Performance Monitor causes crash on iOS 13.4

[IjzerenHein]

Description

Opening the Performance Monitor causes a crash as of iOS 13.4

React Native version:

System:
    OS: macOS 10.15.3
    CPU: (8) x64 Intel(R) Core(TM) i7-8559U CPU @ 2.70GHz
    Memory: 148.41 MB / 16.00 GB
    Shell: 5.7.1 - /bin/zsh
  Binaries:
    Node: 10.16.0 - ~/.nvm/versions/node/v10.16.0/bin/node
    Yarn: 1.21.1 - /usr/local/bin/yarn
    npm: 6.9.0 - ~/.nvm/versions/node/v10.16.0/bin/npm
    Watchman: 4.9.0 - /usr/local/bin/watchman
  SDKs:
    iOS SDK:
      Platforms: iOS 13.4, DriverKit 19.0, macOS 10.15, tvOS 13.4, watchOS 6.2
    Android SDK:
      API Levels: 22, 23, 25, 26, 27, 28, 29
      Build Tools: 25.0.3, 26.0.3, 27.0.3, 28.0.2, 28.0.3, 29.0.2
      System Images: android-22 | Intel x86 Atom_64, android-23 | Google APIs Intel x86 Atom, android-25 | Android TV Intel x86 Atom, android-26 | Google APIs Intel x86 Atom_64, android-27 | Google Play Intel x86 Atom, android-28 | Google Play Intel x86 Atom, android-29 | Google APIs Intel x86 Atom, android-29 | Google Play Intel x86 Atom
      Android NDK: 21.0.6113669
  IDEs:
    Android Studio: 3.6 AI-192.7142.36.36.6241897
    Xcode: 11.4/11E146 - /usr/bin/xcodebuild
  Languages:
    Python: 2.7.15 - /usr/local/bin/python
  npmPackages:
    @react-native-community/cli: Not Found
    react: 16.11.0 => 16.11.0
    react-native: 0.62.0 => 0.62.0
  npmGlobalPackages:
    *react-native*: Not Found

Steps To Reproduce

• Start react-native on an iOS 13.4 simulator

npx react-native init PerfCrash
cd PerfCrash
yarn ios

• Open debug-menu
• Tap on "Show Perf Monitor"

Expected Results

Shows Performance Monitor; and doesn't crash.

Additional info

I've debugged the issue and seem to have found the problem. JavaScriptCore has been updated in iOS 13.4 and it seems it is no longer possible to set the JavaScript Core options after initializing the VM.

The RCTJSCSetOption function now causes an EXC_BAD_ACCESS exception. The setOption function is resolved correctly but when calling it, it throws the exception. I've debugged the assembly and providing invalid values (logGC2=1 and logGC=3) do not produce a crash. So it doesn't appear to be a parsing issue, and the crash seems to occur when actually updating the option to 1.

static BOOL RCTJSCSetOption(const char *option)
{
  static RCTJSCSetOptionType setOption;
  static dispatch_once_t onceToken;

  dispatch_once(&onceToken, ^{
    /**
     * JSC private C++ static method to toggle options at runtime
     *
     * JSC::Options::setOptions - JavaScriptCore/runtime/Options.h
     */
    setOption = dlsym(RTLD_DEFAULT, "_ZN3JSC7Options9setOptionEPKc");

    if (RCT_DEBUG && setOption == NULL) {
      RCTLogWarn(@"The symbol used to enable JSC runtime options is not available in this iOS version");
    }
  });

  if (setOption) {
    return setOption(option); // <-- This throws EXC_BAD_ACCESS exception
  } else {
    return NO;
  }
}

After inspection on the JavaScriptCore code it was found that the JavaScriptCore options can no longer be changed after the VM was initialized.
https://github.com/WebKit/webkit/blob/master/Source/JavaScriptCore/runtime/OptionsList.h#L74

https://raw.githubusercontent.com/WebKit/webkit/master/Source/JavaScriptCore/ChangeLog

2019-09-12  Mark Lam  <[email protected]>

        Harden JSC against the abuse of runtime options.
        https://bugs.webkit.org/show_bug.cgi?id=201597
        <rdar://problem/55167068>

        Reviewed by Filip Pizlo.

        Linux parts contributed by Carlos Garcia Campos <[email protected]>.

        1. Introduce a JSC::Config struct that will be protected as ReadOnly once the
           first VM instance is constructed.  The end of the VM constructor calls
           Config::permanentlyFreeze() which will make the Config ReadOnly.

[IjzerenHein]

Additionally I noticed that the GC metric in the Performance Monitor also doesn't update in iOS 13.1. So it might be broken in earlier versions as well.

[gorhom]

@IjzerenHein good job, i have tried your solutions and works fine, would you mind submit a pr ?

[IjzerenHein]

@IjzerenHein good job, i have tried your solutions and works fine, would you mind submit a pr ?

@gorhom Done! 👊

[arnoldc]

This is crashing at React Native 0.60.4 , is this only fixed at latest version of react native?