Revert "[iOS] Delete GN flags for mach absolute time ticks"

This reverts commit 734471f.

Reason for revert:
LUCI Bisection identified this CL as the culprit of a build failure. See the analysis: https://luci-bisection.appspot.com/analysis/b/8770136478150458481

Sample failed build: https://ci.chromium.org/b/8770136478150458481

If this is a false positive, please report it at https://bugs.chromium.org/p/chromium/issues/entry?comment=Analysis%3A+https%3A%2F%2Fluci-bisection.appspot.com%2Fanalysis%2Fb%2F8770136478150458481&components=Tools%3ETest%3EFindit&labels=LUCI-Bisection-Wrong%2CPri-3%2CType-Bug&status=Available&summary=Wrongly+blamed+https%3A%2F%2Fchromium-review.googlesource.com%2Fc%2Fchromium%2Fsrc%2F%2B%2F4850577

Original change's description:
> [iOS] Delete GN flags for mach absolute time ticks
>
> Mach absolute time ticks have been enabled by default for a month
> with no known issues, so this CL cleans up the corresponding GN
> flags.
>
> Bug: 1414153
> Change-Id: I981f7e823295a5f8c9a9d186e356243e7f76eef1
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4850577
> Commit-Queue: Ali Juma <ajuma@chromium.org>
> Reviewed-by: Ian Vollick <vollick@chromium.org>
> Reviewed-by: Mark Mentovai <mark@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1195534}
>

Bug: 1414153
Change-Id: I9bd6656f514dc19a9c647f9ff845420762c462f4
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4858437
Commit-Queue: luci-bisection@appspot.gserviceaccount.com <luci-bisection@appspot.gserviceaccount.com>
Bot-Commit: luci-bisection@appspot.gserviceaccount.com <luci-bisection@appspot.gserviceaccount.com>
Owners-Override: luci-bisection@appspot.gserviceaccount.com <luci-bisection@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1195555}

base/BUILD.gn

@@ -48,6 +48,11 @@ if (is_mac) {
   import("//third_party/protobuf/proto_library.gni")
 }
 
+if (is_apple) {
+  # Buildflags to control time behavior on iOS in file shared with mac.
+  import("//base/time/buildflags/buildflags.gni")
+}
+
 if (is_win) {
   import("//build/config/win/control_flow_guard.gni")
 }
@@ -88,6 +93,14 @@ assert(!is_nacl || is_nacl_saigo,
 assert(!is_win || is_clang,
        "only clang-cl is supported on Windows, see https://crbug.com/988071")
 
+if (is_apple) {
+  assert(!use_blink || enable_mach_absolute_time_ticks,
+         "use_blink requires mach absolute time ticks")
+
+  assert(!is_mac || enable_mach_absolute_time_ticks,
+         "mac requires mach absolute time ticks")
+}
+
 # Determines whether libevent should be dep.
 dep_libevent = !is_fuchsia && !is_win && !is_mac && !is_nacl
 
@@ -1053,6 +1066,10 @@ component("base") {
   # to provide the appropriate `#define` here.
   defines += [ "IS_RAW_PTR_IMPL" ]
 
+  if (is_apple) {
+    deps += [ "//base/time/buildflags:buildflags" ]
+  }
+
   if (build_rust_json_reader) {
     deps += [ "//third_party/rust/serde_json_lenient/v0_1/wrapper" ]
   }
@@ -3723,7 +3740,7 @@ test("base_unittests") {
     ]
   }
 
-  if (is_apple) {
+  if (is_apple && enable_mach_absolute_time_ticks) {
     sources += [ "time/time_apple_unittest.mm" ]
   }
 

base/allocator/partition_allocator/BUILD.gn

@@ -730,6 +730,13 @@ buildflag_header("partition_alloc_buildflags") {
     "ENABLE_PKEYS=$enable_pkeys",
     "ENABLE_THREAD_ISOLATION=$enable_pkeys",
   ]
+
+  if (is_apple) {
+    # TODO(crbug.com/1414153): once TimeTicks::Now behavior is unified on iOS,
+    # this should be removed.
+    flags += [ "PARTITION_ALLOC_ENABLE_MACH_ABSOLUTE_TIME_TICKS=" +
+               "$partition_alloc_enable_mach_absolute_time_ticks" ]
+  }
 }
 
 buildflag_header("chromecast_buildflags") {

base/allocator/partition_allocator/partition_alloc.gni

@@ -204,6 +204,12 @@ declare_args() {
   # Shadow metadata is still under development and only supports Linux
   # for now.
   enable_shadow_metadata = false
+
+  if (is_apple) {
+    # TODO(crbug.com/1414153): this should be removed once the use of mach
+    # absolute time ticks is successfully launched on iOS.
+    partition_alloc_enable_mach_absolute_time_ticks = true
+  }
 }
 
 # *Scan is currently only used by Chromium, and supports only 64-bit.
@@ -306,6 +312,14 @@ assert(!use_asan_backup_ref_ptr || is_asan,
 assert(!use_asan_unowned_ptr || is_asan,
        "AsanUnownedPtr requires AddressSanitizer")
 
+if (is_apple) {
+  assert(!use_blink || partition_alloc_enable_mach_absolute_time_ticks,
+         "use_blink requires partition_alloc_enable_mach_absolute_time_ticks")
+
+  assert(!is_mac || partition_alloc_enable_mach_absolute_time_ticks,
+         "mac requires partition_alloc_enable_mach_absolute_time_ticks")
+}
+
 # AsanBackupRefPtr is not supported outside Chromium. The implementation is
 # entangled with `//base`. The code is only physically located with the rest of
 # `raw_ptr` to keep it together.

base/allocator/partition_allocator/partition_alloc_base/time/time.h

@@ -140,7 +140,9 @@ class PA_COMPONENT_EXPORT(PARTITION_ALLOC) TimeDelta {
   static TimeDelta FromZxDuration(zx_duration_t nanos);
 #endif
 #if BUILDFLAG(IS_APPLE)
+#if BUILDFLAG(PARTITION_ALLOC_ENABLE_MACH_ABSOLUTE_TIME_TICKS)
   static TimeDelta FromMachTime(uint64_t mach_time);
+#endif  // BUILDFLAG(PARTITION_ALLOC_ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 #endif  // BUILDFLAG(IS_APPLE)
 
   // Converts an integer value representing TimeDelta to a class. This is used
@@ -849,12 +851,14 @@ class PA_COMPONENT_EXPORT(PARTITION_ALLOC) TimeTicks
 #endif
 
 #if BUILDFLAG(IS_APPLE)
+#if BUILDFLAG(PARTITION_ALLOC_ENABLE_MACH_ABSOLUTE_TIME_TICKS)
   static TimeTicks FromMachAbsoluteTime(uint64_t mach_absolute_time);
 
   // Sets the current Mach timebase to `timebase`. Returns the old timebase.
   static mach_timebase_info_data_t SetMachTimebaseInfoForTesting(
       mach_timebase_info_data_t timebase);
 
+#endif  // BUILDFLAG(PARTITION_ALLOC_ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 #endif  // BUILDFLAG(IS_APPLE)
 
 #if BUILDFLAG(IS_ANDROID) || BUILDFLAG(PA_IS_CHROMEOS_ASH)

base/allocator/partition_allocator/partition_alloc_base/time/time_apple.mm

@@ -28,6 +28,7 @@
 
 namespace {
 
+#if BUILDFLAG(PARTITION_ALLOC_ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 // Returns a pointer to the initialized Mach timebase info struct.
 mach_timebase_info_data_t* MachTimebaseInfo() {
   static mach_timebase_info_data_t timebase_info = []() {
@@ -80,14 +81,29 @@ int64_t MachTimeToMicroseconds(uint64_t mach_time) {
   // 9223372036854775807 / (1e6 * 60 * 60 * 24 * 365.2425) = 292,277).
   return checked_cast<int64_t>(microseconds);
 }
+#endif  // BUILDFLAG(PARTITION_ALLOC_ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 
 // Returns monotonically growing number of ticks in microseconds since some
 // unspecified starting point.
 int64_t ComputeCurrentTicks() {
+#if !BUILDFLAG(PARTITION_ALLOC_ENABLE_MACH_ABSOLUTE_TIME_TICKS)
+  struct timespec tp;
+  // clock_gettime() returns 0 on success and -1 on failure. Failure can only
+  // happen because of bad arguments (unsupported clock type or timespec
+  // pointer out of accessible address space). Here it is known that neither
+  // can happen since the timespec parameter is stack allocated right above and
+  // `CLOCK_MONOTONIC` is supported on all versions of iOS that Chrome is
+  // supported on.
+  int res = clock_gettime(CLOCK_MONOTONIC, &tp);
+  PA_BASE_DCHECK(0 == res) << "Failed clock_gettime, errno: " << errno;
+
+  return (int64_t)tp.tv_sec * 1000000 + tp.tv_nsec / 1000;
+#else
   // mach_absolute_time is it when it comes to ticks on the Mac.  Other calls
   // with less precision (such as TickCount) just call through to
   // mach_absolute_time.
   return MachTimeToMicroseconds(mach_absolute_time());
+#endif  // !BUILDFLAG(PARTITION_ALLOC_ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 }
 
 int64_t ComputeThreadTicks() {
@@ -172,10 +188,12 @@ Time TimeNowFromSystemTimeIgnoringOverride() {
 
 // TimeDelta ------------------------------------------------------------------
 
+#if BUILDFLAG(PARTITION_ALLOC_ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 // static
 TimeDelta TimeDelta::FromMachTime(uint64_t mach_time) {
   return Microseconds(MachTimeToMicroseconds(mach_time));
 }
+#endif  // BUILDFLAG(PARTITION_ALLOC_ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 
 // TimeTicks ------------------------------------------------------------------
 
@@ -195,6 +213,7 @@ TimeTicks TimeTicksNowIgnoringOverride() {
   return true;
 }
 
+#if BUILDFLAG(PARTITION_ALLOC_ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 // static
 TimeTicks TimeTicks::FromMachAbsoluteTime(uint64_t mach_absolute_time) {
   return TimeTicks(MachTimeToMicroseconds(mach_absolute_time));
@@ -210,9 +229,15 @@ TimeTicks TimeTicksNowIgnoringOverride() {
   return orig_timebase;
 }
 
+#endif  // BUILDFLAG(PARTITION_ALLOC_ENABLE_MACH_ABSOLUTE_TIME_TICKS)
+
 // static
 TimeTicks::Clock TimeTicks::GetClock() {
+#if !BUILDFLAG(PARTITION_ALLOC_ENABLE_MACH_ABSOLUTE_TIME_TICKS)
+  return Clock::IOS_CF_ABSOLUTE_TIME_MINUS_KERN_BOOTTIME;
+#else
   return Clock::MAC_MACH_ABSOLUTE_TIME;
+#endif  // !BUILDFLAG(PARTITION_ALLOC_ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 }
 
 // ThreadTicks ----------------------------------------------------------------

base/time/buildflags/BUILD.gn

@@ -0,0 +1,15 @@
+# Copyright 2023 The Chromium Authors
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//build/buildflag_header.gni")
+import("buildflags.gni")
+
+# Generate a buildflag header for compile-time checking of mach absolute time
+# support in TimeTicks
+# TODO(crbug.com/1414153): this should be removed once there is a unified
+# approach to TimeTicks::Now on iOS.
+buildflag_header("buildflags") {
+  header = "buildflags.h"
+  flags = [ "ENABLE_MACH_ABSOLUTE_TIME_TICKS=$enable_mach_absolute_time_ticks" ]
+}

base/time/buildflags/buildflags.gni

@@ -0,0 +1,13 @@
+# Copyright 2023 The Chromium Authors
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//build/config/features.gni")
+
+# TODO(crbug.com/1414153): this should be removed once the use of mach absolute
+# time ticks is successfully launched on iOS.
+declare_args() {
+  # use_blink currently assumes mach absolute time ticks (eg, to ensure that
+  # trace events cohere).
+  enable_mach_absolute_time_ticks = true
+}

base/time/time.h

@@ -143,7 +143,9 @@ class BASE_EXPORT TimeDelta {
   static TimeDelta FromZxDuration(zx_duration_t nanos);
 #endif
 #if BUILDFLAG(IS_APPLE)
+#if BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
   static TimeDelta FromMachTime(uint64_t mach_time);
+#endif  // BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 #endif  // BUILDFLAG(IS_APPLE)
 
   // Converts an integer value representing TimeDelta to a class. This is used
@@ -1196,12 +1198,14 @@ class BASE_EXPORT TimeTicks : public time_internal::TimeBase<TimeTicks> {
 #endif
 
 #if BUILDFLAG(IS_APPLE)
+#if BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
   static TimeTicks FromMachAbsoluteTime(uint64_t mach_absolute_time);
 
   // Sets the current Mach timebase to `timebase`. Returns the old timebase.
   static mach_timebase_info_data_t SetMachTimebaseInfoForTesting(
       mach_timebase_info_data_t timebase);
 
+#endif  // BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 #endif  // BUILDFLAG(IS_APPLE)
 
 #if BUILDFLAG(IS_ANDROID) || BUILDFLAG(IS_CHROMEOS_ASH)

base/time/time_apple.mm

@@ -22,8 +22,15 @@
 #include "base/time/time_override.h"
 #include "build/build_config.h"
 
+#if !BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
+#include <errno.h>
+#include <time.h>
+#include "base/ios/ios_util.h"
+#endif  // !BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
+
 namespace {
 
+#if BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 // Returns a pointer to the initialized Mach timebase info struct.
 mach_timebase_info_data_t* MachTimebaseInfo() {
   static mach_timebase_info_data_t timebase_info = []() {
@@ -77,14 +84,29 @@ int64_t MachTimeToMicroseconds(uint64_t mach_time) {
   // 9223372036854775807 / (1e6 * 60 * 60 * 24 * 365.2425) = 292,277).
   return base::checked_cast<int64_t>(microseconds);
 }
+#endif  // BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 
 // Returns monotonically growing number of ticks in microseconds since some
 // unspecified starting point.
 int64_t ComputeCurrentTicks() {
+#if !BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
+  struct timespec tp;
+  // clock_gettime() returns 0 on success and -1 on failure. Failure can only
+  // happen because of bad arguments (unsupported clock type or timespec pointer
+  // out of accessible address space). Here it is known that neither can happen
+  // since the timespec parameter is stack allocated right above and
+  // `CLOCK_MONOTONIC` is supported on all versions of iOS that Chrome is
+  // supported on.
+  int res = clock_gettime(CLOCK_MONOTONIC, &tp);
+  DCHECK_EQ(res, 0) << "Failed clock_gettime, errno: " << errno;
+
+  return (int64_t)tp.tv_sec * 1000000 + tp.tv_nsec / 1000;
+#else
   // mach_absolute_time is it when it comes to ticks on the Mac.  Other calls
   // with less precision (such as TickCount) just call through to
   // mach_absolute_time.
   return MachTimeToMicroseconds(mach_absolute_time());
+#endif  // !BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 }
 
 int64_t ComputeThreadTicks() {
@@ -172,10 +194,12 @@ Time TimeNowFromSystemTimeIgnoringOverride() {
 
 // TimeDelta ------------------------------------------------------------------
 
+#if BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 // static
 TimeDelta TimeDelta::FromMachTime(uint64_t mach_time) {
   return Microseconds(MachTimeToMicroseconds(mach_time));
 }
+#endif  // BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 
 // TimeTicks ------------------------------------------------------------------
 
@@ -195,6 +219,7 @@ TimeTicks TimeTicksNowIgnoringOverride() {
   return true;
 }
 
+#if BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 // static
 TimeTicks TimeTicks::FromMachAbsoluteTime(uint64_t mach_absolute_time) {
   return TimeTicks(MachTimeToMicroseconds(mach_absolute_time));
@@ -210,9 +235,15 @@ TimeTicks TimeTicksNowIgnoringOverride() {
   return orig_timebase;
 }
 
+#endif  // BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
+
 // static
 TimeTicks::Clock TimeTicks::GetClock() {
+#if !BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
+  return Clock::IOS_CF_ABSOLUTE_TIME_MINUS_KERN_BOOTTIME;
+#else
   return Clock::MAC_MACH_ABSOLUTE_TIME;
+#endif  // !BUILDFLAG(ENABLE_MACH_ABSOLUTE_TIME_TICKS)
 }
 
 // ThreadTicks ----------------------------------------------------------------