Crash in cn_slow_hash()

[Pei116]

Trying to use monero wallet api in Android using JNI after pre-building the libraries.
It's always crashed with following error:
`

---

Build fingerprint: 'samsung/hero2ltektt/hero2ltektt:8.0.0/R16NW/G935KKKU1EREA:user/release-keys'
Revision: '8'
ABI: 'arm64'
pid: 28690, tid: 28709, name: roidJUnitRunner  >>> ... <<<
signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 0x7f6aabb230
    x0   0000000000000000  x1   0000000000000000  x2   0000007f6acbb6e8  x3   0000000000000000
    x4   0000000000000000  x5   0000007f73cf5485  x6   6a616d5f64616568  x7   222c30353a22726f
    x8   0000007f6aabb230  x9   0000007f6aabb2f0  x10  0000000000000000  x11  14c79abb30e83214
    x12  627573222c303a22  x13  5f73736572646461  x14  0000000000000020  x15  0000007f73c092f0
    x16  0000007f6a3fec68  x17  0000007f69c8bc24  x18  0000007f73cf4e20  x19  0000007f73c59200
    x20  0000007f84b08100  x21  0000007f73c59200  x22  0000007f6acbdbcc  x23  0000007f6b04d97e
    x24  0000000000000014  x25  0000007f73c59298  x26  0000000000000000  x27  0000000000000003
    x28  0000000000000005  x29  0000007f6acbb690  x30  0000007f69513e1c
    sp   0000007f6aabb1f0  pc   0000007f69c8bc4c  pstate 0000000060000000
backtrace:
    #00 pc 000000000142dc4c  /data/app/...-_E9DVGmcYSuB5P5kBSedRg==/lib/arm64/libmoneroj.so (cn_slow_hash+40)
    #01 pc 0000000000cb5e18  /data/app/...-_E9DVGmcYSuB5P5kBSedRg==/lib/arm64/libmoneroj.so (_ZN6crypto19generate_chacha_keyEPKvmRN5tools8scrubbedINSt6__ndk15arrayIhLm32EEEEE+68)
    #02 pc 0000000000cb5e18  /data/app/...-_E9DVGmcYSuB5P5kBSedRg==/lib/arm64/libmoneroj.so (_ZN6crypto19generate_chacha_keyEPKvmRN5tools8scrubbedINSt6__ndk15arrayIhLm32EEEEE+68)
    #03 pc 0000000000bae31c  /data/app/...-_E9DVGmcYSuB5P5kBSedRg==/lib/arm64/libmoneroj.so (_ZN5tools7wallet210store_keysERKNSt6__ndk112basic_stringIcNS1_11char_traitsIcEENS1_9allocatorIcEEEERKN4epee15wipeable_stringEb+5864)
    #04 pc 0000000000bb8ec8  /data/app/...-_E9DVGmcYSuB5P5kBSedRg==/lib/arm64/libmoneroj.so (_ZN5tools7wallet28generateERKNSt6__ndk112basic_stringIcNS1_11char_traitsIcEENS1_9allocatorIcEEEERKN4epee15wipeable_stringERKNS_8scrubbedIN6crypto9ec_scalarEEEbbb+2044)
    #05 pc 00000000009b43e4  /data/app/...-_E9DVGmcYSuB5P5kBSedRg==/lib/arm64/libmoneroj.so (_ZN6Monero10WalletImpl6createERKNSt6__ndk112basic_stringIcNS1_11char_traitsIcEENS1_9allocatorIcEEEES9_S9_+1228)
    #06 pc 0000000000a63354  /data/app/...-_E9DVGmcYSuB5P5kBSedRg==/lib/arm64/libmoneroj.so (_ZN6Monero17WalletManagerImpl12createWalletERKNSt6__ndk112basic_stringIcNS1_11char_traitsIcEENS1_9allocatorIcEEEES9_S9_NS_11NetworkTypeE+100)
    #07 pc 00000000009a6f08  /data/app/...-_E9DVGmcYSuB5P5kBSedRg==/lib/arm64/libmoneroj.so (Java_network_pyxis_moneroj_WalletManager_createWalletJ+480)
    #08 pc 0000000000013668  /data/app/...-_E9DVGmcYSuB5P5kBSedRg==/oat/arm64/base.odex (offset 0xf000)

`

[hyc]

cn_slow_hash() requires a fairly large stack. Make sure your calling thread has at least 5MB stack.

[Pei116]

Thanks for your quick answer. But how do i ensure that?

[moneromooo-monero]

For example, to set the GNU linker to setup a large stack:

set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,--stack,10485760")

Otherwise, use your threading library to set stack size, eg pthread_attr_setstacksize.

[Pei116]

I tried to add this line in CMakesList.txt of the monero repo but there's no luck yet.
set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,--stack,10485760")

[naughtyfox]

I encountered this issue either. The problem is not every arm8 cpu supports aes instruction set. By default monero compiles with flag -march=${ARCH}+crypto. Try to compile it with just -march=${ARCH} (it will be slower, but it probably will work on your cpu), it helped me.

If you want to check if your cpu supports aes instruction set run the following command on your device:

$ cat /proc/cpuinfo | grep aes

and if you get nothing - probably current cpu has no aes instruction set.

[moneromooo-monero]

Not a monero bug.

+invalid

[Pei116]

@naughtyfox You saved my life! It's now working fine after I removed crypto flag from the build command.
Btw I was wondering if it affects any functionality of monero library.

[naughtyfox]

It doesn't. AES instructions are used to speed up slow hash

[Pei116]

It's started crashing in x86 also with the same exception. It's been breaking my heart.

[MoroccanMalinois]

@Pei116

If you can't set the stack size like suggested by hyc and mooo, you can try
https://github.com/monero-project/monero/blob/master/src/crypto/CMakeLists.txt#L99

[Pei116]

@MoroccanMalinois Where do I need to put it in? I tried to add it to the end of the monero CMakeLists but there's the same crash.

[MoroccanMalinois]

OK @Pei116, here goes the full explanation :)

Look at https://github.com/monero-project/monero/blob/master/src/crypto/slow-hash.c#L1127

By default, the program use the stack :

uint8_t long_state[MEMORY];

MEMORY is a define holding the size of the scratchpad, i.e. 2MB. On android, the default stack size is 1MB (when it's not the main thread), hence the crash.

So the first natural thing to do is to increase the stack size (like suggested by hyc and mooo). Except sometimes you simply cannot control that parameter, like monero-wallet-gui (It's done in Qt internals and clang does not support -Wl,--stack).

So if we can't use the stack, we have to use the heap.
That's what the define FORCE_USE_HEAP does. By activating it, the program will use malloc for allocating the memory of the variable long_state.

Now to answer your question, you have multiple ways to activate this flag: you can either:

• add the define flag to the cmake command, e.g. cmake -DFORCE_USE_HEAP=1 ....
• make sure that ANDROID and BUILD_GUI_DEPS are defined
• modify src/crypto/CMakeLists.txt to include add_definitions(-DFORCE_USE_HEAP=1) on the conditions that suits you
• modify src/crypto/slow-hash.c to always use malloc (most uggly solution, but might be usefull to make sure that this is indeed the problem, before start debugging cmake 😅 )