Red Hat Linux 9 Professional Secrets [Electronic resources] نسخه متنی

Binary Utilities

Just as the text utilities are meant for working with text files, the GNU binary utilities are meant for performing various tasks on binary files. Some of these utilities, such as

ar ,

as , and

ld , are used when building and managing object files that are generated when source files are compiled. A number of other binary utilities enable you to examine the contents of binary files. For example, the

strings command prints all strings of printable characters in a file. Here is what the

strings command displays for a simple C program that prints

Hello, World! (the name of the binary executable is

a.out ):

strings a.out
/lib/ld-linux.so.2
libc.so.6
printf
_IO_stdin_used
__libc_start_main
__gmon_start__
GLIBC_2.0
PTRh
QVh(
Hello, World!

Notice that the output includes the

Hello World! string, as well names of libraries (

/lib/ld-linux.so.2 and

libc.so.6 ) and C functions (

printf ).

You can use the

size command to look at the number of bytes that various sections (such as the code size, data area, and stack space) of a program would need. Here is the output of size for the

a.out file that contains the Hello, World! program:

size a.out
text    data     bss     dec     hex filename
790     256       4    1050     41a a.out

In this case, the program requires 790 bytes for the code (called text, but it’s the binary executable code of a program), 256 bytes for the data, and 4 bytes for stack. Thus, the program requires a total of 1,050 bytes of memory. Note that the actual size of the

a.out file is about 10KB, which is much larger than 1,050 bytes because other information, such as symbols, is included in the file. Programmers would find the output of the

size command useful because it tells them about the memory required to load and run a program.

Table 8-5 briefly describes the programs in the GNU binary utilities package. You can try some of these programs on any binary file in the system. For example, here’s the result of running size on

/bin/bash —the executable for the Bash shell:

size /bin/bash
text    data     bss     dec     hex filename
602431   22200   17044  641675   9ca8b /bin/bash