Red Hat ENTERPRISE LINUX 3 - SECURITY GUIDE User manual

Red Hat Enterprise Linux 3
Developer Tools Guide

Red Hat Enterprise Linux 3: Developer Tools Guide
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Table of Contents
1. Overview of Red Hat Enterprise Linux Developer Tools............................................................ 1
2. Basic Principles of the Tools........................................................................................................... 3
2.1. Compiler and Development Tools ..................................................................................... 3
2.2. Libraries ............................................................................................................................. 3
2.3. Auxiliary Development Tools ............................................................................................ 4
2.4. gcc, the GNU Compiler Collection................................................................................... 4
2.5. cpp, the GNU Preprocessor............................................................................................... 5
2.6. as, the GNU Assembler..................................................................................................... 6
2.6.1. Object Files ......................................................................................................... 6
2.6.2. Assembler Directives .......................................................................................... 7
2.7. ld, the GNU Linker ............................................................................................................ 7
2.8. gcov, the Test Coverage Tool............................................................................................ 8
2.9. gdb, the Debugging Tool.................................................................................................... 8
2.10. make, the GNU Recompiling Tool .................................................................................. 8
2.10.1. Example Makefile .......................................................................................... 9
2.11. binutils, the GNU Binary Utilities ................................................................................. 10
2.12. Using info, the Documentation Tools ............................................................................ 10
2.12.1. Reading info Documentation .......................................................................... 11
2.13. Learn More About the Tools.......................................................................................... 11
3. Developing with Red Hat Enterprise Linux Developer Tools ................................................... 13
3.1. Create Source Code.......................................................................................................... 13
3.2. Compile, Assemble, and Link from Source Code ........................................................... 13
3.3. Run the Executable .......................................................................................................... 13
3.4. Debug the Executable ...................................................................................................... 14
3.5. Assembler Listings........................................................................................................... 16
3.6. Disassembling.................................................................................................................. 16
Index................................................................................................................................................... 19

Chapter 1.
Overview of Red Hat Enterprise Linux
Developer Tools
This manual introduces you to the Red Hat Enterprise Linux Developer Tools and its documentation
set. After you read this, refer to the following documentation for details about the Red Hat Enterprise
Linux Developer Tools:
•Compiler Tools
•Using the GNU Compiler Collection (GCC)
•Using cpp, the C Preprocessor
•Debugging Tools
•Debugging with GDB
•Development Tools
•Using ld, the Gnu Linker
•Auxiliary Development Tools
•Using as, the Gnu Assembler
•Using binutils, the Gnu Binary Utilities
HTML, PDF, and RPM versions of the manuals are available on the Documentation CD and online at
http://www.redhat.com/docs/.
For more information on the tools and their history, see the following websites:
•http://sources.redhat.com/
•http://www.linuxdoc.org/
•http://www.opensource.org/products.html
•http://www.gnu.org/
•http://www.fsf.org/manual/
•http://www.openbsd.org/docum.html

2 Chapter 1. Overview of Red Hat Enterprise Linux Developer Tools

Chapter 2.
Basic Principles of the Tools
Red Hat Enterprise Linux Developer Tools’s C and C++ compilers, macro-assembler, debugger, bi-
nary utilities, libraries, and other development tools provide productivity, flexibility, performance, and
portability. This chapter begins with a summary of the tools, then describes each tool in more detail.
To use a tool, open your system’s terminal shell window and enter the tool’s name as a command
(gcc, for instance, invokes the compiler. For a summary of the Red Hat Enterprise Linux Developer
Tools, refer to Section 2.1 Compiler and Development Tools, Section 2.2 Libraries, and Section 2.3
Auxiliary Development Tools.
To learn about working with the tools, refer to Chapter 3 Developing with Red Hat Enterprise Linux
Developer Tools.
2.1. Compiler and Development Tools
The following lists the main tools for developing projects with Red Hat Enterprise Linux Developer
Tools.
Tool Description
cpp C preprocessor (refer to Section 2.5 cpp, the GNU Preprocessor; and Using
cpp, the C Preprocessor)
diff, diff3,
sdiff
Comparison tools for text files.
gcc ISO-conforming compiler collection (refer to Section 2.4 gcc, the GNU
Compiler Collection and Using the GNU Compiler Collection (GCC))
g++ A frontend to gcc that defaults to interpreting files as being C++ source files
even if they look like C source files
gcov Coverage analyzer, for testing code for efficiency and performance, and for
use as a profiling tool (refer to Using the GNU Compiler Collection (GCC))
gdb -nw Debugger for debugging with command line input (refer to Section 2.9 gdb,
the Debugging Tool and Debugging with GDB)
gdb Debugger for making applications work better (refer to Debugging with
GDB)
ld Linker (refer to Section 2.7 ld, the GNU Linker and Using ld, the Gnu
Linker)
make Compilation control program (refer to Section 2.10 make, the GNU
Recompiling Tool)
patch Installation tool for source fixes
2.2. Libraries
Library Description

4 Chapter 2. Basic Principles of the Tools
Library Description
libc ANSI C runtime library
libm C math subroutine library
libstdc++ C++ class library
2.3. Auxiliary Development Tools
The following components are also provided for general development:
Component Description
as Assembler (refer to Section 2.6 as, the GNU Assembler and Using as, the
Gnu Assembler)
info Online documentation tools (refer to Section 2.12 Using info, the
Documentation Tools)
man man pages, the standard UNIX online documentation
The GNU binary utilities provide functionality beyond the main development tools (refer to Using
binutils, the Gnu Binary Utilities).
Utility Description
addr2line Converts addresses into file names and line numbers
ar Creates, modifies and extracts from object code archives
c++filt Demangles and deciphers encoded C++ symbol names
dlltool Creates files for builds, using dynamic link libraries (DLLs)
nm Lists symbols from object files
objcopy Copies and translates object files
objdump Displays information from object files
ranlib Generates index to archive contents
readelf Displays information about ELF format object files
size Lists file section sizes and total sizes
strings Lists printable strings from files
strip Discards symbols
2.4. gcc, the GNU Compiler Collection
The GNU Compiler Collection (GCC), is a complete set of tools for compiling programs written in
C, C++, Objective C, or languages for which you have installed front-ends. The GNU compiler uses
the following utilities:
•cpp GNU preprocessor that processes all the header files and macros that your target requires (refer
to Section 2.5 cpp, the GNU Preprocessor).

Chapter 2. Basic Principles of the Tools 5
•as GNU assembler that produces binary code from assembly language code and puts it in an object
file (refer to Section 2.6 as, the GNU Assembler).
•ld GNU linker that binds the code to addresses, links the startup file and libraries to an object file,
and then produces an executable binary image (refer to Section 2.7 ld, the GNU Linker).
To invoke the compiler, type:
gcc option, option...
Each option signifies input that allows you to control how the program compiles (for example, you
can interrupt a compile process at intermediate stages). Use commas to separate options. There are
many options available that provide specific types of compiled output, some for preprocessing, others
controlling assembly, linking, optimization, debugging, and still others for target-specific functions.
For instance, call the compiler with a -v option to refer to precisely which options are in use for each
compilation pass.
gcc implicitly recognizes the following file extensions:
•.c (for C source code that must be preprocessed)
•.C (for C++ source code that must be preprocessed)
•.s (for assembler code)
•.S (for assembler code that must be preprocessed).
When referring to C++ compilation, g++ is its customary name. Because there is only one compiler, it
is also accurate to use the gcc call, no matter what the language context. The g++ distinction is more
useful when the emphasis is on compiling C++ programs, with the GNU compiler acting not merely
as a preprocessor, but building object code directly from your C++ program source.
There is no intermediate C version of the program; avoiding an intermediate C representation of the
program means that you get better object code and better debugging information. The GNU debugger
works with this information in the object code to give you comprehensive C++ source-level editing
capabilities.
When you compile C or C++ programs, the compiler inserts a call at the beginning of main to a _
_main support subroutine. To avoid linking to the standard libraries, specify the -nostdlib option.
(Including -lgcc at the end of your compiler command line resolves this reference and links only
with the compiler support library libgcc.a; ending your command’s input with it ensures that you
get a chance to link first with any of your own special libraries).
_ _main is the initialization routine for C++ constructors. Because GNU C is meant to interoperate
with GNU C++, even C programs must have this call; otherwise, C++ object files linked with a C
main might fail.
Compilation can involve up to four stages, always in the following order:
•preprocessing
•compiling
•assembling
•linking
The first three stages apply to an individual source file: preprocessing establishes the type of source
code to process, compiling produces an object file, assembling establishes the syntax that the com-
piler expects for symbols, constants, expressions and the general directives. The last stage, linking,
completes the compilation process, combining all object files (newly compiled, and those specified as
input) into an executable file.
For more information on the GNU compiler and its options, refer to Using the GNU Compiler Col-
lection (GCC).

6 Chapter 2. Basic Principles of the Tools
2.5. cpp, the GNU Preprocessor
cpp is a C-compatible macro preprocessor that works with the GNU compiler to direct the parsing of
C preprocessor directives. Preprocessing directives are the lines in your program that start with a #
directive name (a #sign followed by an identifier). For instance, cpp merges #include files, expands
macro definitions, and processes #ifdef sections. Another example is #define, a directive that
defines a macro (#define must be followed by a macro name and the macro’s intended expansion).
To refer to the output of cpp, invoke gcc with the -E option; the preprocessed file will print on
stdout
The C preprocessor provides the following separate facilities:
•Inclusion of header files — Declarations that can be substituted into your program.
•Macro expansion When defining macros, which are abbreviations for arbitrary fragments of C code,
the C preprocessor replaces them with their definitions throughout a program.
•Conditional compilation — Using special preprocessing directives, include or exclude parts of a
program according to replaceableious conditions.
•Line control — Using a program to combine or rearrange source files into an intermediate file that
is then compiled, use line control to provide a source line’s origin.
There are two convenient options to assemble files that require C-style preprocessing. Both options
depend on using the compiler driver program, gcc, instead of directly calling the assembler.
•Name the source file using the extension .S (capitalized), rather than .s (the .S indicates an as-
sembly language program that requires C-style preprocessing).
•Specify a source language explicitly for a situation, using the -xassembler-with-cpp option.
For more information on cpp, refer to Using cpp, the C Preprocessor.
2.6. as, the GNU Assembler
as, the GNU assembler, translates text-based assembly language source files into binary-based object
files. Normally it operates without you being aware of it, as the compiler driver program (gcc) invokes
it automatically. However, if you are creating your own assembler source files, you must invoke as
directly.
If, while using gcc, you want to pass special command-line options to the assembler to control its be-
havior, you need to use the ‘-Wa,<text>’ command-line option. This option passes <text> directly
to the assembler’s command line. For example:
gcc -c -g -O -Wa,-alh,-L file.c
passes the -alh command line option on to the assembler. (This causes the assembler to emit a listing
file that shows the assembler source generated by the compiler for each line of the C source file
file.c).
For more information, refer to Using as, the Gnu Assembler.
2.6.1. Object Files
The assembler creates object files that, by convention, have the .o extension. These are binary files
that contain the assembled source code, information to help the linker integrate the object file into an
executable program, debugging information and tables of all of the symbols used in the source code.

Chapter 2. Basic Principles of the Tools 7
Special programs exist to manipulate object files. For example, objdump can disassemble an object
file back into assembler source code and ar can group together multiple object files into an archive or
library file.
2.6.2. Assembler Directives
Assembler directives are commands inside the assembler source files that control how the object file
is generated. They are also known as pseudo-ops, or pseudo-operations, because they can look like
commands in the assembler programming language.
Assembler directives always start with a period (.). The rest of their name is letters, usually in lower
case. They have a wide range of different uses, such as specifying alignments, inserting constants into
the output, and selecting in which sections of the output file the assembled machine instructions are
placed.
2.7. ld, the GNU Linker
The GNU linker, ld, combines multiple object files together and creates an executable program from
them. It does this by resolving references between the different object files, grouping together similar
sections in the object files into one place, arranging for these sections to be loaded at the correct
addresses in memory, and generating the necessary header information at the start of a file that allows
it to be run.
The linker moves blocks of bytes of your program to their load-time addresses. These blocks slide
to their addresses as rigid units; their length does not change and neither does the order of the bytes
within them. Such a rigid unit is called a section. Assigning runtime addresses to sections is called
relocation. It includes the task of adjusting mentions of object-file addresses so they refer to the proper
runtime addresses.
Each section in an object file has a name and a size. Most sections also have an associated block
of data, known as the section contents. A section may be marked as allocatable, meaning that space
should be reserved for it in memory when the executable starts running. A section may also be marked
as loadable, meaning that its contents should be loaded into memory when the executable starts. A
section which is allocatable but not loadable will have a zero-filled area of memory created for it.
A section, which is neither loadable nor allocatable, typically contains some sort of debugging infor-
mation. Every loadable or allocatable output section has two addresses associated with it. The first is
the virtual memory address (VMA), the address the section will have when the executable is running.
The second is the load memory address (LMA), which is the address in memory where the section will
loaded. In most cases the two addresses will be the same. An example of when they might be different
is when a data section is loaded into ROM, and then copied into RAM when the program starts. This
technique is often used to initialize global variables in a ROM-based system. In this case, the ROM
address would be the LMA, and the RAM address would be the VMA. To review the sections in an
object file, use the objdump binary utility with the -h option.
Every object file also has a list of symbols, known as the symbol table. A symbol may be defined or
undefined. Each symbol has a name, and each defined symbol has an address. If you compile a C or
C++ program into an object file, you get a defined symbol for every defined function and global or
static variable. Every undefined function or global variable, which is referenced in the input file, will
become an undefined symbol. You can refer to the symbols in an object file by using the nm binary
utility, or by using the objdump binary utility with the -t option.
The linker is controlled by a linker script which is a text file containing commands in a simple lan-
guage. The main purpose of the script is to describe how sections in the input files should be mapped
into sections in the output file and to control memory layout of the output file. When necessary, the
linker script also directs the linker to perform other operations.

8 Chapter 2. Basic Principles of the Tools
The linker uses a default script that compiles into the linker executable, if you do not supply one via
the -T command line option. Use the --verbose option to display the default linker script. Certain
options (such as -r or -N) affect the default linker script. Linker scripts are written in a superset of
AT&T’s Link Editor Command Language syntax.
For more information, refer to Using ld, the Gnu Linker.
2.8. gcov, the Test Coverage Tool
gcov, the code coverage/basic block profile display tool, enables you to analyze the basic block profile
of your program by recording how often each basic block is executed. This information enables you
to determine the sections of code on critical paths and the code blocks that are not executed at all.
2.9. gdb, the Debugging Tool
GDB, the GNU debugger, has the principal purpose of allowing you to stop your program before it
terminates. If your program terminates, the debugger helps you determine where it failed. To debug a
file named file.c, first compile the file using gcc -g file.c as a command, where -g produces
the debugging information. You then run the debugger. Refer to Section 3.4 Debug the Executable,
for the steps involved in debugging.
Set breakpoints with the breakpoint command.
Navigate through the program with the step command or the next command.
The debugger debugs threads, signals, trace information, and other data in a program. Each time your
program performs a function call, a block of data (the stack frame), which shows the location of the
call, the arguments, and the local variables of the function is generated. The debugger allows you to
examine the stack frame to get your program to work.
For more information, refer to Debugging with GDB.
2.10. make, the GNU Recompiling Tool
make, the GNU recompiling tool, determines automatically which pieces of a large program you need
to recompile and then issues commands to recompile them. make conforms to IEEE Standard 1003.2-
1992 (POSIX.2) and is compatible with any programming language whose compiler can run with
command line input from a shell. make is not limited only to building programs; it can be used for
any task in which some files must update automatically whenever associated files change.
To use make, you must write a file (a makefile) that describes the relationships among files in your
program and provides commands for updating each file. In a program, typically, the executable file is
updated from object files, which are in turn made by compiling source files.
When using make to recompile an executable, the result may change source files in a directory. If you
changed a header file, to be safe, you must recompile each source file that includes that header file.
Each compilation produces an object file corresponding to the source file. If any source file has been
recompiled, all the object files, whether newly made or saved from previous compilations, must be
linked together to produce the new executable.
make uses the makefile database and the last modified files to decide which of the other files needs
updating. For each of those files, make implements the commands recorded in the data base of the
makefile. The makefile has rules which explain how and when to remake certain files that are the
targets of a particular rule. A simple makefile rule has the following form:
target... : dependency... command

Chapter 2. Basic Principles of the Tools 9
target is usually the name of a file that a program generates; examples of targets are executable or
object files. A target can also be the name of an action to carry out, such as with the clean command (a
command that, deletes all files from a build directory before building). A dependency is a file that
is used as input to create the target. A target often depends on several files. command is activated by
make wnen dependancy has changed. A rule may have more than one command, with each command
on its own line. Usually a command is in a rule with dependencies and serves to create a target file if
any dependencies change. However, the rule that specifies commands for the target does not require
dependencies; for instance, the rule containing the delete command that associates with the target,
clean, does not have dependencies. make activates commands on the dependencies to create or to
update the target. A rule can also explain how and when to activate a command. A makefile can
contain other text besides rules; a simple makefile requires only rules. Rules generally follow the
same pattern.
Note that every command line in a makefile must begin with a tab character.
2.10.1. Example Makefile
edit : main.o kbd.o command.o display.o insert.o search.o \
files.o utils.o
cc -o edit main.o kbd.o command.o display.o insert.o \
search.o files.o utils.o
main.o : main.c defs.h
cc -c main.c
kbd.o : kbd.c defs.h command.h
cc -c kbd.c
command.o : command.c defs.h command.h
cc -c command.c
display.o : display.c defs.h buffer.h
cc -c display.c
insert.o : insert.c defs.h buffer.h
cc -c insert.c
search.o : search.c defs.h buffer.h
cc -c search.c
files.o : files.c defs.h buffer.h command.h
cc -c files.c
utils.o : utils.c defs.h
cc -c utils.c
clean :
rm edit main.o kbd.o command.o display.o insert.o \
search.o files.o utils.o
The targets in the example makefile include the executable file, edit, and the main.o and kbd.o
object files. main.c and defs.h are the dependency files. Each .o file is both a target and a depen-
dency. When a target is a file, it needs to be recompiled or relinked if any of its dependencies change.
You must first update any dependencies that automatically generate. In the example Makefile,edit
depends on eight object files; the object file, main.o, depends on the source file, main.c, and on
the defs.h header file. A shell command follows each line that contains a target and dependencies,
saying how to update the target file; a tab character must come at the beginning of every command line
to distinguish command lines from other lines in the makefile.make does not know anything about

10 Chapter 2. Basic Principles of the Tools
how the commands work; it is up to you to supply commands that update the target file properly. All
make does is execute the commands in the rule you have specified when the target file needs updating.
For more details, refer to Using make.
2.11. binutils, the GNU Binary Utilities
binutils, the GNU binary utilities, include ar,nm,objcopy,objdump,ranlib,size,strings,
and strip. For targets that use the ELF file format, there is also a tool called readelf.
There are three binary utilities, addr2line,windres, and dlltool, that are for use with Cygwin,
the porting layer application for Win32 development. The most important of the binary utilities are
objcopy and objdump.
•objcopy is a tool to convert object and executable files. It can add and remove sections and sym-
bols, but the most commonly used feature is its ability to change the file format. For example, it can
convert an ELF or COFF format executable into an S-record or Intel I-Hex format file. These two
formats are often used in building ROM images for standalone and embedded systems. For more
information, refer to the objcopy Utility section in Using binutils, the Gnu Binary Utilities.
•objdump is a tool to display information about the contents of an object or executable file. It can
display symbol tables and section headers and it can also act as a disassembler. Objdump also
knows about archives and libraries and can be used to display information on all of the object files
inside them. For more information, refer to the objdump Utility section in Using binutils, the Gnu
Binary Utilities.
A few of the more useful options for objdump include: -h (to display section headers), -t (to
display symbols), -p (to display private header information) and -d for assembler (to display a
disassembly). -d normally only disassembles sections that are expected to contain instructions. To
disassemble all sections, use -D instead. The option --prefix-addresses can be used to print a
complete address on each line of the disassembler’s output.
2.12. Using info, the Documentation Tools
info provides the sources for documentation for the GNU tools; it requires the following tools, in-
cluding the TeX tools.
Texinfo,texindex,texi2dvi
Documentation formatting tools. Texinfo requires TEX, the free technical documentation format-
ting tool written by Donald Knuth. Refer to Texinfo: The GNU Documentation Format (ISBN:
1-882114 67 1).
makeinfo,info
Online documentation tools.
man pages
Includes documentation on all the tools and programs in this release.
FLEX: A Fast Lexical Analyzer Generator
Generates lexical analyzers suitable for GCC and other compilers. Refer to Flex: The Lexical
Scanner Generator (ISBN: 1-882114 21 3).

Chapter 2. Basic Principles of the Tools 11
Using and Porting GNU CC
Contains information about requirements for putting GCC on different platforms, or for modify-
ing GCC; includes documentation from Using the GNU Compiler Collection (GCC).
BYacc
Discusses the Berkeley Yacc parser generator. Refer to Bison Manual: Using the
YACC-compatible Parser Generator (ISBN: 1-882114 44 2).
Texinfo: The GNU Documentation Format
Details TEX and the printing and generating of documentation, as well as how to write manuals
in the TEX style.
Configuration program
Describes the configuration program that Red Hat Enterprise Linux Developer Tools uses.
GNU Coding Standards
Elaborates on the coding standards with which the GNU projects develop.
GNU gprof
Details the GNU performance analyzer (only for the Solaris systems).
You have the freedom to copy the documentation using the accompanying copyright statements, which
include the necessary permissions. To get the documentation in HTML or printable form, refer to
http://www.fsf.org/doc/doc.html and http://www.fsf.org/doc/other-free-books.html.
For more information on using info tools (requiring the TEX tools), refer to Using info.
2.12.1. Reading info Documentation
Browse through the documentation using either Emacs or the info documentation browser program.
The information is in nodes, which correspond to the sections of a printed book. Follow them in
sequence, as in books, or, using the hyperlinks, find the node that has the information you need.
info has hot references (if one section refers to another section, info takes you directly to that other
section, but gives you the ability to return easily. You can also search for particular words or phrases.
Use info by typing its name at a shell prompt; no options or arguments are necessary. Check that
info is in your shell path. If you have problems running info, contact your system administrator.
To get help with using info, type hfor a programmed instruction sequence, or [Ctrl]-[h] for a short
summary of commands. To stop using info, type [q].
2.13. Learn More About the Tools
There are many sources to teach you more about GNU tools:
•For general information about the tools, see: http://www.redhat.com/docs/manuals/gnupro/
•For help with using the tools, see Chapter 3 Developing with Red Hat Enterprise Linux Developer
Tools.

12 Chapter 2. Basic Principles of the Tools

Chapter 3.
Developing with Red Hat Enterprise Linux
Developer Tools
Use the tutorials in this chapter to learn about standard native development with the tools.
See http://www.redhat.com/docs/manuals/gnupro/ for details about the tools.
3.1. Create Source Code
To start, create the following sample source code file and save it as hello.c. The following sections
show you how to compile this file to form an executable and how to run it.
#include <stdio.h>
int a, c;
static void
foo (int b)
{
c = a + b;
printf ("%d + %d = %d\n", a, b, c);
}
int
main (void)
{
int b;
a = 3;
b = 4;
printf ("Hello, world!\n");
foo (b);
return 0;
}
Example 3-1. Source code to save as hello.c
3.2. Compile, Assemble, and Link from Source Code
To compile the code, use the following command:
gcc -g hello.c -o hello
The -g option generates debugging information and -o specifies the name of the executable to be pro-
duced. Both of these can be omitted. Other useful options include -O to enable standard optimizations
and -O2 for extensive optimizations. If no -O is specified, GCC will not optimize.
See Using the GNU Compiler Collection (GCC) for additional basic compiler information.

14 Chapter 3. Developing with Red Hat Enterprise Linux Developer Tools
3.3. Run the Executable
To run the program, use the following example:
./hello
The program generates
hello world!
3+4=7
and returns when the program exits.
3.4. Debug the Executable
To start GDB, use the following commands:
gdb hello
After the initial copyright and configuration information, GDB returns its own prompt, (gdb). The
following is a sample debugging session:
1. To set a breakpoint, type:
break main
The following output displays:
Breakpoint 1 at 0x132: file hello.c, line 15.
Note the exact address and line number may vary, depending upon the target architecture being
debugged and the exact layout of the C code in the hello.c file.
2. To run the program, type:
run
The following output displays (when the program stops at a breakpoint):
Starting program: hello
Breakpoint 1, main () at hello.c:15
15 a = 3;
Again note that the exact line number and instruction displayed is dependent upon the source
code layout.
3. To print the value of variable, a, type:
print a
The following output displays:
$1 = 0
4. To execute the next command, type next:
next
The following output displays:
16 b = 4;
5. To display the value of a again, type:
print a
The following output displays:
$2 = 3
6. To display the program being debugged, type:
list

Chapter 3. Developing with Red Hat Enterprise Linux Developer Tools 15
The following output displays:
12 int
13 main (void)
14 {
15 int b;
16
17 a = 3;
18 b = 4;
19
20 printf ("Hello, world!\n");
21
22 foo (b);
23
24 return 0;
25 }
7. To list a specific function code, use the list command with the name of the function to be
display. For example, type:
list foo
The following output displays:
1 #include <stdio.h>
2
3 int a, c;
4
5 static void
6 foo (int b)
7 {
8 c = a + b;
9 printf ("%d + %d = %d\n", a, b, c);
10 }
8. To set a breakpoint at line seven, enter the following input (set a breakpoint at any line by
entering break linenumber, where linenumber is the specific line number to break):
break 8
The following output displays:
Breakpoint 2 at 0xf4: file hello.c, line 8.
9. To resume normal execution of the program until the next breakpoint, type:
continue
The following output displays:
Continuing.
Hello, world!
Breakpoint 2, foo (b=4) at hello.c:8
8c=a+b;
10. To step to the next instruction and execute it, type:
step
The following output displays:
9 printf ("%d + %d = %d\n", a, b, c);
11. To display the value of c, type:
print c
The following output displays:
$3 = 7
12. To see how you got to where you are, type:
backtrace
The following output displays:
#0 foo (b=4) at hello.c:9

16 Chapter 3. Developing with Red Hat Enterprise Linux Developer Tools
#1 0x15c in main () at hello.c:18
13. To exit the program and quit the debugger, type:
quit
3.5. Assembler Listings
The compiler normally turns a text based source file into a binary object file. It is possible however
to instruct it to just convert the source code into assembler and stop there. The -S option does this.
It also possible to instruct the compiler to produce an assembler listing as well as an object file. That
can be done as follows:
gcc -c -O2 -Wa,-al hello.c
-c tells GCC to compile or assemble source files, but not to link them. -O2 produces more fully
optimized code. These are both optional. -Wa tells the compiler to pass the comma-separated list of
options which follows it on to the assembler. The -al option is an assembler option to request an
assembler listing.
This example shows a partial excerpt of an assembler listing for an x386-based target.
29 .text
30 0027 90 .p2align 2„3
31 .globl main
32 .type main,@function
33 main:
34 0028 55 pushl %ebp
35 0029 89E5 movl %esp, %ebp
36 002b 83EC08 subl $8, %esp
37 002e 83E4F0 andl $-16, %esp
38 0031 83EC0C subl $12, %esp
39 0034 680E0000 pushl $.LC1
39 00
40 0039 C7050000 movl $3, a
40 00000300
40 0000
41 0043 E8FCFFFF call puts
41 FF
42 0048 C7042404 movl $4, (%esp)
Example 3-2. Assembly listing excerpt
It also possible to produce an assembler listing that intermixes the original input source code with
the assembler instructions produced by the compiler. This can help track down bugs, discover how
the compiler handles certain language constructs (such as function calls) and to learn more about
assembly language. To do this, just add an hto the assembler option like this:
gcc -c -g -O2 -Wa,-alh hello.c
3.6. Disassembling
The objdump tool can be used to to produce an disassembly of an object or executable file. It is used
like this:
objdump -d hello.o