30cc (Pronounced as CCC, because in the Persian language, the number 30 is pronounced as C) is a toy C compiler written in C, with the goal of being able to compile itself 🤝 This is my first attempt in writing a self-hosting software! What is a self-hosting software?
- Imagine
30ccgets strong enough to be able to compile itself. - I will first compile
30ccwithgccto get the30cccompiler's binary. - I will then use the
gcc-generated30ccbinary file to compile the30ccagain. - I now have a
30cc-compiled version of30cc, which I can use for further developing the compiler! - I can forget about
gcc, as if it never existed! Beautiful hah?30ccis now all alive by itself!
30cc emits x86-64 assembly as its output. The outputs are totally unoptimized, but that's fine, the project aims to be educational.
Currently, this is the most complicated code 30cc is able to successfully parse and compile a simple implementation of a linked-list:
void *malloc(int sz);
void printf(char *s, ...);
struct node
{
int val;
void *next;
};
struct linked_list
{
struct node *first;
};
struct linked_list *new_list()
{
struct linked_list *ret = (struct linked_list *)malloc(8);
return ret;
}
void add_val(struct linked_list *lst, int val)
{
struct node *new = (struct node *)malloc(16);
*((int *)(&new->next)) = new;
new->val = val;
if (lst->first)
{
struct node *curr = lst->first;
while (curr->next)
{
curr = (struct node *)curr->next;
}
curr->next = (void *)new;
}
else
{
lst->first = new;
}
}
int main()
{
struct linked_list *lst = new_list();
add_val(lst, 123);
add_val(lst, 432);
add_val(lst, 999);
add_val(lst, 873);
struct node *curr = lst->first;
while (curr)
{
printf("%u\n", curr->val);
curr = (struct node *)curr->next;
}
}- First build the compiler using
gccby running:make - Compile to NASM x86-64 assembly:
./a.out INP_FILE.c --asm > out.asm - Assemble with NASM:
nasm -f elf64 out.asm -o out.o - Link with the C standard-library:
ld -dynamic-linker /lib64/ld-linux-x86-64.so.2 -lc -o out out.o - Run the output:
./out
The missing parts are:
-
#includemacro. -
#ifdef,#defineand#ifndefmacros. - Field-access in structs (The
.and->operators) - Type-checker
- Some binary expressions (
+=,-=,*=) - Unary expressions (
++,--,-,!) - Pointer-integer addition (Based on the type-size)