I try to understand this whole "compiling" topic in a way more detailed than all those "what is a compiler (doing)?" articles out there.
One big question to me is processor- and os-platform dependency when compiling directly to machine code (e.g. C). I try to formulate concrete questions that needs to be resolved in order to get my picture clearer:
I compile my C code via gcc on a Linux distribution... :
Can I run the resulting executable on any other Linux Distribution?
Is that executable bound the processor platform compiled on? Do I need to search for another e.g. power-pc gcc when I am running a x86 distro?
Can I somehow execute this on windows? I know executables differs but the binary code is the same, isn't it?
So in the end my questions aims on: Is compiling about targeting a specifiy OS paltform, processor platform or both?
Thanks!
Compiling targets both, OS, and Architecture.
The OS needs to be targeted because:
The format of what is an "executable" file is different among operating systems.
Programs call the operating system even for common tasks like writing to the console, reading from a file, or terminating cleanly (standards like POSIX mitigate OS dependencies by defining a common layer between the program and the OS).
The CPU architecture must be targeted because the CPU instructions are different, even among different generations of the "same architecture".
Can I run the resulting executable on any other Linux Distribution?
In general, Yes, but on specific cases it may depend on the type of program (f.i. GUI) and the services assumed available on the OS.
Is that executable bound the the processor platform compiled on? Do I need to search for another e.g. power-pc gcc when I am running a x86 distro?
I don't understand what you mean by "search", but, Yes, you can cross-compile from, say, x86 targeting PPC.
Can I somehow execute this on Windows? I know executables differ but the binary code is the same, isn't it?
These days Windows has Ubuntu integration, and that allows for some kind of exceptions, but the general answer is No, because of the above.
Related
I am currently taking a class on Assembly Language and Computer Architecture. We're programming in MASM for x86 processors. I have a Macbook Air, so of course I have to run Windows on a virtual machine to program in MASM for our assignments.
What I'm confused about: We're learning about, and programming for x86 architecture. When I looked up my Macbook Air's processor, it seemed to be in the x86 family. Considering that, why doesn't MASM work with Mac OS X?
Furthermore, if assembly language communicates directly w/ hardware, why does merely installing the Windows OS (or running it through a VM) on Apple Hardware suddenly allow me to program in MASM?
Thanks,
Ian
[EDIT for clarification: My understanding -- please tell me if i'm wrong -- is that Assembly Language is as "low as you can go." I.e. it's pre-operating system, and provides instructions directly to the hardware itself. Thus, I don't understand why an assembly language for x86 architecture doesn't work on ALL x86 machines, regardless of OS]
Programs are made up of more than just the raw machine code. The executable needs to have a special format that the OS can understand, so it can load and run the code. Also, the code expects a certain environment, such as libraries and system calls (along with the appropriate calling conventions).
To compile and run your assembly program you need to assemble it first, that is run it through MASM in this case. However, MASM itself is a windows executable. It is in the executable format for windows, and it uses libraries and operating system functions accordingly. As such, you can't run it directly on mac os. Afterwards, you typically also need to link your code, which has the same issues. The next problem is with the program itself. MASM (and the rest of the toolchain) is by default also targeting windows (or dos) and so the created program has the appropriate format.
You can theoretically create a program intended to run on mac os using windows and masm. This is called cross-compiling in general. If your toolchain does not support the required mac format, you will need to create everything by hand. You obviously also need to write your program such that it expects the mac environment. For example, you can't use dos interrupts or windows libraries.
Since the architecture is the same, you don't need to virtualize the cpu. You can get away with emulating just the environment. An example for this is the windows emulator, wine, or cygwin emulating unix on windows.
A very rough analogy: there are human languages that use the same alphabet, but you still need to translate. There are also languages that do not even use the same alphabet, or don't even have letters. You will need to do more work in these cases.
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 :-)
Since I have started to learn Golang since yesterday :) I have a question about the compiled file.
Let's assume that I compile my project. It generates an .exec file in /bin folder.
Now my question is Since the file has been compiled on Mac with Intel based CPU, should it be compiled on other OS and other CPU architectures such as AMD, ARM, etc. if I want to publish it to public?
I guess this should not be problem if I'm using GO lang for my backend since I run it on a server. However, what happens if I publish my .exec file, let's say on AWS, with lots of instances that they are automatically increases/decreases based on load? Does it problem?
Edit:
This is nice solution for those how are looking Go cross compiling tool https://github.com/mitchellh/gox
The answer to the first question is yes. The current implementations of Go produce a native binary, so you will probably need a different one for Linux x86 (32-bit), Linux x64 (64-bit), and Linux ARM. You will probably need a different one for Mac OS X also. You should be able to run the 32-bit executable on a 64-bit system as long as any libraries you depend on are available in 32-bit form on that system, so you might be able to skip making a 64-bit executable.
In the future, there may be other implementations of Go that compile for a virtual machine (such as JVM or .NET), in which case you wouldn't need to compile multiple versions for different architectures. Your question is more about existing Go implementations than the language itself.
I don't know anything about AWS, but I suggest you ask that as a separate question.
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.
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.