Tutorial part 1: “Hello world”¶
Before we look at the details of the API, let’s look at building and running programs that use the library.
Here’s a toy “hello world” program that uses the library’s C++ API to synthesize a call to printf and uses it to write a message to stdout.
Don’t worry about the content of the program for now; we’ll cover the details in later parts of this tutorial.
/* Smoketest example for libgccjit.so C++ API Copyright (C) 2014-2019 Free Software Foundation, Inc. This file is part of GCC. GCC is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version. GCC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GCC; see the file COPYING3. If not see <http://www.gnu.org/licenses/>. */ #include <libgccjit++.h> #include <stdlib.h> #include <stdio.h> static void create_code (gccjit::context ctxt) { /* Let's try to inject the equivalent of this C code: void greet (const char *name) { printf ("hello %s\n", name); } */ gccjit::type void_type = ctxt.get_type (GCC_JIT_TYPE_VOID); gccjit::type const_char_ptr_type = ctxt.get_type (GCC_JIT_TYPE_CONST_CHAR_PTR); gccjit::param param_name = ctxt.new_param (const_char_ptr_type, "name"); std::vector<gccjit::param> func_params; func_params.push_back (param_name); gccjit::function func = ctxt.new_function (GCC_JIT_FUNCTION_EXPORTED, void_type, "greet", func_params, 0); gccjit::param param_format = ctxt.new_param (const_char_ptr_type, "format"); std::vector<gccjit::param> printf_params; printf_params.push_back (param_format); gccjit::function printf_func = ctxt.new_function (GCC_JIT_FUNCTION_IMPORTED, ctxt.get_type (GCC_JIT_TYPE_INT), "printf", printf_params, 1); gccjit::block block = func.new_block (); block.add_eval (ctxt.new_call (printf_func, ctxt.new_rvalue ("hello %s\n"), param_name)); block.end_with_return (); } int main (int argc, char **argv) { gccjit::context ctxt; gcc_jit_result *result; /* Get a "context" object for working with the library. */ ctxt = gccjit::context::acquire (); /* Set some options on the context. Turn this on to see the code being generated, in assembler form. */ ctxt.set_bool_option (GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE, 0); /* Populate the context. */ create_code (ctxt); /* Compile the code. */ result = ctxt.compile (); if (!result) { fprintf (stderr, "NULL result"); exit (1); } ctxt.release (); /* Extract the generated code from "result". */ typedef void (*fn_type) (const char *); fn_type greet = (fn_type)gcc_jit_result_get_code (result, "greet"); if (!greet) { fprintf (stderr, "NULL greet"); exit (1); } /* Now call the generated function: */ greet ("world"); fflush (stdout); gcc_jit_result_release (result); return 0; }
Copy the above to tut01-hello-world.cc.
Assuming you have the jit library installed, build the test program using:
$ gcc \
tut01-hello-world.cc \
-o tut01-hello-world \
-lgccjit
You should then be able to run the built program:
$ ./tut01-hello-world
hello world