rust: alloc: remove `allocator_test`

//! Implementation of the kernel's memory allocation infrastructure.

#[cfg(not(testlib))]

pub mod allocator;

pub mod kbox;

pub mod kvec;

pub mod layout;

#[cfg(testlib)]

pub mod allocator_test;

#[cfg(testlib)]

pub use self::allocator_test as allocator;

pub use self::kbox::Box;

pub use self::kbox::KBox;

pub use self::kbox::KVBox;

// SPDX-License-Identifier: GPL-2.0

//! So far the kernel's `Box` and `Vec` types can't be used by userspace test cases, since all users

//! of those types (e.g. `CString`) use kernel allocators for instantiation.

//!

//! In order to allow userspace test cases to make use of such types as well, implement the

//! `Cmalloc` allocator within the `allocator_test` module and type alias all kernel allocators to

//! `Cmalloc`. The `Cmalloc` allocator uses libc's `realloc()` function as allocator backend.

#![allow(missing_docs)]

use super::{flags::*, AllocError, Allocator, Flags};

use core::alloc::Layout;

use core::cmp;

use core::ptr;

use core::ptr::NonNull;

/// The userspace allocator based on libc.

pub struct Cmalloc;

pub type Kmalloc = Cmalloc;

pub type Vmalloc = Kmalloc;

pub type KVmalloc = Kmalloc;

extern "C" {

    #[link_name = "aligned_alloc"]

    fn libc_aligned_alloc(align: usize, size: usize) -> *mut crate::ffi::c_void;

    #[link_name = "free"]

    fn libc_free(ptr: *mut crate::ffi::c_void);

}

// SAFETY:

// - memory remains valid until it is explicitly freed,

// - passing a pointer to a valid memory allocation created by this `Allocator` is always OK,

// - `realloc` provides the guarantees as provided in the `# Guarantees` section.

unsafe impl Allocator for Cmalloc {

    unsafe fn realloc(

        ptr: Option<NonNull<u8>>,

        layout: Layout,

        old_layout: Layout,

        flags: Flags,

    ) -> Result<NonNull<[u8]>, AllocError> {

        let src = match ptr {

            Some(src) => {

                if old_layout.size() == 0 {

                    ptr::null_mut()

                } else {

                    src.as_ptr()

                }

            }

            None => ptr::null_mut(),

        };

        if layout.size() == 0 {

            // SAFETY: `src` is either NULL or was previously allocated with this `Allocator`

            unsafe { libc_free(src.cast()) };

            return Ok(NonNull::slice_from_raw_parts(

                crate::alloc::dangling_from_layout(layout),

                0,

            ));

        }

        // ISO C (ISO/IEC 9899:2011) defines `aligned_alloc`:

        //

        // > The value of alignment shall be a valid alignment supported by the implementation

        // [...].

        //

        // As an example of the "supported by the implementation" requirement, POSIX.1-2001 (IEEE

        // 1003.1-2001) defines `posix_memalign`:

        //

        // > The value of alignment shall be a power of two multiple of sizeof (void *).

        //

        // and POSIX-based implementations of `aligned_alloc` inherit this requirement. At the time

        // of writing, this is known to be the case on macOS (but not in glibc).

        //

        // Satisfy the stricter requirement to avoid spurious test failures on some platforms.

        let min_align = core::mem::size_of::<*const crate::ffi::c_void>();

        let layout = layout.align_to(min_align).map_err(|_| AllocError)?;

        let layout = layout.pad_to_align();

        // SAFETY: Returns either NULL or a pointer to a memory allocation that satisfies or

        // exceeds the given size and alignment requirements.

        let dst = unsafe { libc_aligned_alloc(layout.align(), layout.size()) }.cast::<u8>();

        let dst = NonNull::new(dst).ok_or(AllocError)?;

        if flags.contains(__GFP_ZERO) {

            // SAFETY: The preceding calls to `libc_aligned_alloc` and `NonNull::new`

            // guarantee that `dst` points to memory of at least `layout.size()` bytes.

            unsafe { dst.as_ptr().write_bytes(0, layout.size()) };

        }

        if !src.is_null() {

            // SAFETY:

            // - `src` has previously been allocated with this `Allocator`; `dst` has just been

            //   newly allocated, hence the memory regions do not overlap.

            // - both` src` and `dst` are properly aligned and valid for reads and writes

            unsafe {

                ptr::copy_nonoverlapping(

                    src,

                    dst.as_ptr(),

                    cmp::min(layout.size(), old_layout.size()),

                )

            };

        }

        // SAFETY: `src` is either NULL or was previously allocated with this `Allocator`

        unsafe { libc_free(src.cast()) };

        Ok(NonNull::slice_from_raw_parts(dst, layout.size()))

    }

}