Wrote an assembler (transpiles brainfuck into assembly code)
Provides: + Transpilation from brainfuck code into intel style assembly + functions to assemble and link code
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assembler.c
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203
assembler.c
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/* assembler.c
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* Created: 2024-12-03
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* Author: Aryadev Chavali
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* Description: Compile brainfuck into native
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*/
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#include "./assembler.h"
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#include <string.h>
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// Structure representing a loop operative as indices into an ASM label array.
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struct Label
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{
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u64 cur, next;
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};
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/* First, the functions to call external utilities (badly written, I know). They
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* presume a filled asm_buffer. */
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void asm_write(buffer_t **asm_buffer)
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{
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FILE *fp = fopen(asm_buffer[0]->name, "w");
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fwrite(asm_buffer[0]->data, asm_buffer[0]->size, 1, fp);
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fclose(fp);
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}
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int asm_assemble(const char *srcname, const char *objname)
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{
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#ifdef DEBUG
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char *format_str = "yasm -f elf64 -g dwarf2 -o %s %s";
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#else
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char *format_str = "yasm -f elf64 -o %s %s";
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#endif
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char command[snprintf(NULL, 0, format_str, objname, srcname) + 1];
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sprintf(command, format_str, objname, srcname);
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return system(command);
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}
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int asm_link(const char *objname, const char *outname)
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{
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char *format_str = "ld -o %s %s";
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char command[snprintf(NULL, 0, format_str, outname, objname) + 1];
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sprintf(command, format_str, outname, objname);
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return system(command);
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}
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int asm_compile(buffer_t **asm_buffer, const char *objname, const char *outname)
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{
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asm_write(asm_buffer);
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asm_assemble(asm_buffer[0]->name, objname);
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return asm_link(objname, outname);
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}
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void asm_setup_buffer(buffer_t **asm_buffer, const char *outname)
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{
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*asm_buffer = buffer_init_str(outname, NULL, 1024);
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asm_buffer[0]->size = 0;
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}
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// Write the initial boilerplate of the assembly file
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void asm_write_init(buffer_t **asm_buffer)
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{
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const char format_string[] = "section .bss\n"
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" memory resb %d\n"
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"section .text\n"
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"global _start\n"
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"_start:\n"
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" mov r9, memory\n";
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char initial_assembly[snprintf(NULL, 0, format_string, MEMORY_DEFAULT) + 1];
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snprintf(initial_assembly, sizeof(initial_assembly), format_string,
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MEMORY_DEFAULT);
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buffer_append_bytes(asm_buffer, (u8 *)initial_assembly,
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sizeof(initial_assembly) - 1);
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}
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// Write the exit code for the assembly file
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void asm_write_exit(buffer_t **asm_buffer)
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{
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buffer_append_bytes(asm_buffer,
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(u8 *)" mov rax, 60\n"
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" mov rdi, 0\n"
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" syscall\n",
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37);
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}
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// A table which translates brainfuck operations into generic assembly code (I
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// love C's array indexing)
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static const struct
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{
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char *str;
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u64 len;
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} table[] = {
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[NEXT] = {.str = " add r9, 1\n", .len = 12},
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[PREV] = {.str = " sub r9, 1\n", .len = 12},
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[INC] = {.str = " add byte [r9], 1\n", .len = 19},
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[DEC] = {.str = " sub byte [r9], 1\n", .len = 19},
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[OUT] = {.str = " mov rax, 1\n"
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" mov rdi, 1\n"
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" mov rsi, r9\n"
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" mov rdx, 1\n"
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" syscall\n",
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.len = 63},
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[READ] = {.str = " mov rax, 0\n"
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" mov rdi, 0\n"
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" mov rsi, r9\n"
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" mov rdx, 1\n"
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" syscall\n",
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.len = 63},
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};
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// Linear search in the ASM label array for a label with the current AST
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// relative index
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i64 get_abs_label(u64, struct Label *, u64);
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// Translate an AST relative jump to a specific ASM label, storing the current
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// and next items in given pointers.
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void ast_ref_to_asm_label(u64, struct Label *, u64, i64 *, i64 *);
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void asm_translate_nodes(buffer_t **asm_buffer, struct PResult nodes,
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const char *src_name)
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{
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// First pass: Setup the ASM label array
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struct Label labels[nodes.labels * 2];
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u64 label_ptr = 0;
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for (size_t i = 0; i < nodes.size; ++i)
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if (nodes.nodes[i].type == LIN || nodes.nodes[i].type == LOUT)
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labels[label_ptr++] =
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(struct Label){.cur = i, .next = nodes.nodes[i].loop_ref};
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// Second pass: Translating to assembly
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for (size_t i = 0; i < nodes.size; ++i)
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{
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node_t node = nodes.nodes[i];
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if (node.type == LIN || node.type == LOUT)
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{
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// Translate the node-relative addresses to assembly-label-relative
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// addresses
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i64 cur_asm_label = 0, next_asm_label = 0;
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ast_ref_to_asm_label(i, labels, nodes.labels * 2, &cur_asm_label,
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&next_asm_label);
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if (cur_asm_label == -1 || next_asm_label == -1)
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{
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print_error(
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src_name, node.row, node.col,
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"[ASSEMBLY ERROR]: Could not find label for current jump!\n");
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exit(1);
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}
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// Format labels
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char current_label[128], next_label[128];
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sprintf(current_label, ".L%lu", cur_asm_label);
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sprintf(next_label, ".L%lu", next_asm_label);
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// Setup format string for assembly jump code
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char *format_string = NULL;
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if (node.type == LIN)
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{
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format_string = "%s:\n"
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" cmp byte [r9], 0\n"
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" je %s\n";
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}
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else
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{
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format_string = "%s:\n"
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" cmp byte [r9], 0\n"
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" jne %s\n";
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}
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char formatted_string[snprintf(NULL, 0, format_string, current_label,
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next_label) +
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1];
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snprintf(formatted_string, sizeof(formatted_string), format_string,
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current_label, next_label);
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buffer_append_bytes(asm_buffer, (u8 *)formatted_string,
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sizeof(formatted_string) - 1);
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}
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else
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{
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// I love tables so goddamn much
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buffer_append_bytes(asm_buffer, (u8 *)table[node.type].str,
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table[node.type].len);
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}
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}
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}
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/* Implementations for throwaway functions */
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i64 get_abs_label(u64 ref, struct Label *labels, u64 size)
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{
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for (u64 i = 0; i < size; ++i)
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if (labels[i].cur == ref)
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return (i64)i;
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return -1;
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}
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void ast_ref_to_asm_label(u64 ref, struct Label *labels, u64 size, i64 *cur,
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i64 *next)
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{
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*cur = get_abs_label(ref, labels, size);
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if (*cur == -1)
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return;
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*next = get_abs_label(labels[*cur].next, labels, size);
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}
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17
assembler.h
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17
assembler.h
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@@ -0,0 +1,17 @@
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#ifndef ASSEMBLER_H
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#define ASSEMBLER_H
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#include "./lib.h"
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#include "./parser.h"
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void asm_setup_buffer(buffer_t **asm_buffer, const char *outname);
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void asm_translate_nodes(buffer_t **asm_buffer, struct PResult nodes,
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const char *src_name);
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void asm_write(buffer_t **asm_buffer);
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int asm_assemble(const char *srcname, const char *objname);
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int asm_link(const char *objname, const char *outname);
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int asm_compile(buffer_t **asm_buffer, const char *objname,
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const char *outname);
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#endif
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