A backtrace is a summary of how the program got where it is. It shows one
line per frame, for many frames, starting with the currently executing
frame (frame zero), followed by its caller (frame one), and on up the
stack.
`backtracé
`bt'
Print a backtrace of the entire stack: one line per frame for all
frames in the stack.
You can stop the backtrace at any time by typing the system interrupt
character, normally `Control-C'.
`backtrace N'
`bt N'
Similar, but stop after N frames.
Each line in a backtrace shows the frame number, the program counter, the
function and its arguments, and the source file name and line number (if
known). The program counter is omitted if is the beginning of the code for
the source line. This is the same as the first of the two lines printed
when you select a frame.