IOS invalid memory access when calling _mi_process_init

[phthegreat]

I build an test app static link with the .a library. But the app crashes when calling _mi_process_init.
The backtrace is as below:

`(lldb) bt

• thread Fix spelling errors #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
  • frame #0: 0x00000001000e9550 rack_mi_process_init + 28 frame #1: 0x0000000100164a34 dyldImageLoaderMachO::doModInitFunctions(ImageLoader::LinkContext const&) + 468
    frame Return usable allocation size on allocation #2: 0x0000000100164e44 dyldImageLoaderMachO::doInitialization(ImageLoader::LinkContext const&) + 56 frame #3: 0x000000010015f198 dyldImageLoader::recursiveInitialization(ImageLoader::LinkContext const&, unsigned int, char const*, ImageLoader::InitializerTimingList&, ImageLoader::UninitedUpwards&) + 580
    frame WebAssembly support? #4: 0x000000010015d3c4 dyldImageLoader::processInitializers(ImageLoader::LinkContext const&, unsigned int, ImageLoader::InitializerTimingList&, ImageLoader::UninitedUpwards&) + 192 frame #5: 0x000000010015d490 dyldImageLoader::runInitializers(ImageLoader::LinkContext const&, ImageLoader::InitializerTimingList&) + 96
    frame Windows CMake+Ninja build warning due to duplicate basename #6: 0x000000010014e744 dylddyld::initializeMainExecutable() + 220 frame #7: 0x00000001001531ec dylddyld::_main(macho_header const*, unsigned long, int, char const**, char const**, char const**, unsigned long*) + 4588
    frame Readme contains invisible \u200b ZERO WIDTH SPACE, breaking URLs #8: 0x000000010014d22c dylddyldbootstrap::start(dyld3::MachOLoaded const*, int, char const**, dyld3::MachOLoaded const*, unsigned long*) + 432 frame #9: 0x000000010014d038 dyld_dyld_start + 56
    (lldb) `

I think mi_tls_slot does not work properly on IOS (arm64)

void** tcb; UNUSED(ofs); asm volatile ("mrs %0, tpidr_el0" : "=r" (tcb)); res = tcb[slot];

tcb equals NULL and this is the reason why it crashes.

Any idea how to fix it?

[daanx]

ouch :-( ah, the testing I have done on macOS has been limited to OSX on a macbook. Thanks for reporting this and I hope we can make it work well on iOS as well.

1. Can you try linking with a dynamic library for mimalloc (.so) ?

2. I thought that the TCB should have been always initialized by the time mimalloc is initialized; here that seems not to be the case though. Not sure why.

(a) Perhaps accessing a (dummy) thread local as the first thing in process_init may force initialization? Can you try that out? [1]. e.g. in init.c change around line 448 to access a thread local on process load (which I think is inlined in _mi_process_init in your stack trace):

static mi_decl_thread uintptr_t dummy;
// Called once by the process loader
static void mi_process_load(void) {
  mi_heap_main_init();
  dummy = 1;                     // hopefully causes tcb to be initialized
  #if defined(MI_TLS_RECURSE_GUARD)
   ...

(b) If the above does not work, perhaps we need to just guard against tcb being NULL; that should work as reading the slot itself is already guarded against it being NULL (line 331 in mimalloc-internal.h). In mimalloc-internal.h change line 706 to

res = (tcb==NULL ? NULL : tcb[slot]);

and line 727 to

if (tcb != NULL) tcb[slot] = value;

(that last change may not be quite right but let's first find out if this is the root cause or not)

Apologies if this is too much trouble, but I have no easy way myself to develop on iOS. Let me know how it goes if you are able to try it out. Thanks, Daan

[phthegreat]

I saw your advice on #263
Here is what I've tried:

1. build a dynamic overide version.
2. guard against tcb being NULL.
   3.1 comment out the #define MI_TLS_SLOT 89
   3.2 replace #define MI_TLS_SLOT 89 with #define MI_TLS_PTHREAD

But both 3.1 and 3.2 do not work :(

error of 3.1

error of 3.2

I also test mi_tls_slot alone in main to see if the register is initialized or not.
just as below

But tcb is still NULL :(

[daanx]

I close this issue to consolidate porting to iOS in #263