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1 A Sample GDB Session
This chapter describes the most common GDB commands with the help of an example.
The following topics are discussed:
• Loading the Executable
• Setting the Display Width
• Setting Breakpoints
• Running the Executable under GDB
• Stepping to the next line
• Stepping into a Subroutine
• Examining the Stack
• Printing Variable Values
• Listing the Source Code
• Setting Variable Values During a Debug Session
In this sample session, we emphasize user input like this: input, to make it easier to
pick out from the surrounding output.
One of the preliminary versions of GNU m4 (a generic macro processor) exhibits the
following bug: sometimes, when we change its quote strings from the default, the
commands used to capture one macro definition within another stop working. In the
following short m4 session, we define a macro foo which expands to 0000; we then
use the m4 built-in defn to define bar as the same thing. However, when we
change the open quote string to <QUOTE> and the close quote string to <UNQUOTE>,
the same procedure fails to define a new synonym baz:
$ cd gnu/m4 //change your current directory to the location where the m4 executable is stored.
$ ./m4 //run the m4 application
define(foo,0000)
foo
0000
define (bar,defn('foo'))
bar
0000
changequote(<QUOTE>,<UNQUOTE>)
define(baz,defn(<QUOTE>foo<UNQUOTE>))
baz
C-d
m4: End of input: 0: fatal error: EOF in string
1.1 Loading the Executable
Let us use GDB to try to see what is going on.
1.1 Loading the Executable 19