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Hello dev:

I export a haskell function for c like below:

foreign export ccall "namesMatching" _namesMatchingC :: CString -> IO (Ptr CString)

_namesMatchingC filePath = do
    filePath' <- peekCString filePath
    pathNames <- namesMatching filePath'
    pathNames' <- forM pathNames mapFilePath
    withArray pathNames' $ \cstrArr -> return cstrArr
  where
    mapFilePath = (`withCString` (\cstr -> do return cstr))

This function return IO (Ptr CString) that interface with char** in c++.

My android jni cpp code that calling namesMatching exported from haskell:

#include <jni.h>

#include <unistd.h>
#include <sstream>
#include <string>

#include "ghcversion.h"
#include "HsFFI.h"
#include "Rts.h"

#include "my_log.h"
#include "Lib_stub.h"
#include "FileSystem_stub.h"

extern "C" {

// ........

JNIEXPORT jobjectArray
JNICALL
Java_com_zw3rk_helloworld_MainActivity_namesMatchingJNI(
        JNIEnv *env,
        jobject thiz,
        jstring path) {

    LOG_ASSERT(NULL != env, "JNIEnv cannot be NULL.");
    LOG_ASSERT(NULL != thiz, "jobject cannot be NULL.");
    LOG_ASSERT(NULL != path, "jstring cannot be NULL.");

    const char *c_value = env->GetStringUTFChars(path, NULL);
    const char **result = static_cast<const char **>(namesMatching(
            const_cast<char *>(c_value)));
    jsize len = 0;
    for (; result[len] != NULL; len++);

    env->ReleaseStringUTFChars(path, c_value);
    jobjectArray strs = env->NewObjectArray(len, env->FindClass("java/lang/String"), env->NewStringUTF(""));
    for (int i = 0; i < len; i++) {
        jstring str = env->NewStringUTF(result[i]);  // <-----------  crash here
        env->SetObjectArrayElement(strs, i, str);
    }
    // freeCStringArray frees the newArray pointer created in haskell module
    // freeCStringArray(len, result);
    return strs;
}

}

My android kotlin code that calling Java_com_zw3rk_helloworld_MainActivity_namesMatchingJNI:

private fun doSthAfterAllPermissionGranted() {
        // Example of a call to a native method
        val tv = findViewById(R.id.sample_text) as TextView

        Handler(Looper.getMainLooper()).postDelayed(
                {
                    tv.text = stringFromJNI()
                    Log.e("test1", "--------- begin --------namesMatchingJNI")
                    Log.w("test2", "${namesMatchingJNI("/sdcard/*.txt").joinToString()}}")
                    Log.e("test3", "---------- end --------namesMatchingJNI")

                    doSthAfterAllPermissionGranted()
                }
                , 2000)
    }

   external fun namesMatchingJNI(path: String): Array<String>

EveryThing is ok, but sometimes crash at jstring str = env->NewStringUTF(result[i]);

result[i] is obtained from haskell.

The Crash dump is here:

********** Crash dump: **********
Build fingerprint: 'HONOR/COR-AL00/HWCOR:8.1.0/HUAWEICOR-AL00/151(C00GT):user/release-keys'
pid: 19991, tid: 19991, name: w3rk.helloworld  >>> com.zw3rk.helloworld <<<
signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x9
Stack frame #00 pc 000000000001cea0  /system/lib64/libc.so (strlen+16)
Stack frame #01 pc 00000000003bfbe0  /system/lib64/libart.so (art::mirror::String::AllocFromModifiedUtf8(art::Thread*, char const*)+28)
Stack frame #02 pc 000000000037be84  /system/lib64/libart.so (art::JNI::NewStringUTF(_JNIEnv*, char const*)+572)
Stack frame #03 pc 0000000000b55b90  /data/app/com.zw3rk.helloworld-VAuV-C-ri9T0r3qoc_cgzQ==/lib/arm64/libnative-lib.so (_JNIEnv::NewStringUTF(char const*)+48)
Stack frame #04 pc 0000000000b562d8  /data/app/com.zw3rk.helloworld-VAuV-C-ri9T0r3qoc_cgzQ==/lib/arm64/libnative-lib.so (Java_com_zw3rk_helloworld_MainActivity_namesMatchingJNI+652)
Stack frame #05 pc 0000000000012558  /data/app/com.zw3rk.helloworld-VAuV-C-ri9T0r3qoc_cgzQ==/oat/arm64/base.odex (offset 0x12000)

I think the AllocFromModifiedUtf8 in error log means that cstring return from haskell has been changed? Or Sth Else cause it?