__builtin_available is intermittently not available on macOS

[jdm]

When building mozjs on macOS arm64, I intermittently receive linker errors like this:

          Undefined symbols for architecture arm64:
            "___isPlatformVersionAtLeast", referenced from:
                js::jit::AutoMarkJitCodeWritableForThread::markExecutable(bool) in libmozjs_sys-13c131082aca4d88.rlib[85](Unified_cpp_js_src_jit9.o)
          ld: symbol(s) not found for architecture arm64
          clang: error: linker command failed with exit code 1 (use -v to see invocation)

There is one use of this function in mozjs:

mozjs/mozjs-sys/mozjs/js/src/jit/ProcessExecutableMemory.cpp

Line 1010 in 10fb074

if (__builtin_available(macOS 11.0, *)) {

The most recent spidermonkey upgrade removed a patch that removed a previous use of __builtinAvailable: bf41ed0#diff-5c427df1c88acdb6a3478df156bdd162ecf6bc6abd7231cfdec3b4ccb5a35138L1

curl/curl#4314 suggests that the issue here is that __builtinAvailable is only available in dynamic libraries, but we're building a static library. I have no idea why I would only hit this intermittently, or why CI never appears to run into this problem.

[jdm]

Just removing the __builtin_available check results in:

  In file included from Unified_cpp_js_src_jit9.cpp:29:
  /Users/jdm/src/mozjs/mozjs-sys/mozjs/js/src/jit/ProcessExecutableMemory.cpp:1010:3: error: 'pthread_jit_write_protect_np' is only available on macOS 11.0 or newer [-Werror,-Wunguarded-availability-new]
    pthread_jit_write_protect_np(executable);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
  /Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/pthread.h:588:6: note: 'pthread_jit_write_protect_np' has been marked as being introduced in macOS 11.0 here, but the deployment target is macOS 10.10.0
  void pthread_jit_write_protect_np(int enabled);
       ^
  /Users/jdm/src/mozjs/mozjs-sys/mozjs/js/src/jit/ProcessExecutableMemory.cpp:1010:3: note: enclose 'pthread_jit_write_protect_np' in a __builtin_available check to silence this warning
    pthread_jit_write_protect_np(executable);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

[jdm]

Strangely,

mozjs/mozjs-sys/mozjs/build/moz.configure/toolchain.configure

Lines 54 to 66 in 10fb074

	option(
	"--enable-macos-target",
	env="MACOSX_DEPLOYMENT_TARGET",
	nargs=1,
	default=depends(target, developer_options)
	# We continue to target 10.15 on Intel, but can target 11.0 for
	# aarch64 since the earliest hardware was released alongside 11.0.
	# For local builds, we want to target 10.15 regardless of the
	# underlying platform to catch any errors or warnings that wouldn't
	# show up when targeting 11.0, since these would later show up on
	# CI for Intel builds.
	(lambda t, d: "11.0" if (t.cpu == "aarch64" and not d) else "10.15"),
	help="Set the minimum MacOS version needed at runtime{|}",

looks like it should be setting a 11.0 deployment target in this case, and I have no idea where the 10.10 value comes from.

[jdm]

I am able to build after removing the __builtin_available check with ./mach clean and MACOSX_DEPLOYMENT_TARGET=11.0.

[mrobinson]

Servo is setting the MACOSX_DEPLOYMENT_TARGET to 10.10 in .cargo/config.toml. I believe this was previously set in the environment by mach.

[sagudev]

Then we should probably set MACOSX_DEPLOYMENT_TARGET in mozjs-sys and remove __builtin_available check.

[jschwe]

Shouldn't we just bump MACOSX_DEPLOYMENT_TARGET in servo? The oldest available version in github CI is macOS-12, so I don't think we can even test at all if servo can actually run on 10.10.