HP gnu source-level debugger 5992-4701 - Manual (Page 295)

is formatted using the Emacs function format; otherwise the
number is passed as an argument to the corresponding list
element.
In any source file, the Emacs command C-x SPC (gdb-break) tells GDB to set a
break- point on the source line point is on.
If you accidentally delete the source-display buffer, an easy way to get it back is to type
the command f in the GDB buffer, to request a frame display; when you run under
Emacs, this recreates the source buffer if necessary to show you the context of the
current frame.
The source files displayed in Emacs are in ordinary Emacs buffers which are visiting
the source files in the usual way. You can edit the files with these buffers if you wish;
but keep in mind that GDB communicates with Emacs in terms of line numbers. If you
add or delete lines from the text, the line numbers that GDB knows cease to correspond
properly with the code.
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