(ptr as *mut c_void, flags)
 }
@@ -295,12 +298,12 @@ pub unsafe extern "C" fn secp256k1_context_create(flags: c_uint) -> *mut Context
 ///
 pub unsafe extern "C" fn secp256k1_context_destroy(ctx: *mut Context) {
     secp256k1_context_preallocated_destroy(ctx);
-    let ctx: *mut usize = ctx as *mut usize;
+    let ctx: *mut AlignType = ctx as *mut AlignType;
 
-    let n_words_ptr: *mut usize = ctx.offset(-1);
-    let n_words: usize = ::core::ptr::read(n_words_ptr);
-    let slice: &mut [usize] = slice::from_raw_parts_mut(n_words_ptr , n_words+1);
-    let _ = Box::from_raw(slice as *mut [usize]);
+    let n_words_ptr: *mut AlignType = ctx.offset(-1);
+    let n_words: AlignType = ::core::ptr::read(n_words_ptr);
+    let slice: &mut [AlignType] = slice::from_raw_parts_mut(n_words_ptr , (n_words+1) as usize);
+    let _ = Box::from_raw(slice as *mut [AlignType]);
 }
 
 

src/lib.rs

@@ -143,7 +143,9 @@
 #[cfg(any(test, feature = "rand"))] use rand::Rng;
 #[cfg(any(test, feature = "std"))] extern crate core;
 
-use core::{fmt, ptr, str};
+use core::{fmt, mem, ptr, str};
+
+pub use context::AlignType;
 
 #[macro_use]
 mod macros;
@@ -502,7 +504,7 @@ impl std::error::Error for Error {
 pub struct Secp256k1<C: Context> {
     ctx: *mut ffi::Context,
     phantom: PhantomData<C>,
-    buf: *mut [u8],
+    buf: *mut [AlignType],
 }
 
 // The underlying secp context does not contain any references to memory it does not own
@@ -572,7 +574,15 @@ impl<C: Context> Secp256k1<C> {
 
     /// Returns the required memory for a preallocated context buffer in a generic manner(sign/verify/all)
     pub fn preallocate_size_gen() -> usize {
-        unsafe { ffi::secp256k1_context_preallocated_size(C::FLAGS) }
+        assert!(mem::align_of::<AlignType>() >= mem::align_of::<u8>());
+        assert!(mem::align_of::<AlignType>() >= mem::align_of::<usize>());
+        assert!(mem::size_of::<AlignType>() >= mem::size_of::<usize>());
+        assert_eq!(mem::size_of::<AlignType>(), mem::size_of::<&AlignType>());
+
+        let bytes_size = unsafe { ffi::secp256k1_context_preallocated_size(C::FLAGS) };
+        let word_size = mem::size_of::<AlignType>();
+        let n_words = (bytes_size + word_size - 1) / word_size;
+        n_words
     }
 
     /// (Re)randomizes the Secp256k1 context for cheap sidechannel resistance;
@@ -706,7 +716,7 @@ mod tests {
         let ctx_sign = unsafe { ffi::secp256k1_context_create(SignOnlyPreallocated::FLAGS) };
         let ctx_vrfy = unsafe { ffi::secp256k1_context_create(VerifyOnlyPreallocated::FLAGS) };
 
-        let buf: *mut [u8] = &mut [0u8;0] as _;
+        let buf: *mut [AlignType] = &mut [0 as AlignType;0] as _;
         let full: Secp256k1<AllPreallocated> = Secp256k1{ctx: ctx_full, phantom: PhantomData, buf};
         let sign: Secp256k1<SignOnlyPreallocated> = Secp256k1{ctx: ctx_sign, phantom: PhantomData, buf};
         let vrfy: Secp256k1<VerifyOnlyPreallocated> = Secp256k1{ctx: ctx_vrfy, phantom: PhantomData, buf};
@@ -730,10 +740,10 @@ mod tests {
 
     #[test]
     fn test_preallocation() {
-        let mut buf_ful = vec![0u8; Secp256k1::preallocate_size()];
-        let mut buf_sign = vec![0u8; Secp256k1::preallocate_signing_size()];
-        let mut buf_vfy = vec![0u8; Secp256k1::preallocate_verification_size()];
-//
+        let mut buf_ful = vec![0; Secp256k1::preallocate_size()];
+        let mut buf_sign = vec![0; Secp256k1::preallocate_signing_size()];
+        let mut buf_vfy = vec![0; Secp256k1::preallocate_verification_size()];
+
         let full = Secp256k1::preallocated_new(&mut buf_ful).unwrap();
         let sign = Secp256k1::preallocated_signing_only(&mut buf_sign).unwrap();
         let vrfy = Secp256k1::preallocated_verification_only(&mut buf_vfy).unwrap();