iOS Simulator build fails: 'arm64-apple-ios-sim' target invalid

[gezihuzi]

Problem:

Unable to build aws-lc-sys on iOS Simulator due to bindgen failing to recognize the iOS simulator architecture. Build succeeds on physical iOS devices but fails on simulators with "version 'sim' in target triple 'arm64-apple-ios-sim' is invalid" error.

Relevant details

AWS-LC for Rust versions or commit: aws-lc-sys v0.28.0
System information:

CPU architecture: ARM64 (Apple Silicon)
CPU name: Apple M-series
OS: macOS 15.4 (24E248) (with Xcode 16.3 (16E140) for iOS development)

Additional information:

• Rust version: rustc 1.85.1 (4eb161250 2025-03-15)
• Cargo version: cargo 1.85.1 (d73d2caf9 2024-12-31)

Installed targets

• aarch64-apple-ios
• aarch64-apple-ios-sim

Build log:

warning: aws-lc-sys@0.28.0: Building with: CMake
warning: aws-lc-sys@0.28.0: Symbol Prefix: Some("aws_lc_0_28_0")
warning: aws-lc-sys@0.28.0: CMAKE environment variable set: cmake
warning: aws-lc-sys@0.28.0: Clang version: Apple clang version 17.0.0 (clang-1700.0.13.3)
warning: aws-lc-sys@0.28.0: Generating bindings - internal bindgen. Platform: aarch64-apple-ios-sim
error: failed to run custom build command for `aws-lc-sys v0.28.0`

Caused by:
  process didn't exit successfully: [build script path removed] (exit status: 101)

  --- stderr
  thread 'main' panicked at [path removed]/aws-lc-sys-0.28.0/builder/sys_bindgen.rs:106:10:
  Unable to generate bindings.: ClangDiagnostic("error: version 'sim' in target triple 'arm64-apple-ios-sim' is invalid\n")

[justsmth]

Hello! I'm not sure why you would be seeing this error. Our CI does build and test for aarch64-apple-ios-sim. You might try installing llvm/clang (and optionally bindgen-cli) as described here in our User Guide. You might also check the bindgen user guide.

Please let us know if you continue to have trouble building for this target!

[chairmanwow]

I am also seeing this error. I had to add BINDGEN_EXTRA_CLANG_ARGS to get it to find stdlib.h for the sim target by pointing it at .../SDKs/iPhoneSimulator.sdk/usr/include. After doing that, I encounter this error.

Relevant details

AWS-LC for Rust versions or commit: aws-lc-sys v0.28.2
System information:

CPU architecture: ARM64 (Apple Silicon)
OS: macOS 15.4.1 (24E248) (with Xcode 16.3 (16E140) for iOS development)
iOS Simulator: 18.3.1 (22D8075)

Additional information:

• Rust version: 1.88.0
• Cargo version: 1.88.0

Same build log.

The Tauri project reported a similar issue with devs running XCode 16.3 and bindgen. Below is an example fix: tauri-apps/tauri#13128. Seems like aarch64-apple-ios-sim needs to be arm64-sim now, not arm64-apple-ios-sim.

[justsmth]

Hello!

This appears to be an issue that has been fixed upstream in bindgen-rs. Unfortunately, they've not posted a new release since early December.

I'll try to poke around to see when they plan to do another new release. Once they've released the fix, you might want to install the bindgen-cli and set AWS_LC_SYS_EXTERNAL_BINDGEN=1 in your build environment to ensure it gets used.

Thanks for letting us know about this issue. Hopefully, it can be resolved soon.

[chairmanwow]

Thanks for letting me know. For anybody else, if you're stuck, it's pretty easy to build rust-bindgen's main branch. Adding the main branch bindgen to my PATH and using AWS_LC_SYS_EXTERNAL_BINDGEN=1 has me up and running again for aarch64-apple-ios-sim.

Thanks @justsmth, I'll keep my eyes peeled for the new bindgen release.

[justsmth]

rust-lang/rust-bindgen#3199

[setoelkahfi]

Just stumbled upon this. So, is there no workaround for this?

These issues add the issues with the Xcode 16.3 release. We had several major issues with our project when updating our code to Xcode 16.3 I'm surprised it got rolled out by Apple.

[gezihuzi]

Hello @justsmth, I see that rust-bindgen v0.72.0 has been released with the upstream fix for the iOS simulator compilation issue I reported earlier.

Are there any plans to update aws-lc-rs to incorporate this fix? Any timeline update would be appreciated. Thanks!

[justsmth]

We should be bumping our MSRV to (most likely) 1.71.0 very soon. This will allow us to take a dependency on bindgen-v0.72.0. We will be sure to mention it in our release announcement when it's published! 😀

[ospfranco]

Hi, just FYI, at least in the macOS tahoe beta, it completely ditches support 16.x branches of Xcode. As in they don't even start any more. I've worked around this issue by having 16.2 installed (via xcodes) but it only works for the CLI tools. It would be good to get this working before the release of macOS Tahoe

[ospfranco]

For those who need more explicit steps for a workaround. As mentioned by @chairmanwow.

1. Install bindgen-cli locally. I use mise which gives my team a reproducible environment everywhere:

2. On the compilation command for the crate set AWS_LC_SYS_EXTERNAL_BINDGEN=1. I also had to uninstall a copy of bindgen-cli I had installed via pure cargo as that took precedence over the mise injected PATH variables.

Afterwards, it compiles just fine with Tahoe Beta 6 and Xcode 26