Whenever GDB prints a frame, it annotates it. For example, this applies
to frames printed when GDB stops, output from commands such as
backtrace or up, etc.
The frame annotation begins with
^Z^Zframe-begin leveladdresslevel-string
where level is the number of the frame (0 is the innermost frame,
and other frames have positive numbers), address is the address of
the code executing in that frame, and level-string is a string
designed to convey the level to the user. address is in the form
`0x' followed by one or more lowercase hex digits (note that this
does not depend on the language). The frame ends with
^Z^Zframe-end
Between these annotations is the main body of the frame, which can
consist of
^Z^Zfunction-call
function-call-string
where function-call-string is text designed to convey to the user
that this frame is associated with a function call made by GDB to a
function in the program being debugged.
where signal-handler-caller-string is text designed to convey to
the user that this frame is associated with whatever mechanism is used
by this operating system to call a signal handler (it is the frame which
calls the signal handler, not the frame for the signal handler itself).
A normal frame.
This can optionally (depending on whether this is thought of as
interesting information for the user to see) begin with
where address is the address executing in the frame (the same
address as in the frame-begin annotation, but printed in a form
which is intended for user consumption--in particular, the syntax varies
depending on the language), and separator-string is a string
intended to separate this address from what follows for the user's
benefit.
where function-name is the name of the function executing in the
frame, or `??' if not known, and arguments are the arguments
to the frame, with parentheses around them (each argument is annotated
individually as well, see section 18.3 Values).
If source information is available, a reference to it is then printed:
where source-intro-string separates for the user's benefit the
reference from the text which precedes it, filename is the name of
the source file, and line-number is the line number within that
file (the first line is line 1).
If GDB prints some information about where the frame is from (which
library, which load segment, etc.; currently only done on the RS/6000),
it is annotated with
^Z^Zframe-where
information
Then, if source is to actually be displayed for this frame (for example,
this is not true for output from the backtrace command), then a
source annotation (see section 18.11 Displaying Source) is displayed. Unlike
most annotations, this is output instead of the normal text which would be
output, not in addition.