Gendlopen is a small tool intended to help with the creation of code that dynamically loads shared libraries. It takes text files with C prototype declarations as input and creates C or C++ header files as output.

This is still experimental and the main goal is to simply try out how much can be automized and find out how useful it is.

Features:

• no build dependencies other than a C/C++ compiler and make
• can generate code for C and C++
• win32 API LoadLibraryEx() and POSIX dlopen()
• wide and narrow characters on win32 API
• option to automatically load library and symbols

Limitations:

• auto-loading only works on functions ¹
• auto-loading does not work on functions with variable arguments ²

¹ I recommend using your own get/set wrapper functions to auto-load objects
² You can however replace a prototype such as int myprintf(const char *format, ...) with one that has a fixed number of arguments: int myprintf(const char *format, int arg1, const char *arg2, float arg3)

Input format

Here's how the input text format must be:

• all symbols that should be loaded must be listed as C-style prototypes, ending on semi-colon (;)
• comments and preprocessor lines are ignored
• line-breaks are treated as spaces
• you can set some options on a line beginning with %option, for example %option format=c++ prefix=mydl library=libfoo.so

You can create such a file with GCC: echo '#include "foobar.h"' | gcc -xc -c - -o /dev/null -aux-info aux.txt

Alternatively the input text can be a Clang AST file: clang -Xclang -ast-dump foobar.h > foo.txt

It's recommended to use the options -S or -P if you want to parse a Clang AST file or GCC generated prototype list.

Example

Let's assume you want to load int foobar_foo(foo_t *f) and void foobar_bar(bar_t b) from foo.so. First create a text file with the prototypes, each function prototype ending on a semicolon:

int foobar_foo(foo_t *f);
void foobar_bar(bar_t b);

Create a header file load_foo.h from the input: gendlopen foo.txt -o load_foo.h

Include load_foo.h it in your source file and use the provided functions to load the symbols:

    /* load library and symbols */
    if (!gdo_load_lib_name("foo.so") || !gdo_load_symbols(false))
    {
        fprintf(stderr, "%s\n", gdo_last_error());
        gdo_free_lib();
        return 1;
    }

    /* your code */
    foobar_foo(x);
    foobar_bar(y);

    /* free library */
    gdo_free_lib();

Or in C++ using the gdo::dl class: gendlopen foo.txt -format=c++ -o load_foo.hpp

    /* load library; resources are freed by the class d'tor */
    gdo::dl loader("foo.so");

    if (!loader.load_lib_and_symbols()) {
        std::cerr << loader.error() << std::endl;
        return 1;
    }

    /* your code */
    foobar_foo(x);
    foobar_bar(y);

You can find more information in the files from the examples and test directories, in the comments of the template files in src/templates as well as in the generated output files.

Compiling

./configure && make && make test

On Windows (MSVC) you can run nmake or make inside the msvc directory.

Cross-compiling with MinGW and clang-cl:

./configure host=x86_64-w64-mingw32 && make
./configure cl=clang-cl && make

Cross-compiling tests:

# compile the native tool first
./configure && make
cp src/gendlopen xgendlopen

# MinGW
./configure gdo="$PWD/xgendlopen" host=x86_64-w64-mingw32
make clean && make check

# clang-cl with lld-link
./configure gdo="$PWD/xgendlopen" cl=clang-cl ld=lld-link
make clean && make check

Links

A similar albeit less portable approach is the project dynload-wrapper.

If you want to use dlopen() on Windows try dlfcn-win32.