Binary Utilities (binutils)

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This document describes the binary utilities binutilsthe set of tools used for compiling, inspecting, and transforming binaries machine code files. Other, more specialized ones, might be new to you. Learning these tools and what they can do will greatly improve your productivity as a programmer.

This guide refers to each tool with its short name e. For example, gcc on a myth machine is a version of the Gnu C Compiler for Linux on an x86 processor. These tools are prefixed with arm-none-eabi. So you want to use arm-none-eabi-ld not ld. This section discusses the core utilities that you use very often: This is the assembler. It takes assembly code human readable text of machine code and turns it into a binary that a processor can execute.

When you invoke gcc and tell it to generate a binary e. Almost all executables you run in Linux, for example, are ELF. ELF includes not only machine code the E part but also gnu binutils a collection of binary tools linuxnames that provide information on where different variables and functions reside see nm and objdump below. That way, when you compile a program that invokes the library function, binutils can find where it is and link the two files together correctly see ld below.

Just as the gnu binutils a collection of binary tools linux to as might not be a executable program, the output of as might not be executable. For example, a library is a set of gnu binutils a collection of binary tools linux that other programs can call, but does not have any entry point main function.

It can also be that the compiled assembly code references functions that are in another binary file. For example, your program that calls a library, when compiled into machine code, does not have the actual instructions of those library calls.

The tool that takes multiple binary files and links them together is lddescribed below. This tells the assembler that code.

If you do not include -o code. If you do not include code. These two invocations are therefore equivalent:. For example, when you have a library written in multiple source files, you typically compile each source file independently into an ELF object file, then link all of those files together into a larger ELF object file for the library. When you compile a program that uses the library, you compile your program code into one or more object files, then link those against the library, producing a final executable.

The linker operates by resolving symbols. Whenever your code creates or uses a name that is not on the stack e. Some symbols, such as those your program defines, are resolved and exist.

For example, when you define a variable int a; in global scope, gnu binutils a collection of binary tools linux creates a symbol for awhich says at what memory address a resides. When the linker links your program to the library, it sees that f is an unresolved symbol, sees that f is defined in the library, then fixes the binary code in your program so that when it calls f it jumps to where f exists.

This takes two object files, links them together, and outputs the result as code. When you invoke GCC without the -c option, it typically runs ld as its last step. The most commonly used options for ld are -l and -L. The -l option tells ld to link a library, which is basically just an object file.

The -L option tells ld what directories to look for libraries in. You can pass multiple -l and -L options. Displays the symbol table of a binary file. It takes one or more file names as parameters and outputs their symbol tables. Gnu binutils a collection of binary tools linux output looks like this:. The first column states the address of the symbol.

For a function, this is the first instruction to jump to when you call the function. For a variable, this is its location in memory.

The second column states what kind of symbol it is. So in the above example, the object file defines a function fa function mainand a variable a. Lists the size of sections and total size of object files. Can be invoked on multiple files at once simply by listing the desired files. Under text you see the size of the actual machine code that makes up your program. Similarly to the symbol types listed under nm above, the data section is the size of storing your initialized global variables, and bss is the size of storing your uninitialized global variables.

The options for the size command are mostly to change the format of the output. For example, to see the section sizes in hexadecimal, use the -x option size -x test. You can also specify the file type if it is not automatically recognized. For example if you want to know the size of a raw binary file, you could use. Prints text strings embedded in the input file. For example, if you wanted to search an object file for a particular string, you could call strings and pipe the result to grep, like this:.

By default, strings looks for strings of at least 4 printable characters followed by a NUL character indicating the end of a string. To set a minimum string length other than 4, use the -n option. Removes gnu binutils a collection of binary tools linux from object files. Symbols indicate where in memory variables and functions reside, see ld above. By stripping out symbol tables and debug information, strip decreases the size of object files.

Compare the file before and after you strip it using nm above. You will find that the symbols have been removed. Transforms binary objects between different formats. For example, you can use objcopy to transform an ELF executable which has symbols and all kinds of other information into a simple binary.

The principal options to objcopy are -O and -Iwhich specify the output and input formats. Example formats are elfbigarm, ihex, and binary. In its most basic use, objcopy just makes a copy of the file. Displays information about object files. To use objdumpyou must specify at least one of the many options, which indicate what type of information you would like to view.

There are many different gnu binutils a collection of binary tools linux, check out man objdump to see what it can show. A very useful option is the -d option, which allows you to view the assembly instructions associated with the executable part of the binary file -d is for dissassemble:. Allows you to create, modify, and extract archives.

Archives are single files holding collections of other usually binary files, similar to a zip or tar file. The linker see ld above is often used to link to functions in these archive library files.

To create an archive from object files, use the cr or crs options, followed by your object files. The c option means it will not warn you that it needs to create the library since that is what you are trying to do. The r option says to insert the new files or replace existing ones. If you specify the s option, the archive maintains an index to all symbols defined in files in the archive to allow for quicker linking to the library functions.

Then you can link to this library by specifying -ltest in the ld command see ld above. For more options on how to modify archives, see man ar or ar --help. Toggle navigation CSe Spring Binary Utilities binutils This document describes the binary utilities binutilsthe set of tools used for compiling, inspecting, and transforming binaries machine code files. Core utilities This section discusses the core utilities that you use very often: The most gnu binutils a collection of binary tools linux use of as is as follows:

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Richard Stallman founded the GNU project in to create a complete Unix-like operating system as free software, to promote freedom and cooperation among computer users and programmers. The mother site for GCC is http: The current version is GCC 7. The GNU Toolchain includes:. GCC is portable and run in many operating platforms. GCC is also a cross-compiler , for producing executables on different platform.

It is the standard compiler for most Unix-like operating systems. To differentiate these variations, you need to understand the followings:. The col utility is needed to strip the backspace. For Cygwin, it is available in "Utils", "util-linux" package. Alternatively, you could look for an online man pages, e.

The default output executable is called " a. We use the -o option to specify the output file name. The above command compile the source file into object file and link with other object files and system libraries into executable in one step.

You may separate compile and link in two steps as follows:. Suppose that your program has two source files: You could compile all of them in a single command:.

However, we usually compile each of the source files separately into object file, and link them together in the later stage. In this case, changes in one file does not require re-compilation of the other files. Read " Java Native Interface " for example. For example, a " gcc -o hello. You can see the detailed compilation process by enabling -v verbose option. The value should be enclosed in double quotes if it contains spaces. A library is a collection of pre-compiled object files that can be linked into your programs via the linker.

Examples are the system functions such as printf and sqrt. Because of the advantage of dynamic linking, GCC, by default, links to the shared library if it is available. When compiling the program, the compiler needs the header files to compile the source codes; the linker needs the libraries to resolve external references from other object files or libraries. For each of the headers used in your source via include directives , the compiler searches the so-called include-paths for these headers.

Since the header's filename is known e. The linker searches the so-called library-paths for libraries needed to link the program into an executable. In addition, you also have to specify the library name. In Unixes, the library lib xxx. In Windows, provide the full name such as -lxxx. The linker needs to know both the directories as well as the library names. Hence, two options need to be specified. Try running the compilation in verbose mode -v to study the library-paths -L and libraries -l used in your system:.

The settings are applicable to the selected project only. For all the GNU utilities, you can use " command --help " to list the help menu; or " man command " to display the man pages. The utility " file " can be used to display the type of object files and executable files. A 'T' in the second column indicates a function that is defined , while a 'U' indicates a function which is undefined and should be resolved by the linker.

The utility " ldd " examines an executable and displays a list of the shared libraries that it needs. The " make " utility automates the mundane aspects of building executable from source code. You can issue " make --help " to list the command-line options; or " man make " to display the man pages.

Let's begin with a simple example to build the Hello-world program hello. Create the following file named "makefile" without any file extension , which contains rules to build the executable, and save in the same directory as the source file. Use "tab" to indent the command NOT spaces. Running make without argument starts the target " all " in the makefile. A makefile consists of a set of rules. A rule consists of 3 parts: The target and pre-requisites are separated by a colon: The command must be preceded by a tab NOT spaces.

When make is asked to evaluate a rule, it begins by finding the files in the prerequisites. If any of the prerequisites has an associated rule, make attempts to update those first. In the above example, the rule " all " has a pre-requisite " hello.

The rule " hello. Again, it does not exist, so make looks for a rule to create it. It runs the command " gcc -c hello. Finally, the rule " all " does nothing. More importantly, if the pre-requisite is not newer than than target, the command will not be run.

In other words, the command will be run only if the target is out-dated compared with its pre-requisite. For example, if we re-run the make command:.

You can also specify the target to be made in the make command. For example, the target " clean " removes the " hello. You can then run the make without target, which is the same as " make all ". A comment begins with a and lasts till the end of the line. The rules are usually organized in such as way the more general rules come first. The overall rule is often name " all ", which is the default target for make.

A target that does not represent a file is called a phony target. For example, the " clean " in the above example, which is just a label for a command. If the target is a file, it will be checked against its pre-requisite for out-of-date-ness. Phony target is always out-of-date and its command will be run. The standard phony targets are: Single character variables do not need the parentheses.

You can also use vpath lowercase to be more precise about the file type and its search directory. Make comes with a huge set of implicit pattern rules. You can list all the rule via --print-data-base option. Make is actually quite complex, and can be considered as a programming language by itself!! The GNU Toolchain includes: A build system including Autoconf, Autoheader, Automake and Libtool.

GCC version 1 Initial version that support C. GCC version 2 GCC version 3 GCC version 4 GCC version 5 GCC Version 6 GCC Version 7 Cygwin is a Unix-like environment and command-line interface for Microsoft Windows. Cygwin is huge and includes most of the Unix tools and utilities. It also included the commonly-used Bash shell. To differentiate these variations, you need to understand the followings: If the target is native Windows, the code can be distributed and run under Windows.

However, if the target is Cygwin, to distribute, you need to distribute Cygwin runtime environment cygwin1. This is because Cygwin is a Unix emulator under Windows. The executable is " iwmingwgcc ". Run the executables and check the versions: You probably should install these two packages too. However, to distribute the code produced, you need to distribute Cygwin Runtime Environment cygwin1.

Versions You could display the version of GCC via --version option: