Debugging_with_gdb (ARM电子书)

Summary of gdb
The purpose of a debugger such as gdb is to allow you to see what is going on “inside”
another program while it executes—or what another program was doing at the moment it
crashed.
gdb can do four main kinds of things (plus other things in support of these) to help you
catch bugs in the act:
• Start your program, specifying anything that might affect its behavior.
• Make your program stop on specified conditions.
• Examine what has happened, when your program has stopped.
• Change things in your program, so you can experiment with correcting the effects of
one bug and go on to learn about another.
You can use gdb to debug programs written in C and C++. For more information, see
Section 12.4 [Supported languages], page 115. For more information, see Section 12.4.1 [C
and C++], page 115.
Support for Modula-2 is partial. For information on Modula-2, see Section 12.4.5
[Modula-2], page 123.
Debugging Pascal programs which use sets, subranges, file variables, or nested functions
does not currently work. gdb does not support entering expressions, printing values, or
similar features using Pascal syntax.
gdb can be used to debug programs written in Fortran, although it may be necessary
to refer to some variables with a trailing underscore.
gdb can be used to debug programs written in Objective-C, using either the Apple/
NeXT or the GNU Objective-C runtime.
Free software
gdb is free software, protected by the gnu General Public License (GPL). The GPL gives
you the freedom to copy or adapt a licensed program—but every person getting a copy also
gets with it the freedom to modify that copy (which means that they must get access to the
source code), and the freedom to distribute further copies. Typical software companies use
copyrights to limit your freedoms; the Free Software Foundation uses the GPL to preserve
these freedoms.
Fundamentally, the General Public License is a license which says that you have these
freedoms and that you cannot take these freedoms away from anyone else.
Free Software Needs Free Documentation
The biggest deficiency in the free software community today is not in the software—it is the
lack of good free documentation that we can include with the free software. Many of our
most important programs do not come with free reference manuals and free introductory
texts. Documentation is an essential part of any software package; when an important free
software package does not come with a free manual and a free tutorial, that is a major gap.
We have many such gaps today.