HP gnu source-level debugger 5992-4701 manual Sample GDB Session, Loading the Executable

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