[Lldb-commits] [lldb] r202956 - Add support for JIT debugging on Linux using the GDB JIT interface. Patch written with Keno Fischer.

[Jim Ingham]

This part of the patch worries me.  If I am debugging a process that doesn’t have this JIT loader symbol, this bit means every time that the process stops for any reason you will search the whole world for some symbol that won’t be found.  That’s something we really avoid doing if we can, programs get pretty big and this is not the sort of thing you want to do.

I don’t know how this symbol comes about, is there no event (shared library load or something) that you can hook into to find this symbol?

This patch is also causing a crash on Mac OS X just running a program.  The crash looks like:

(lldb) bt
* thread #8: tid = 0xf68e5, name = <lldb.process.internal-state(pid=40372)>, function: lldb_private::Process::GetTarget() , stop reason = EXC_BAD_ACCESS (code=1, address=0x100)
    frame #0: 0x0000000106f8072c LLDB`lldb_private::Process::GetTarget() at Process.h:2516
    frame #1: 0x0000000108e7aa5a LLDB`JITLoaderGDB::GetSymbolAddress(lldb_private::ConstString const&, lldb::SymbolType) const at JITLoaderGDB.cpp:368
    frame #2: 0x0000000108e7a8bf LLDB`JITLoaderGDB::SetJITBreakpoint() at JITLoaderGDB.cpp:99
    frame #3: 0x0000000108e7a6d8 LLDB`JITLoaderGDB::ProcessStateChangedCallback(void*, lldb_private::Process*, lldb::StateType) at JITLoaderGDB.cpp:354
    frame #4: 0x0000000108b7b29b LLDB`lldb_private::Process::SynchronouslyNotifyStateChanged(lldb::StateType) at Process.cpp:1223
    frame #5: 0x0000000108b89762 LLDB`lldb_private::Process::ShouldBroadcastEvent(lldb_private::Event*) at Process.cpp:3846
    frame #6: 0x0000000108b8454d LLDB`lldb_private::Process::HandlePrivateEvent(std::__1::shared_ptr<lldb_private::Event>&) at Process.cpp:4141
    frame #7: 0x0000000108b8a755 LLDB`lldb_private::Process::RunPrivateStateThread() at Process.cpp:4290
    frame #8: 0x0000000108b89bfd LLDB`lldb_private::Process::PrivateStateThread(void*) at Process.cpp:4221
    frame #9: 0x00000001087d811a LLDB`ThreadCreateTrampoline(void*) at Host.cpp:629
    frame #10: 0x00007fff815df899 libsystem_pthread.dylib`_pthread_body
    frame #11: 0x00007fff815df72a libsystem_pthread.dylib`_pthread_start
    frame #12: 0x00007fff815e3fc9 libsystem_pthread.dylib`thread_start
(lldb) f 2
frame #2: 0x0000000108e7a8bf LLDB`JITLoaderGDB::SetJITBreakpoint() at JITLoaderGDB.cpp:99
   96  	        log->Printf("JITLoaderGDB::%s looking for JIT register hook",
   97  	                    __FUNCTION__);
   98  	
-> 99  	    addr_t jit_addr = GetSymbolAddress(ConstString("__jit_debug_register_code"),
   100 	                                       eSymbolTypeAny);
   101 	    if (jit_addr == LLDB_INVALID_ADDRESS)
   102 	        return;
(lldb) expr *this
(JITLoaderGDB) $13 = {
  lldb_private::JITLoader = {
    m_process = 0x0000000000000000 Public: lldb_private::ThreadSafeValue<lldb::StateType> @  Private: lldb_private::ThreadSafeValue<lldb::StateType> @ 
  }
  m_jit_objects = size=160215376 {
    [0] = {
      first = <parent is NULL>
      second = <parent is NULL>
    }
    ...
  }
  m_jit_break_id = 0
  m_notification_callbacks = {
    baton = 0x0000000000000001
    initialize = 0x00007fc54b00f3b0
    process_state_changed = 0x00000001098cb150 (vtable for std::__1::__shared_ptr_pointer<lldb_private::Section*, std::__1::default_delete<lldb_private::Section>, std::__1::allocator<lldb_private::Section> > + 16)
  }
}

Looks like the JIT instance that is getting passed in is not good for some reason.

Jim


On Mar 5, 2014, at 2:12 AM, Andrew MacPherson <andrew.macp at gmail.com> wrote:

> +void
> +JITLoaderGDB::ProcessStateChangedCallback(void *baton,
> +                                          lldb_private::Process *process,
> +                                          lldb::StateType state)
> +{
> +    JITLoaderGDB* instance = static_cast<JITLoaderGDB*>(baton);
> +
> +    switch (state)
> +    {
> +    case eStateConnected:
> +    case eStateAttaching:
> +    case eStateLaunching:
> +    case eStateInvalid:
> +    case eStateUnloaded:
> +    case eStateExited:
> +    case eStateDetached:
> +        // instance->Clear(false);
> +        break;
> +
> +    case eStateRunning:
> +    case eStateStopped:
> +        // Keep trying to set our JIT breakpoint each time we stop until we
> +        // succeed
> +        if (!instance->DidSetJITBreakpoint() && process->IsAlive())
> +            instance->SetJITBreakpoint();
> +        break;
> +
> +    case eStateStepping:
> +    case eStateCrashed:
> +    case eStateSuspended:
> +        break;
> +    }
> +}
> +

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