I'm trying to write a method 'compile' that gets a string and a collection and see if the string matches the conditions.
the method signature is:
compile: stringCode where: argTypeCollection
example of use (assuming C is the class):
C compile:
'first: i second: any third: n
| local |
local := i + n.
^(local*local)'
where: #(Integer nil Number).
the first thing the method should do is analyze the string by check if the number of arguments is correct, I thought of doing so with regex.
I tried to look for regex use explanation here and here but the only example is for files and I didn't succeed to scan the string and count matches for [a-zA-z][a-zA-Z0-9]*: the same way.
any example of using regex on string in squeak will help.
When analyzing Smalltalk source code, the best option is to use the very same objects the Smalltalk compiler employs for parsing, compiling and evaluating methods and code snnipets. In other words, having the full range of compiling tools at your disposal it makes little sense to use regex for these kinds of tasks.
For instance, you can analyze the header of your method (i.e., the part of the source code defining the selector and formal arguments) using the Parser like this
Parser new parse: aString class: aClass
where aString is the method's source code and aClass is the target class, i.e., the class for which the method would make sense.
In your example the class is C. Note however that when the source code contains no reference to ivars (or for that matter class or shared variables) the argument aClass becomes irrelevant and can be replaced by Object.
The result of the parse:class: message, if the parsing succeeds, will be an Abstract Parse Tree (a.k.a. AST) whose nodes will bring more information useful for further analysis. If the parsing fails, you will get access to the parsing error object that will let you determine why the code is non-conformant with the Smalltalk syntax. As you can see, you will have everything you need to reflect on the source code under analysis.
Related
I am trying to find all places in a large and old code base where certain constructors or functions are called. Specifically, these are certain constructors and member functions in the std::string class (that is, basic_string<char>). For example, suppose there is a line of code:
std::string foo(fiddle->faddle(k, 9).snark);
In this example, it is not obvious looking at this that snark may be a char *, which is what I'm interested in.
Attempts To Solve This So Far
I've looked into some of the dump features of gcc, and generated some of them, but I haven't been able to find any that tell me that the given line of code will generate a call to the string constructor taking a const char *. I've also compiled some code with -s to save the generated equivalent assembly code. But this suffers from two things: the function names are "mangled," so it's impossible to know what is being called in C++ terms; and there are no line numbers of any sort, so even finding the equivalent place in the source file would be tough.
Motivation and Background
In my project, we're porting a large, old code base from HP-UX (and their aCC C++ compiler) to RedHat Linux and gcc/g++ v.4.8.5. The HP tool chain allowed one to initialize a string with a NULL pointer, treating it as an empty string. The Gnu tools' generated code fails with some flavor of a null dereference error. So we need to find all of the potential cases of this, and remedy them. (For example, by adding code to check for NULL and using a pointer to a "" string instead.)
So if anyone out there has had to deal with the base problem and can offer other suggestions, those, too, would be welcomed.
Have you considered using static analysis?
Clang has one called clang analyzer that is extensible.
You can write a custom plugin that checks for this particular behavior by implementing a clang ast visitor that looks for string variable declarations and checks for setting it to null.
There is a manual for that here.
See also: https://github.com/facebook/facebook-clang-plugins/blob/master/analyzer/DanglingDelegateFactFinder.cpp
First I'd create a header like this:
#include <string>
class dbg_string : public std::string {
public:
using std::string::string;
dbg_string(const char*) = delete;
};
#define string dbg_string
Then modify your makefile and add "-include dbg_string.h" to cflags to force include on each source file without modification.
You could also check how is NULL defined on your platform and add specific overload for it (eg. dbg_string(int)).
You can try CppDepend and its CQLinq a powerful code query language to detect where some contructors/methods/fields/types are used.
from m in Methods where m.IsUsing ("CClassView.CClassView()") select new { m, m.NbLinesOfCode }
This question already has answers here:
Listing Unused Symbols
(2 answers)
Closed 7 years ago.
How do I detect function definitions which are never getting called and delete them from the file and then save it?
Suppose I have only 1 CPP file as of now, which has a main() function and many other function definitions (function definition can also be inside main() ). If I were to write a program to parse this CPP file and check whether a function is getting called or not and delete if it is not getting called then what is(are) the way(s) to do it?
There are few ways that come to mind:
I would find out line numbers of beginning and end of main(). I can do it by maintaining a stack of opening and closing braces { and }.
Anything after main would be function definition. Then I can parse for function definitions. To do this I can parse it the following way:
< string >< open paren >< comma separated string(s) for arguments >< closing paren >
Once I have all the names of such functions as described in (2), I can make a map with its names as key and value as a bool, indicating whether a function is getting called once or not.
Finally parse the file once again to check for any calls for functions with their name as in this map. The function call can be from within main or from some other function. The value for the key (i.e. the function name) could be flagged according to whether a function is getting called or not.
I feel I have complicated my logic and it could be done in a smarter way. With the above logic it would be hard to find all the corner cases (there would be many). Also, there could be function pointers to make parsing logic difficult. If that's not enough, the function pointers could be typedefed too.
How do I go about designing my program? Are a map (to maintain filenames) and stack (to maintain braces) the right data structures or is there anything else more suitable to deal with it?
Note: I am not looking for any tool to do this. Nor do I want to use any library (if it exists to make things easy).
I think you should not try to build a C++ parser from scratch, becuse of other said in comments that is really hard. IMHO, you'd better start from CLang libraries, than can do the low-level parsing for you and work directly with the abstract syntax tree.
You could even use crange as an example of how to use them to produce a cross reference table.
Alternatively, you could directly use GNU global, because its gtags command directly generates definition and reference databases that you have to analyse.
IMHO those two ways would be simpler than creating a C++ parser from scratch.
The simplest approach for doing it yourself I can think of is:
Write a minimal parser that can identify functions. It just needs to detect the start and ending line of a function.
Programmatically comment out the first function, save to a temp file.
Try to compile the file by invoking the complier.
Check if there are compile errors, if yes, the function is called, if not, it is unused.
Continue with the next function.
This is a comment, rather than an answer, but I post it here because it's too long for a comment space.
There are lots of issues you should consider. First of all, you should not assume that main() is a first function in a source file.
Even if it is, there should be some functions header declarations before the main() so that the compiler can recognize their invocation in main.
Next, function's opening and closing brace needn't be in separate lines, they also needn't be the only characters in their lines. Generally, almost whole C++ code can be put in a single line!
Furthermore, functions can differ with parameters' types while having the same name (overloading), so you can't recognize which function is called if you don't parse the whole code down to the parameters' types. And even more: you will have to perform type lists matching with standard convertions/casts, possibly considering inline constructors calls. Of course you should not forget default parameters. Google for resolving overloaded function call, for example see an outline here
Additionally, there may be chains of unused functions. For example if a() calls b() and b() calls c() and d(), but a() itself is not called, then the whole four is unused, even though there exist 'calls' to b(), c() and d().
There is also a possibility that functions are called through a pointer, in which case you may be unable to find a call. Example:
int (*testfun)(int) = whattotest ? TestFun1 : TestFun2; // no call
int testResult = testfun(paramToTest); // unknown function called
Finally the code can be pretty obfuscated with #define–s.
Conclusion: you'll probably have to write your own C++ compiler (except the machine code generator) to achieve your goal.
This is a very rough idea and I doubt it's very efficient but maybe it can help you get started. First traverse the file once, picking out any function names (I'm not entirely sure how you would do this). But once you have those names, traverse the file again, looking for the function name anywhere in the file, inside main and other functions too. If you find more than 1 instance it means that the function is being called and should be kept.
I am currently writing a program that sits on top of a C++ interpreter. The user inputs C++ commands at runtime, which are then passed into the interpreter. For certain patterns, I want to replace the command given with a modified form, so that I can provide additional functionality.
I want to replace anything of the form
A->Draw(B1, B2)
with
MyFunc(A, B1, B2).
My first thought was regular expressions, but that would be rather error-prone, as any of A, B1, or B2 could be arbitrary C++ expressions. As these expressions could themselves contain quoted strings or parentheses, it would be quite difficult to match all cases with a regular expression. In addition, there may be multiple, nested forms of this expression
My next thought was to call clang as a subprocess, use "-dump-ast" to get the abstract syntax tree, modify that, then rebuild it into a command to be passed to the C++ interpreter. However, this would require keeping track of any environment changes, such as include files and forward declarations, in order to give clang enough information to parse the expression. As the interpreter does not expose this information, this seems infeasible as well.
The third thought was to use the C++ interpreter's own internal parsing to convert to an abstract syntax tree, then build from there. However, this interpreter does not expose the ast in any way that I was able to find.
Are there any suggestions as to how to proceed, either along one of the stated routes, or along a different route entirely?
What you want is a Program Transformation System.
These are tools that generally let you express changes to source code, written in source level patterns that essentially say:
if you see *this*, replace it by *that*
but operating on Abstract Syntax Trees so the matching and replacement process is
far more trustworthy than what you get with string hacking.
Such tools have to have parsers for the source language of interest.
The source language being C++ makes this fairly difficult.
Clang sort of qualifies; after all it can parse C++. OP objects
it cannot do so without all the environment context. To the extent
that OP is typing (well-formed) program fragments (statements, etc,.)
into the interpreter, Clang may [I don't have much experience with it
myself] have trouble getting focused on what the fragment is (statement? expression? declaration? ...). Finally, Clang isn't really a PTS; its tree modification procedures are not source-to-source transforms. That matters for convenience but might not stop OP from using it; surface syntax rewrite rule are convenient but you can always substitute procedural tree hacking with more effort. When there are more than a few rules, this starts to matter a lot.
GCC with Melt sort of qualifies in the same way that Clang does.
I'm under the impression that Melt makes GCC at best a bit less
intolerable for this kind of work. YMMV.
Our DMS Software Reengineering Toolkit with its full C++14 [EDIT July 2018: C++17] front end absolutely qualifies. DMS has been used to carry out massive transformations
on large scale C++ code bases.
DMS can parse arbitrary (well-formed) fragments of C++ without being told in advance what the syntax category is, and return an AST of the proper grammar nonterminal type, using its pattern-parsing machinery. [You may end up with multiple parses, e.g. ambiguities, that you'll have decide how to resolve, see Why can't C++ be parsed with a LR(1) parser? for more discussion] It can do this without resorting to "the environment" if you are willing to live without macro expansion while parsing, and insist the preprocessor directives (they get parsed too) are nicely structured with respect to the code fragment (#if foo{#endif not allowed) but that's unlikely a real problem for interactively entered code fragments.
DMS then offers a complete procedural AST library for manipulating the parsed trees (search, inspect, modify, build, replace) and can then regenerate surface source code from the modified tree, giving OP text
to feed to the interpreter.
Where it shines in this case is OP can likely write most of his modifications directly as source-to-source syntax rules. For his
example, he can provide DMS with a rewrite rule (untested but pretty close to right):
rule replace_Draw(A:primary,B1:expression,B2:expression):
primary->primary
"\A->Draw(\B1, \B2)" -- pattern
rewrites to
"MyFunc(\A, \B1, \B2)"; -- replacement
and DMS will take any parsed AST containing the left hand side "...Draw..." pattern and replace that subtree with the right hand side, after substituting the matches for A, B1 and B2. The quote marks are metaquotes and are used to distinguish C++ text from rule-syntax text; the backslash is a metaescape used inside metaquotes to name metavariables. For more details of what you can say in the rule syntax, see DMS Rewrite Rules.
If OP provides a set of such rules, DMS can be asked to apply the entire set.
So I think this would work just fine for OP. It is a rather heavyweight mechanism to "add" to the package he wants to provide to a 3rd party; DMS and its C++ front end are hardly "small" programs. But then modern machines have lots of resources so I think its a question of how badly does OP need to do this.
Try modify the headers to supress the method, then compiling you'll find the errors and will be able to replace all core.
As far as you have a C++ interpreter (as CERN's Root) I guess you must use the compiler to intercept all the Draw, an easy and clean way to do that is declare in the headers the Draw method as private, using some defines
class ItemWithDrawMehtod
{
....
public:
#ifdef CATCHTHEMETHOD
private:
#endif
void Draw(A,B);
#ifdef CATCHTHEMETHOD
public:
#endif
....
};
Then compile as:
gcc -DCATCHTHEMETHOD=1 yourfilein.cpp
In case, user want to input complex algorithms to the application, what I suggest is to integrate a scripting language to the app. So that the user can write code [function/algorithm in defined way] so the app can execute it in the interpreter and get the final results. Ex: Python, Perl, JS, etc.
Since you need C++ in the interpreter http://chaiscript.com/ would be a suggestion.
What happens when someone gets ahold of the Draw member function (auto draw = &A::Draw;) and then starts using draw? Presumably you'd want the same improved Draw-functionality to be called in this case too. Thus I think we can conclude that what you really want is to replace the Draw member function with a function of your own.
Since it seems you are not in a position to modify the class containing Draw directly, a solution could be to derive your own class from A and override Draw in there. Then your problem reduces to having your users use your new improved class.
You may again consider the problem of automatically translating uses of class A to your new derived class, but this still seems pretty difficult without the help of a full C++ implementation. Perhaps there is a way to hide the old definition of A and present your replacement under that name instead, via clever use of header files, but I cannot determine whether that's the case from what you've told us.
Another possibility might be to use some dynamic linker hackery using LD_PRELOAD to replace the function Draw that gets called at runtime.
There may be a way to accomplish this mostly with regular expressions.
Since anything that appears after Draw( is already formatted correctly as parameters, you don't need to fully parse them for the purpose you have outlined.
Fundamentally, the part that matters is the "SYMBOL->Draw("
SYMBOL could be any expression that resolves to an object that overloads -> or to a pointer of a type that implements Draw(...). If you reduce this to two cases, you can short-cut the parsing.
For the first case, a simple regular expression that searches for any valid C++ symbol, something similar to "[A-Za-z_][A-Za-z0-9_\.]", along with the literal expression "->Draw(". This will give you the portion that must be rewritten, since the code following this part is already formatted as valid C++ parameters.
The second case is for complex expressions that return an overloaded object or pointer. This requires a bit more effort, but a short parsing routine to walk backward through just a complex expression can be written surprisingly easily, since you don't have to support blocks (blocks in C++ cannot return objects, since lambda definitions do not call the lambda themselves, and actual nested code blocks {...} can't return anything directly inline that would apply here). Note that if the expression doesn't end in ) then it has to be a valid symbol in this context, so if you find a ) just match nested ) with ( and extract the symbol preceding the nested SYMBOL(...(...)...)->Draw() pattern. This may be possible with regular expressions, but should be fairly easy in normal code as well.
As soon as you have the symbol or expression, the replacement is trivial, going from
SYMBOL->Draw(...
to
YourFunction(SYMBOL, ...
without having to deal with the additional parameters to Draw().
As an added benefit, chained function calls are parsed for free with this model, since you can recursively iterate over the code such as
A->Draw(B...)->Draw(C...)
The first iteration identifies the first A->Draw( and rewrites the whole statement as
YourFunction(A, B...)->Draw(C...)
which then identifies the second ->Draw with an expression "YourFunction(A, ...)->" preceding it, and rewrites it as
YourFunction(YourFunction(A, B...), C...)
where B... and C... are well-formed C++ parameters, including nested calls.
Without knowing the C++ version that your interpreter supports, or the kind of code you will be rewriting, I really can't provide any sample code that is likely to be worthwhile.
One way is to load user code as a DLL, (something like plugins,)
this way, you don't need to compile your actual application, just the user code will be compiled, and you application will load it dynamically.
I need to parse a C++ class file (.h) and extract the following informations:
Function names
Return types
List of parameter types of each function
Assume that there is a special tag using which I can recognize if I need to parse a function or not.
For eg.
#include <someHeader>
class Test
{
public:
Test();
void fun1();
// *Expose* //
void fun2();
};
So I need to parse only fun2().
I read the basic grammar here, but found it too complex to comprehend.
Q1. I can't make out how complex this task is. Can someone provide a simpler grammar for a function declaration to perform this parsing?
Q2. Is my approach right or should I consider using some library rather than reinventing?
Edit: Just to clarify, I don't have problem parsing, problem is more of understanding the grammar I need to parse.
A C++ header may include arbitrary C++ code. Hence, parsing the header might be as hard as parsing all kinds of C++ code.
Your task becomes easier, if you can make certain assumptions about your header file. For instance, if you always have an EXPOSE-tag in front of your function and the functions are always on a single line, you could first grep for those lines:
grep -A1 EXPOSE <files>
And then you could apply a regular expression to filter out the information you need.
Nevertheless, I'd recommend using existing tools. This seems to be a tutorial on how to do it with clang and Python.
GCC XML is an open source tool that emits the AST (Abstract Syntax Tree). See this other answer where I posted about the usage I made of it.
You should consider to use only if you are proficient (or akin to learn) with an XML analyzer for inspecting the AST. It's a fairly complex structure...
You will need anyway to 'grep' for the comments identifying your required snippets, as comments are lost in output XML.
IF you are doing this just for documentation doxygen could be a good bet.
Either way it may give you some pointers as to how to do this.
It should turn this
int Yada (int yada)
{
return yada;
}
into this
int Yada (int yada)
{
SOME_HEIDEGGER_QUOTE;
return yada;
}
but for all (or at least a big bunch of) syntactically legal C/C++ - function and method constructs.
Maybe you've heard of some Perl library that will allow me to perform these kinds of operations in a view lines of code.
My goal is to add a tracer to an old, but big C++ project in order to be able to debug it without a debugger.
Try Aspect C++ (www.aspectc.org). You can define an Aspect that will pick up every method execution.
In fact, the quickstart has pretty much exactly what you are after defined as an example:
http://www.aspectc.org/fileadmin/documentation/ac-quickref.pdf
If you build using GCC and the -pg flag, GCC will automatically issue a call to the mcount() function at the start of every function. In this function you can then inspect the return address to figure out where you were called from. This approach is used by the linux kernel function tracer (CONFIG_FUNCTION_TRACER). Note that this function should be written in assembler, and be careful to preserve all registers!
Also, note that this should be passed only in the build phase, not link, or GCC will add in the profiling libraries that normally implement mcount.
I would suggest using the gcc flag "-finstrument-functions". Basically, it automatically calls a specific function ("__cyg_profile_func_enter") upon entry to each function, and another function is called ("__cyg_profile_func_exit") upon exit of the function. Each function is passed a pointer to the function being entered/exited, and the function which called that one.
You can turn instrumenting off on a per-function or per-file basis... see the docs for details.
The feature goes back at least as far as version 3.0.4 (from February 2002).
This is intended to support profiling, but it does not appear to have side effects like -pg does (which compiles code suitable for profiling).
This could work quite well for your problem (tracing execution of a large program), but, unfortunately, it isn't as general purpose as it would have been if you could specify a macro. On the plus side, you don't need to worry about remembering to add your new code into the beginning of all new functions that are written.
There is no such tool that I am aware of. In order to recognise the correct insertion point, the tool would have to include a complete C++ parser - regular expressions are not enough to accomplish this.
But as there are a number of FOSS C++ parsers out there, such a tool could certainly be written - a sort of intelligent sed for C++ code. The biggest problem would probably be designing the specification language for the insert/update/delete operation - regexes are obviously not the answer, though they should certainly be included in the language somehow.
People are always asking here for ideas for projects - how about this for one?
I use this regex,
"(?<=[\\s:~])(\\w+)\\s*\\([\\w\\s,<>\\[\\].=&':/*]*?\\)\\s*(const)?\\s*{"
to locate the functions and add extra lines of code.
With that regex I also get the function name (group 1) and the arguments (group 2).
Note: you must filter out names like, "while", "do", "for", "switch".
This can be easily done with a program transformation system.
The DMS Software Reengineering Toolkit is a general purpose program transformation system, and can be used with many languages (C#, COBOL, Java, EcmaScript, Fortran, ..) as well as specifically with C++.
DMS parses source code (using full langauge front end, in this case for C++),
builds Abstract Syntax Trees, and allows you to apply source-to-source patterns to transform your code from one C# program into another with whatever properties you wish. THe transformation rule to accomplish exactly the task you specified would be:
domain CSharp.
insert_trace():function->function
"\visibility \returntype \fnname(int \parametername)
{ \body } "
->
"\visibility \returntype \fnname(int \parametername)
{ Heidigger(\CppString\(\methodname\),
\CppString\(\parametername\),
\parametername);
\body } "
The quote marks (") are not C++ quote marks; rather, they are "domain quotes", and indicate that the content inside the quote marks is C++ syntax (because we said, "domain CSharp"). The \foo notations are meta syntax.
This rule matches the AST representing the function, and rewrites that AST into the traced form. The resulting AST is then prettyprinted back into source form, which you can compile. You probably need other rules to handle other combinations of arguments; in fact, you'd probably generalize the argument processing to produce (where practical) a string value for each scalar argument.
It should be clear you can do a lot more than just logging with this, and a lot more than just aspect-oriented programming, since you can express arbitrary transformations and not just before-after actions.