Is there a standard that defines the syntax and semantics of assembly language? Similarly as language C has ISO standard and language C# has ECMA standard? Is there only one standard, or are there more of them?
I'm asking because I noticed that assembly language code looked different on Windows and Linux environment. I hoped that assembly language is not dependent on OS, that it's only language with some defined standard and via assembler (compiler of assembly language) is translated into machine instructions for particular processor.
thank you for answer
Yes, there is a standard.
People that built assemblers even up til the 1980s chose an incredible variety of syntax schemes.
The IEEE community reacted with a standard to try to avoid that problem:
694-1985 - IEEE Standard for Microprocessor Assembly Language
As with many things in the software world, it was and continues to be largely ignored.
The closest thing to a standard is that the vendor that created the processor/instruction set will have a document describing that language and often that vendor will provide some sort of an assembler (program). Some vendors are more detail and standard oriented than others so you get what you get. Then things like this intel/at&t happen to mess things up. Add to that gnu assembler loves to mess up the assembly language for the chips it supports as well so in general you have chaos.
If there were an assembly language whose use were comparable to C or C++ then you would expect an organization to try to come up with a standard. Part of the problem would still be that with things like the C language there is an interpretation before it hits the hardware, with assembler there is none to very little so a chip vendor is going to make whatever they want to make due to market factors and the standard would have to be dragged along to match the hardware, instead of the other way around where a standard drives the vendors.
The opencore processor might be one that could be standards driven since it is not vendor specific, perhaps it is already.
With assembly assume that each version of each assembler program/software/tool has its own syntax rules within the same instruction set as well as across different instruction sets. (which is actually what you get with C/C++ but that is another topic) either choose your favorite tool and only know it, or try to memorize all the variations across all the tools, or my preference is to try to avoid as many tool specific syntax and nuances, and try to find the middle ground that works or at least has a chance to work or port across tools.
No, there is no standard.
There are even two different types of syntax: the intel-syntax which is predominant on Windows plattforms and the AT&T-sytanx which is dominant in the *nix-world.
Regarding the differently looking code in the wikipedia: the windows example uses the Win32API and the linux example uses a system call of the 0x80 interrupt.
Assembly languages differ from processor to processor so no, there is no standard.
In general, the "standard" assembly language for a particular family of processor is whatever the processor designers say it is. For example, the "standard" syntax for x86 is whatever Intel says it is. However, that doesn't prevent other people from creating a variant of the assembly language that targets the processor with slightly different syntax or additional features (Nasm is one example).
Well, I'm not sure if you are asking about syntax for x86 processors (I suppose yes, because you're mentioning NASM).
But there are two common standards:
Intel syntax that was originally used for documentation of the x86 platform
AT&T syntax which is common in Linux/Unix worlds.
NASM you have mentioned prefers the Intel syntax.
You can find some examples of the syntax differences in this article: http://www.ibm.com/developerworks/linux/library/l-gas-nasm/index.html.
There's none because there are many different CPUs with different instructions and other peculiarities and it's entirely up to their designer what syntax to use and how to name things. And there's little need to standardize that because assembly code is inherently unportable and needs to be rewritten for a different CPU anyway.
Assembly language is not OS-specific per se, it's CPU-specific, but for an assembly routine to access things that appear standard to you (e.g. some subroutine to print text in the console) OS-specific code is needed. For MSDOS you'd use BIOS and DOS interrupt service routines (invokable on the x86 CPU through int 13h, int 10h, int 21h, int 33h, etc instructions), for Windows you'd use Windows' (available through int 2eh and sysenter/syscall instructions), for Linux you'd use Linux' (e.g. int 80h). All of them are implemented differently in different OSes and expect different number and kinds of parameters and in different places (registers or memory). You can't standardize this part. The only thing you can do about it is build a compatibility/abstraction layer on top of the OS functionality so it looks the same from your assembly routines' point of view.
Assembly syntax / language depends on CPU rather then OS. For the x86 CPU family there are however two syntax's AT&T (used by Unix like operating systems by default) and Intel (used by Windows and DOS etc.)
However the two assembly examples on the wiki are both doing different things. The windows example uses the WIN32 API and to show a message box, so all function arguments are pushed onto the stack in reversed order and then calls the function MessageBox() which on his turn creates the messagebox.
The linux example uses the write syscall to write a string to stdout. Here all 'arguments' are stored in the registers and then the int 0x80 creates an 'interrupt' now the OS is entering kernel land and the kernel prints the string to stdout.
The linux assemly could be rewritten like:
section .data
msg: db "Hello, world!", 10
.len: equ $ - msg
section .text
extern write
extern exit
global _start
_start:
push msg.len
push msg
push dword 1
call write
push dword 0
call exit
The above assembly must be linked against libc and then this will call write in libc which on his turn executes exactly the same code as the example on the wiki.
Another thing to note, is that Windows and Unix like operating system use different file formats in there libraries and applications.
Unix like systems use ELF http://en.wikipedia.org/wiki/Executable_and_Linkable_Format and windows uses PE http://en.wikipedia.org/wiki/Portable_Executable
This is why you see different sections in the assemblies on the wiki page.
Related
I started to learn OpenCl.
I read these links:
https://en.wikipedia.org/wiki/OpenCL
https://github.com/KhronosGroup/OpenCL-Guide/blob/main/chapters/os_tooling.md
https://www.khronos.org/opencl/
but I did not understand well that OpenCl is a library by including header file in source code or it is a compiler by using OpenCl C Compiler?!
It is both a library and a compiler.
The OpenCL C/C++ bindings that you include as header files and that you link against are a library. These provide the necessary functions and commands in C/C++ to control the device (GPU).
For the device, you write OpenCL C code. This language is not C or C++, but rather based on C99 and has some specific limitations (for example only 1D arrays) as well as extensions (math and vector functionality).
The OpenCL compiler sits in between the C/C++ bindings and the OpenCL C part. Using the C/C++ bindings, you run the compiler at runtime of the executable with the command clBuildProgram (C bindings) or program.build(...) (C++). It then at runtime once compiles the OpenCL C code to the device-specific assembly, which is different for every vendor. With an Nvidia GPU, you can for example look at the Compiler PTX assembly for the device.
If you know OpenGL then OpenCL works on the same principle.
Disclaimer: Self-learned knowledge ahead. I wanted to learn OpenCL and found the OpenCL term as confusing as you do. So I did some painful research until I got my first OpenCL hello-world program working.
Overview
OpenCL is an open standard - i.e. just API specification which targets heterogeneous computing hardware in particular.
The standard comprises a set of documents available here. It is up to the manufacturers to implement the standard for their devices and make OpenCL available e.g. through GPU drivers to users. Perhaps in the form of a shared library.
It is also up to the manufacturers to provide tools for developer to make applications using OpenCL.
Here's where it gets complicated.
SDKs
Manufacturers provide SDKs - software packages that contain everything the said developer needs. (See the link above). But they are specific for each - e.g. NVIDIA SDK won't work without their gpu.
ICD Loader
Because of SDKs being tied to a signle vendor, the most portable(IMHO) solution is to use what is known as Khronos' ICD loader. It is kind of "meta-driver" that will, during run-time, search for other ICDs present in the system by AMD, Intel, NVIDIA, and others; then forward them calls from our application. So, as a developer, we can develop against this generic driver and use clGetPlatformIDs to fetch the available platforms and devices. It is availble as libOpenCL.so, at least on Linux, and we should link against it.
Counterpart for OpenGL's libOpenGL, well almost, because the vast majority of OpenGL(1.1+) is present in the form of extensions and must be loaded separately with e.g. GLAD. In that sense, GLAD is very similar to the ICD loader.
Again, it does not contain any actual "computing" code, only stub implementations of the API which forward everything to the chosen platform's ICD.
Headers
We are still missing the headers, thankfully Khronos organization releases C headers and also C++ bindings. But nothing is stopping you from writing them yourself based on the official API documents. It would just be really tedious and error-prone.
Here we can find yet another parallel with OpenGL because the headers are also just the consequence of the Standard and GLAD generates them directly from its XML version! How cool is that?!
Summary
To write a simple OpenCL application we need to:
Download an ICD from the device's manufactures - e.g. up-to-date GPU drivers is enough.
Download the headers and place them in some folder.
Download, build, and install an ICD loader. It will likely need the headers too.
Include the headers, use API in them, and link against the ICD loader.
For Debian, maybe Ubuntu and others there is a simpler approach:
Download the drivers... look for <vendor>-opencl-icd, the drivers on Linux are usually not as monolithic as on Windows and might span many packages.
Install ocl-icd-opencl-dev which contains C, C++ headers + the loader.
Use the headers and link the library.
Which programming languages provide the best support for self-modifying code?
In particular, since the program will need to make extensive use of self-modifying code, I am looking forward at the ability to remove from memory some parts of code, after they are no longer needed, thus freeing that memory. Also, it would be a plus if there was the ability to identify and index the routines (procedures, functions, etc) with some sort of serial number, so that they could be easily managed in the memory (deleted, cloned etc) at runtime.
Operating systems need to have some more-or-less "self-modifying code" in order to load programs and dynamic link libraries from storage into RAM and later free up that RAM for other things, do relocation fix-ups, etc.
My understanding is that currently the C programming language is by far the most popular language for writing an operating systems.
The OSDev.org wiki has many tips of writing a new custom operating system, including a brief discussion of languages suitable for writing an operating system -- C, Assembly language, Lisp, Forth, C++, C#, PL/1, etc.
Just-in-time (JIT) compilers also need to have some more-or-less "self-modifying code" to compile source text into native instructions and run them, then later free up that memory for the next hot-spot.
Perhaps you could find some OS project or JIT project and use their code with relatively little modification.
A few people, when they say they want "self-modifying code", really want a language that supports homoiconicity such Scheme or some other dialect of Lisp, Prolog, TCL, Curl, etc.
I would want to compile existing software into presentation that can later be run on different architectures (and OS).
For that I need a (byte)code that can be easily run/emulated on another arch/OS (LLVM IR? Some RISC assemby?)
Some random ideas:
Compiling into JVM bytecode and running with java. Too restricting? C-compilers available?
MS CIL. C-Compilers available?
LLVM? Can Intermediate representation be run later?
Compiling into RISC arch such as MMIX. What about system calls?
Then there is the system call mapping thing, but e.g. BSD have system call translation layers.
Are there any already working systems that compile C/C++ into something that can later be run with an interpreter on another architecture?
Edit
Could I compile existing unix software into not-so-lowlevel binary, which could be "emulated" more easily than running full x86 emulator? Something more like JVM than XEN HVM.
There are several C to JVM compilers listed on Wikipedia's JVM page. I've never tried any of them, but they sound like an interesting exercise to build.
Because of its close association with the Java language, the JVM performs the strict runtime checks mandated by the Java specification. That requires C to bytecode compilers to provide their own "lax machine abstraction", for instance producing compiled code that uses a Java array to represent main memory (so pointers can be compiled to integers), and linking the C library to a centralized Java class that emulates system calls. Most or all of the compilers listed below use a similar approach.
C compiled to LLVM bit code is not platform independent. Have a look at Google portable native client, they are trying to address that.
Adobe has alchemy which will let you compile C to flash.
There are C to Java or even JavaScript compilers. However, due to differences in memory management, they aren't very usable.
Web Assembly is trying to address that now by creating a standard bytecode format for the web, but unlike the JVM bytecode, Web Assembly is more low level, working at the abstraction level of C/C++, and not Java, so it's more like what's typically called an "assembly language", which is what C/C++ code is normally compiled to.
LLVM is not a good solution for this problem. As beautiful as LLVM IR is, it is by no means machine independent, nor was it intended to be. It is very easy, and indeed necessary in some languages, to generate target dependent LLVM IR: sizeof(void*), for example, will be 4 or 8 or whatever when compiled into IR.
LLVM also does nothing to provide OS independence.
One interesting possibility might be QEMU. You could compile a program for a particular architecture and then use QEMU user space emulation to run it on different architectures. Unfortunately, this might solve the target machine problem, but doesn't solve the OS problem: QEMU Linux user mode emulation only works on Linux systems.
JVM is probably your best bet for both target and OS independence if you want to distribute binaries.
As Ankur mentions, C++/CLI may be a solution. You can use Mono to run it on Linux, as long as it has no native bits. But unless you already have a code base you are trying to port at minimal cost, maybe using it would be counter productive. If it makes sense in your situation, you should go with Java or C#.
Most people who go with C++ do it for performance reasons, but unless you play with very low level stuff, you'll be done coding earlier in a higher level language. This in turn gives you the time to optimize so that by the time you would have been done in C++, you'll have an even faster version in whatever higher level language you choose to use.
The real problem is that C and C++ are not architecture independent languages. You can write things that are reasonably portable in them, but the compiler also hardcodes aspects of the machine via your code. Think about, for example, sizeof(long). Also, as Richard mentions, there's no OS independence. So unless the libraries you use happen to have the same conventions and exist on multiple platforms then it you wouldn't be able to run the application.
Your best bet would be to write your code in a more portable language, or provide binaries for the platforms you care about.
I am looking for a JIT compiler or a small compiler library that can be embedded in my program. I indent to use it to compile dynamically generated code that perform complex number arithmetics. The generated code are very simple in structure: no loops, no conditionals, but they can be quite long (a few MB when compiled by GCC). The performance of the resulting machine code is important, while I don't really care about the speed of compilation itself. Which JIT compiler is best for my purpose? Thanks!
Detailed requirements
Support double precision complex number arithmetics
Support basic optimization
Support many CPUs (x86 and x86-64 at least)
Make use of SSE on supported CPUs
Support stack or a large set of registers for local variables
ANSI-C or C++ interface
Cross platform (mainly Linux, Unix)
You might want to take a look at LLVM.
Cint is a c++(ish) environment that offers the ability to mix compiled code and interpreted code. There is a set of optimization tools for the interpreter. ROOT extends this even further by supporting compile and link at run-time at run-time (see the last section of http://root.cern.ch/drupal/content/cint-prompt), though it appears to use the system compiler and thus may not help. All the code is open source.
I make regular use of all these features as part of my work.
I don't know if it makes active use of SIMD instructions, but it seems to meet all your other requirements.
As I see that you are currently using the compile to dynamic library at link on the fly methond, you might consider TCC, though I don't believe that it does much optimization and suspect that it does not support SIMD.
Sounds like you want to be able to compile on the fly and then dynamically load the compiled library (.DLL or .so). This would give you the best performance, with an ANSI-C or C++ interface. So, forget about JITing and consider spawning a C/C++ compiler to do the compilation.
This of course assumes that a compiler can be installed at the point where the dynamically generated code is actually generated.
The article Porting Qt for Embedded Linux to Another Operating System lists five things you have to do to port Qt for Embedded Linux to another OS. From the article:
There are several issues to be aware of if you plan to do your own port to another operating system. In particular you must resolve Qt for Embedded Linux's shared memory and semaphores (used to share window regions), and you must provide something similar to Unix-domain sockets for inter-application communication. You must also provide a screen driver, and if you want to implement sound you must provide your own sound server. Finally you must modify the event dispatcher used by Qt for Embedded Linux.
Is it really this easy to port Qt to another OS, or have i missed some information?
Another important component to port would be QAtomic, to ensure that you can have atomic operations and implicit sharing working well. See also
http://labs.trolltech.com/blogs/2007/08/28/say-hello-to-qatomicint-and-qatomicpointer/
Since Qt has been ported a large number of times it seems logical that it would be inherently simple. However the issue really is on the platform you are porting to and how many features it currently supports.
Assuming you find all those things easy, then the port is easy.
After investigating this in more detail I have come to the conclusion that the article "Porting Qt for Embedded Linux to Another Operating System" assumes that you are porting Qt to a very "linux-like" OS.
I have attempted this and currently making progress.
Some difficulties:
IDE - I have to manually add all Qt files and fight the compiler with #ifdefs until it builds with all dependencies in place.
Linux(ness) - I've had to disable all Linux/Windows things that are not supported in my target OS: threads, sockets, processes. Even the timers are slightly different.
Tips:
Start small : I compiled QtCore as a standard lib within my IDE, next up is QtGui which is a behemoth compared to QtCore.
I plan to run only a single QThread, so I have to artificially made a Thread object to avoid null pointers. You cannot compile out Thread information as it is key to all QObjects.
So far I have an qeventloop running within a qcoreapplication.
I wrote some inline assembly but had serious difficulties with my IDE and compilation. I left it in C++ and let the assembler handle it for me. Because I am single-threaded, I am not too concerned with shared data/ exclusive access as required by the atomic operations.