Red Hat ENTERPRISE LINUX 3 - DEVELOPER TOOLS GUIDE Uživatelský manuál stáhnout pdf (Strana 12)

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

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Red Hat ENTERPRISE LINUX 3 - DEVELOPER TOOLS GUIDE Uživatelský manuál Strana 12