[PATCH olang v2 1/3] be: create linux-x86_64 gas asm codegen

[Johnny Richard <johnny@johnnyrichard.com>]

This patch creates basic functions to generate GAS assembly for
examples/main_exit.0.

Signed-off-by: Johnny Richard <johnny@johnnyrichard.com>
---
 src/codegen_linux_x86_64.c | 81 ++++++++++++++++++++++++++++++++++++++
 src/codegen_linux_x86_64.h | 25 ++++++++++++
 2 files changed, 106 insertions(+)
 create mode 100644 src/codegen_linux_x86_64.c
 create mode 100644 src/codegen_linux_x86_64.h

diff --git a/src/codegen_linux_x86_64.c b/src/codegen_linux_x86_64.c
new file mode 100644
index 0000000..3d4b17e
--- /dev/null
+++ b/src/codegen_linux_x86_64.c
@@ -0,0 +1,81 @@
+/*
+ * Copyright (C) 2024 olang maintainers
+ *
+ * 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 <assert.h>
+#include <stdint.h>
+#include <stdio.h>
+
+#include "codegen_linux_x86_64.h"
+#include "list.h"
+
+#define SYS_exit (60)
+
+static void
+codegen_linux_x86_64_emit_start_entrypoint(FILE *out);
+
+static void
+codegen_linux_x86_64_emit_function(FILE *out, ast_fn_definition_t *fn);
+
+void
+codegen_linux_x86_64_emit_program(FILE *out, ast_node_t *prog)
+{
+    codegen_linux_x86_64_emit_start_entrypoint(out);
+
+    assert(prog->kind == AST_NODE_FN_DEF);
+    ast_fn_definition_t fn = prog->data.as_fn_def;
+
+    assert(string_view_eq_to_cstr(fn.identifier, "main"));
+    codegen_linux_x86_64_emit_function(out, &fn);
+}
+
+static void
+codegen_linux_x86_64_emit_start_entrypoint(FILE *out)
+{
+    fprintf(out, ".text\n");
+    fprintf(out, ".globl _start\n\n");
+
+    fprintf(out, "_start:\n");
+    fprintf(out, "    call main\n");
+    fprintf(out, "    mov %%eax, %%edi\n");
+    fprintf(out, "    mov $%d, %%eax\n", SYS_exit);
+    fprintf(out, "    syscall\n");
+}
+
+static void
+codegen_linux_x86_64_emit_function(FILE *out, ast_fn_definition_t *fn)
+{
+    ast_node_t *block_node = fn->block;
+    assert(block_node->kind == AST_NODE_BLOCK);
+    ast_block_t block = block_node->data.as_block;
+
+    assert(list_size(block.nodes) == 1);
+
+    list_item_t *nodes_item = list_get(block.nodes, 0);
+    ast_node_t *return_node = nodes_item->value;
+    assert(return_node->kind == AST_NODE_RETURN_STMT);
+    ast_return_stmt_t return_stmt = return_node->data.as_return_stmt;
+
+    ast_node_t *literal_node = return_stmt.data;
+    assert(literal_node->kind == AST_NODE_LITERAL);
+    ast_literal_t literal_u32 = literal_node->data.as_literal;
+
+    assert(literal_u32.kind == AST_LITERAL_U32);
+    uint32_t exit_code = literal_u32.value.as_u32;
+
+    fprintf(out, "" SV_FMT ":\n", SV_ARG(fn->identifier));
+    fprintf(out, "    mov $%d, %%eax\n", exit_code);
+    fprintf(out, "    ret\n");
+}
diff --git a/src/codegen_linux_x86_64.h b/src/codegen_linux_x86_64.h
new file mode 100644
index 0000000..2050c91
--- /dev/null
+++ b/src/codegen_linux_x86_64.h
@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2024 olang maintainers
+ *
+ * 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/>.
+ */
+#ifndef CODEGEN_X86_64_H
+#define CODEGEN_X86_64_H
+
+#include "ast.h"
+
+void
+codegen_linux_x86_64_emit_program(FILE *out, ast_node_t *prog);
+
+#endif /* CODEGEN_X86_64_H */
-- 
2.44.0