Make futexes 100x better on x86 MacOS

Thanks to @autumnjolitz (in #876) the Cosmopolitan codebase is now
acquainted with Apple's outstanding ulock system calls which offer
something much closer to futexes than Grand Central Dispatch which
wasn't quite as good, since its wait function can't be interrupted
by signals (therefore necessitating a busy loop) and it also needs
semaphore objects to be created and freed. Even though ulock is an
internal Apple API, strictly speaking, the benefits of futexes are
so great that it's worth the risk for now especially since we have
the GCD implementation still as a quick escape hatch if it changes

Here's why this change is important for x86 XNU users. Cosmo has a
suboptimal polyfill when the operating system doesn't offer an API
that let's us implement futexes properly. Sadly we had to use that
on X86 XNU until now. The polyfill works using clock_nanosleep, to
poll the futex in a busy loop with exponential backoff. On XNU x86
clock_nanosleep suffers from us not being able to use a fast clock
gettime implementation, which had a compounding effect that's made
the polyfill function even more poorly. On X86 XNU we also need to
polyfill sched_yield() using select(), which made things even more
troublesome. Now that we have futexes we don't have any busy loops
anymore for both condition variables and thread joining so optimal
performance is attained. To demonstrate, consider these benchmarks

Before:

    $ ./lockscale_test.com -b
    consumed 38.8377   seconds real time and
              0.087131 seconds cpu time

After:

    $ ./lockscale_test.com -b
    consumed 0.007955 seconds real time and
             0.011515 seconds cpu time

Fixes #876

libc/calls/syscall_support-sysv.internal.h

@@ -10,6 +10,8 @@ long __syscall2(long, long, int);
 int __syscall2i(long, long, int) asm("__syscall2");
 long __syscall3(long, long, long, int);
 int __syscall3i(long, long, long, int) asm("__syscall3");
+long __syscall4(long, long, long, long, int);
+int __syscall4i(long, long, long, long, int) asm("__syscall4");
 
 bool __is_linux_2_6_23(void);
 bool32 sys_isatty_metal(int);

libc/intrin/kprintf.greg.c

@@ -568,25 +568,37 @@ privileged static size_t kformat(char *b, size_t n, const char *fmt,
           goto FormatUnsigned;
 
         case 'P':
+          if (!(tib && (tib->tib_flags & TIB_FLAG_VFORKED))) {
+            x = __pid;
+#ifdef __x86_64__
+          } else if (IsLinux()) {
+            asm volatile("syscall"
+                         : "=a"(x)
+                         : "0"(__NR_getpid)
+                         : "rcx", "rdx", "r11", "memory");
+#endif
+          } else {
+            x = 666;
+          }
+          if (!__nocolor && p + 7 <= e) {
+            *p++ = '\e';
+            *p++ = '[';
+            *p++ = '1';
+            *p++ = ';';
+            *p++ = '3';
+            *p++ = '0' + x % 8;
+            *p++ = 'm';
+            ansi = 1;
+          }
+          goto FormatDecimal;
+
+        case 'H':
           if (!(tib && (tib->tib_flags & TIB_FLAG_VFORKED))) {
             if (tib) {
               x = atomic_load_explicit(&tib->tib_tid, memory_order_relaxed);
-              if (IsNetbsd() && x == 1) {
-                x = __pid;
-              }
             } else {
               x = __pid;
             }
-            if (!__nocolor && p + 7 <= e) {
-              *p++ = '\e';
-              *p++ = '[';
-              *p++ = '1';
-              *p++ = ';';
-              *p++ = '3';
-              *p++ = '0' + x % 8;
-              *p++ = 'm';
-              ansi = 1;
-            }
 #ifdef __x86_64__
           } else if (IsLinux()) {
             asm volatile("syscall"
@@ -597,6 +609,17 @@ privileged static size_t kformat(char *b, size_t n, const char *fmt,
           } else {
             x = 666;
           }
+          if (!__nocolor && p + 7 <= e) {
+            // xnu thread ids are always divisible by 8
+            *p++ = '\e';
+            *p++ = '[';
+            *p++ = '1';
+            *p++ = ';';
+            *p++ = '3';
+            *p++ = '0' + x % 7;
+            *p++ = 'm';
+            ansi = 1;
+          }
           goto FormatDecimal;
 
         case 'u':
@@ -1080,7 +1103,8 @@ privileged void kvprintf(const char *fmt, va_list v) {
  * - `X` uppercase
  * - `T` timestamp
  * - `x` hexadecimal
- * - `P` PID (or TID if TLS is enabled)
+ * - `P` process id
+ * - `H` thread id
  *
  * Types:
  *

libc/intrin/strace.internal.h

@@ -3,15 +3,15 @@
 #include "libc/intrin/likely.h"
 #include "libc/runtime/runtime.h"
 
-#define _NTTRACE    1 /* not configurable w/ flag yet */
+#define _NTTRACE    0 /* not configurable w/ flag yet */
 #define _POLLTRACE  0 /* not configurable w/ flag yet */
 #define _DATATRACE  1 /* not configurable w/ flag yet */
 #define _LOCKTRACE  0 /* not configurable w/ flag yet */
 #define _STDIOTRACE 0 /* not configurable w/ flag yet */
 #define _KERNTRACE  0 /* not configurable w/ flag yet */
 #define _TIMETRACE  0 /* not configurable w/ flag yet */
 
-#define STRACE_PROLOGUE "%rSYS %6P %'18T "
+#define STRACE_PROLOGUE "%rSYS %6P %6H %'18T "
 
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 COSMOPOLITAN_C_START_

libc/intrin/ulock.c

@@ -0,0 +1,54 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2023 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ 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.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/intrin/ulock.h"
+#include "libc/assert.h"
+#include "libc/calls/calls.h"
+#include "libc/calls/syscall_support-sysv.internal.h"
+#include "libc/dce.h"
+#include "libc/intrin/describeflags.internal.h"
+#include "libc/intrin/strace.internal.h"
+
+// XNU futexes
+// https://opensource.apple.com/source/xnu/xnu-7195.50.7.100.1/bsd/sys/ulock.h.auto.html
+// https://opensource.apple.com/source/xnu/xnu-3789.41.3/bsd/kern/sys_ulock.c.auto.html
+
+int sys_ulock_wait(uint32_t operation, void *addr, uint64_t value,
+                   uint32_t timeout_micros) asm("sys_futex_cp");
+
+// returns -1 w/ errno
+int ulock_wait(uint32_t operation, void *addr, uint64_t value,
+               uint32_t timeout_micros) {
+  int rc;
+  operation |= ULF_WAIT_CANCEL_POINT;
+  STRACE("ulock_wait(%#x, %p, %lx, %u) → ...", operation, addr, value,
+         timeout_micros);
+  rc = sys_ulock_wait(operation, addr, value, timeout_micros);
+  STRACE("ulock_wait(%#x, %p, %lx, %u) → %d% m", operation, addr, value,
+         timeout_micros, rc);
+  return rc;
+}
+
+// returns -errno
+int ulock_wake(uint32_t operation, void *addr, uint64_t wake_value) {
+  int rc;
+  rc = __syscall3i(operation, (long)addr, wake_value, 0x2000000 | 516);
+  STRACE("ulock_wake(%#x, %p, %lx) → %s", operation, addr, wake_value,
+         DescribeErrno(rc));
+  return rc;
+}

libc/intrin/ulock.h

@@ -0,0 +1,27 @@
+#ifndef COSMOPOLITAN_ULOCK_H_
+#define COSMOPOLITAN_ULOCK_H_
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+/* both wake and wait take one of these */
+#define UL_COMPARE_AND_WAIT          1 /* multi-thread */
+#define UL_UNFAIR_LOCK               2
+#define UL_COMPARE_AND_WAIT_SHARED   3 /* multi-thread/process */
+#define UL_UNFAIR_LOCK64_SHARED      4
+#define UL_COMPARE_AND_WAIT64        5
+#define UL_COMPARE_AND_WAIT64_SHARED 6
+
+#define ULF_WAKE_ALL             0x00000100
+#define ULF_WAKE_THREAD          0x00000200 /* takes wake_value */
+#define ULF_WAKE_ALLOW_NON_OWNER 0x00000400
+
+#define ULF_WAIT_WORKQ_DATA_CONTENTION 0x00010000
+#define ULF_WAIT_CANCEL_POINT          0x00020000 /* raises eintr */
+#define ULF_WAIT_ADAPTIVE_SPIN         0x00040000
+
+int ulock_wake(uint32_t, void *, uint64_t);
+int ulock_wait(uint32_t, void *, uint64_t, uint32_t);
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_ULOCK_H_ */

libc/log/oncrash_arm64.c

@@ -230,6 +230,11 @@ static relegated void __oncrash_impl(int sig, struct siginfo *si,
   }
   Append(b, " %s %s %s %s\n", names.sysname, names.version, names.nodename,
          names.release);
+  Append(
+      b, " cosmoaddr2line %s%s %lx %s\n", __argv[0],
+      endswith(__argv[0], ".com") ? ".dbg" : "", ctx ? ctx->uc_mcontext.PC : 0,
+      DescribeBacktrace(ctx ? (struct StackFrame *)ctx->uc_mcontext.BP
+                            : (struct StackFrame *)__builtin_frame_address(0)));
   if (ctx) {
     long pc;
     char *mem = 0;
@@ -240,6 +245,7 @@ static relegated void __oncrash_impl(int sig, struct siginfo *si,
     struct StackFrame *fp;
     struct SymbolTable *st;
     struct fpsimd_context *vc;
+
     st = GetSymbolTable();
     debugbin = FindDebugBinary();
     addr2line = GetAddr2linePath();

libc/runtime/clone.c

@@ -30,6 +30,7 @@
 #include "libc/intrin/atomic.h"
 #include "libc/intrin/describeflags.internal.h"
 #include "libc/intrin/strace.internal.h"
+#include "libc/intrin/ulock.h"
 #include "libc/intrin/weaken.h"
 #include "libc/limits.h"
 #include "libc/macros.internal.h"
@@ -197,12 +198,20 @@ XnuThreadMain(void *pthread,                    // rdi
   //                                %rsi = size_t freesize,
   //                                %rdx = uint32_t port,
   //                                %r10 = uint32_t sem);
-  asm volatile("movl\t$0,%0\n\t"         // *wt->ztid = 0
-               "xor\t%%r10d,%%r10d\n\t"  // sem = 0
-               "syscall"                 // __bsdthread_terminate()
-               : "=m"(*wt->ztid)
-               : "a"(0x2000000 | 361), "D"(0), "S"(0), "d"(0L)
-               : "rcx", "r10", "r11", "memory");
+  asm volatile("movl\t$0,(%%rsi)\n\t"        // *wt->ztid = 0
+               "mov\t$0x101,%%edi\n\t"       // wake all
+               "xor\t%%edx,%%edx\n\t"        // wake_value
+               "mov\t$0x02000204,%%eax\n\t"  // ulock_wake()
+               "syscall\n\t"                 //
+               "xor\t%%edi,%%edi\n\t"        // freeaddr
+               "xor\t%%esi,%%esi\n\t"        // freesize
+               "xor\t%%edx,%%edx\n\t"        // kport
+               "xor\t%%r10d,%%r10d\n\t"      // joinsem
+               "mov\t$0x02000169,%%eax\n\t"  // bsdthread_terminate()
+               "syscall"
+               : /* no outputs */
+               : "S"(wt->ztid)
+               : "rax", "rcx", "r10", "r11", "memory");
   __builtin_unreachable();
 }
 
@@ -443,6 +452,7 @@ static void *SiliconThreadMain(void *arg) {
   *wt->ctid = wt->this;
   __stack_call(wt->arg, wt->this, 0, 0, wt->func, wt);
   *wt->ztid = 0;
+  ulock_wake(UL_COMPARE_AND_WAIT | ULF_WAKE_ALL, wt->ztid, 0);
   return 0;
 }
 

libc/runtime/enable_tls.c

@@ -206,6 +206,7 @@ textstartup void __enable_tls(void) {
     tid = sys_gettid();
   }
   atomic_store_explicit(&tib->tib_tid, tid, memory_order_relaxed);
+  // TODO(jart): set_tid_address?
 
   // initialize posix threads
   _pthread_static.tib = tib;

libc/sysv/calls/sys_futex.S

@@ -1,2 +1,2 @@
 #include "libc/sysv/macros.internal.h"
-.scall sys_futex,0x0a60531c6ffff0ca,98,4095,globl,hidden
+.scall sys_futex,0x0a60531c622030ca,98,515,globl,hidden

libc/sysv/calls/sys_futex_cp.S

@@ -1,2 +1,2 @@
 #include "libc/sysv/macros.internal.h"
-.scall sys_futex_cp,0x8a68539c6ffff8ca,2146,4095,globl,hidden
+.scall sys_futex_cp,0x8a68539c62a038ca,2146,2563,globl,hidden

libc/sysv/syscall2.S

@@ -26,6 +26,8 @@
 //
 //	The returned value follows the Linux kernel convention ie
 //	errors are returned as `-errno`, rather than -1 w/ errno.
+//
+//	This helper should not be used to do cancelation points.
 __syscall2:
 #ifdef __aarch64__
 	mov	x8,x2				// syscall number (linux)

libc/sysv/syscall3.S

@@ -26,6 +26,8 @@
 //
 //	The return value follows the Linux Kernel (System V) ABI
 //	where -errno is returned, rather than doing -1 w/ errno.
+//
+//	This helper should not be used to do cancelation points.
 __syscall3:
 #ifdef __aarch64__
 	mov	x8,x3				// syscall number (linux)

libc/sysv/syscall4.S

@@ -0,0 +1,53 @@
+/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8     -*-│
+│vi: set et ft=asm ts=8 tw=8 fenc=utf-8                                     :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2023 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ 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.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/macros.internal.h"
+
+//	Invokes system call w/ arity of four.
+//
+//	This function takes four params. The first four, are for
+//	args passed along to the system call. The 5th is for the
+//	the magic number, indicating which system call is called
+//
+//	The return value follows the Linux Kernel (System V) ABI
+//	where -errno is returned, rather than doing -1 w/ errno.
+//
+//	This helper should not be used to do cancelation points.
+__syscall4:
+#ifdef __aarch64__
+	mov	x8,x4				// syscall number (linux)
+	mov	x16,x4				// syscall number (xnu)
+	mov	x9,0				// clear carry flag
+	adds	x9,x9,0				// clear carry flag
+	svc	0
+	bcs	1f
+	ret
+1:	neg	x0,x0
+	ret
+#elif defined(__x86_64__)
+	mov	%rcx,%r10			// avoid intel cx clobber
+	mov	%r8d,%eax			// arg5 -> syscall number
+	clc					// linux saves carry flag
+	syscall					// bsds set carry on errs
+	jnc	1f
+	neg	%rax				// normalizes to system v
+1:	ret
+#else
+#error "unsupported architecture"
+#endif
+	.endfn	__syscall4,globl

libc/sysv/syscalls.sh

@@ -100,8 +100,8 @@ scall	sys_killpg		0x092fff092fffffff	0xfff	globl hidden
 scall	sys_clone		0x11fffffffffff038	0x0dc	globl hidden
 scall	sys_tkill		0x13e0771b121480c8	0x082	globl hidden # thr_kill() on FreeBSD; _lwp_kill() on NetBSD; thrkill() on OpenBSD where arg3 should be 0 or tcb; __pthread_kill() on XNU
 scall	sys_tgkill		0xffffff1e1ffff0ea	0x083	globl hidden # thr_kill2() on FreeBSD
-scall	sys_futex		0x0a60531c6ffff0ca	0x062	globl hidden # raises SIGSYS on NetBSD; _umtx_op() on FreeBSD
-scall	sys_futex_cp		0x8a68539c6ffff8ca	0x862	globl hidden # intended for futex wait ops
+scall	sys_futex		0x0a60531c622030ca	0x062	globl hidden # raises SIGSYS on NetBSD; _umtx_op() on FreeBSD
+scall	sys_futex_cp		0x8a68539c62a038ca	0x862	globl hidden # intended for futex wait ops
 scall	sys_set_robust_list	0x0a7ffffffffff111	0x063	globl # no wrapper
 scall	sys_get_robust_list	0x0a8ffffffffff112	0x064	globl # no wrapper
 scall	sys_uname		0x0a4fff0a4ffff03f	0x0a0	globl hidden

libc/sysv/sysv.mk

@@ -40,6 +40,7 @@ LIBC_SYSV_A_FILES :=					\
 	libc/sysv/restorert.S				\
 	libc/sysv/syscall2.S				\
 	libc/sysv/syscall3.S				\
+	libc/sysv/syscall4.S				\
 	libc/sysv/systemfive.S				\
 	libc/sysv/sysret.c				\
 	libc/sysv/sysv.c				\
@@ -170,6 +171,8 @@ o/$(MODE)/libc/sysv/syscall2.o: libc/sysv/syscall2.S
 	@$(COMPILE) -AOBJECTIFY.S $(OBJECTIFY.S) $(OUTPUT_OPTION) $<
 o/$(MODE)/libc/sysv/syscall3.o: libc/sysv/syscall3.S
 	@$(COMPILE) -AOBJECTIFY.S $(OBJECTIFY.S) $(OUTPUT_OPTION) $<
+o/$(MODE)/libc/sysv/syscall4.o: libc/sysv/syscall4.S
+	@$(COMPILE) -AOBJECTIFY.S $(OBJECTIFY.S) $(OUTPUT_OPTION) $<
 o/$(MODE)/libc/sysv/restorert.o: libc/sysv/restorert.S
 	@$(COMPILE) -AOBJECTIFY.S $(OBJECTIFY.S) $(OUTPUT_OPTION) $<
 o/$(MODE)/libc/sysv/calls/%.o: libc/sysv/calls/%.S

libc/thread/pthread_exit.c

@@ -155,7 +155,7 @@ wontreturn void pthread_exit(void *rc) {
   // note that the main thread is joinable by child threads
   if (pt->pt_flags & PT_STATIC) {
     atomic_store_explicit(&tib->tib_tid, 0, memory_order_release);
-    nsync_futex_wake_(&tib->tib_tid, INT_MAX, !IsWindows());
+    nsync_futex_wake_(&tib->tib_tid, INT_MAX, !IsWindows() && !IsXnu());
     _Exit1(0);
   }
 

libc/thread/pthread_timedjoin_np.c

@@ -65,7 +65,7 @@ static errno_t _pthread_wait(atomic_int *ctid, struct timespec *abstime) {
   if (!(rc = pthread_testcancel_np())) {
     BEGIN_CANCELLATION_POINT;
     while ((x = atomic_load_explicit(ctid, memory_order_acquire))) {
-      e = nsync_futex_wait_(ctid, x, !IsWindows(), abstime);
+      e = nsync_futex_wait_(ctid, x, !IsWindows() && !IsXnu(), abstime);
       if (e == -ECANCELED) {
         rc = ECANCELED;
         break;

test/libc/calls/sigbus_test.c

@@ -100,7 +100,12 @@ TEST(sigbus, test) {
 
   // verify the signal was raised
   EXPECT_EQ(SIGBUS, gotsig);
-  EXPECT_EQ(BUS_ADRERR, gotcode);
+  if (IsXnuSilicon()) {
+    // TODO: Why does it say it's an alignment error?
+    EXPECT_EQ(BUS_ADRALN, gotcode);
+  } else {
+    EXPECT_EQ(BUS_ADRERR, gotcode);
+  }
 
   // clean up
   sigaction(SIGBUS, &oldsa, 0);