uref

uref allows the programmer to create weak references to objects

Requirements

• llvm >= 4.0
• x86/x64
  • *nix
  • Darwin
  • FreeBSD
• bravery

LLVM

Following components must be available:

• Target
• Native
• MCDisassembler

llvm-config should be in path, or LLVM_CONFIG set in ENV (for configure)

API

<?php
final class uref {
	public function __construct(object $object);

	public function get() : ?object;
	public function valid() : bool;
}
?>

Note: uref does not support properties

Implementation

uref leverages mprotect to intercept writes to the objects store, the resulting SIGSEGV⚔ is handled by disassembling the current machine code instruction (using llvm) to determine it's length (and so the offset of the next instruction); The first byte of the next instruction is backed up and replaced with 0xCC _int3, the store is unprotected to allow the write to go ahead, urefs are at this point updated. Upon the next instruction (which uref replaced), SIGTRAP is raised and uref replaces the 0xCC that it inserted with the first byte of the original instruction and the object store is write protected again.

⚔ Darwin may raise SIGBUS, depending on the position of the moon relative to the fourteenth ... no but, we don't know why ...

Thanks

Thanks to @bwoebi for help developing the idea, and then providing me access to a mac to make it work there ...