> 
> vax:~/Development/c/vax$ cc -O0 -g -o atan atan.c -lm
> vax:~/Development/c/vax$ ./atan
> Illegal instruction (core dumped)
> 
[...]
> 
> How could I debug this further ? I took a brief look with objdump
> and gdb before my morning coffee but unfortunately I didn't gain
> any insight into the matter.
> 
Run it under gdb, break at atan(), and single-step into the lib to see
what is happening.  Obviously it is some weirdness with shared
libraries here.

-- Ragge