what is cross compilation?
Cross-compilation is the act of compiling code for one computer system (often known as the target) on a different system, called the host.
It's a very useful technique, for instance when the target system is too small to host the compiler and all relevant files.
Common examples include many embedded systems, but also typical game consoles.
A cross-compiler is compiles the source code from one architecture to another architecture.
For example: hello.c
gcc hello.c (gcc is a compiler for x86 architecture.)
arm-cortexa8-linux-gnueabihf-gcc hello.c
(arm-....-gcc is a compiler for the arm architecture.) This you are compiling on the host pc for a target board (e.g rpi, beaglebone, wega board). In this example arm-cortexa8-linux-gnueabihf-gcc is called the 'cross compiler'.
This process is called cross compilation.
see the link for more info cross compilation
To "cross compile" is to compile source on say a Linux box with intent on running it on a MAC or Windows box. This is usually done using a cross compilation plugin, which are readily available from various web servers across the net. If one is to install a cross compilation plugin onto their Linux box that is designed to compile for Windows boxes. Then they may compile for either a Linux/*NIX box as well as have the option to compile and link a Windows-ready executable. This is extremely convenient for a freelance programmer whom has access to no more than a single Linux/Windows/MAC box. Note that various cross compilation plugins will allow for multitudes of applications, some of which you may or may not perceive as useful, thus a thorough perusal of the plugin's README file.
Did you have a particular project in mind that you would like to apply the method of cross compilation to?
In a strict sense, it is the compilation of code on one host that is intended to run on another.
Most commonly it is used with reference to compilation for architectures that are not binary-compatible with the host -- for instance, building RISC binaries on a CISC CPU platform, or 64-bit binaries on a 32-bit system. Or, for example, building firmware intended to run on embedded devices (perhaps using the ARM CPU architecture) on Intel PC-based OSs.
A Cross Compiler is a compiler capable of creating executable code for a platform other than the one on which the compiler is running.
For e.g. a compiler that runs on a Windows 7 PC but generates code that runs on Android smartphone is a cross compiler.
A cross compiler is necessary to compile for multiple platforms from one machine.
A platform could be infeasible for a compiler to run on, such as for the microcontroller of an embedded system because those systems contain no operating system.
In paravirtualization one machine runs many operating systems, and a cross compiler could generate an executable for each of them from one main source.
Related
I'm seeing a lot of conflict information and would like some clarification.
build, host and target
There are three system names that the build knows about: the machine you are building on (build), the machine that you are building for (host), and the machine that GCC will produce code for (target). When you configure GCC, you specify these with --build=, --host=, and --target=.
Actually, I don't understand what the difference between host and target in the above definition.
Some other page says
‘host’ is the machine (or architecture, or platform) that you are using to compile the code;
‘target’ is the machine (or architecture, or platform) that is intended to run the code.
This makes sense to me, but in this explanation, is the host always the same as the build ?? I'm pretty confused.
In my case, I am configuring such that
the compiler (GCC) runs on x86_64 machine and the binary executable runs on ARM. The program is written in C, so the compiler is GCC.
./configure --build=x86_64 --host=x86_64 --target=arm-linux-gnueabihf
make
make install
It sounds like
build, host are both x86_64 and target is arm. Is that correct?
I am compiling my own embedded program that runs on Jenkins machine (x86_64). And the embedded program runs on ARM based machine.
Lets say I have a PowerPC machine making a compiler that you will use (run) on an x86 machine that will make binaries that run on an ARM.
That makes the PPC the build, the x86 the host, and the target is the ARM. As Basile commented, this is a Canadian-cross.
It's less common to have a build and host that are different, but it certainly does happen. Sometimes the build and host are even the same architecture, but there's something different about the environments that cause this. Making a custom toolchain on my x86 will mean that build and host are x86, but the host may have different libraries, or versions of dependencies, than the build. This is the case when building sand-boxed toolchains for embedded development that run on a build server, for example.
"There are three system names that the build knows about: the machine you are building on (build), the machine that you are building for (host), and the machine that GCC will produce code for (target). When you configure GCC, you specify these with --build=, --host=, and --target="
...
If build, host, and target are all the same, this is called a native.
If build and host are the same but target is different, this is called a cross.
If build, host, and target are all different this is called a canadian (for obscure reasons dealing with Canada’s political party and the background of the person working on the build at that time).
If host and target are the same, but build is different, you are using a cross-compiler to build a native for a different system.
Some people call this a host-x-host, crossed native, or cross-built native.
If build and target are the same, but host is different, you are using a cross compiler to build a cross compiler that produces code for the machine you’re building on.
This is rare, so there is no common way of describing it. There is a proposal to call this a crossback.
Source: https://gcc.gnu.org/onlinedocs/gccint/Configure-Terms.html
Someone already gave an example of the 'Canadian'.
An example of a cross-compilation is that when building sox from source (the Linux sound library) you need to provide 32-bit binaries for the codecs etc. I just came across this situation on a 64-bit machine, and I want to build it for my own use, which means in this case:
The build is the host (my machine)
The target is a 32-bit system
This is my understanding anyway, I agree this can be a bit confusingly explained, hope this helps :-)
I am very new to linux and GCC. The price of raspberry pi lured me in. I am interested in using GCC to cross compile some C Code to target some embedded hardware, specifically a Cortex-M3 micro. I eventually want to have a full suite of compiler/programmer/debugger, but for now I'm starting with compiler.
So I did a quick non-cross compile test on the RP3, and all was well. Now I am researching how to cross compile and target my uc. The gcc documentation online seems to indicate that I can use the plain vanilla gcc, and just specify some command line options to perform cross compilation: https://gcc.gnu.org/onlinedocs/gcc/ARM-Options.html
But searching around, I find a lot of people mentioning building a gcc cross compiler. What does this mean?
Does gcc have options to double as a cross compiler? If so, why would one desire "building" a cross compiler?
A cross-compiler is one that is created on machine type A (combination of hardware and o/s) and either runs on a different machine type B or runs on type A but produces software to be run on a different machine type B.
Thus, if you have a Linux machine using an x86_64 CPU and running on some version of Linux, but you compile GCC so that it will run on an IBM PowerPC platform running some version of AIX, you would be creating a cross-compiler.
Another variant might be having a compiler on Linux using an x86_64 CPU that runs on the Linux machine but produces code for an embedded hardware chip. You'd then benefit from the CPU power of the Linux machine while deploying to a much smaller, less powerful system that maybe has no o/s of its own, or only a minimal o/s.
I have an embedded system on a portable ARM device, and it runs a customized Linux. How can I build a native compiler for that Linux distro?
For example, I am now using machine A, and on A, I have both native compiler, and a cross-compiler for machine B. How can I build a compiler that can run directly on B?
I searched a bit, but only to find some tutorials of how to build cross compiler for B, but did not find how to build a native compiler through a cross compiler.
I'm not sure the marked answer is correct. I'm working on a project that mirrors the one in the original question and according to the link that n.m. posted, the original asker is attempting is called one of three things: a host-x-host, crossed native, or cross-built native...NOT a Canadian-Cross.
Unfortunately there does not seem to be any tutorials on this subject...at least none that I could find.
As I understand your question, you have fast non-ARM host and slow ARM. You want to build a compiler on your fast host; and compiler will be used on ARM system to compile code to ARM machine.
This setup is almost classic Canadian Cross:
Given three machines A, B, and C, one uses machine A (e.g. running Windows XP on an IA-32 processor) to build a cross compiler that runs on machine B (e.g. running Mac OS X on an x86-64 processor) to create executables for machine C (e.g. running Android on an ARM processor).
You have B=C and can use Canadian Cross build systems.
Unfortunately, this type of cross compilers are the hardest one. There are some manual to build such Cross: http://airs.com/ian/configure/configure_6.html ... or try to google "canadian cross gcc".
There are also some scripts to build embedded systems based on Linux. Will try to search some and add them here:
http://crosstool-ng.org/ (toolchain building with some canadian support)
Is it possible for gcc, installed on fedora 16, to cross compile for a different CPU, say SPARC?
I have build a certain understanding, need some expert to correct me if I am wrong. Different operating systems differ by the system calls they use to access the kernel or entirely by the kernel they use. IS THIS CORRECT? different kernels understands different systems calls for accessing underlying hardware. binaries or executables or programs are nothing but a bunch of system calls only. therefore every OS has its own executable. an executable meant to run to on windows wound not run on linux. by cross compiling the source code of any windown's executable we can generate executable for other OSs. word PLATFORM means operating system. POSIX are certain design standards for UNIX-like OSs.
we usually cross compile for different OSs. BUT can we cross compile for different hardware too? for example, in case of a microcontroller which does not have an OS?
No. You can't use native machine (x86) gcc for compiling program files for a different architecture. For that you require a cross-compiler-gcc that is specific to that processor architecture.
Your understanding about system calls for OS is correct. Each OS has its own set of system call which is been used by library. These libraries at the end will be translated into machine language for the processor.
Each Processor Architecture has its own set of instruction know as Instruction Set Architecture(ISA). So when a program written in high-level-language (like C) is compiled, it should be converted into machine language from its ISA. This job is done by the compiler(gcc). A compiler will be specific to only one processor architecture. For example gcc is for x86 processor. So if you want a compiler for different processor in you x86 machine you should go for a cross-compiler of that processor.
You would have to build such a version. That's part of the process of porting gcc to a new platform. You build a version that cross-compiles, then you cross-compile that version, then you test that version on the new platform, debug, rinse, and repeat.
I wish to build a compiler (GCC port) for Linux, so that the built GCC runs on Windows and creates executables for an embedded platform.
Is the above possible?
Yes, it is possible.
It also utterly painful to try to do this yourself -- it is OK on Linux, mostly, but very tricky on Windows. My suggestion is to see if some ready-built compiler from a place like DENX.de, CodeSourcery, or the manufacturer of your embedded platform is available.
I have become a huge fan of the CodeSourcery compilers for platforms like MIPS and Power Architecture. They tend to come with variants for big- and little-endian, various Libc flavors, and to have both bare-metal and linux-target versions available. See their pages about their Lite edition
Building your own cross-compiler and toolset is a right pain.
If your target is running Linux, I suggest doing your cross-work on a Linux box as well, saving you plenty of pain. I use VmWare for that express purpose. You cannot expect to build a Linux for a target on Windows, for example.
In embedded systems compilers are referred based on processor architecture and not on OS. What you probably want is to build a "cross compiler" for a processor other than the one running in your Windows machine. This is of course possible. See for example the WinAVR and WinARM projects. These are compilers for AVR and ARM processor architectures, based on GCC and running in Windows machines. Another example is yagarto. These aren't just a compiler, but a full tool chain that will allow you to built Linux executables (for ARM processors), if the requires libraries are available.
Because GCC relies on POSIX functionality that is not available in Windows natively, you need a Linux-like environment for Windows (such as Cygwin or MinGW).
http://cegcc.sourceforge.net
If you are satisfied to running it on Windows then at www.gnupit.org you can donwload ready GCC cross toolchain for free. There are many target platforms.
You have to build GCC on Windows using MinGW or Cygwin for your target platform (e.g. ARM little endian).