efficiently debugging using gdb

i am in a Layer2 process that has 20,000
lines of code.It is concerning packet data transfer between mobiles.
My program core-dumps…in the malloc() fn.
I am shooting in the dark….i am presuming that i allocated some memory,but writingmore that the allocated size.
how do i pinpoint the error by seeing the
assembly code pointed by the address in gdb
where the malloc fails..??