Add AlignType and use it for buffer allocations

secp256k1-sys/src/lib.rs

@@ -39,6 +39,12 @@ pub mod recovery;
 use core::{hash, slice, ptr};
 use types::*;
 
+#[cfg(any(target_pointer_width = "32", target_pointer_width = "16", target_pointer_width = "8"))]
+pub type AlignType = u64;
+
+#[cfg(not(any(target_pointer_width = "32", target_pointer_width = "16", target_pointer_width = "8")))]
+pub type AlignType = usize;
+
 /// Flag for context to enable no precomputation
 pub const SECP256K1_START_NONE: c_uint = 1;
 /// Flag for context to enable verification precomputation
@@ -300,14 +306,18 @@ pub unsafe extern "C" fn rustsecp256k1_v0_1_1_context_create(flags: c_uint) -> *
     use std::mem;
     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!(mem::align_of::<AlignType>() >= mem::align_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: *mut AlignType = 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)
 }
@@ -327,12 +337,12 @@ pub unsafe fn secp256k1_context_create(flags: c_uint) -> *mut Context {
 #[cfg(all(feature = "std", not(feature = "external-symbols")))]
 pub unsafe extern "C" fn rustsecp256k1_v0_1_1_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]);
 }
 
 #[cfg(all(feature = "std", not(feature = "external-symbols")))]

src/context.rs

@@ -1,7 +1,7 @@
 use core::marker::PhantomData;
 use core::mem::ManuallyDrop;
 use ptr;
-use ffi::{self, CPtr};
+use ffi::{self, CPtr, AlignType};
 use ffi::types::{c_uint, c_void};
 use Error;
 use Secp256k1;
@@ -17,7 +17,7 @@ pub unsafe trait Context : private::Sealed {
     /// A constant description of the context.
     const DESCRIPTION: &'static str;
     /// A function to deallocate the memory when the context is dropped.
-    unsafe fn deallocate(ptr: *mut [u8]);
+    unsafe fn deallocate(ptr: *mut [AlignType]);
 }
 
 /// Marker trait for indicating that an instance of `Secp256k1` can be used for signing.
@@ -80,7 +80,7 @@ mod std_only {
         const FLAGS: c_uint = ffi::SECP256K1_START_SIGN;
         const DESCRIPTION: &'static str = "signing only";
 
-        unsafe fn deallocate(ptr: *mut [u8]) {
+        unsafe fn deallocate(ptr: *mut [AlignType]) {
             let _ = Box::from_raw(ptr);
         }
     }
@@ -89,7 +89,7 @@ mod std_only {
         const FLAGS: c_uint = ffi::SECP256K1_START_VERIFY;
         const DESCRIPTION: &'static str = "verification only";
 
-        unsafe fn deallocate(ptr: *mut [u8]) {
+        unsafe fn deallocate(ptr: *mut [AlignType]) {
             let _ = Box::from_raw(ptr);
         }
     }
@@ -98,7 +98,7 @@ mod std_only {
         const FLAGS: c_uint = VerifyOnly::FLAGS | SignOnly::FLAGS;
         const DESCRIPTION: &'static str = "all capabilities";
 
-        unsafe fn deallocate(ptr: *mut [u8]) {
+        unsafe fn deallocate(ptr: *mut [AlignType]) {
             let _ = Box::from_raw(ptr);
         }
     }
@@ -109,7 +109,7 @@ mod std_only {
             #[cfg(target_arch = "wasm32")]
             ffi::types::sanity_checks_for_wasm();
 
-            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) },
@@ -149,7 +149,7 @@ 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,
@@ -169,7 +169,7 @@ unsafe impl<'buf> Context for SignOnlyPreallocated<'buf> {
     const FLAGS: c_uint = ffi::SECP256K1_START_SIGN;
     const DESCRIPTION: &'static str = "signing only";
 
-    unsafe fn deallocate(_ptr: *mut [u8]) {
+    unsafe fn deallocate(_ptr: *mut [AlignType]) {
         // Allocated by the user
     }
 }
@@ -178,7 +178,7 @@ unsafe impl<'buf> Context for VerifyOnlyPreallocated<'buf> {
     const FLAGS: c_uint = ffi::SECP256K1_START_VERIFY;
     const DESCRIPTION: &'static str = "verification only";
 
-    unsafe fn deallocate(_ptr: *mut [u8]) {
+    unsafe fn deallocate(_ptr: *mut [AlignType]) {
         // Allocated by the user
     }
 }
@@ -187,14 +187,14 @@ unsafe impl<'buf> Context for AllPreallocated<'buf> {
     const FLAGS: c_uint = SignOnlyPreallocated::FLAGS | VerifyOnlyPreallocated::FLAGS;
     const DESCRIPTION: &'static str = "all capabilities";
 
-    unsafe fn deallocate(_ptr: *mut [u8]) {
+    unsafe 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> {
         #[cfg(target_arch = "wasm32")]
         ffi::types::sanity_checks_for_wasm();
 
@@ -208,14 +208,14 @@ 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
@@ -238,14 +238,14 @@ impl<'buf> Secp256k1<AllPreallocated<'buf>> {
         ManuallyDrop::new(Secp256k1 {
             ctx: raw_ctx,
             phantom: PhantomData,
-            buf: ptr::null_mut::<[u8;0]>() as *mut [u8] ,
+            buf: ptr::null_mut::<[AlignType;0]>() as *mut [AlignType] ,
         })
     }
 }
 
 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)
     }
 
@@ -270,14 +270,14 @@ impl<'buf> Secp256k1<SignOnlyPreallocated<'buf>> {
         ManuallyDrop::new(Secp256k1 {
             ctx: raw_ctx,
             phantom: PhantomData,
-            buf: ptr::null_mut::<[u8;0]>() as *mut [u8] ,
+            buf: ptr::null_mut::<[AlignType;0]>() as *mut [AlignType] ,
         })
     }
 }
 
 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)
     }
 
@@ -302,7 +302,7 @@ impl<'buf> Secp256k1<VerifyOnlyPreallocated<'buf>> {
         ManuallyDrop::new(Secp256k1 {
             ctx: raw_ctx,
             phantom: PhantomData,
-            buf: ptr::null_mut::<[u8;0]>() as *mut [u8] ,
+            buf: ptr::null_mut::<[AlignType;0]>() as *mut [AlignType] ,
         })
     }
 }

src/lib.rs

@@ -155,7 +155,9 @@ pub use secp256k1_sys as ffi;
 #[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 ffi::AlignType;
 
 #[macro_use]
 mod macros;
@@ -530,7 +532,7 @@ 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
@@ -602,7 +604,15 @@ 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!(mem::align_of::<AlignType>() >= mem::align_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;