I'm writing a DSL front end using ANTLR v4 that I'd like to bolt on to GCC framework. The goal is to have a C language AST to leverage the rest of the GCC framework.
I haven't found any info or preexisting work to use an example of how to proceed. What I'm looking for is how to move the ANTLR 4 AST to GCC Generic/GIMBLE.
ANTLR 4 does not support a C language target, so I'll have to cludge up the C++ target to the GCC C language framework.
Help is appreciated
Gluing a C++ implementation of ANTLR into GCC so that GCC will call it is likely to be the easy step.
[Don't expect to be easy; GCC wants to be GCC, not your pet. You might get some help from GCC Melt, a package for interfacing to GCC machinery.]
The AST produced for an arbitrary (e.g., your custom DSL) language doesn't "just move (easily)" to a C AST or to the GCC Gimple (not GIMBLE) framework.
You will have to build, in essence, your DSL-AST to C-AST translator, or your DSL-AST to Gimple translator. There is no a priori reason to believe that building such a translator is easy; for example, you didn't tell us your DSL was "just like C except ...". So, you're going to have to build a translator. In the absence of evidence this is easy, you'll have to translate your DSL concepts to C concepts. The better ("non C-like") your DSL is, the harder this is going to be.
This SO link discusses the issues behind translation in more detail: What kinds of patterns could I enforce on the code to make it easier to translate to another programming language?
Related
If I have such a structure：
struct test{
float c,
f,
ops;
};
How can I modify the GCC compiler source code to make it as follows：
struct test{
double c,
f,
ops;
};
I now have such a requirement, I need to modify the gcc source code so that when he compiles a structure of a certain mode, he changes its type to a specified type.
Thank you！
your goal is very ambitious!
A possible approach could be to develop your own GCC plugin doing that job.
My recommendations:
budget several months of your time for that work (and perhaps several years) - at least 6 months full time to get a "proof of concept" thing which would fail on most code bases (in C). For C++, add another full year.
read carefully the C11 standard n1570 (if you target C), and the C++11 standard n3337 (if you target C++). That effort alone may take you a full month.
make your plugin open source software, and put its code quickly (e.g. under LGPL license) on some repository such as github or gitlab.
target the latest available version of GCC. In September 2020, that means GCC 10. Plugins and GCC APIs are changing incompatibly from one version to the next. If you need to stick to GCC 8 specifically, be prepared to spend a big amount of money for companies like AdaCore.
read carefully the documentation on GCC internals. You need to understand the GENERIC representation.
study very carefully the gcc/tree.def and gcc/treestruct.def and gcc/gimple.def files of GCC source code. You need to basically understand every line in them.
study very carefully the gcc/passes.def file of GCC source code. Again, you need to understand every line in that file.
learn to compile GCC from its source code. You certainly want to build it with g++ -Wall -Wextra -g -O1
read this draft report.
ask help in written English on the gcc#gcc.gnu.org mailing list, but have some working plugin before.
consider making a PhD out of this work. It is worth one. Alexandre Lissy in France got a PhD on a very similar topic.
If your code base is in C, consider using Frama-C (or Clang) and design your tool as a C to C transpiler.
Perhaps clever preprocessor tricks like #define float double followed by #undef float might be enough.
I'm trying to locate where __builtin_va_start is defined in GCC's source code, and see how it is implemented. (I was looking for where va_start is defined and then found that this macro is defined as __builtin_va_start.) I used cscope -r in GCC 9.1's source code directory to search the definition but haven't found it. Can anyone point where this function is defined?
That __builtin_va_start is not defined anywhere. It is a GCC compiler builtin (a bit like sizeof is a compile-time operator). It is an implementation detail related to the <stdarg.h> standard header (provided by the compiler, not the C standard library implementation libc). What really matters are the calling conventions and ABI followed by the generated assembler.
GCC has special code to deal with compiler builtins. And that code is not defining the builtin, but implementing its ad-hoc behavior inside the compiler. And __builtin_va_start is expanded into some compiler-specific internal representation of your compiled C/C++ code, specific to GCC (some GIMPLE perhaps)
From a comment of yours, I would infer that you are interested in implementation details. But that should be in your question
If you study GCC 9.1 source code, look inside some of gcc-9.1.0/gcc/builtins.c (the expand_builtin_va_start function there), and for other builtins inside gcc-9.1.0/gcc/c-family/c-cppbuiltin.c, gcc-9.1.0/gcc/cppbuiltin.c, gcc-9.1.0/gcc/jit/jit-builtins.c
You could write your own GCC plugin (in 2Q2019, for GCC 9, and the C++ code of your plugin might have to change for the future GCC 10) to add your own GCC builtins. BTW, you might even overload the behavior of the existing __builtin_va_start by your own specific code, and/or you might have -at least for research purposes- your own stdarg.h header with #define va_start(v,l) __my_builtin_va_start(v,l) and have your GCC plugin understand your __my_builtin_va_start plugin-specific builtin. Be however aware of the GCC runtime library exception and read its rationale: I am not a lawyer, but I tend to believe that you should (and that legal document requires you to) publish your GCC plugin with some open source license.
You first need to read a textbook on compilers, such as the Dragon book, to understand that an optimizing compiler is mostly transforming internal representations of your compiled code.
You further need to spend months in studying the many internal representations of GCC. Remember, GCC is a very complex program (of about ten millions lines of code). Don't expect to understand it with only a few days of work. Look inside the GCC resource center website.
My dead GCC MELT project had references and slides explaining more of GCC (the design philosophy and architecture of GCC changes slowly; so the concepts are still relevant, even if individual details changed). It took me almost ten years full time to partly understand some of the middle-end layers of GCC. I cannot transmit that knowledge in a StackOverflow answer.
My draft Bismon report (work in progress, funded by H2020, so lot of bureaucracy) has a dozen of pages (in its sections §1.3 and 1.4) introducing the internal representations of GCC.
I am working on a project right now, and I would greatly enjoy being able to extend a cross compiler to convert some code into other languages. For example, I might have an AST of some code, and I would like to pass that off to a cross compiler with the intended language and receive some code in the language specified in return.
So to sum it up: is there any extensible cross compiler that I can just give an AST or equivalent and receive code in return?
(I know about Haxe, but the compiler is not very extensible and I would prefer to not transpile)
I have made the decision to use LLVM as the native compiler, and will write my own custom transpilers to other languages, as I could find no other decent option. If you would like to follow my project, head over to Provalang.
I want to use the aspectc++ compiler for a C++11-project. I have read in the manual, that c++11 support will come with version 2. I thought that aspect weaving happens only on the code level, so why does it depend on the used C++ version? Why does aspectc++ care the source code when it just has to weave the aspects to generate a composed piece of code? Is there a way to use aspectc++ for C++11 source code? Or is there an alternative which can handle it?
This post is already a bit older, i know.
Nevertheless I'd like to answer the question why aspectC++ depends on the C++-version:
aspectC++ internally parses the code (amongst other things to identify the locations where to weave the code). Not all of this can be done by external parsers therefore it needs to understand the syntax basically itself.
Some new c++-constructions from C++11 like attributes ([[...]]) could not be handeled by the AspectC++-compiler version < 2.0.
To use c++11 for compiling just use -std=c++11
I don't know if this is the right place for things like this, but I am curious about a few aspects of the GCC front-end/back-end architecture:
I know I can compile .o files from C code and link them to C++ code, and I think I can do it the other way round, too. Does this work because the two languages are similar, or because the GCC back-end is really language-independent? Would this work with ADA code too? (I don't even know if that makes sense, since I don't know ADA or if it even has "functions", but the question is understood. If it makes no sense, think "Pascal" or even "my own custom language front-end")
Where would garbage-collection be implemented? For example, a Java front-end. The way I understand, if compiling to a JVM back-end, the "platform" will take care of the GC, and so the front-end needs not do anything about it, but if compiling to native code, would the front-end send garbage-collecting GENERIC code to the back-end, or does it turn on some flag telling the back-end to produce garbage-collecting code? The first makes more sense to me, but that would mean the front-end produces different output based on the target, which seems to miss the point of the GCC's front-end/back-end architecture.
Where would language-specific libraries go? For instance, the standard Java classes or standard C headers. If they are linked in at the end, then could a C program theoretically call functions from the Java library or something like that, since it is just another linked library?
Yes, the backend is at least reasonably language independent. Yes, it works with Ada.
GCJ generates native code which uses a runtime library. The garbage collector is part of the runtime library.
GCJ implements the CNI, which allows you to write code in C++ that can be used as native methods by Java code -- but being able to do this is a consequence of them having designed it in, not just an accidental byproduct of using the same back-end.
It is possible because calling convention is compatible, but name mangling is different (no mangling in C). To call C function from C++ you should declare it with extern "C". And to call C++ function from C you should declare it with mangled name (and may be with additional or different type args). The calling Fortran code is possible in some cases too, but argument passing convention is different (pass by ref in Fortran).
There were actually a converters from C++ to C (cfront) and from fortran to c (f2c) and some solutions from them are still used.
garbage-collection is implemented in run-time library, e.g. boehm. Backend should generate objects compatible with selected GC library.
Compiler driver (g++, gfortran, ..) will add language-specific libraries to linking step.