Struct sunrise_libuser::thread_local_storage::ThreadLocalStaticRegion

struct ThreadLocalStaticRegion {
    ptr: usize,
    layout: Layout,
    tcb_offset: usize,
}

Represents an allocated thread local static region.

Because TLS regions have a really specific layout, we don't use Box and instead interact with the allocator directly. This type is the equivalent of a Box, it stores the pointer to the allocated memory, and deallocates it on Drop.

Fields

ptr: usize

Pointer to the allocated memory

layout: Layout

Layout of the allocated memory. Used when deallocating.

tcb_offset: usize

Offset of the TCB in this allocation.

Implementations

impl ThreadLocalStaticRegion

fn tcb(&self) -> &ThreadControlBlock

Returns a pointer to the ThreadControlBlock in the allocated region. All TLS arithmetic are done relative to this pointer.

For TLS to work, the value stored at this address should be the address itself, i.e. having a pointer pointing to itself.

fn allocate(block_src: &[u8], block_size: usize, block_align: usize) -> Self

Allocates a ThreadLocalStaticRegion.

The region's content is copied from the TLS initialisation image described by block_src, padded with 0s for block_size, to which is appended a ThreadControlBlock.

The ThreadLocalStaticRegion uses PT_TLS's p_align field passed in block_align to compute its layout and total size.

Alignment

        V----------------------V  tls_align_up(tls_size_1, align_1)

                               +-- gs:0
                               |
        +----------------------|-- tlsoffset_1 = gs:0 - tls_align_up(tls_size_1, align_1)
        |                      |
        V                      V

        j----------------~-----j---------j
   ...  |    tls_size_1  | pad |   TCB   |
        j----------------~-----j---------j

   ^    ^                      ^
   |    |                      |
   |    |                      +-- TCB_align: Determines alignment of everything.
   |    |                          = max(align_of::<TCB>(), align_1). e.g. : 16.
   |    |
   |    +------------------------- TCB_align - n * align_1
   |                               => still aligned to align_1 because TCB is aligned to align_1.
   |
   +------------------------------ alloc_align == TCB_align
                                   => &TCB = &alloc + tls_align_up(gs:0 - tls_offset_1, TCB_align)

   ^---^                           alloc_pad

Trait Implementations

impl Debug for ThreadLocalStaticRegion

fn fmt(&self, f: &mut Formatter) -> Result<(), Error>

Formats the value using the given formatter.

impl Drop for ThreadLocalStaticRegion

fn drop(&mut self)

Dropping a ThreadLocalStaticRegion deallocates it.