[swift-inspect] implement Android support including remote heap iteration

[andrurogerz]

Purpose

Implement swift-inspect Android support, building on the Linux implementation added in #77938. The bulk of this PR is focused on implementing remote heap iteration using Android's malloc_iterate, which is not supported on Linux.

Overview

• Extend the LinuxRemoteProcess class with a new AndroidRemoteProcess class, overriding and implementing the iterateHeap method
• Add Swift wrappers for ptrace calls to the SwiftInspectLinux module for use in heap iteration
• Use existing memory map parsing for /proc/<pid>/maps to identify heap regions in the target process
• Implement a mechanism to call remote functions in the remote process using ptrace
• Allocate memory for heap-iteration callback and metadata in the remote process by remotely calling mmap (and munmap) using ptrace
• Implement heap-iteration by remotely calling malloc_iterate using ptrace with a custom callback copied to the the process using process_vm_writev
• Call malloc_disable and malloc_enable before and after calls to malloc_iterate in the remote process to ensure a consistent snapshot of heap allocations
• Use simple signal-based IPC and process_vm_readv to fetch heap-iteration metadata from the remote process
• Fix a few minor Android-specific build quirks
• Update README.md to reflect Android support

Background

While there is no standard heap iteration interface on Linux, Android supports malloc_iterate to walk all heap allocations in the current process. This API is supported on the newer scudo heap as well as older jemalloc heap (which may still be used on low memory devices). The API is not part of the public NDK, but is used by the AOSP libmemunreachable tool.

Validation

• Built release and debug for Android x86_64 and arm64 with swift build on Windows 11 using recent Android Swift SDK and NDK r26b

swift build --triple %ANDROID_ARCH%-unknown-linux-android%ANDROID_API_LEVEL% ^
    --sdk %ANDROID_NDK_ROOT%\toolchains\llvm\prebuilt\windows-x86_64\sysroot ^
    -Xswiftc -sdk -Xswiftc %SDKROOT_ANDROID% ^
    -Xswiftc -sysroot -Xswiftc %ANDROID_NDK_ROOT%\toolchains\llvm\prebuilt\windows-x86_64\sysroot ^
    -Xswiftc -I -Xswiftc %SDKROOT_ANDROID%\usr\include ^
    -Xlinker -L%ANDROID_NDK_ROOT%\toolchains\llvm\prebuilt\windows-x86_64\lib\clang\17.0.2\lib\linux\%ANDROID_ARCH% ^
    -Xcc -I%SDKROOT_ANDROID%\usr\include\swift\SwiftRemoteMirror ^
    -Xlinker %SDKROOT_ANDROID%\usr\lib\swift\android\%ANDROID_ARCH%\libswiftRemoteMirror.so ^

• Built release and debug for Android x86_64 and arm64 with CMake on Windows 11 using recent Android Swift SDK and NDK r26b

cmake -B build -S . -G Ninja ^
    -D CMAKE_BUILD_WITH_INSTALL_RPATH=YES ^
    -D CMAKE_SYSTEM_NAME=Android ^
    -D CMAKE_ANDROID_ARCH_ABI=%ANDROID_ARCH_ABI% ^
    -D CMAKE_SYSTEM_VERSION=%ANDROID_API_LEVEL% ^
    -D CMAKE_Swift_COMPILER_TARGET=%ANDROID_ARCH%-unknown-linux-android%ANDROID_API_LEVEL% ^
    -D CMAKE_Swift_FLAGS="-sdk %SDKROOT_ANDROID% -L%ANDROID_NDK_ROOT%\toolchains\llvm\prebuilt\windows-x86_64\lib\clang\17.0.2\lib\linux\%ANDROID_ARCH% -Xcc -I%SDKROOT_ANDROID%\usr\include -I%SDKROOT_ANDROID%\usr\include\swift\SwiftRemoteMirror" ^
    -D ArgumentParser_DIR=S:\swift-argument-parser\build\cmake\modules

• Manually tested all commands against a trivial command-line Swift app run with SWIFT_DEBUG_ENABLE_METADATA_ALLOCATION_ITERATION=1 and SWIFT_DEBUG_ENABLE_METADATA_BACKTRACE_LOGGING=1 on an x86_64 emulator (Android 15) and arm64 device (Pixel 6a + Android 13)
• Manually tested all commands against the android-swift-support (modified to set SWIFT_DEBUG_ env vars from Application.onCreate) with swift-inspect copied to its sandbox on an x86_64 emulator (Android 15) and arm64 device (Pixel 6a + Android 13)

adb -d push S:\swift\tools\swift-inspect\.build\aarch64-unknown-linux-android29\release\swift-inspect /data/local/tmp
adb -d push %SDKROOT%\usr\lib\swift\android\aarch64\libswiftRemoteMirror.so /data/local/tmp
adb -d shell
bluejay:/ $ run-as com.thebrowsercompany.SwiftSupportTestApp
bluejay:/data/user/0/com.thebrowsercompany.SwiftSupportTestApp $ cp /data/local/tmp/swift-inspect ./swift-inspect
bluejay:/data/user/0/com.thebrowsercompany.SwiftSupportTestApp $ chmod +x ./swift-inspect
bluejay:/data/user/0/com.thebrowsercompany.SwiftSupportTestApp $ export LD_LIBRARY_PATH=$(dirname $(pm path com.thebrowsercompany.SwiftSupportTestApp | sed 's/package://'))/lib/arm64
bluejay:/data/user/0/com.thebrowsercompany.SwiftSupportTestApp $ export SWIFT_DEBUG_ENABLE_METADATA_ALLOCATION_ITERATION=1
bluejay:/data/user/0/com.thebrowsercompany.SwiftSupportTestApp $ export SWIFT_DEBUG_ENABLE_METADATA_BACKTRACE_LOGGING=1
bluejay:/data/user/0/com.thebrowsercompany.SwiftSupportTestApp $ ./swift-inspect dump-arrays <pid>
bluejay:/data/user/0/com.thebrowsercompany.SwiftSupportTestApp $ ./swift-inspect dump-cache-nodes <pid>
bluejay:/data/user/0/com.thebrowsercompany.SwiftSupportTestApp $ ./swift-inspect dump-conformance-cache <pid>

• Confirmed backtraces are printed with the --backtrace and --backtrace-long arguments

bluejay:/data/user/0/com.thebrowsercompany.SwiftSupportTestApp $ ./swift-inspect dump-raw-metadata --backtrace-long <pid>
bluejay:/data/user/0/com.thebrowsercompany.SwiftSupportTestApp $ ./swift-inspect dump-generic-metadata --backtrace-long <pid>

• Confirmed swift-inspect still builds for Linux with CMake and swift build

[compnerd]

This looks pretty good to me!

[compnerd]

@swift-ci please test

[compnerd]

@swift-ci please test

[andrurogerz]

I made a couple of updates since this PR is still pending:

1. Added CMake build support and documentation for Android.
2. Re-worked how the remote heap function size is calculated. I was not able to get .local linkage symbols to work between C and asm in the CMake build, and I opted to make a more robust solution by just moving the function to its own section and adding a linker-defined global to mark the end of the section in a custom linker script (see section-text-remote.ld). This solution avoids inline assembly and allows us to easily and correctly calculate the size of the callback function.

@compnerd please have a look when you get a chance and request test run if you're good with the changes. Thanks!

[compnerd]

@swift-ci please test

[compnerd]

@swift-ci please smoke test

[compnerd]

@swift-ci please test Windows platform