What is a core dump file in linux? What all information does it provide?
It's basically the process address space in use (from the mm_struct structure which contains all the virtual memory areas), and any other supporting information(1), at the time it crashed.
For example, let's say you try to dereference a NULL pointer and receive a SEGV signal, causing you to exit. As part of that process, the operating system tries to write your information to a file for later post-mortem analysis.
You can load the core file into a debugger along with the executable file (for symbols and other debugging information, for example) and poke around to try and discover what caused the problem.
(1) in kernel version 2.6.38, fs/exec.c/do_coredump() is the one responsible for core dumps and you can see that it's passed the signal number, exit code and registers. It in turn passes the signal number and registers to a binary-format-specific (ELF, a.out, etc) dumper.
The ELF dumper is fs/binfmt_elf.c/elf_core_dump() and you can see that it outputs non-memory-based information, like thread details, in fs/binfmt_elf.c/fill_note_info(), then returns to output the process space.