Stuck at tracking a SIGFPE/Arithmetic exception

Question

I'm trying to debug a SIGFPE signal that is raised inside a library that I don't have it's source code. I'm using gdb and the asm layout to see what is going on.

These are the instructions before the exception:

   0xcd3fffa <_ZN8name_space11ClassName1MethodNameEdddd+830>     fstpl  -0x68(%ebp)                                    
B+ 0xcd3fffd <_ZN8name_space11ClassName1MethodNameEdddd+833>     fldl   -0x58(%ebp)                                    
   0xcd40000 <_ZN8name_space11ClassName1MethodNameEdddd+836>     fstpl  0x4(%esp)                                      
   0xcd40004 <_ZN8name_space11ClassName1MethodNameEdddd+840>     mov    0x8(%ebp),%eax                                 
   0xcd40007 <_ZN8name_space11ClassName1MethodNameEdddd+843>     mov    %eax,(%esp)                                    
  >0xcd4000a <_ZN8name_space11ClassName1MethodNameEdddd+846>     call   0xcd408c0 <_ZN8name_space11ClassName1AnotherMethodNameEd>   
   0xcd4000f <_ZN8name_space11ClassName1MethodNameEdddd+851>     mov    0x8(%ebp),%eax   

When I type ni to go from the instruction at 0xcd4000a to the one at 0xcd4000f I get the following error

Program received signal SIGFPE, Arithmetic exception.
0x0cd408e8 in name_space::ClassName::AnotherMethodName(double) () at /Path/to/ClassName.h:69

I am not familiar with assembly but I was expecting the instrcution pointer to be 0xcd408c0 where the instructions for AnotherMethodName start. But the instruction pointer has jumped to 0xcd408e8 address. Which is still inside AnotherMethodName() method.

    0xcd408e4 <_ZN8name_space11ClassName1AnotherMethodNameEd+36> fldz                                                          
    0xcd408e6 <_ZN8name_space11ClassName1AnotherMethodNameEd+38> fdivrp %st,%st(1)                                             
   >0xcd408e8 <_ZN8name_space11ClassName1AnotherMethodNameEd+40> fldz                                                          
    0xcd408ea <_ZN8name_space11ClassName1AnotherMethodNameEd+42> fucomip %st(1),%st   

After the instruction at 0xcd408e8 it jumps to my exception handler.

I have searched a lot to even get to this point. But at the moment I have no clue how I should continue.

I have also checked the floating point registers and they don't seem to contain any weird values.

What is raising this exception?

Answer 1

Cannot be fldz since it just sets a register to 0

The exception occurred at fdivrp %st,%st(1)

You said you checked "wierd" values. But above must be a division by zero. Did you check st for zero too? must be zero. No weird, just zero.

FDIVRP ST(i), ST(0) Divide ST(0) by ST(i), store result in ST(i), and pop the register stack

Edit: not sure of what's happening there. Check the parameters you're calling your third party software with. You may have passed some zero value for say, number of items, maybe because of uninitialized variables which the library does not like. (sorry for all the guesswork!)