What is the use of linux cross compilation?

In Linux, cross-compilation is a compilation program that runs in a computer environment and can compile code that runs in another environment; the cross-compiled program can be run in various target environments. Resources are relatively limited, so it is difficult to perform direct local compilation. Sometimes it is because the target platform does not allow or cannot install the compiler we need, and we need certain features of this compiler, so we need to use cross Compile.

#The operating environment of this tutorial: linux7.3 system, Dell G3 computer.

What is the use of linux cross compilation

What is cross compilation

Local compilation

Before explaining what cross-compilation is, we must first understand a concept: local compilation

Our common software development before was all local compilation: under the current PC, under the x86 CPU, directly The compiled program is a program (or library file) that can be run, which can be run directly in the current environment, that is, under the x86 CPU, in the current computer.

The compilation at this time can be called: local compilation, that is, under the current target platform, the compiled program can be run just under the current platform.

Cross-compilation

Cross-compilation is a concept corresponding to local compilation.

The so-called cross-compilation means: when compiled on one platform, the compiled program will be run on another platform, that is, the compiled environment. It is different from the running environment and is cross-compiled. , this is called cross.

Cross-compilation, this concept, is mainly related to embedded development.

For example: Compile on x86 platform and run on ARM platform.

One of the most common examples is:

When you are doing embedded development, you have an embedded development board. The CPU is arm and you develop it on an x86 platform, such as Ubuntu. Linux, or Win 10, then you need:

On the x86 platform, (use a cross-compiler) to compile the program code you wrote

Compile and generate (executable) The program is placed on the target development board and run on the ARM CPU

This is so-called: compiled on the x86 platform and run on the ARM platform.

Cross compilation is often written as cross compile in English. There are also other ways of writing: crosscompile, cross compiling, etc.

Why there is cross compilation

The main reason why there is cross compilation is: there are too few resources in the embedded system

The specific explanation is: the target environment in which the cross-compiled program is to be run has relatively limited resources, so it is difficult to directly compile it locally.

The most common situation is: when doing embedded development, the target platform, that is, the embedded development board, for example, is an ARM CPU with a maximum frequency of 200MHz, plus 32M RAM, plus 1G Nand Flash and so on. Under the premise of such relatively tight hardware resources, and on the premise that embedded Linux is already running, it is not convenient to directly compile it locally under embedded Linux or compile it under ARM CPU. Provides programs that ARM CPUs can run. Because compilation and development require relatively large amounts of CPU, memory, hard disk and other resources, and the few resources for embedded development are only enough to run the embedded (Linux) system, there are not many remaining resources for you to use locally. Compile.

BusyBox contains make and other tools related to compilation and development

Correspondingly, when you become familiar with embedded development and Busybox later, for example, configure Busybox in Buildroot, or separately When cross-compiling BusyBox:

[Record] Cross-compile BusyBox for QEMU's arm platform under Ubuntu

You will see that the later BusyBox, after the functions are added, has also included some, and Compilation and development related tools, such as make, etc.

These tools are originally only used on the PC side, that is, when developing under the x86 platform, they are only used during cross-compilation. The tool is now also supported in the embedded environment (BusyBox).

At this time, if you select all relevant development tools in BusyBox,

In addition, if the hardware configuration of your target development board is powerful enough, such as CPU The unit is GHz, etc.

If the relevant development libraries and tools are complete

In fact, at least in theory, it can also be used in your embedded Linux, To carry out, limited, or even to a large extent, local development, that is, directly on the ARM development board, embedded Linux, direct embedded development, and local compilation for ARM

For example, It is estimated that it is possible to compile a helloworld.

In this way, the cross-compilation mentioned here does not exist, or is avoided, and becomes local compilation.

is equivalent to the previous compilation on the PC side of x86. The local compilation of the program running on the x86 CPU is also implemented in ARM CPU and embedded Linux.

But obviously, for more complex programs or libraries, in The feasibility and efficiency of direct compilation on ARM development boards are relatively low

And if you are tossing Uboot and other things yourself, and the target operating environment does not have a complete (embedded Linux) system, then it will be even more impossible to achieve local compilation on the target platform.

You can still do it, as mentioned here, cross-compilation

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