{"abstract":[{"text":"Update your just-in-time (JIT) compiler to work with the Hardened Runtime capability,","type":"text"},{"text":" ","type":"text"},{"text":"and with Apple silicon.","type":"text"}],"hierarchy":{"paths":[["doc:\/\/com.apple.documentation\/documentation\/technologies","doc:\/\/com.apple.Apple-Silicon\/documentation\/apple-silicon"]]},"identifier":{"interfaceLanguage":"swift","url":"doc:\/\/com.apple.Apple-Silicon\/documentation\/Apple-Silicon\/porting-just-in-time-compilers-to-apple-silicon"},"kind":"article","legalNotices":{"copyright":"Copyright © 2026 Apple Inc. All rights reserved.","privacyPolicy":"https:\/\/www.apple.com\/privacy\/privacy-policy","termsOfUse":"https:\/\/www.apple.com\/legal\/internet-services\/terms\/site.html"},"metadata":{"availableLanguages":["de-DE","en-US","es-419","fr-FR","it-IT","ja-JP","ko-KR","pt-BR","zh-CN"],"role":"article","roleHeading":"Article","title":"Porting just-in-time compilers to Apple silicon"},"primaryContentSections":[{"content":[{"anchor":"overview","level":2,"text":"Overview","type":"heading"},{"content":[{"inlineContent":[{"text":"","type":"text"},{"text":" ","type":"text"},{"text":"If you need to build for Intel-based processors","type":"text"},{"text":" ","type":"text"},{"text":"using Xcode 27 to target macOS 27 or DriverKit 27,","type":"text"},{"text":" ","type":"text"},{"text":"add ","type":"text"},{"code":"x86_64","type":"codeVoice"},{"text":" to the Architectures (","type":"text"},{"code":"ARCHS","type":"codeVoice"},{"text":") build setting in Xcode,","type":"text"},{"text":" ","type":"text"},{"text":"as described in the Architectures section of","type":"text"},{"text":" ","type":"text"},{"identifier":"doc:\/\/com.apple.documentation\/documentation\/Xcode\/build-settings-reference","isActive":true,"type":"reference"},{"text":" ","type":"text"},{"text":"and ","type":"text"},{"identifier":"doc:\/\/com.apple.documentation\/documentation\/Xcode\/configuring-the-build-settings-of-a-target","isActive":true,"type":"reference"},{"text":".","type":"text"},{"text":" ","type":"text"},{"text":"If you need to run Xcode on an Intel-based processor,","type":"text"},{"text":" ","type":"text"},{"text":"use Xcode 26 or earlier.","type":"text"}],"type":"paragraph"}],"name":"Important","style":"important","type":"aside"},{"inlineContent":[{"text":"A just-in-time (JIT) compiler translates byte-code or intermediate script code into","type":"text"},{"text":" ","type":"text"},{"text":"machine-language instructions, and makes those instructions available for execution.","type":"text"},{"text":" ","type":"text"},{"text":"An app initiates JIT compilation as needed to support relevant tasks, and the compilation","type":"text"},{"text":" ","type":"text"},{"text":"process takes place within the app’s process space. For example, a web browser uses","type":"text"},{"text":" ","type":"text"},{"text":"JIT compilation to transform a web page’s script code into runnable code when the","type":"text"},{"text":" ","type":"text"},{"text":"user interacts with the appropriate page elements.","type":"text"}],"type":"paragraph"},{"inlineContent":[{"identifier":"porting-just-in-time-compilers-to-apple-silicon-1.png","type":"image"}],"type":"paragraph"},{"inlineContent":[{"text":"Because JIT compilation uses some techniques that the Hardened Runtime capability","type":"text"},{"text":" ","type":"text"},{"text":"specifically disallows, you need to update your app if it supports that capability.","type":"text"},{"text":" ","type":"text"},{"text":"Even if your app doesn’t adopt the Hardened Runtime, you need to still make changes","type":"text"},{"text":" ","type":"text"},{"text":"to support Apple silicon.","type":"text"},{"text":" ","type":"text"},{"text":"For more information about configuring the Hardened Runtime capability, see ","type":"text"},{"identifier":"doc:\/\/com.apple.documentation\/documentation\/Security\/hardened-runtime","isActive":true,"type":"reference"},{"text":".","type":"text"}],"type":"paragraph"},{"anchor":"Enable-the-JIT-entitlements-for-the-Hardened-Runtime","level":3,"text":"Enable the JIT entitlements for the Hardened Runtime","type":"heading"},{"inlineContent":[{"text":"The Hardened Runtime capability prohibits the execution of code in a memory page,","type":"text"},{"text":" ","type":"text"},{"text":"unless that code is accompanied by a valid code signature. Because a JIT compiler","type":"text"},{"text":" ","type":"text"},{"text":"doesn’t sign the code it generates, it technically violates the rules of the Hardened","type":"text"},{"text":" ","type":"text"},{"text":"Runtime. To fix this issue, you need to adjust your Hardened Runtime settings to allow","type":"text"},{"text":" ","type":"text"},{"text":"JIT-related activities.","type":"text"}],"type":"paragraph"},{"inlineContent":[{"text":"To allow JIT compilation in your app, navigate to the Hardened Runtime capability","type":"text"},{"text":" ","type":"text"},{"text":"in Xcode and enable the Allow Execution of JIT-compiled Code option for your app.","type":"text"},{"text":" ","type":"text"},{"text":"When you enable this option, Xcode adds the ","type":"text"},{"code":"com.apple.security.cs.allow-jit","type":"codeVoice"},{"text":" entitlement","type":"text"},{"text":" ","type":"text"},{"text":"to your app. When this entitlement is present, the system allows your app to call","type":"text"},{"text":" ","type":"text"},{"code":"mmap","type":"codeVoice"},{"text":" with the ","type":"text"},{"code":"MAP_JIT","type":"codeVoice"},{"text":" flag. If you don’t have this entitlement, calls using that","type":"text"},{"text":" ","type":"text"},{"text":"flag return an error.","type":"text"}],"type":"paragraph"},{"inlineContent":[{"text":"When your app has the Hardened Runtime capability and the ","type":"text"},{"code":"com.apple.security.cs.allow-jit","type":"codeVoice"},{"text":" entitlement, it can only create one memory region with the ","type":"text"},{"code":"MAP_JIT","type":"codeVoice"},{"text":" flag set.","type":"text"},{"text":" ","type":"text"},{"text":"The ","type":"text"},{"code":"com.apple.security.cs.allow-jit","type":"codeVoice"},{"text":" entitlement is required only when an","type":"text"},{"text":" ","type":"text"},{"text":"app adopts the Hardened Runtime capability. If you don’t adopt this capability, you","type":"text"},{"text":" ","type":"text"},{"text":"don’t need the entitlement to use the ","type":"text"},{"code":"MAP_JIT","type":"codeVoice"},{"text":" flag. For more information about","type":"text"},{"text":" ","type":"text"},{"text":"the entitlement, see ","type":"text"},{"identifier":"doc:\/\/com.apple.documentation\/documentation\/BundleResources\/Entitlements\/com.apple.security.cs.allow-jit","isActive":true,"type":"reference"},{"text":".","type":"text"}],"type":"paragraph"},{"inlineContent":[{"text":"Additionally, add the ","type":"text"},{"code":"com.apple.security.cs.jit-write-allowlist","type":"codeVoice"},{"text":" entitlement with the value ","type":"text"},{"code":"true","type":"codeVoice"},{"text":", to enable JIT callback allow lists.","type":"text"},{"text":" ","type":"text"},{"text":"Adding this entitlement allows your to call ","type":"text"},{"code":"pthread_jit_write_with_callback_np()","type":"codeVoice"},{"text":", which you use to write to your app’s JIT region.","type":"text"}],"type":"paragraph"},{"content":[{"inlineContent":[{"text":"","type":"text"},{"text":" ","type":"text"},{"text":"On macOS, when you add the ","type":"text"},{"code":"com.apple.security.cs.jit-write-allowlist","type":"codeVoice"},{"text":" entitlement, your app can no longer call ","type":"text"},{"code":"pthread_jit_write_protect_np()","type":"codeVoice"},{"text":".","type":"text"},{"text":" ","type":"text"},{"text":"The ","type":"text"},{"code":"pthread_jit_write_protect_np()","type":"codeVoice"},{"text":" function isn’t available on iOS.","type":"text"}],"type":"paragraph"}],"name":"Note","style":"note","type":"aside"},{"inlineContent":[{"text":"When memory protection is enabled, a thread cannot write to a memory region and execute","type":"text"},{"text":" ","type":"text"},{"text":"instructions in that region at the same time. Apple silicon enables memory protection","type":"text"},{"text":" ","type":"text"},{"text":"for all apps, regardless of whether they adopt the Hardened Runtime. Intel-based","type":"text"},{"text":" ","type":"text"},{"text":"Mac computers enable memory protection only for apps that adopt the Hardened Runtime.","type":"text"}],"type":"paragraph"},{"anchor":"Create-a-callback-to-write-JIT-instructions","level":3,"text":"Create a callback to write JIT instructions","type":"heading"},{"inlineContent":[{"text":"Your app writes to the ","type":"text"},{"code":"MAP_JIT","type":"codeVoice"},{"text":" memory region in a callback function, that you pass to the ","type":"text"},{"code":"pthread_jit_write_with_callback_np()","type":"codeVoice"},{"text":" function.","type":"text"},{"text":" ","type":"text"},{"text":"The callback needs to take a context pointer as an argument, and return its result as an integer.","type":"text"},{"text":" ","type":"text"},{"text":"The callback needs to assume that the memory pointed to by the context pointer can be controlled by an attacker, and validate that the instructions to be written are permitted.","type":"text"},{"text":" ","type":"text"},{"text":"For example:","type":"text"}],"type":"paragraph"},{"code":["\/\/ Initialize this pointer using mmap() with the MAP_JIT flag.","static void *jit_region;","","struct jit_code {","  void *instructions;","  ptrdiff_t entry_point;","  size_t instructions_length;","}","","enum jit_code_safety {","  JIT_CODE_VALID,","  JIT_CODE_INVALID,","};","","\/\/ Ensure that the JIT code is safe to execute.","enum jit_code_safety validate_jit_code(struct jit_code *code);","","int jit_writing_callback(void *context) {","  struct jit_code *code = (struct jit_code *)context;","  if (validate_jit_code(code) == JIT_CODE_VALID) {","    memcpy(jit_region, code->instructions, code->instructions_length);","\treturn 0;","  } else {","    return -1;","  }","}"],"copyToClipboard":true,"lineAnnotations":[],"showLineNumbers":false,"syntax":"c","type":"codeListing","wrap":0},{"anchor":"Add-your-JIT-callback-to-the-allowlist","level":3,"text":"Add your JIT callback to the allowlist","type":"heading"},{"inlineContent":[{"text":"Each executable, for example, your app binary, can define at most one allowlist of functions that the executable uses as callbacks to ","type":"text"},{"code":"pthread_jit_write_with_callback_np()","type":"codeVoice"},{"text":".","type":"text"}],"type":"paragraph"},{"content":[{"inlineContent":[{"text":"","type":"text"},{"text":" ","type":"text"},{"text":"Your app crashes if you call ","type":"text"},{"code":"pthread_jit_write_with_callback_np()","type":"codeVoice"},{"text":" with a callback function that isn’t in the allowlist.","type":"text"}],"type":"paragraph"}],"name":"Important","style":"important","type":"aside"},{"inlineContent":[{"text":"Define your app’s allowlist using the ","type":"text"},{"code":"PTHREAD_JIT_WRITE_ALLOW_CALLBACKS_NP","type":"codeVoice"},{"text":" macro:","type":"text"}],"type":"paragraph"},{"code":["PTHREAD_JIT_WRITE_ALLOW_CALLBACKS_NP(jit_writing_callback)"],"copyToClipboard":true,"lineAnnotations":[],"showLineNumbers":false,"syntax":"c","type":"codeListing","wrap":0},{"inlineContent":[{"text":"On macOS, if you need to update the allowlist with callbacks you load at runtime, for example from dynamic libraries you load using ","type":"text"},{"code":"dlopen()","type":"codeVoice"},{"text":", follow these steps:","type":"text"}],"type":"paragraph"},{"items":[{"content":[{"inlineContent":[{"text":"Add the ","type":"text"},{"code":"com.apple.security.cs.jit-write-allowlist-freeze-late","type":"codeVoice"},{"text":" entitlement with the value ","type":"text"},{"code":"true","type":"codeVoice"},{"text":".","type":"text"}],"type":"paragraph"}]},{"content":[{"inlineContent":[{"text":"Define at most one allowlist in each dynamic library using ","type":"text"},{"code":"PTHREAD_JIT_WRITE_ALLOW_CALLBACKS_NP","type":"codeVoice"},{"text":".","type":"text"}],"type":"paragraph"}]},{"content":[{"inlineContent":[{"text":"Load the dynamic libraries in your main executable.","type":"text"}],"type":"paragraph"}]},{"content":[{"inlineContent":[{"text":"Call ","type":"text"},{"code":"pthread_jit_write_freeze_callbacks_np()","type":"codeVoice"},{"text":".","type":"text"}],"type":"paragraph"}]}],"type":"orderedList"},{"inlineContent":[{"text":"If you add the ","type":"text"},{"code":"com.apple.security.cs.jit-write-allowlist-freeze-late","type":"codeVoice"},{"text":" entitlement, you need to call ","type":"text"},{"code":"pthread_jit_write_freeze_callbacks_np()","type":"codeVoice"},{"text":" before your first call to ","type":"text"},{"code":"pthread_jit_write_with_callback_np()","type":"codeVoice"},{"text":".","type":"text"},{"text":" ","type":"text"},{"text":"If you call ","type":"text"},{"code":"pthread_jit_write_with_callback_np()","type":"codeVoice"},{"text":" before freezing the callbacks allowlist, the system terminates your process with an error.","type":"text"}],"type":"paragraph"},{"content":[{"inlineContent":[{"text":"","type":"text"},{"text":" ","type":"text"},{"text":"Freeze the callback allowlist by calling ","type":"text"},{"code":"pthread_jit_write_freeze_callbacks_np()","type":"codeVoice"},{"text":" early in your app’s startup process, before the app starts processing untrusted inputs.","type":"text"}],"type":"paragraph"}],"name":"Important","style":"important","type":"aside"},{"anchor":"Write-instructions-to-your-JIT-memory-region","level":3,"text":"Write instructions to your JIT memory region","type":"heading"},{"inlineContent":[{"text":"Pass your callback and context pointer to ","type":"text"},{"code":"pthread_jit_write_with_callback_np()","type":"codeVoice"},{"text":" to write code to the ","type":"text"},{"code":"MAP_JIT","type":"codeVoice"},{"text":" memory region.","type":"text"},{"text":" ","type":"text"},{"text":"This function:","type":"text"}],"type":"paragraph"},{"items":[{"content":[{"inlineContent":[{"text":"Checks that your callback function is in the allowlist.","type":"text"}],"type":"paragraph"}]},{"content":[{"inlineContent":[{"text":"Makes the memory region writable, and not executable, for the current thread only.","type":"text"}],"type":"paragraph"}]},{"content":[{"inlineContent":[{"text":"Runs your callback function, passing the context pointer as the argument.","type":"text"}],"type":"paragraph"}]},{"content":[{"inlineContent":[{"text":"Makes the memory region executable, and not writable, for the current thread.","type":"text"}],"type":"paragraph"}]},{"content":[{"inlineContent":[{"text":"Returns the value that your callback function returned.","type":"text"}],"type":"paragraph"}]}],"type":"orderedList"},{"code":["struct jit_code code = {0};","int 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On Apple silicon, the instruction caches aren’t","type":"text"},{"text":" ","type":"text"},{"text":"coherent with data caches, and unexpected results might occur if you execute instructions","type":"text"},{"text":" ","type":"text"},{"text":"without invalidating the caches. 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