I'm trying to understand about UVM automation macro.
among other things, i found some sentence "UVM system Verilog call library also includes macros that automatically implement the print, copy, clone, compare, pack and unpack methods and more" from text.
and I found that lots of example used with the following usage.
For example,
....
uvm_object_utils_begin(apb_transfer)
'uvm_field_int(addr, UVM_DEFAULT)
'uvm_field_int(data, UVM_DEFAULT)
...
uvm_object_utils_end
but I didn't get it. that usage of 'uvm_field_int() is just defining the variable not copy, clone, compare....
How do I understand what uvm automation macro to do?
even I also curious about why those things are named as a automation? I can't find any something auto kind of thing.
As you say, the UVM field automation macros generate a number of class utility methods such as copy, print and clone that include the registered fields. That's it. I guess the name "automation" is used, because they automatically write code so you don't have to.
My company (Doulos) recommends you don't use these macros useless you know what you're doing. This is because they can be hard to debug, can generate more code than you need and have a strange side effect (values can be read from the configuration database automatically without your knowledge). Of course, the advantage of using them is that you get a whole bunch of code for free - the copy, compare,, print methods etc.
The HTML documentation supplied with a UVM download is very good. Search for `uvm_object_utils and follow your nose.
I often spend lots of time trying to find out where the exact implementation is located. It gets very frustrating when dealing with some low-level code that might end up somewhere in kernel.
I usually just google or try to guess the location and/or method names, but it is not always very effective.
Is there some methodical way to trace the flow up to the implementation? How do you guys usually do it?
Load the whole the code with relevant dependencies to a graphical IDE (NetBeans can do it, for instance) which can to call graph, declaration-definition jumps, etc. or use LibClang and its wrapper for the text editor of your choice, it is also very good at indexing. At last, you can consider classics, ctags, which can link definition and declaration points.
There used to be a ctrace program that did just that but I don't think it is actively maintained.
Ultimately, it depends what exactly you are trying to achieve. It actually looks like you want to look up a specific function rather than trace it. If that is the case indeed, consider using some kind of source browser: from etags to cscope to OpenGrok.
How can I get the abstract syntax tree of a c program in gcc?
I'm trying to automatically insert OpenMP pragmas to the input c program.
I need to analyze nested for loops for finding dependencies so that I can insert appropriate OpenMP pragmas.
So basically what I want to do is traverse and analyze the abstract syntax tree of the input c program.
How do I achieve this?
You need full dataflow to find 'dependencies'. Then you will need to actually insert the OpenMP calls.
What you want is a program transformation system. GCC probably has the dependency information, but it is famously difficult to work with for custom projects. Others have mentioned Clang and Rose. Clang might be a decent choice, but custom analysis/transformation isn't its main purpose. Rose is designed to support custom tools, but IMHO is a rather complicated scheme to use in practice because of its use of the EDG front end, which isn't designed to support transformation.
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Our DMS Software Reengineering Toolkit with its C front end is explicitly designed to be a program transformation system. It has full data flow analysis (including points-to analysis, call graph construction and range analyses) tied to the AST in sensible ways. It provides source-to-source rewrite rules enabling changes to the ASTs expressed in surface syntax form; you can read the transformations rather than inspect a bunch of procedural code. With a modified AST, DMS can regenerate source code including the comments in a compilable form.
Not exactly an AST but GCCXML might help http://linux.die.net/man/1/gccxml
edit : as stated by Ira Baxter gccxml does not output information about function/methods bodies. Here's a fork that seems to fix that lack http://sourceforge.net/projects/gccxml-bodies/
I have been doing OOP (C++/Java/PHP/Ruby) for a long time and really have a hard time imagining how large programs and libraries such as Linux or Apache can be written entirely in an imperative style. What would be small open source C projects I could look at to get a feel of how things are done in C?
Bonus points if the project is hosted on GitHub.
Things are done exactly the same way in C, but with less overt support from the language. Instead of creating a class to encapsulate some state, you create a struct. Instead of creating class members, with implicit this parameters, you create functions that you explicitly pass a struct* as the first parameter, that then operate on the struct.
To ensure that encapsulation is not broken you can declare the struct in a header, but only define it in the .c file where it is used. Virtual functions require more work - but again, its just a case of putting function pointers in the struct. Which is actually more convenient in C than C++ because in C you get to fill in your vtables manually, getting quite a fine level of control over which part of code implements part of what COM interface (if you are into COM in C of course).
You might find the ccan (Comprehensive C Archive Network, modeled after Perl's CPAN) interesting.
It's small at the moment, but the contributions are of high quality. Many of the contributions are by linux kernel developers.
Almost everything in there falls into the "few thousand LOC" or less category, too.
If you want a small example to start with, try looking at the source for the basic Linux CLI utilities. GNU binutils, make, or any of the other GNU utilities have full source code available and are relatively small code bases (some are larger than others). The easiest thing is usually to start with a utility that you have used before and are already familiar with.
Look at GLib for an almost canonical example of how to do object oriented programming in C.
I've heard that there are some things one cannot do as a computer programmer, but I don't know what they are. One thing that occurred to me recently was: wouldn't it be nice to have a class that could make a copy of the source of the program it runs, modify that program and add a method to the class that it is, and then run the copy of the program and terminate itself. Is it possible for code to write code?
If you want to learn about the limits of computability, read about the halting problem
In computability theory, the halting
problem is a decision problem which
can be stated as follows: given a
description of a program and a finite
input, decide whether the program
finishes running or will run forever,
given that input.
Alan Turing proved in 1936 that a
general algorithm to solve the halting problem for all
possible program-input pairs cannot exist
Start by looking at quines, then at Macro-Assemblers and then lex & yacc, and flex & bison. Then consider self-modifying code.
Here's a quine (formatted, use the output as the new input):
#include<stdio.h>
main()
{
char *a = "main(){char *a = %c%s%c; int b = '%c'; printf(a,b,a,b,b);}";
int b = '"';
printf(a,b,a,b,b);
}
Now if you're just looking for things programmers can't do look for the opposite of np-complete.
Sure it is. That's how a lot of viruses work!
Get your head around this: computability theory.
Yes, that's what most Lisp macros do (for just one example).
Yes it certainly is, though maybe not in the context you are referring to check out this post on t4.
If you look at Functional Programming that has many opportunities to write code that generates further code, the way that a language like Lisp doesn't differentiate between code and data is a significant part of it's power.
Rails generates the various default model and controller classes from the database schema when it's creating a new application. It's quite standard to do this kind of thing with dynamic languages- I have a few bits of PHP around that generate php files, just because it was the simplest solution to the problem I was dealing with at the time.
So it is possible. As for the question you are asking, though- that is perhaps a little vague- what environment and language are you using? What do you expect the code to do and why does it need to be added to? A concrete example may bring more directly relevant responses.
Yes it is possible to create code generators.
Most of the time they take user input and produce valid code. But there are other possibilities.
Self modifying programes are also possible. But they were more common in the dos era.
Of course you can! In fact, if you use a dynamic language, the class can change itself (or another class) while the program is still running. It can even create new classes that didn't exist before. This is called metaprogramming, and it lets your code become very flexible.
You are confusing/conflating two meanings of the word "write". One meaning is the physical writing of bytes to a medium, and the other is designing software. Of course you can have the program do the former, if it was designed to do so.
The only way for a program to do something that the programmer did not explicitly intend it to do, is to behave like a living creature: mutate (incorporate in itself bits of environment), and replicate different mutants at different rates (to avoid complete extinction, if a mutation is terminal).
Sure it is. I wrote an effect for Paint.NET* that gives you an editor and allows you to write a graphical effect "on the fly". When you pause typing it compiles it to a dll, loads it and executes it. Now, in the editor, you only need to write the actual render function, everything else necessary to create a dll is written by the editor and sent to the C# compiler.
You can download it free here: http://www.boltbait.com/pdn/codelab/
In fact, there is even an option to see all the code that was written for you before it is sent to the compiler. The help file (linked above) talks all about it.
The source code is available to download from that page as well.
*Paint.NET is a free image editor that you can download here: http://getpaint.net
In relation to artificial intelligence, take a look at Evolutionary algorithms.
make a copy of the source of the program it runs, modify that program and add a method to the class that it is, and then run the copy of the program and terminate itself
You can also generate code, build it into a library instead of an executable, and then dynamically load the library without even exiting the program that is currently running.
Dynamic languages usually don't work quite as you suggest, in that they don't have a completely separate compilation step. It isn't necessary for a program to modify its own source code, recompile, and start from scratch. Typically the new functionality is compiled and linked in on the fly.
Common Lisp is a very good language to practice this in, but there are others where you can created code and run it then and there. Typically, this will be through a function called "eval" or something similar. Perl has an "eval" function, and it's generally common for scripting languages to have the ability.
There are a lot of programs that write other programs, such as yacc or bison, but they don't have the same dynamic quality you seem to be looking for.
Take a look at Langtom's loop. This is the simplest example of self-reproducing "program".
There is a whole class of such things called "Code Generators". (Although, a compiler also fits the description as you set it). And those describe the two areas of these beasts.
Most code generates, take some form of user input (most take a Database schema) and product source code which is then compiled.
More advanced ones can output executable code. With .NET, there's a whole namespace (System.CodeDom) dedicated to the create of executable code. The these objects, you can take C# (or another language) code, compile it, and link it into your currently running program.
I do this in PHP.
To persist settings for a class, I keep a local variable called $data. $data is just a dictionary/hashtable/assoc-array (depending on where you come from).
When you load the class, it includes a php file which basically defines data. When I save the class, it writes the PHP out for each value of data. It's a slow write process (and there are currently some concurrency issues) but it's faster than light to read. So much faster (and lighter) than using a database.
Something like this wouldn't work for all languages. It works for me in PHP because PHP is very much on-the-fly.
It has always been possible to write code generators. With XML technology, the use of code generators can be an essential tool. Suppose you work for a company that has to deal with XML files from other companies. It is relatively straightforward to write a program that uses the XML parser to parse the new XML file and write another program that has all the callback functions set up to read XML files of that format. You would still have to edit the new program to make it specific to your needs, but the development time when a new XML file (new structure, new names) is cut down a lot by using this type of code generator. In my opinion, this is part of the strength of XML technology.
Lisp lisp lisp lisp :p
Joking, if you want code that generates code to run and you got time to loose learning it and breaking your mind with recursive stuff generating more code, try to learn lisp :)
(eval '(or true false))
wouldn't it be nice to have a class that could make a copy of the source of the program it runs, modify that program and add a method to the class that it is, and then run the copy of the program and terminate itself
There are almost no cases where that would solve a problem that cannot be solved "better" using non-self-modifying code..
That said, there are some very common (useful) cases of code writing other code.. The most obvious being any server-side web-application, which generates HTML/Javascript (well, HTML is markup, but it's identical in theory). Also any script that alters a terminals environment usually outputs a shell script that is eval'd by the parent shell. wxGlade generates code to that creates bare-bone wx-based GUIs.
See our DMS Software Reengineering Toolkit. This is general purpose machinery to read and modify programs, or generate programs by assembling fragments.
This is one of the fundamental questions of Artificial Intelligence. Personally I hope it is not possible - otherwise soon I'll be out of a job!!! :)
It is called meta-programming and is both a nice way of writing useful programs, and an interesting research topic. Jacques Pitrat's Artificial Beings: the conscience of a conscious machine book should interest you a lot. It is mostly related to meta-knowledge based computer programs.
Another related term is multi-staged programming (because there are several stages of programs, each generating the next one).