ast: Create AST visitor to traverse the tree

In the future we want to have the possibility of traverse the tree and
pretty print it or generate binary for other platform like LLVM or
transpile to C.

This solution also implements the gas assembly x86_64 Linux code
generation by using the visitor interface.

Signed-off-by: Johnny Richard <johnny@johnnyrichard.com>

1 files changed, 66 insertions, 0 deletions

diff --git a/src/gas_assembly_generator.c b/src/gas_assembly_generator.c
new file mode 100644
index 0000000..d164b7d
--- /dev/null
+++ b/src/gas_assembly_generator.c
@@ -0,0 +1,66 @@
+/*
+* Copyright (C) 2023 Johnny Richard
+*
+* This program 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 of the License, or
+* (at your option) any later version.
+*
+* This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+#include "gas_assembly_generator.h"
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static void gas_assembly_generator_visit_function(ast_visitor_t *visitor, ast_function_t *func);
+static void gas_assembly_generator_visit_return_stmt(ast_visitor_t *visitor, ast_return_stmt_t *return_stmt);
+
+void
+gas_assembly_generator_init(gas_assembly_generator_t *gen, FILE *out)
+{
+  assert(gen && out);
+  gen->super = (ast_visitor_t) {
+    .visit_function = &gas_assembly_generator_visit_function,
+    .visit_return_stmt = &gas_assembly_generator_visit_return_stmt
+  };
+  gen->out = out;
+}
+
+static void
+gas_assembly_generator_visit_function(ast_visitor_t *visitor, ast_function_t *func)
+{
+  assert(visitor && func);
+
+  if (!string_view_eq(func->name, string_view_from_str("main"))) {
+    fprintf(stderr, "[ERROR]: no main function has been defined!\n");
+    exit(EXIT_FAILURE);
+  }
+
+  gas_assembly_generator_t *gen = (gas_assembly_generator_t *) visitor;
+
+  fprintf(gen->out,".global _start\n");
+  fprintf(gen->out,".text\n");
+  fprintf(gen->out,"_start:\n");
+
+  ast_visitor_visit(visitor, &func->body);
+}
+
+static void
+gas_assembly_generator_visit_return_stmt(ast_visitor_t *visitor, ast_return_stmt_t *return_stmt)
+{
+  assert(visitor && return_stmt);
+  gas_assembly_generator_t *gen = (gas_assembly_generator_t *) visitor;
+
+  fprintf(gen->out, "  mov $1, %%al\n");
+  fprintf(gen->out, "  mov $%d, %%ebx\n", return_stmt->number);
+  fprintf(gen->out, "  int $0x80\n");
+}
+