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Fix heap allocator alignment on all platforms

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Tetralux
2020-01-14 18:21:51 +00:00
parent f0c6f29f82
commit a4b60b78c8
1 changed files with 41 additions and 60 deletions
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101
core/os/os.odin
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@@ -129,85 +129,66 @@ read_ptr :: proc(fd: Handle, data: rawptr, len: int) -> (int, Errno) {
heap_allocator_proc :: proc(allocator_data: rawptr, mode: mem.Allocator_Mode,
size, alignment: int,
old_memory: rawptr, old_size: int, flags: u64 = 0, loc := #caller_location) -> rawptr {
/*
//
// NOTE(tetra, 2019-11-10): The heap doesn't respect alignment.
// HACK: Overallocate, align forwards, and then use the two bytes immediately before
// the address we return, to store the padding we inserted.
// This allows us to pass the original pointer we got back from the heap to `free` later.
// NOTE(tetra, 2020-01-14): The heap doesn't respect alignment.
// Instead, we overallocate by `alignment + size_of(rawptr) - 1`, and insert
// padding. We also store the original pointer returned by heap_alloc right before
// the pointer we return to the user.
//
align_and_store_padding :: proc(ptr: rawptr, alignment: int) -> rawptr {
ptr := mem.ptr_offset(cast(^u8) ptr, 2);
new_ptr := cast(^u8) mem.align_forward(ptr, uintptr(alignment));
offset := mem.ptr_sub(new_ptr, cast(^u8) ptr) + 2;
assert(offset < int(max(u16)));
(^[2]u8)(mem.ptr_offset(new_ptr, -2))^ = transmute([2]u8) u16(offset);
return new_ptr;
aligned_alloc :: proc(size, alignment: int, old_ptr: rawptr = nil) -> rawptr {
a := max(alignment, align_of(rawptr));
space := size + a - 1;
allocated_mem: rawptr;
if old_ptr != nil {
original_old_ptr := mem.ptr_offset((^rawptr)(old_ptr), -1)^;
allocated_mem = heap_resize(original_old_ptr, space+size_of(rawptr));
} else {
allocated_mem = heap_alloc(space+size_of(rawptr));
}
aligned_mem := rawptr(mem.ptr_offset((^u8)(allocated_mem), size_of(rawptr)));
ptr := uintptr(aligned_mem);
aligned_ptr := (ptr - 1 + uintptr(a)) & -uintptr(a);
diff := int(aligned_ptr - ptr);
if (size + diff) > space {
return nil;
}
aligned_mem = rawptr(aligned_ptr);
mem.ptr_offset((^rawptr)(aligned_mem), -1)^ = allocated_mem;
return aligned_mem;
}
recover_original_pointer :: proc(ptr: rawptr) -> rawptr {
ptr := cast(^u8) ptr;
offset := transmute(u16) (^[2]u8)(mem.ptr_offset(ptr, -2))^;
ptr = mem.ptr_offset(ptr, -int(offset));
return ptr;
aligned_free :: proc(p: rawptr) {
if p != nil {
heap_free(mem.ptr_offset((^rawptr)(p), -1)^);
}
}
aligned_heap_alloc :: proc(size: int, alignment: int) -> rawptr {
// NOTE(tetra): Alignment 1 will mean we only have one extra byte.
// This is not enough for a u16 - so we ensure there is at least two bytes extra.
// This also means that the pointer is always aligned to at least 2.
extra := alignment;
if extra <= 1 do extra = 2;
orig := cast(^u8) heap_alloc(size + extra);
if orig == nil do return nil;
ptr := align_and_store_padding(orig, alignment);
assert(recover_original_pointer(ptr) == orig);
return ptr;
aligned_resize :: proc(p: rawptr, old_size: int, new_size: int, new_alignment: int) -> rawptr {
if p == nil do return nil;
return aligned_alloc(new_size, new_alignment, p);
}
switch mode {
case .Alloc:
return aligned_heap_alloc(size, alignment);
return aligned_alloc(size, alignment);
case .Free:
if old_memory != nil {
ptr := recover_original_pointer(old_memory);
heap_free(ptr);
}
return nil;
aligned_free(old_memory);
case .Free_All:
// NOTE(bill): Does nothing
// NOTE(tetra): Do nothing.
case .Resize:
if old_memory == nil {
return aligned_heap_alloc(size, alignment);
return aligned_alloc(size, alignment);
}
ptr := recover_original_pointer(old_memory);
ptr = heap_resize(ptr, size);
assert(ptr != nil);
return align_and_store_padding(ptr, alignment);
}
return nil;
*/
switch mode {
case .Alloc:
return heap_alloc(size);
case .Free:
if old_memory != nil {
heap_free(old_memory);
}
return nil;
case .Free_All:
// NOTE(bill): Does nothing
case .Resize:
return heap_resize(old_memory, size);
return aligned_resize(old_memory, old_size, size, alignment);
}
return nil;