Some code I used to help write FB11698739. Very rough and posted as-is: don't copy things blindly from the internet, but that applies doubly so here!

path_hook.mm

// clang path_hook.mm -shared -ldl -g -framework Foundation path_hook.o -L/usr/lib/swift

#include <cassert>
#include <cstdint>
#include <dlfcn.h>
#include <mach/arm/vm_param.h>
#include <mach/kern_return.h>
#include <mach/mach_init.h>
#include <mach/vm_map.h>
#include <mach/vm_prot.h>
#include <sys/mman.h>
#include <os/log.h>
#include <Foundation/Foundation.h>
#include <unistd.h>

extern "C" {
extern const struct mach_header *_dyld_get_dlopen_image_header(void *handle);
[[noreturn]]
extern void *trampoline();
void logger(uint64_t tag, id string);
void setup();
};

__asm__ (
	"_trampoline:\n"
	"sub sp, sp, #0x20\n"
	"stp     x29, x30, [sp, #0x0]\n"
	"stp     x0, x1, [sp, #0x10]\n"
	"bl _logger\n"
	"ldp     x29, x30, [sp, #0x0]\n"
	"ldp     x0, x1, [sp, #0x10]\n"
	"add sp, sp, #0x20\n"
	"sub     sp, sp, #0x70\n"
	"stp     x28, x27, [sp, #0x10]\n"
	"stp     x26, x25, [sp, #0x20]\n"
	"stp     x24, x23, [sp, #0x30]\n"
	"adrp x9, _function@PAGE\n"
	"add x9, x9, _function@PAGEOFF\n"
	"ldr x9, [x9]\n"
	"br x9\n"
);

uintptr_t function;

__attribute__((constructor)) static void init() {
	sleep(1);
	setup();
	auto handle = dlopen("/Applications/Xcode-beta.app/Contents/SharedFrameworks/XCBuild.framework/Versions/A/PlugIns/XCBBuildService.bundle/Contents/Frameworks/XCBUtil.framework/XCBUtil", RTLD_LAZY);
	auto base = _dyld_get_dlopen_image_header(handle);
	function = (uintptr_t)base + 0x0007e7fc;
	os_log(OS_LOG_DEFAULT, "asdf done 1");
	assert(vm_protect(mach_task_self(), function, PAGE_SIZE, false, VM_PROT_READ | VM_PROT_WRITE | VM_PROT_COPY) == KERN_SUCCESS);
	memcpy((void *)function, "\x49\x00\xc0\xd2\x29\x01\x40\xf9\x20\x01\x1f\xd6", 12);
	assert(vm_protect(mach_task_self(), function, PAGE_SIZE, false, VM_PROT_READ | VM_PROT_EXECUTE) == KERN_SUCCESS);
	os_log(OS_LOG_DEFAULT, "asdf done 2");
	auto ptr = mmap((void *)0x200000000, 0x4000, PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
	*(uintptr_t *)ptr = (uintptr_t)trampoline;
	assert(ptr);
	function += 12;
	// assert(mprotect((void *)(function & ~0x4000), 0x400, PROT_READ | PROT_WRITE) == 0);
	os_log(OS_LOG_DEFAULT, "asdf done 3");
}

path_hook.swift

// swiftc path_hook.swift -emit-object -g

import Foundation
import os

var counts: UnsafeMutablePointer<[String: Int]>!
var lock: UnsafeMutablePointer<os_unfair_lock>!

@_cdecl("setup")
func setup() {
	counts = .allocate(capacity: 1)
	counts.pointee = [:]
	NSLog("asdf \(counts)")
	lock = .allocate(capacity: 1)
}

@_silgen_name("logger")
func log(_ string: String) {
	os_unfair_lock_lock(lock)
	counts.pointee[string, default: 0] += 1
	os_unfair_lock_unlock(lock)
	// NSLog("asdf \(string)")
}