Crashes during QR code generation

[jonahbeckford]

When debugging through com.example.squirrelscout_scouter.ui.viewmodels.ScoutingSessionViewModel#generateQrCode, get a SIGSEGV at:

art_sigsegv_fault 0x00000078e6b410b0
art::FaultManager::HandleFault(int, siginfo*, void*) 0x00000078e6b415e4
art::SignalChain::Handler(int, siginfo*, void*) 0x0000005b240dcea0
<unknown> 0x0000007b7dd27678
st_tls_get 0x00000078d4c4fec0
caml_thread_leave_blocking_section 0x00000078d4c4febc
caml_leave_blocking_section 0x00000078d4e2bae8
memmove_blocking_section ffi_bytes.c:80
dksdk_ffi_ocaml_hostsegment_blit_from_bytes ffi_bytes.c:140
caml_c_call 0x00000078d4e4fc78
camlDkSDKFFI_OCaml__HostStorage__blit_from_string_702 SonicScoutAndroid:104
camlCapnp__BuilderInc__uint8_list_of_string_4485 SonicScoutAndroid:78
camlCapnp__BuilderInc__set_blob_5641 SonicScoutAndroid:849
camlObjsEntry__qr_code_of_raw_match_data_4087 SonicScoutAndroid:56
camlDkSDKFFI_OCaml__Com__g_5562 SonicScoutAndroid:459
caml_start_program 0x00000078d4e4fce8
caml_callback2_exn 0x00000078d4e44df4
execute_helper dksdk_ffi_ocaml_callback.c:177
dksdk_ffi_c_cls_generic_method_dispatch dksdk_ffi_c_cls_generic.c:385
Java_com_diskuv_dksdk_ffi_java_jn_c_NativeCLib_native_1dk_1cls_1call_1method_1execute NativeCLib.c:754
art_quick_generic_jni_trampoline 0x00000078e6a43ed8
<unknown> 0x00000078e6a44210

[jonahbeckford]

However, when set a breakpoint in dksdk-ffi-ocaml/src/DkSDKFFI_OCaml/core/ffi_bytes.c:129 (dksdk-ffi-ocaml/src/DkSDKFFI_OCaml/core/ffi_bytes.c) then QR code is generated.

Which sounds like the CAML thread or a CAMLparam is incorrect during dksdk_ffi_ocaml_hostsegment_blit_from_bytes when leaving the blocking section at:

    memmove_blocking_section(src_data, src_pos, dst_data, dst_pos, len);

[jonahbeckford]

Possible solutions:

• Per https://stackoverflow.com/questions/54433385/art-sigsegv-fault-when-entering-jni-function-in-c-code-within-android-studio it may be solved with a different NDK or minimum API

But from the stack trace the real culprit may be that the Android JNI thread is not registered as an (OCaml) pthread:

Caml_inline void * st_tls_get(st_tlskey k)
{
  return pthread_getspecific(k);
}

That is, https://pubs.opengroup.org/onlinepubs/009696799/functions/pthread_getspecific.html will:

The effect of calling pthread_getspecific() or pthread_setspecific() with a key value not obtained from pthread_key_create() or after key has been deleted with pthread_key_delete() is undefined.