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/* assembler.c
* Created: 2024-12-03
* Author: Aryadev Chavali
* Description: Compile brainfuck into native
*/
#include "./assembler.h"
#include <string.h>
// Structure representing a loop operative as indices into an ASM label array.
struct Label
{
u64 cur, next;
};
// A table which translates brainfuck operations into generic assembly code (I
// love C's array indexing)
static const struct
{
char *str;
u64 len;
} table[] = {
[NEXT] = {.str = " add r9, 1\n", .len = 12},
[PREV] = {.str = " sub r9, 1\n", .len = 12},
[INC] = {.str = " add byte [r9], 1\n", .len = 19},
[DEC] = {.str = " sub byte [r9], 1\n", .len = 19},
[OUT] = {.str = " mov rax, 1\n"
" mov rdi, 1\n"
" mov rsi, r9\n"
" mov rdx, 1\n"
" syscall\n",
.len = 63},
[READ] = {.str = " mov rax, 0\n"
" mov rdi, 0\n"
" mov rsi, r9\n"
" mov rdx, 1\n"
" syscall\n",
.len = 63},
};
// Linear search in the ASM label array for a label with the current AST
// relative index
i64 get_abs_label(u64, struct Label *, u64);
// Translate an AST relative jump to a specific ASM label, storing the current
// and next items in given pointers.
void ast_ref_to_asm_label(u64, struct Label *, u64, i64 *, i64 *);
// Write the initial boilerplate of the assembly file
void asm_write_init(vec_t *asm_buffer);
// Write the exit code boilerplate for the assembly file
void asm_write_exit(vec_t *asm_buffer);
void asm_translate_nodes(vec_t *asm_buffer, struct PResult nodes,
const char *src_name)
{
asm_write_init(asm_buffer);
// First pass: Setup the ASM label array
struct Label labels[nodes.labels ? nodes.labels * 2 : 1];
if (nodes.labels)
{
u64 label_ptr = 0;
for (size_t i = 0; i < nodes.size; ++i)
if (nodes.nodes[i].type == LIN || nodes.nodes[i].type == LOUT)
labels[label_ptr++] =
(struct Label){.cur = i, .next = nodes.nodes[i].loop_ref};
}
// Second pass: Translating to assembly
for (size_t i = 0; i < nodes.size; ++i)
{
node_t node = nodes.nodes[i];
if (node.type == LIN || node.type == LOUT)
{
// Translate the node-relative addresses to assembly-label-relative
// addresses
i64 cur_asm_label = 0, next_asm_label = 0;
ast_ref_to_asm_label(i, labels, nodes.labels * 2, &cur_asm_label,
&next_asm_label);
if (cur_asm_label == -1 || next_asm_label == -1)
{
print_error(
src_name, node.row, node.col,
"[ASSEMBLY ERROR]: Could not find label for current jump!\n");
exit(1);
}
// Format labels
char current_label[128], next_label[128];
sprintf(current_label, ".L%lu", cur_asm_label);
sprintf(next_label, ".L%lu", next_asm_label);
// Setup format string for assembly jump code
char *format_string = NULL;
if (node.type == LIN)
{
format_string = "%s:\n"
" cmp byte [r9], 0\n"
" je %s\n";
}
else
{
format_string = "%s:\n"
" cmp byte [r9], 0\n"
" jne %s\n";
}
char formatted_string[snprintf(NULL, 0, format_string, current_label,
next_label) +
1];
snprintf(formatted_string, sizeof(formatted_string), format_string,
current_label, next_label);
vec_append(asm_buffer, formatted_string, sizeof(formatted_string) - 1);
}
else
{
// I love tables so goddamn much
vec_append(asm_buffer, table[node.type].str, table[node.type].len);
}
}
asm_write_exit(asm_buffer);
}
/* Implementations for throwaway functions */
i64 get_abs_label(u64 ref, struct Label *labels, u64 size)
{
for (u64 i = 0; i < size; ++i)
if (labels[i].cur == ref)
return (i64)i;
return -1;
}
void ast_ref_to_asm_label(u64 ref, struct Label *labels, u64 size, i64 *cur,
i64 *next)
{
*cur = get_abs_label(ref, labels, size);
if (*cur == -1)
return;
*next = get_abs_label(labels[*cur].next, labels, size);
}
// Write the initial boilerplate of the assembly file
void asm_write_init(vec_t *asm_buffer)
{
const char format_string[] = "section .bss\n"
" memory resb %d\n"
"section .text\n"
"global _start\n"
"_start:\n"
" mov r9, memory\n";
char initial_assembly[snprintf(NULL, 0, format_string, MEMORY_DEFAULT) + 1];
snprintf(initial_assembly, sizeof(initial_assembly), format_string,
MEMORY_DEFAULT);
vec_append(asm_buffer, initial_assembly, sizeof(initial_assembly) - 1);
}
// Write the exit code for the assembly file
void asm_write_exit(vec_t *asm_buffer)
{
vec_append(asm_buffer,
" mov rax, 60\n"
" mov rdi, 0\n"
" syscall\n",
37);
}
/* The system calling code - not exactly pretty, but it is what it is. */
void asm_write(const char *asm_name, vec_t *asm_buffer)
{
FILE *fp = fopen(asm_name, "w");
fwrite(asm_buffer->data, asm_buffer->size, 1, fp);
fclose(fp);
}
int asm_assemble(const char *asm_name, const char *objname)
{
#ifdef DEBUG
char *format_str = "yasm -f elf64 -g dwarf2 -o %s %s";
#else
char *format_str = "yasm -f elf64 -o %s %s";
#endif
char command[snprintf(NULL, 0, format_str, objname, asm_name) + 1];
sprintf(command, format_str, objname, asm_name);
return system(command);
}
int asm_link(const char *objname, const char *outname)
{
char *format_str = "ld -o %s %s";
char command[snprintf(NULL, 0, format_str, outname, objname) + 1];
sprintf(command, format_str, outname, objname);
return system(command);
}
int asm_compile(vec_t *asm_buffer, const char *asm_name, const char *objname,
const char *outname)
{
asm_write(asm_name, asm_buffer);
asm_assemble(asm_name, objname);
return asm_link(objname, outname);
}
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