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fix(main): improve the way the kernel calculates how many pages to allocate (#472)

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Same as #471 for `main` branch

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: zshipko <zshipko@users.noreply.github.com>
This commit is contained in:
zach
2023-09-20 16:25:48 -07:00
committed by GitHub
parent 98a4244915
commit 6e8c28b0e9
5 changed files with 37 additions and 8 deletions
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18
kernel/src/lib.rs
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@@ -87,19 +87,22 @@ pub enum MemoryStatus {
///
/// The overall layout of the Extism-manged memory is organized like this:
/// |------|-------|---------|-------|--------------|
/// | Root | Block | Data | Block | Data | ...
/// |------|-------|---------|-------|--------------|
/// |------|-------+---------|-------+--------------|
/// | Root | Block + Data | Block + Data | ...
/// |------|-------+---------|-------+--------------|
///
/// Where `Root` and `Block` are fixed to the size of the `MemoryRoot` and `MemoryBlock` structs. But
/// the size of `Data` is dependent on the allocation size.
///
/// This means that the offset of a `Block` is the size of `Root` plus the size of all existing `Blocks`
/// including their data.
#[repr(C)]
pub struct MemoryRoot {
/// Position of the bump allocator, relative to `START_PAGE`
pub position: AtomicU64,
/// The total size of all data allocated using this allocator
pub length: AtomicU64,
/// A pointer to where the blocks begin
/// A pointer to the start of the first block
pub blocks: [MemoryBlock; 0],
}
@@ -194,6 +197,7 @@ impl MemoryRoot {
while (block as u64) < self.blocks.as_ptr() as u64 + self_position {
let b = &mut *block;
// Get the block status, this lets us know if we are able to re-use it
let status = b.status.load(Ordering::Acquire);
// An unused block is safe to use
@@ -246,13 +250,13 @@ impl MemoryRoot {
let curr = self.blocks.as_ptr() as u64 + self_position;
// Get the number of bytes available
let mem_left = self_length - self_position;
let mem_left = self_length - self_position - core::mem::size_of::<MemoryRoot>() as u64;
// When the allocation is larger than the number of bytes available
// we will need to try to grow the memory
if length >= mem_left {
// Calculate the number of pages needed to cover the remaining bytes
let npages = num_pages(length);
let npages = num_pages(length - mem_left);
let x = core::arch::wasm32::memory_grow(0, npages);
if x == usize::MAX {
return None;
@@ -309,7 +313,7 @@ impl MemoryBlock {
}
}
// Extism functions - these functions should be
// Extism functions
/// Allocate a block of memory and return the offset
#[no_mangle]