xUnwind

xUnwind is a collection of Android native stack unwinding solutions.

README 中文版

Features

• Support unwinding by:
  • CFI (Call Frame Info): Provided by Android system library.
  • EH (Exception handling GCC extension): Provided by compiler.
  • FP (Frame Pointer): ARM64 only.
• Support unwinding from:
  • Current execution position.
  • A specified context (which may be obtained from a signal handler).
• Support unwinding for process:
  • Local process.
  • Remote process: CFI only.
• Support unwinding for thread(s):
  • Current thread.
  • Specified thread: CFI only.
  • All threads: CFI only.
• Provide java method to get native backtrace directly in java code.
• Support Android 4.1 - 13 (API level 16 - 33).
• Support armeabi-v7a, arm64-v8a, x86 and x86_64.
• MIT licensed.

Usage

1. Add dependency in build.gradle

xUnwind is published on Maven Central, and uses Prefab package format for native dependencies, which is supported by Android Gradle Plugin 4.0+.

android {
buildFeatures {
prefab true
}
}
dependencies {
implementation 'io.github.hexhacking:xunwind:2.0.0'
}

NOTE:

1. Starting from version 2.0.0 of xUnwind, group ID changed from io.hexhacking to io.github.hexhacking.

version range	group ID	artifact ID	Repository URL
[1.0.1, 1.1.1]	io.hexhacking	xunwind	repo
[2.0.0, )	io.github.hexhacking	xunwind	repo

2. xUnwind uses the prefab package schema v2, which is configured by default since Android Gradle Plugin 7.1.0. If you are using Android Gradle Plugin earlier than 7.1.0, please add the following configuration to gradle.properties:

android.prefabVersion=2.0.0

2. Add dependency in CMakeLists.txt or Android.mk

If you only use the java interface of xUnwind, please skip this step.

CMakeLists.txt

find_package(xunwindREQUIREDCONFIG)
add_library(mylibSHAREDmylib.c)
target_link_libraries(mylibxunwind::xunwind)

Android.mk

include $(CLEAR_VARS)
LOCAL_MODULE := mylib
LOCAL_SRC_FILES := mylib.c
LOCAL_SHARED_LIBRARIES += xunwind
include $(BUILD_SHARED_LIBRARY)
$(call import-module,prefab/xunwind)

3. Specify one or more ABI(s) you need

android {
defaultConfig {
ndk {
abiFilters 'armeabi-v7a', 'arm64-v8a', 'x86', 'x86_64'
}
}
}

4. Add packaging options

If you are using xUnwind in an SDK project, you may need to avoid packaging libxunwind.so into your AAR, so as not to encounter duplicate libxunwind.so file when packaging the app project.

android {
packagingOptions {
exclude '**/libxunwind.so'
}
}

On the other hand, if you are using xUnwind in an APP project, you may need to add some options to deal with conflicts caused by duplicate libxunwind.so file.

android {
packagingOptions {
pickFirst '**/libxunwind.so'
}
}

There is a sample app in the xunwind-sample folder you can refer to.

Native API

#include"xunwind.h"

1. CFI unwinding

#defineXUNWIND_CURRENT_PROCESS (-1)
#defineXUNWIND_CURRENT_THREAD (-1)
#defineXUNWIND_ALL_THREADS (-2)
voidxunwind_cfi_log(pid_tpid, pid_ttid, void*context, constchar*logtag, android_LogPrioritypriority, constchar*prefix);
voidxunwind_cfi_dump(pid_tpid, pid_ttid, void*context, intfd, constchar*prefix);
char*xunwind_cfi_get(pid_tpid, pid_ttid, void*context, constchar*prefix);

These three functions correspond to three ways of obtaining backtrace. They are:

• log to Android logcat.
• dump to a place associated with FD (such as file, pipe, socket, etc.).
• get and return a string (which is allocated on the heap with malloc(), you need to free() it yourself).

The pid parameter is used to specify the backtrace of which process needs to be obtained, which can be the current process (XUNWIND_CURRENT_PROCESS / getpid()) or another process.

The tid parameter is used to specify the backtrace of which thread or threads need to be obtained, which can be the current thread (XUNWIND_CURRENT_THREAD / gettid()), a specified thread, or all threads (XUNWIND_ALL_THREADS).

The optional context parameter is used to pass a register context information. For example, in signal handler, you may need to start unwinding from a specific context.

The optional prefix parameter is used to specify a prefix string for each line of backtrace.

2. FP and EH unwinding

size_txunwind_fp_unwind(uintptr_t*frames, size_tframes_cap, void*context);
size_txunwind_eh_unwind(uintptr_t*frames, size_tframes_cap, void*context);
voidxunwind_frames_log(uintptr_t*frames, size_tframes_sz, constchar*logtag, android_LogPrioritypriority, constchar*prefix);
voidxunwind_frames_dump(uintptr_t*frames, size_tframes_sz, intfd, constchar*prefix);
char*xunwind_frames_get(uintptr_t*frames, size_tframes_sz, constchar*prefix);

Currently, FP unwinding is ARM64 only.

xunwind_fp_unwind and xunwind_eh_unwind saves the absolute-PCs of the unwinding result in the array pointed to by frames (frames_cap is the size of the array), and returns the number of absolute-PCs actually obtained.

The meaning of the optional context parameter is the same as that of CFI unwinding.

The remaining three functions are used to convert the absolute-PCs in the frames array into backtrace (the size of the array is specified by frames_sz). Same as CFI unwinding, respectively output to Android logcat, FD, and return as a string.

Java API

importio.github.hexhacking.xunwind.XUnwind;

1. Initialize

publicstaticvoidinit();

The only thing init() does is System.loadLibrary("xunwind"). If you only use xUnwind in native code, no initialization is required.

2. CFI unwinding

publicstaticvoidlogLocalCurrentThread(Stringlogtag, intpriority, Stringprefix);
publicstaticvoidlogLocalThread(inttid, Stringlogtag, intpriority, Stringprefix);
publicstaticvoidlogLocalAllThread(Stringlogtag, intpriority, Stringprefix);
publicstaticvoidlogRemoteThread(intpid, inttid, Stringlogtag, intpriority, Stringprefix);
publicstaticvoidlogRemoteAllThread(intpid, Stringlogtag, intpriority, Stringprefix);
publicstaticvoiddumpLocalCurrentThread(intfd, Stringprefix);
publicstaticvoiddumpLocalThread(inttid, intfd, Stringprefix);
publicstaticvoiddumpLocalAllThread(intfd, Stringprefix);
publicstaticvoiddumpRemoteThread(intpid, inttid, intfd, Stringprefix);
publicstaticvoiddumpRemoteAllThread(intpid, intfd, Stringprefix);
publicstaticStringgetLocalCurrentThread(Stringprefix);
publicstaticStringgetLocalThread(inttid, Stringprefix);
publicstaticStringgetLocalAllThread(Stringprefix);
publicstaticStringgetRemoteThread(intpid, inttid, Stringprefix);
publicstaticStringgetRemoteAllThread(intpid, Stringprefix);

All native CFI unwinding capabilities have corresponding java functions. They call the native CFI unwinding functions through JNI.

FP and EH unwinding do not have corresponding java functions. Because compared to CFI unwinding, their main advantage is faster execution speed (but the backtrace is not as complete as CFI unwinding), so they are always only used in native code. If you are a java programmer, just use the CFI unwinding functions here.

Support

• GitHub Issues
• GitHub Discussions

Contributing

• Code of Conduct
• Contributing Guide
• Reporting Security vulnerabilities

License

xUnwind is MIT licensed, as found in the LICENSE file.