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 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 Copyright (C) 2014-2017 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 (gcc_jit_context *ctxt) { /* Let's try to inject the equivalent of: void greet (const char *name) { printf ("hello %s\n", name); } */ gcc_jit_type *void_type = gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_VOID); gcc_jit_type *const_char_ptr_type = gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_CONST_CHAR_PTR); gcc_jit_param *param_name = gcc_jit_context_new_param (ctxt, NULL, const_char_ptr_type, "name"); gcc_jit_function *func = gcc_jit_context_new_function (ctxt, NULL, GCC_JIT_FUNCTION_EXPORTED, void_type, "greet", 1, ¶m_name, 0); gcc_jit_param *param_format = gcc_jit_context_new_param (ctxt, NULL, const_char_ptr_type, "format"); gcc_jit_function *printf_func = gcc_jit_context_new_function (ctxt, NULL, GCC_JIT_FUNCTION_IMPORTED, gcc_jit_context_get_type ( ctxt, GCC_JIT_TYPE_INT), "printf", 1, ¶m_format, 1); gcc_jit_rvalue *args[2]; args[0] = gcc_jit_context_new_string_literal (ctxt, "hello %s\n"); args[1] = gcc_jit_param_as_rvalue (param_name); gcc_jit_block *block = gcc_jit_function_new_block (func, NULL); gcc_jit_block_add_eval ( block, NULL, gcc_jit_context_new_call (ctxt, NULL, printf_func, 2, args)); gcc_jit_block_end_with_void_return (block, NULL); } int main (int argc, char **argv) { gcc_jit_context *ctxt; gcc_jit_result *result; /* Get a "context" object for working with the library. */ ctxt = gcc_jit_context_acquire (); if (!ctxt) { fprintf (stderr, "NULL ctxt"); exit (1); } /* Set some options on the context. Let's see the code being generated, in assembler form. */ gcc_jit_context_set_bool_option ( ctxt, GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE, 0); /* Populate the context. */ create_code (ctxt); /* Compile the code. */ result = gcc_jit_context_compile (ctxt); if (!result) { fprintf (stderr, "NULL result"); exit (1); } /* 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_context_release (ctxt); gcc_jit_result_release (result); return 0; }
Copy the above to tut01-hello-world.c.
Assuming you have the jit library installed, build the test program using:
$ gcc \
tut01-hello-world.c \
-o tut01-hello-world \
-lgccjit
You should then be able to run the built program:
$ ./tut01-hello-world
hello world