[llvm-commits] Enable exceptions in JIT for Darwin

[Nicolas Geoffray]

Hi Evan,

New patch with new un-gcc documentation :)

Thanks for reviewing!

Nicolas

Evan Cheng wrote:
> Hi Nicolas,
>
> Comments in line.
>
> On Aug 19, 2008, at 8:04 AM, Nicolas Geoffray wrote:
>
>   
>> Dear all,
>>
>> Here's a patch that enables exception handling on Darwin with the  
>> JIT. It's really ugly, it's a workaround to work with libgcc which  
>> is doing crazy stuff when unwinding the stack. The __register_frame  
>> function was sufficient enough for Linux, but unfortunately, the  
>> code for darwin erases by default the registered frames. In a  
>> perfect world, I think libgcc should be modified....
>>
>>
>> I'd be totally OK if you don't want this patch in, as it's an ugly  
>> workaround. I can move the patch to vmkit, and that would be fine by  
>> me. However, this makes lli work out of the box with exceptions and  
>> darwin, so it's still an improvement.
>>
>> Nicolas
>> Index: lib/ExecutionEngine/JIT/JIT.cpp
>> ===================================================================
>> --- lib/ExecutionEngine/JIT/JIT.cpp	(revision 54920)
>> +++ lib/ExecutionEngine/JIT/JIT.cpp	(working copy)
>> @@ -64,10 +64,73 @@
>>   }
>> }
>>
>> +
>> #if defined (__GNUC__)
>> extern "C" void __register_frame(void*);
>> -#endif
>>
>> +#if defined (__APPLE__)
>> +struct object {
>> +  void *pc_begin;
>> +  void *tbase;
>> +  void *dbase;
>> +  void* real_begin;
>> +
>> +    union {
>> +    struct {
>> +      unsigned long sorted : 1;
>> +      unsigned long from_array : 1;
>> +      unsigned long mixed_encoding : 1;
>> +      unsigned long encoding : 8;
>> +      unsigned long count : 21;
>> +    } b;
>> +    size_t i;
>> +  } s;
>>     
>
> Please pick more descriptive names than object, etc. Also, please try  
> to match the naming convention used in the file. Some documentation is  
> definitely welcome. :-)
>   
>> +
>> +  // Be pessimistic, include this field even if GCC
>> +  // may not have it.
>> +  char *fde_end;
>> +
>> +  struct object *next;
>> +};
>> +
>> +extern "C" void _keymgr_set_and_unlock_processwide_ptr (int, void *);
>> +extern "C" void *_keymgr_get_and_lock_processwide_ptr (int);
>> +#define KEYMGR_GCC3_DW2_OBJ_LIST        302     /* Dwarf2 object  
>> list  */
>> +
>> +struct km_object_info {
>> +  struct object* seen_objects;
>> +  struct object* unseen_objects;
>> +  unsigned spare[2];
>> +};
>> +
>> +extern "C" void darwin_register_frame(void* begin) {
>> +  struct km_object_info* the_obj_info = (struct km_object_info*)
>> +    _keymgr_get_and_lock_processwide_ptr (KEYMGR_GCC3_DW2_OBJ_LIST);
>> +
>> +  struct object* ob = (struct object*)malloc(sizeof(struct object));
>>     
>
> Who frees this?
>
>   
>> +  ob->pc_begin = (void *)-1;
>> +  ob->tbase = 0;
>> +  ob->dbase = 0;
>> +  ob->real_begin = begin;
>> +  ob->s.i = 0;
>> +  //ob->s.b.encoding = DW_EH_PE_omit;
>>     
>
> Why is this commented out?
>
>   
>> +  ob->s.b.encoding = 0xff;
>> +
>> +  // Put the info on both places, as libgcc uses the first or the
>> +  // the second field.
>> +  ob->fde_end = (char*)the_obj_info->unseen_objects;
>> +  ob->next = (struct object*)the_obj_info->unseen_objects;
>>     
>
> Are the casting necessary? Why not just define the types correctly.
>
>   
>> +
>> +  the_obj_info->unseen_objects = ob;
>> +
>> +  _keymgr_set_and_unlock_processwide_ptr (KEYMGR_GCC3_DW2_OBJ_LIST,
>> +                                          the_obj_info);
>> +
>> +}
>>     
>
> Function level documentation please.
>
> Thanks!
>
> Evan
>
>   
>> +
>> +#endif // __APPLE__
>> +#endif // __GNUC__
>> +
>> /// createJIT - This is the factory method for creating a JIT for  
>> the current
>> /// machine, it does not fall back to the interpreter.  This takes  
>> ownership
>> /// of the module provider.
>> @@ -108,8 +171,20 @@
>>
>>   // Register routine for informing unwinding runtime about new EH  
>> frames
>> #if defined(__GNUC__)
>> +#if defined(__APPLE__)
>> +  struct km_object_info* the_obj_info = (struct km_object_info*)
>> +    _keymgr_get_and_lock_processwide_ptr (KEYMGR_GCC3_DW2_OBJ_LIST);
>> +
>> +  if (!the_obj_info) {
>> +    the_obj_info = (km_object_info*)malloc(sizeof(struct  
>> km_object_info));
>> +    _keymgr_set_and_unlock_processwide_ptr (KEYMGR_GCC3_DW2_OBJ_LIST,
>> +                                            the_obj_info);
>> +  }
>> +  InstallExceptionTableRegister(darwin_register_frame);
>> +#else
>>   InstallExceptionTableRegister(__register_frame);
>> -#endif
>> +#endif // __APPLE__
>> +#endif // __GNUC__
>>
>>
>>   // Initialize passes.
>>   PM.doInitialization();
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>>     
>
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