A very simple compiler that comiles an integer.

.gitignore

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+*~
+*.o
+tmp*
+9cc

9cc.c

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+#include <stdio.h>
+#include <stdlib.h>
+
+int main(int argc, char **argv) {
+    if (argc != 2) {
+        fprintf(stderr, "Arguments number not right.\n");
+        return 1;
+    }
+
+    printf(".intel_syntax noprefix\n");
+    printf(".global main\n");
+    printf("main:\n");
+    printf("  mov rax, %d\n", atoi(argv[1]));
+    printf("  ret\n");
+    return 0;
+}

Makefile

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+9cc: 9cc.c
+
+test: 9cc
+	./test.sh
+
+clean:
+	rm -f 9cc *.o *~ tmp*

test.sh

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+#!/bin/bash
+
+try() {
+    expected="$1"
+    input="$2"
+
+    ./9cc "$input" > tmp.s
+    gcc -o tmp tmp.s
+    ./tmp
+    actual="$?"
+
+    if [ "$actual" != "$expected" ]; then
+        echo "$input expected, but got $actual"
+        exit 1
+    fi
+}
+
+try 0 0
+try 42 42
+
+echo OK