Missing support for iPhoneSimulator platform on arm64

[mrosales]

I've been stuck on this for awhile now. Since the introduction of Xcode 12, the default behavior when building a binary for all architecture is to include the iPhoneSimulator target for arm64, which would be to support Apple Silicon computers.

I'm trying to build an apple_static_library for the simulator with something like a --ios_multi_cpus=arm64,x86_64 option to build a simulator fat archive with both simulator slices.

Ultimately my goal is to create a simulator fat archive and a device fat archive and then merge them into an XCFramework that is importable by an Xcode based project, but I am stuck on figuring out how to configure bazel to build something that doesn't always assume that arm64 is iphoneos and iphonesimulator is x86_64 or i386.

I've been looking through the rules and configuration in this repo and don't think that this is possible. Am I missing something, or is this a missing feature?

[keith]

I haven't heard of anyone successfully doing this yet (although I doubt many have tried). I also haven't audited the rules or bazel core for where these assumptions are (i imagine many are in bazel itself)

[mrosales]

I did a little bit more digging and found the following assumption in the bazel project:

https://github.com/bazelbuild/bazel/blob/450c7ad65bfcffebf753159ee2b617e557ffb4fd/src/main/java/com/google/devtools/build/lib/rules/apple/ApplePlatform.java#L44

More critically, though, it looks like the method for selecting the build platform to use assumes a 1:1 mapping between (PlatformType, CPU) and the ApplePlatform, which is an assumption that is broken with the introduction of new arm-based Apple Silicon machines.

https://github.com/bazelbuild/bazel/blob/450c7ad65bfcffebf753159ee2b617e557ffb4fd/src/main/java/com/google/devtools/build/lib/rules/apple/ApplePlatform.java#L108

[keith]

Related: bazelbuild/bazel#11628

I def agree there's some UX question here because of the archs overlap

[ihomway]

Facing the same problem here.
After trying and searching for many days, I found the problem is the assumption too. I hope there will be a workaround to fix this issue.

[keith]

I wouldn't expect there to be much investment in Apple Silicon in the near term so if this is blocking you I would suggest submitting a PR to bazel core with the fix

[indragiek]

For anyone blocked on being able to build an arm64 iOS simulator slice, I came up with a small patch to bazel core that adds support -- check out bazel at the 3.7.1 tag and apply this: https://gist.github.com/indragiek/e14162c0098d97ee976bceae9441f04d

Then generate an arm64 iOS Simulator slice by running:

$ bazel build ... --cpu=ios_sim_arm64 --apple_platform_type=ios

I don't have a plan to contribute this as-is to bazel as it seems like this may not be the right approach to fixing the archs overlap issue, but it's good enough to solve the immediate problem.

[ihomway]

indragiek's solution works for me, but if you have Swift files in your project, you may need a small change in rules_swift library, you can find this small change here 👇:

ihomway/rules_swift@a3699bf

[acecilia]

@indragiek Trying to use your solution to get the arm64 simulator slice from an intel mac in Catalina 10.15.7.

This is the script I am using to build bazel with your patch:

#!/bin/zsh

set -euo pipefail

readonly WORK_DIR="$(pwd)"
readonly BUILD_DIR="${WORK_DIR}/build-frameworks"
readonly OUTPUT_DIR="${BUILD_DIR}/output"
readonly BAZEL_DIR="${BUILD_DIR}/bazel"
readonly BAZEL_BIN="${BAZEL_DIR}/bin/bazel"

download_patched_version_of_bazel() {
    mkdir -p "${BAZEL_DIR}/4.1.0"
    cd "${BAZEL_DIR}/4.1.0"
    curl -O -L "https://github.com/bazelbuild/bazel/releases/download/4.1.0/bazel-4.1.0-darwin-x86_64"
    mv bazel-4.1.0-darwin-x86_64 bazel
    chmod +x bazel

    cd "${BAZEL_DIR}"
    git clone --branch "3.7.2" --depth 1 https://github.com/bazelbuild/bazel.git "3.7.2"
    cd "3.7.2"
    curl -O -L https://gist.githubusercontent.com/indragiek/e14162c0098d97ee976bceae9441f04d/raw/dba3a66a90d0a96d0dc6e236ab3fa1d41a2ce359/ios_sim_arm64.patch
    git apply ios_sim_arm64.patch

    # To install java11 on macos: brew install java11 https://mkyong.com/java/how-to-install-java-on-mac-osx/
    # https://github.com/bazelbuild/bazel/issues/11399#issuecomment-628945756
    # https://github.com/bazelbuild/rules_nodejs/issues/1301
    export JAVA_HOME="/usr/local/opt/openjdk@11/libexec/openjdk.jdk/Contents/Home" && "${BAZEL_DIR}"/4.1.0/bazel build --incompatible_restrict_string_escapes=false -c opt //src:bazel
    mkdir -p "$(dirname ${BAZEL_BIN})"
    cp bazel-bin/src/bazel "${BAZEL_BIN}"
    chmod +x "${BAZEL_BIN}"

    cd "${WORK_DIR}"
}

Which then I am using as:

${BAZEL_BIN} build --config=ios --cpu=ios_sim_arm64 -c opt tensorflow/lite/ios:TensorFlowLiteC_framework

Bazel builds correctly with your patch, but then when using it I am getting the following error:

ERROR: /private/var/tmp/_bazel_andres/5dd7712722979875795c5b78f5afb6d1/external/cpuinfo/BUILD.bazel:100:11: Configurable attribute "srcs" doesn't match this configuration (would a default condition help?).
Conditions checked:
 @cpuinfo//:linux_x86_64
 @cpuinfo//:linux_arm
 @cpuinfo//:linux_armhf
 @cpuinfo//:linux_armv7a
 @cpuinfo//:linux_armeabi
 @cpuinfo//:linux_aarch64
 @cpuinfo//:linux_mips64
 @cpuinfo//:linux_riscv64
 @cpuinfo//:linux_s390x
 @cpuinfo//:macos_x86_64
 @cpuinfo//:macos_arm64
 @cpuinfo//:windows_x86_64
 @cpuinfo//:android_armv7
 @cpuinfo//:android_arm64
 @cpuinfo//:android_x86
 @cpuinfo//:android_x86_64
 @cpuinfo//:ios_x86_64
 @cpuinfo//:ios_x86
 @cpuinfo//:ios_armv7
 @cpuinfo//:ios_arm64
 @cpuinfo//:ios_arm64e
 @cpuinfo//:watchos_x86_64
 @cpuinfo//:watchos_x86
 @cpuinfo//:watchos_armv7k
 @cpuinfo//:watchos_arm64_32
 @cpuinfo//:tvos_x86_64
 @cpuinfo//:tvos_arm64
 @cpuinfo//:emscripten_wasm

Any help would be much appreciated 🙌

EDIT: never mind, seems an issue specific to the project I am building and not bazel 🙏

[peterkorodi]

Hi @acecilia,

I got the same error. It seems that cpuinfo/BUILD.bazeldosen't contain ios_sim_arm64.
Could you solve this issue, and compile tensorflowlite to sim_arm64?

[acecilia]

@peterkorodi yes. I managed to compile an xcframework for tensorflowlite. Find the binary here: https://github.com/revolut-mobile/TensorFlowLiteC-binary/releases/tag/2.5.0

[keith]

Note that this stuff is starting to land upstream, once bazelbuild/bazel#13870 lands building for the arm64 simulator should work

[bvirlet]

bazelbuild/bazel#13870 seems to have been merged for release in Bazel 5.0, targeted release date November 16.

[keith]

Closing this now that ios_sim_arm64 has landed upstream, it should be available in the 5.x RC coming this week. For xcframeworks in general please subscribe to the tracking issue #1249

[bvirlet]

@acecilia are you still using your patches to build TensorFlowLiteC for Apple Silicon or is there an easier path now?

[acecilia]

@bvirlet I did not need to rebuild TensorFlowLiteC yet, so no idea about current status