Make various preparations for upcoming features

A lot of this is random WIP from a while back, at least a month ago, and
is being committed now to get it out of the way so that other patches
can be brought in and integrated against it without causing headaches.

Also rolled into this commit is a way to distinguish plugin_unload from
exiting the game. This is required for another soon-to-be-integrated
feature to avoid crashing on exit, and could in theory also be used to
speed up unloading on exit in future. While we're at it, this also
avoids the need to linearly scan through the plugin list to do the
old branch unloading fix, because we can.

Rough summary of the other smaller stuff I can remember doing:
- Rework bitbuf a bit
- Add some cryptographic nonsense in ac.c (not final at all)
- Introduce the first couple of "chunklets" libraries as a sort-of
  subproject of this one
- Tidy up random small bits and bobs
- Add source for a small keypair generation tool
- Rework democustom to be very marginally more useful

1 files changed, 299 insertions, 0 deletions

diff --git a/src/chunklets/fastspin.c b/src/chunklets/fastspin.c
new file mode 100644
index 0000000..bfaaf9b
--- /dev/null
+++ b/src/chunklets/fastspin.c
@@ -0,0 +1,299 @@
+/*
+ * Copyright © 2023 Michael Smith <mikesmiffy128@gmail.com>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifdef __cplusplus
+#error This file should not be compiled as C++. It relies on C-specific \
+keywords and APIs which have syntactically different equivalents for C++.
+#endif
+
+#include <stdatomic.h>
+
+#include "fastspin.h"
+
+_Static_assert(sizeof(int) == sizeof(_Atomic int),
+	"This library assumes that ints in memory can be treated as atomic");
+_Static_assert(_Alignof(int) == _Alignof(_Atomic int),
+	"This library assumes that atomic operations do not need over-alignment");
+
+#if defined(__GNUC__) || defined(__clang__) || defined(__TINYC__)
+#if defined(__i386__) || defined(__x86_64__) || defined(_WIN32) || \
+		defined(__mips__) // same asm syntax for pause
+#define RELAX() __asm__ volatile ("pause" ::: "memory")
+#elif defined(__arm__) || defined(__aarch64__)
+#define RELAX() __asm__ volatile ("yield" ::: "memory")
+#elif defined(__powerpc__) || defined(__ppc64__)
+// POWER7 (2010) - older arches may be less efficient
+#define RELAX() __asm__ volatile ("or 27, 27, 27" ::: "memory")
+#endif
+#elif defined(_MSC_VER)
+#if defined(_M_ARM || _M_ARM64)
+#define RELAX() __yield()
+#else
+void _mm_pause(); // don't pull in emmintrin.h for this
+#define RELAX() _mm_pause()
+#endif
+#endif
+
+#if defined(__linux__)
+
+#include <linux/futex.h>
+#include <sys/syscall.h>
+
+// some arches only have a _time64 variant. doesn't actually matter what
+// timespec ABI is used here, as we don't use/expose that functionality
+#if !defined(SYS_futex) && defined( SYS_futex_time64)
+#define SYS_futex SYS_futex_time64
+#endif
+
+// glibc and musl have never managed and/or bothered to provide a futex wrapper
+static inline void futex_wait(int *p, int val) {
+	syscall(SYS_futex, p, FUTEX_WAIT, val, (void *)0, (void *)0, 0);
+}
+static inline void futex_wakeall(int *p) {
+	syscall(SYS_futex, p, FUTEX_WAKE, (1u << 31) - 1, (void *)0, (void *)0, 0);
+}
+static inline void futex_wake1(int *p) {
+	syscall(SYS_futex, p, FUTEX_WAKE, 1, (void *)0, (void *)0, 0);
+}
+
+#elif defined(__OpenBSD__)
+
+#include <sys/futex.h>
+
+// OpenBSD just emulates the Linux call but it still provides a wrapper! Yay!
+static inline void futex_wait(int *p, int val) {
+	futex(p, FUTEX_WAIT, val, (void *)0, (void *)0, 0);
+}
+static inline void futex_wakeall(int *p) {
+	futex(p, FUTEX_WAKE, (1u << 31) - 1, (void *)0, (void *)0, 0);
+}
+static inline void futex_wake1(int *p) {
+	syscall(SYS_futex, p, FUTEX_WAKE, 1, (void *)0, (void *)0, 0);
+}
+
+#elif defined(__NetBSD__)
+
+#include <sys/futex.h> // for constants
+#include <sys/syscall.h>
+#include <unistd.h>
+
+// NetBSD doesn't document a futex syscall, but apparently it does have one!?
+// Their own pthreads library still doesn't actually use it, go figure. Also, it
+// takes an extra parameter for some reason.
+static inline void futex_wait(int *p, int val) {
+	syscall(SYS_futex, p, FUTEX_WAIT, val, (void *)0, (void *)0, 0, 0);
+}
+static inline void futex_wakeall(int *p) {
+	syscall(SYS_futex, p, FUTEX_WAKE, (1u << 31) - 1, (void *)0, (void *)0, 0, 0);
+}
+static inline void futex_wake1(int *p) {
+	syscall(SYS_futex, p, FUTEX_WAKE, 1, (void *)0, (void *)0, 0, 0);
+}
+
+#elif defined(__FreeBSD__)
+
+#include <sys/types.h> // ugh still no IWYU everywhere. maybe next year
+#include <sys/umtx.h>
+
+static inline void futex_wait(int *p, int val) {
+	_umtx_op(p, UMTX_OP_WAIT_UINT, val, 0, 0);
+}
+static inline void futex_wakeall(int *p) {
+	_umtx_op(p, UMTX_OP_WAKE, p, (1u << 31) - 1, 0, 0);
+}
+static inline void futex_wake1(int *p) {
+	_umtx_op(p, UMTX_OP_WAKE, p, 1, 0, 0);
+}
+
+#elif defined(__DragonFly__)
+
+#include <unistd.h>
+
+// An actually good interface. Thank you Matt, very cool.
+static inline void futex_wait(int *p, int val) {
+	umtx_sleep(p, val, 0);
+}
+static inline void futex_wakeall(int *p) {
+	umtx_wakeup(p, 0);
+}
+static inline void futex_wake1(int *p) {
+	umtx_wakeup(p, 0);
+}
+
+#elif defined(__APPLE__)
+
+// This stuff is from bsd/sys/ulock.h in XNU. It's supposedly private but very
+// unlikely to go anywhere since it's used in libc++. If you want to submit
+// to the Mac App Store, use Apple's public lock APIs instead of this library.
+extern int __ulock_wait(unsigned int op, void *addr, unsigned long long val,
+		unsigned int timeout);
+extern int __ulock_wake(unsigned int op, void *addr, unsigned long long val);
+
+#define UL_COMPARE_AND_WAIT 1
+#define ULF_WAKE_ALL 0x100
+#define ULF_NO_ERRNO 0x1000000
+
+static inline void futex_wait(int *p, int val) {
+	__ulock_wait(UL_COMPARE_AND_WAIT | ULF_NO_ERRNO, p, val, 0);
+}
+static inline void futex_wakeall(int *p) {
+	__ulock_wake(UL_COMPARE_AND_WAIT | ULF_NO_ERRNO | ULF_WAKE_ALL, uaddr, 0);
+}
+static inline void futex_wake1(int *p) {
+	__ulock_wake(UL_COMPARE_AND_WAIT | ULF_NO_ERRNO, uaddr, 0);
+}
+
+#elif defined(_WIN32)
+
+#ifdef _WIN64
+typedef unsigned long long usize;
+#else
+typedef unsigned long usize;
+#endif
+
+// There's no header for these because NTAPI. Plus Windows.h sucks anyway.
+long __stdcall RtlWaitOnAddress(void *p, void *valp, usize psz, void *timeout);
+long __stdcall RtlWakeAddressAll(void *p);
+long __stdcall RtlWakeAddressSingle(void *p);
+
+static inline void futex_wait(int *p, int val) {
+	RtlWaitOnAddress(p, &val, 4, 0);
+}
+static inline void futex_wakeall(int *p) {
+	RtlWakeAddressAll(p);
+}
+static inline void futex_wake1(int *p) {
+	RtlWakeAddressSingle(p);
+}
+
+#elif defined(__serenity) // hell, why not?
+
+#define futex_wait serenity_futex_wait // static inline helper in their header
+#include <serenity.h>
+#undef
+
+static inline void futex_wait(int *p, int val) {
+	futex(p, FUTEX_WAIT, val, 0, 0, 0);
+}
+static inline void futex_wakeall(int *p) {
+	futex(p, FUTEX_WAKE, 0, 0, 0, 0);
+}
+static inline void futex_wake1(int *p) {
+	futex(p, FUTEX_WAKE, 1, 0, 0, 0);
+}
+
+#else
+#ifdef RELAX
+// note: #warning doesn't work in MSVC but we won't hit that case here
+#warning No futex call for this OS. Falling back on pure spinlock. \
+Performance will suffer during contention.
+#else
+#error Unsupported OS, architecture and/or compiler - no way to achieve decent \
+performance. Need either CPU spinlock hints or futexes, ideally both.
+#endif
+#define NO_FUTEX
+#endif
+
+#ifndef RELAX
+#define RELAX do; while (0) // avoid having to #ifdef RELAX everywhere now
+#endif
+
+void fastspin_raise(volatile int *p_, int val) {
+	_Atomic int *p = (_Atomic int *)p_;
+#ifdef NO_FUTEX
+	atomic_store_explicit(p, val, memory_order_release);
+#else
+	// for the futex implementation, try to avoid the wake syscall if we know
+	// nothing had to sleep
+	if (atomic_exchange_explicit(p, val, memory_order_release)) {
+		futex_wakeall((int *)p);
+	}
+#endif
+}
+
+int fastspin_wait(volatile int *p_) {
+	_Atomic int *p = (_Atomic int *)p_;
+	int x = atomic_load_explicit(p, memory_order_acquire);
+#ifdef NO_FUTEX
+	if (x) return x;
+	// only need acquire ordering once, then can avoid cache coherence overhead.
+	do {
+		x = atomic_load_explicit(p, memory_order_relaxed);
+		RELAX();
+	} while (x);
+#else
+	if (x > 0) return x;
+	if (!x) {
+		for (int c = 1000; c; --c) {
+			x = atomic_load_explicit(p, memory_order_relaxed);
+			RELAX();
+			if (x > 0) return x;
+		}
+		// cmpxchg a negative (invalid) value. this will fail in two cases:
+		// 1. someone else already cmpxchg'd: the futex_wait() will work fine
+		// 2. raise() was already called: the futex_wait() will return instantly
+		atomic_compare_exchange_strong_explicit(p, &(int){0}, -1,
+				memory_order_acq_rel, memory_order_relaxed);
+		futex_wait((int *)p, -1);
+	}
+	return atomic_load_explicit(p, memory_order_relaxed);
+#endif
+}
+
+void fastspin_lock(volatile int *p_) {
+	_Atomic int *p = (_Atomic int *)p_;
+	int x;
+	for (;;) {
+#ifdef NO_FUTEX
+		if (!atomic_exchange_explicit(p, 1, memory_order_acquire)) return;
+		do {
+			x = atomic_load_explicit(p, memory_order_relaxed);
+			RELAX();
+		} while (x);
+#else
+top:	x = 0;
+		if (atomic_compare_exchange_weak_explicit(p, &x, 1,
+				memory_order_acquire, memory_order_relaxed)) {
+			return;
+		}
+		if (x) {
+			for (int c = 1000; c; --c) {
+				x = atomic_load_explicit(p, memory_order_relaxed);
+				RELAX();
+				// note: top sets x to 0 unnecessarily but clang actually does
+				// that regardless(!), probably to break loop-carried dependency
+				if (!x) goto top;
+			}
+			atomic_compare_exchange_strong_explicit(p, &(int){0}, -1,
+					memory_order_acq_rel, memory_order_relaxed);
+			futex_wait((int *)p, -1); // (then spin once more to avoid spuria)
+		}
+#endif
+	}
+}
+
+void fastspin_unlock(volatile int *p_) {
+	_Atomic int *p = (_Atomic int *)p_;
+#ifdef NO_FUTEX
+	atomic_store_explicit((_Atomic int *)p, 0, memory_order_release);
+#else
+	if (atomic_exchange_explicit(p, 0, memory_order_release) < 0) {
+		futex_wake1((int *)p);
+	}
+#endif
+}
+
+// vi: sw=4 ts=4 noet tw=80 cc=80