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compiling-elf.c
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// vim: set tabstop=2 shiftwidth=2 textwidth=79 expandtab:
// gcc -O2 -g -Wall -Wextra -pedantic -fno-strict-aliasing
// assets/code/lisp/compiling-if.c
// In general: https://course.ccs.neu.edu/cs4410sp20/#%28part._lectures%29
// https://course.ccs.neu.edu/cs4410sp20/lec_let-and-stack_notes.html#%28part._let._.Growing_the_language__adding_let%29
#define _GNU_SOURCE
#include <assert.h> // for assert
#include <stdbool.h> // for bool
#include <stddef.h> // for NULL
#include <stdint.h> // for int32_t, etc
#include <stdio.h> // for getline, fprintf
#include <string.h> // for memcpy
#include <sys/mman.h> // for mmap
#undef _GNU_SOURCE
#include "greatest.h"
#define WARN_UNUSED __attribute__((warn_unused_result))
// Objects
typedef int64_t word;
typedef uint64_t uword;
// These constants are defined in a enum because the right hand side of a
// statement like
// static const int kFoo = ...;
// must be a so-called "Integer Constant Expression". Compilers are required to
// support a certain set of these expressions, but are not required to support
// arbitrary arithmetic with other integer constants. Compilers such as gcc
// before gcc-8 just decided not to play this game, while gcc-8+ and Clang play
// just fine.
// Since this arithmetic with constant values works just fine for enums, make
// all these constants enum values instead.
// See https://twitter.com/tekknolagi/status/1328449329472835586 for more info.
enum {
kBitsPerByte = 8, // bits
kWordSize = sizeof(word), // bytes
kBitsPerWord = kWordSize * kBitsPerByte, // bits
kIntegerTag = 0x0, // 0b00
kIntegerTagMask = 0x3, // 0b11
kIntegerShift = 2,
kIntegerBits = kBitsPerWord - kIntegerShift,
kImmediateTagMask = 0x3f,
kCharTag = 0x0f, // 0b00001111
kCharMask = 0xff, // 0b11111111
kCharShift = 8,
kBoolTag = 0x1f, // 0b0011111
kBoolMask = 0x80, // 0b10000000
kBoolShift = 7,
kNilTag = 0x2f, // 0b101111
kErrorTag = 0x3f, // 0b111111
kPairTag = 0x1, // 0b001
kSymbolTag = 0x5, // 0b101
kClosureTag = 0x6, // 0b110
kHeapTagMask = ((uword)0x7), // 0b000...111
kHeapPtrMask = ~kHeapTagMask, // 0b1111...1000
kCarIndex = 0,
kCarOffset = kCarIndex * kWordSize,
kCdrIndex = kCarIndex + 1,
kCdrOffset = kCdrIndex * kWordSize,
kPairSize = kCdrOffset + kWordSize,
};
// These are defined as macros because they will not work as static const int
// constants (per above explanation), and enum constants are only required to
// be an int wide (per ISO C).
#define INTEGER_MAX ((1LL << (kIntegerBits - 1)) - 1)
#define INTEGER_MIN (-(1LL << (kIntegerBits - 1)))
uword Object_encode_integer(word value) {
assert(value < INTEGER_MAX && "too big");
assert(value > INTEGER_MIN && "too small");
return value << kIntegerShift;
}
word Object_decode_integer(uword value) { return (word)value >> kIntegerShift; }
bool Object_is_integer(uword value) {
return (value & kIntegerTagMask) == kIntegerTag;
}
uword Object_encode_char(char value) {
return ((uword)value << kCharShift) | kCharTag;
}
char Object_decode_char(uword value) {
return (value >> kCharShift) & kCharMask;
}
bool Object_is_char(uword value) {
return (value & kImmediateTagMask) == kCharTag;
}
uword Object_encode_bool(bool value) {
return ((uword)value << kBoolShift) | kBoolTag;
}
bool Object_decode_bool(uword value) { return value & kBoolMask; }
uword Object_true() { return Object_encode_bool(true); }
uword Object_false() { return Object_encode_bool(false); }
uword Object_nil() { return kNilTag; }
uword Object_error() { return kErrorTag; }
uword Object_address(void *obj) { return (uword)obj & kHeapPtrMask; }
bool Object_is_pair(uword value) { return (value & kHeapTagMask) == kPairTag; }
uword Object_pair_car(uword value) {
assert(Object_is_pair(value));
return ((uword *)Object_address((void *)value))[kCarIndex];
}
uword Object_pair_cdr(uword value) {
assert(Object_is_pair(value));
return ((uword *)Object_address((void *)value))[kCdrIndex];
}
// End Objects
// Buffer
typedef unsigned char byte;
typedef enum {
kWritable,
kExecutable,
} BufferState;
typedef struct {
byte *address;
BufferState state;
word len;
word capacity;
uword entrypoint;
} Buffer;
byte *Buffer_alloc_writable(word capacity) {
byte *result = mmap(/*addr=*/NULL, capacity, PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE,
/*filedes=*/-1, /*off=*/0);
assert(result != MAP_FAILED);
return result;
}
void Buffer_init(Buffer *result, word capacity) {
result->address = Buffer_alloc_writable(capacity);
assert(result->address != MAP_FAILED);
result->state = kWritable;
result->len = 0;
result->capacity = capacity;
result->entrypoint = 0;
}
word Buffer_len(Buffer *buf) { return buf->len; }
uword Buffer_entrypoint(Buffer *buf) { return buf->entrypoint; }
void Buffer_set_entrypoint(Buffer *buf, uword entrypoint) {
buf->entrypoint = entrypoint;
}
void Buffer_deinit(Buffer *buf) {
munmap(buf->address, buf->capacity);
buf->address = NULL;
buf->len = 0;
buf->capacity = 0;
}
int Buffer_make_executable(Buffer *buf) {
int result = mprotect(buf->address, buf->len, PROT_EXEC);
buf->state = kExecutable;
return result;
}
byte Buffer_at8(Buffer *buf, word pos) { return buf->address[pos]; }
void Buffer_at_put8(Buffer *buf, word pos, byte b) { buf->address[pos] = b; }
word max(word left, word right) { return left > right ? left : right; }
void Buffer_ensure_capacity(Buffer *buf, word additional_capacity) {
if (buf->len + additional_capacity <= buf->capacity) {
return;
}
word new_capacity =
max(buf->capacity * 2, buf->capacity + additional_capacity);
byte *address = Buffer_alloc_writable(new_capacity);
memcpy(address, buf->address, buf->len);
int result = munmap(buf->address, buf->capacity);
assert(result == 0 && "munmap failed");
buf->address = address;
buf->capacity = new_capacity;
}
void Buffer_write8(Buffer *buf, byte b) {
Buffer_ensure_capacity(buf, sizeof b);
Buffer_at_put8(buf, buf->len++, b);
}
void Buffer_write16(Buffer *buf, uint16_t value) {
for (uword i = 0; i < sizeof(value); i++) {
Buffer_write8(buf, (value >> (i * kBitsPerByte)) & 0xff);
}
}
void Buffer_write32(Buffer *buf, uint32_t value) {
for (uword i = 0; i < sizeof(value); i++) {
Buffer_write8(buf, (value >> (i * kBitsPerByte)) & 0xff);
}
}
void Buffer_write64(Buffer *buf, uint64_t value) {
for (uword i = 0; i < sizeof(value); i++) {
Buffer_write8(buf, (value >> (i * kBitsPerByte)) & 0xff);
}
}
void Buffer_at_put16(Buffer *buf, word offset, uint16_t value) {
for (uword i = 0; i < sizeof(value); i++) {
Buffer_at_put8(buf, offset + i, (value >> (i * kBitsPerByte)) & 0xff);
}
}
void Buffer_at_put32(Buffer *buf, word offset, uint32_t value) {
for (uword i = 0; i < sizeof(value); i++) {
Buffer_at_put8(buf, offset + i, (value >> (i * kBitsPerByte)) & 0xff);
}
}
void Buffer_at_put64(Buffer *buf, word offset, uint64_t value) {
for (uword i = 0; i < sizeof(value); i++) {
Buffer_at_put8(buf, offset + i, (value >> (i * kBitsPerByte)) & 0xff);
}
}
void Buffer_write_arr(Buffer *buf, const byte *arr, word arr_size) {
Buffer_ensure_capacity(buf, arr_size);
for (word i = 0; i < arr_size; i++) {
Buffer_write8(buf, arr[i]);
}
}
void Buffer_dump(Buffer *buf, FILE *fp) {
for (word i = 0; i < Buffer_len(buf); i++) {
fprintf(fp, "%.2x ", buf->address[i]);
}
fprintf(fp, "\n");
}
// End Buffer
// Emit
typedef enum {
kRax = 0,
kRcx,
kRdx,
kRbx,
kRsp,
kRbp,
kRsi,
kRdi,
} Register;
typedef enum {
kAl = 0,
kCl,
kDl,
kBl,
kAh,
kCh,
kDh,
kBh,
} PartialRegister;
typedef enum {
kOverflow = 0,
kNotOverflow,
kBelow,
kCarry = kBelow,
kNotAboveOrEqual = kBelow,
kAboveOrEqual,
kNotBelow = kAboveOrEqual,
kNotCarry = kAboveOrEqual,
kEqual,
kZero = kEqual,
kLess = 0xc,
kNotGreaterOrEqual = kLess,
// TODO(max): Add more
} Condition;
typedef struct Indirect {
Register reg;
word disp;
} Indirect;
Indirect Ind(Register reg, word disp) {
return (Indirect){.reg = reg, .disp = disp};
}
// [ Instruction Prefixes (1 byte, optional) ]
// [ Opcode (1, 2, or 3 bytes) ]
// [ ModR/M (1 byte, if required) ]
// [ Scale-Index-Base (1 byte, if required) ]
// [ Displacement (1, 2, or 4 bytes, if required) ]
// [ Immediate data (1, 2, or 4 bytes, if required) ]
// http://www.c-jump.com/CIS77/CPU/x86/lecture.html
// https://wiki.osdev.org/X86-64_Instruction_Encoding
enum {
kRexPrefix = 0x48,
};
typedef enum {
Scale1 = 0,
Scale2,
Scale4,
Scale8,
} Scale;
typedef enum {
kIndexRax = 0,
kIndexRcx,
kIndexRdx,
kIndexRbx,
kIndexNone,
kIndexRbp,
kIndexRsi,
kIndexRdi
} Index;
byte modrm(byte mod, byte rm, byte reg) {
return ((mod & 0x3) << 6) | ((reg & 0x7) << 3) | (rm & 0x7);
}
byte sib(Register base, Index index, Scale scale) {
return ((scale & 0x3) << 6) | ((index & 0x7) << 3) | (base & 0x7);
}
void Emit_mov_reg_imm32(Buffer *buf, Register dst, int32_t src) {
Buffer_write8(buf, kRexPrefix);
Buffer_write8(buf, 0xc7);
Buffer_write8(buf, modrm(/*direct*/ 3, dst, 0));
Buffer_write32(buf, src);
}
void Emit_ret(Buffer *buf) { Buffer_write8(buf, 0xc3); }
void Emit_add_reg_imm32(Buffer *buf, Register dst, int32_t src) {
Buffer_write8(buf, kRexPrefix);
if (dst == kRax) {
// Optimization: add eax, {imm32} can either be encoded as 05 {imm32} or 81
// c0 {imm32}.
Buffer_write8(buf, 0x05);
} else {
Buffer_write8(buf, 0x81);
Buffer_write8(buf, modrm(/*direct*/ 3, dst, 0));
}
Buffer_write32(buf, src);
}
void Emit_sub_reg_imm32(Buffer *buf, Register dst, int32_t src) {
Buffer_write8(buf, kRexPrefix);
if (dst == kRax) {
// Optimization: sub eax, {imm32} can either be encoded as 2d {imm32} or 81
// e8 {imm32}.
Buffer_write8(buf, 0x2d);
} else {
Buffer_write8(buf, 0x81);
Buffer_write8(buf, modrm(/*direct*/ 3, dst, 5));
}
Buffer_write32(buf, src);
}
void Emit_shl_reg_imm8(Buffer *buf, Register dst, int8_t bits) {
Buffer_write8(buf, kRexPrefix);
Buffer_write8(buf, 0xc1);
Buffer_write8(buf, modrm(/*direct*/ 3, dst, 4));
Buffer_write8(buf, bits);
}
void Emit_shr_reg_imm8(Buffer *buf, Register dst, int8_t bits) {
Buffer_write8(buf, kRexPrefix);
Buffer_write8(buf, 0xc1);
Buffer_write8(buf, modrm(/*direct*/ 3, dst, 5));
Buffer_write8(buf, bits);
}
void Emit_or_reg_imm8(Buffer *buf, Register dst, uint8_t tag) {
Buffer_write8(buf, kRexPrefix);
Buffer_write8(buf, 0x83);
Buffer_write8(buf, modrm(/*direct*/ 3, dst, 1));
Buffer_write8(buf, tag);
}
void Emit_and_reg_imm8(Buffer *buf, Register dst, uint8_t tag) {
Buffer_write8(buf, kRexPrefix);
Buffer_write8(buf, 0x83);
Buffer_write8(buf, modrm(/*direct*/ 3, dst, 4));
Buffer_write8(buf, tag);
}
void Emit_cmp_reg_imm32(Buffer *buf, Register left, int32_t right) {
Buffer_write8(buf, kRexPrefix);
if (left == kRax) {
// Optimization: cmp rax, {imm32} can either be encoded as 3d {imm32} or 81
// f8 {imm32}.
Buffer_write8(buf, 0x3d);
} else {
Buffer_write8(buf, 0x81);
Buffer_write8(buf, modrm(/*direct*/ 3, left, 7));
}
Buffer_write32(buf, right);
}
void Emit_setcc_imm8(Buffer *buf, Condition cond, PartialRegister dst) {
// TODO(max): Emit a REX prefix if we need anything above RDI.
Buffer_write8(buf, 0x0f);
Buffer_write8(buf, 0x90 + cond);
Buffer_write8(buf, 0xc0 + (dst & 0x7));
}
uint8_t disp8(int8_t disp) { return disp >= 0 ? disp : 0x100 + disp; }
void Emit_address_disp8(Buffer *buf, Register direct, Indirect indirect) {
if (indirect.reg == kRsp) {
Buffer_write8(buf, modrm(/*disp8*/ 1, kIndexNone, direct));
Buffer_write8(buf, sib(kRsp, kIndexNone, Scale1));
} else {
Buffer_write8(buf, modrm(/*disp8*/ 1, indirect.reg, direct));
}
Buffer_write8(buf, disp8(indirect.disp));
}
// mov [dst+disp], src
// or
// mov %src, disp(%dst)
void Emit_store_reg_indirect(Buffer *buf, Indirect dst, Register src) {
Buffer_write8(buf, kRexPrefix);
Buffer_write8(buf, 0x89);
Emit_address_disp8(buf, src, dst);
}
// add dst, [src+disp]
// or
// add disp(%src), %dst
void Emit_add_reg_indirect(Buffer *buf, Register dst, Indirect src) {
Buffer_write8(buf, kRexPrefix);
Buffer_write8(buf, 0x03);
Emit_address_disp8(buf, dst, src);
}
// sub dst, [src+disp]
// or
// sub disp(%src), %dst
void Emit_sub_reg_indirect(Buffer *buf, Register dst, Indirect src) {
Buffer_write8(buf, kRexPrefix);
Buffer_write8(buf, 0x2b);
Emit_address_disp8(buf, dst, src);
}
// mul rax, [src+disp]
// or
// mul disp(%src), %rax
void Emit_mul_reg_indirect(Buffer *buf, Indirect src) {
Buffer_write8(buf, kRexPrefix);
Buffer_write8(buf, 0xf7);
Emit_address_disp8(buf, /*subop*/ 4, src);
}
// cmp left, [right+disp]
// or
// cmp disp(%right), %left
void Emit_cmp_reg_indirect(Buffer *buf, Register left, Indirect right) {
Buffer_write8(buf, kRexPrefix);
Buffer_write8(buf, 0x3b);
Emit_address_disp8(buf, left, right);
}
// mov dst, [src+disp]
// or
// mov disp(%src), %dst
void Emit_load_reg_indirect(Buffer *buf, Register dst, Indirect src) {
Buffer_write8(buf, kRexPrefix);
Buffer_write8(buf, 0x8b);
Emit_address_disp8(buf, dst, src);
}
uint32_t disp32(int32_t disp) { return disp >= 0 ? disp : 0x100000000 + disp; }
word Emit_jcc(Buffer *buf, Condition cond, int32_t offset) {
Buffer_write8(buf, 0x0f);
Buffer_write8(buf, 0x80 + cond);
word pos = Buffer_len(buf);
Buffer_write32(buf, disp32(offset));
return pos;
}
word Emit_jmp(Buffer *buf, int32_t offset) {
Buffer_write8(buf, 0xe9);
word pos = Buffer_len(buf);
Buffer_write32(buf, disp32(offset));
return pos;
}
void Emit_backpatch_imm32(Buffer *buf, int32_t target_pos) {
word current_pos = Buffer_len(buf);
word relative_pos = current_pos - target_pos - sizeof(int32_t);
Buffer_at_put32(buf, target_pos, disp32(relative_pos));
}
void Emit_mov_reg_reg(Buffer *buf, Register dst, Register src) {
Buffer_write8(buf, kRexPrefix);
Buffer_write8(buf, 0x89);
Buffer_write8(buf, modrm(/*direct*/ 3, dst, src));
}
void Emit_syscall(Buffer *buf) {
Buffer_write8(buf, 0x0f);
Buffer_write8(buf, 0x05);
}
// End Emit
// AST
typedef struct ASTNode ASTNode;
typedef struct Pair {
ASTNode *car;
ASTNode *cdr;
} Pair;
typedef struct Symbol {
word length;
char cstr[];
} Symbol;
bool AST_is_integer(ASTNode *node) {
return ((uword)node & kIntegerTagMask) == kIntegerTag;
}
word AST_get_integer(ASTNode *node) {
return Object_decode_integer((uword)node);
}
ASTNode *AST_new_integer(word value) {
return (ASTNode *)Object_encode_integer(value);
}
bool AST_is_char(ASTNode *node) {
return ((uword)node & kImmediateTagMask) == kCharTag;
}
char AST_get_char(ASTNode *node) { return Object_decode_char((uword)node); }
ASTNode *AST_new_char(char value) {
return (ASTNode *)Object_encode_char(value);
}
bool AST_is_bool(ASTNode *node) {
return ((uword)node & kImmediateTagMask) == kBoolTag;
}
bool AST_get_bool(ASTNode *node) { return Object_decode_bool((uword)node); }
ASTNode *AST_new_bool(bool value) {
return (ASTNode *)Object_encode_bool(value);
}
bool AST_is_nil(ASTNode *node) { return (uword)node == Object_nil(); }
ASTNode *AST_nil() { return (ASTNode *)Object_nil(); }
bool AST_is_error(ASTNode *node) { return (uword)node == Object_error(); }
ASTNode *AST_error() { return (ASTNode *)Object_error(); }
ASTNode *AST_heap_alloc(unsigned char tag, uword size) {
// Initialize to 0
uword address = (uword)calloc(size, 1);
return (ASTNode *)(address | tag);
}
bool AST_is_heap_object(ASTNode *node) {
// For some reason masking out the tag first and then doing the comparison
// makes this branchless
unsigned char tag = (uword)node & kHeapTagMask;
// Heap object tags are between 0b001 and 0b110 except for 0b100 (which is an
// integer)
return (tag & kIntegerTagMask) > 0 && (tag & kImmediateTagMask) != 0x7;
}
void AST_pair_set_car(ASTNode *node, ASTNode *car);
void AST_pair_set_cdr(ASTNode *node, ASTNode *cdr);
ASTNode *AST_new_pair(ASTNode *car, ASTNode *cdr) {
ASTNode *node = AST_heap_alloc(kPairTag, sizeof(Pair));
AST_pair_set_car(node, car);
AST_pair_set_cdr(node, cdr);
return node;
}
bool AST_is_pair(ASTNode *node) {
return ((uword)node & kHeapTagMask) == kPairTag;
}
Pair *AST_as_pair(ASTNode *node) {
assert(AST_is_pair(node));
return (Pair *)Object_address(node);
}
ASTNode *AST_pair_car(ASTNode *node) { return AST_as_pair(node)->car; }
void AST_pair_set_car(ASTNode *node, ASTNode *car) {
AST_as_pair(node)->car = car;
}
ASTNode *AST_pair_cdr(ASTNode *node) { return AST_as_pair(node)->cdr; }
void AST_pair_set_cdr(ASTNode *node, ASTNode *cdr) {
AST_as_pair(node)->cdr = cdr;
}
void AST_heap_free(ASTNode *node) {
if (!AST_is_heap_object(node)) {
return;
}
if (AST_is_pair(node)) {
AST_heap_free(AST_pair_car(node));
AST_heap_free(AST_pair_cdr(node));
}
free((void *)Object_address(node));
}
Symbol *AST_as_symbol(ASTNode *node);
ASTNode *AST_new_symbol(const char *str) {
word data_length = strlen(str) + 1; // for NUL
ASTNode *node = AST_heap_alloc(kSymbolTag, sizeof(Symbol) + data_length);
Symbol *s = AST_as_symbol(node);
s->length = data_length;
memcpy(s->cstr, str, data_length);
return node;
}
bool AST_is_symbol(ASTNode *node) {
return ((uword)node & kHeapTagMask) == kSymbolTag;
}
Symbol *AST_as_symbol(ASTNode *node) {
assert(AST_is_symbol(node));
return (Symbol *)Object_address(node);
}
const char *AST_symbol_cstr(ASTNode *node) {
return (const char *)AST_as_symbol(node)->cstr;
}
bool AST_symbol_matches(ASTNode *node, const char *cstr) {
return strcmp(AST_symbol_cstr(node), cstr) == 0;
}
int node_to_str(ASTNode *node, char *buf, word size);
int list_to_str(ASTNode *node, char *buf, word size) {
if (AST_is_pair(node)) {
word result = 0;
result += snprintf(buf + result, size, " ");
result += node_to_str(AST_pair_car(node), buf + result, size);
result += list_to_str(AST_pair_cdr(node), buf + result, size);
return result;
}
if (AST_is_nil(node)) {
return snprintf(buf, size, ")");
}
word result = 0;
result += snprintf(buf + result, size, " . ");
result += node_to_str(node, buf + result, size);
result += snprintf(buf + result, size, ")");
return result;
}
int node_to_str(ASTNode *node, char *buf, word size) {
if (AST_is_integer(node)) {
return snprintf(buf, size, "%ld", AST_get_integer(node));
}
if (AST_is_char(node)) {
return snprintf(buf, size, "'%c'", AST_get_char(node));
}
if (AST_is_bool(node)) {
return snprintf(buf, size, "%s", AST_get_bool(node) ? "true" : "false");
}
if (AST_is_nil(node)) {
return snprintf(buf, size, "nil");
}
if (AST_is_pair(node)) {
word result = 0;
result += snprintf(buf + result, size, "(");
result += node_to_str(AST_pair_car(node), buf + result, size);
result += list_to_str(AST_pair_cdr(node), buf + result, size);
return result;
}
if (AST_is_symbol(node)) {
return snprintf(buf, size, "%s", AST_symbol_cstr(node));
}
assert(0 && "unknown ast");
}
char *AST_to_cstr(ASTNode *node) {
int size = node_to_str(node, NULL, 0);
char *buf = malloc(size + 1);
assert(buf != NULL);
node_to_str(node, buf, size + 1);
buf[size] = '\0';
return buf;
}
// End AST
// Reader
void advance(word *pos) { ++*pos; }
char next(char *input, word *pos) {
advance(pos);
return input[*pos];
}
ASTNode *read_integer(char *input, word *pos, int sign) {
word result = 0;
for (char c = input[*pos]; isdigit(c); c = next(input, pos)) {
result *= 10;
result += c - '0';
}
return AST_new_integer(sign * result);
}
bool starts_symbol(char c) {
switch (c) {
case '+':
case '-':
case '*':
case '<':
case '>':
case '=':
case '?':
return true;
default:
return isalpha(c);
}
}
bool is_symbol_char(char c) { return starts_symbol(c) || isdigit(c); }
const word ATOM_MAX = 32;
ASTNode *read_symbol(char *input, word *pos) {
char buf[ATOM_MAX + 1]; // +1 for NUL
word length = 0;
for (length = 0; length < ATOM_MAX && is_symbol_char(input[*pos]); length++) {
buf[length] = input[*pos];
advance(pos);
}
buf[length] = '\0';
return AST_new_symbol(buf);
}
ASTNode *read_char(char *input, word *pos) {
char c = input[*pos];
if (c == '\'') {
return AST_error();
}
advance(pos);
if (input[*pos] != '\'') {
return AST_error();
}
advance(pos);
return AST_new_char(c);
}
char skip_whitespace(char *input, word *pos) {
char c = '\0';
for (c = input[*pos]; isspace(c); c = next(input, pos)) {
;
}
return c;
}
ASTNode *read_rec(char *input, word *pos);
ASTNode *read_list(char *input, word *pos) {
char c = skip_whitespace(input, pos);
if (c == ')') {
advance(pos);
return AST_nil();
}
ASTNode *car = read_rec(input, pos);
assert(car != AST_error());
ASTNode *cdr = read_list(input, pos);
assert(cdr != AST_error());
return AST_new_pair(car, cdr);
}
ASTNode *read_rec(char *input, word *pos) {
char c = skip_whitespace(input, pos);
if (isdigit(c)) {
return read_integer(input, pos, /*sign=*/1);
}
if (c == '-' && isdigit(input[*pos + 1])) {
advance(pos);
return read_integer(input, pos, /*sign=*/-1);
}
if (c == '+' && isdigit(input[*pos + 1])) {
advance(pos);
return read_integer(input, pos, /*sign=*/1);
}
if (starts_symbol(c)) {
return read_symbol(input, pos);
}
if (c == '\'') {
advance(pos); // skip '\''
return read_char(input, pos);
}
if (c == '#' && input[*pos + 1] == 't') {
advance(pos); // skip '#'
advance(pos); // skip 't'
return AST_new_bool(true);
}
if (c == '#' && input[*pos + 1] == 'f') {
advance(pos); // skip '#'
advance(pos); // skip 'f'
return AST_new_bool(false);
}
if (c == '(') {
advance(pos); // skip '('
return read_list(input, pos);
}
return AST_error();
}
ASTNode *Reader_read(char *input) {
word pos = 0;
return read_rec(input, &pos);
}
// End Reader
// Env
typedef struct Env {
const char *name;
word value;
struct Env *prev;
} Env;
Env Env_bind(const char *name, word value, Env *prev) {
return (Env){.name = name, .value = value, .prev = prev};
}
bool Env_find(Env *env, const char *key, word *result) {
if (env == NULL)
return false;
if (strcmp(env->name, key) == 0) {
*result = env->value;
return true;
}
return Env_find(env->prev, key, result);
}
// End Env
// Compile
WARN_UNUSED int Compile_expr(Buffer *buf, ASTNode *node, word stack_index,
Env *varenv, Env *labels);
ASTNode *operand1(ASTNode *args) { return AST_pair_car(args); }
ASTNode *operand2(ASTNode *args) { return AST_pair_car(AST_pair_cdr(args)); }
ASTNode *operand3(ASTNode *args) {
return AST_pair_car(AST_pair_cdr(AST_pair_cdr(args)));
}
#define _(exp) \
do { \
int result = exp; \
if (result != 0) \
return result; \
} while (0)
void Compile_compare_imm32(Buffer *buf, int32_t value) {
Emit_cmp_reg_imm32(buf, kRax, value);
Emit_mov_reg_imm32(buf, kRax, 0);
Emit_setcc_imm8(buf, kEqual, kAl);
Emit_shl_reg_imm8(buf, kRax, kBoolShift);
Emit_or_reg_imm8(buf, kRax, kBoolTag);
}
// This is let, not let*. Therefore we keep track of two environments -- the
// parent environment, for evaluating the bindings, and the body environment,
// which will have all of the bindings in addition to the parent. This makes
// programs like (let ((a 1) (b a)) b) fail.
WARN_UNUSED int Compile_let(Buffer *buf, ASTNode *bindings, ASTNode *body,
word stack_index, Env *binding_env, Env *body_env,
Env *labels) {
if (AST_is_nil(bindings)) {
// Base case: no bindings. Compile the body
_(Compile_expr(buf, body, stack_index, body_env, labels));
return 0;
}
assert(AST_is_pair(bindings));
// Get the next binding
ASTNode *binding = AST_pair_car(bindings);
ASTNode *name = AST_pair_car(binding);
assert(AST_is_symbol(name));
ASTNode *binding_expr = AST_pair_car(AST_pair_cdr(binding));
// Compile the binding expression
_(Compile_expr(buf, binding_expr, stack_index, binding_env, labels));
Emit_store_reg_indirect(buf, /*dst=*/Ind(kRsp, stack_index),
/*src=*/kRax);
// Bind the name
Env entry = Env_bind(AST_symbol_cstr(name), stack_index, body_env);
_(Compile_let(buf, AST_pair_cdr(bindings), body, stack_index - kWordSize,
/*binding_env=*/binding_env, /*body_env=*/&entry, labels));
return 0;
}
const int32_t kLabelPlaceholder = 0xdeadbeef;
WARN_UNUSED int Compile_if(Buffer *buf, ASTNode *cond, ASTNode *consequent,
ASTNode *alternate, word stack_index, Env *varenv,
Env *labels) {
_(Compile_expr(buf, cond, stack_index, varenv, labels));
Emit_cmp_reg_imm32(buf, kRax, Object_false());
word alternate_pos = Emit_jcc(buf, kEqual, kLabelPlaceholder); // je alternate
_(Compile_expr(buf, consequent, stack_index, varenv, labels));
word end_pos = Emit_jmp(buf, kLabelPlaceholder); // jmp end
Emit_backpatch_imm32(buf, alternate_pos); // alternate:
_(Compile_expr(buf, alternate, stack_index, varenv, labels));
Emit_backpatch_imm32(buf, end_pos); // end:
return 0;
}
const Register kHeapPointer = kRsi;
WARN_UNUSED int Compile_cons(Buffer *buf, ASTNode *car, ASTNode *cdr,
word stack_index, Env *varenv, Env *labels) {
// Compile and store car on the stack
_(Compile_expr(buf, car, stack_index, varenv, labels));
Emit_store_reg_indirect(buf,
/*dst=*/Ind(kRsp, stack_index),
/*src=*/kRax);
// Compile and store cdr
_(Compile_expr(buf, cdr, stack_index - kWordSize, varenv, labels));
Emit_store_reg_indirect(buf, /*dst=*/Ind(kHeapPointer, kCdrOffset),
/*src=*/kRax);
// Fetch car and store in the heap
Emit_load_reg_indirect(buf, /*dst=*/kRax, /*src=*/Ind(kRsp, stack_index));
Emit_store_reg_indirect(buf, /*dst=*/Ind(kHeapPointer, kCarOffset),
/*src=*/kRax);
// Store tagged pointer in rax
// TODO(max): Rewrite as lea rax, [rsi+kPairTag]
Emit_mov_reg_reg(buf, /*dst=*/kRax, /*src=*/kHeapPointer);
Emit_or_reg_imm8(buf, /*dst=*/kRax, kPairTag);
// Bump the heap pointer
Emit_add_reg_imm32(buf, /*dst=*/kHeapPointer, kPairSize);
return 0;
}
word list_length(ASTNode *node) {
if (AST_is_nil(node)) {
return 0;
}
assert(AST_is_pair(node));
return 1 + list_length(AST_pair_cdr(node));
}
void Emit_rsp_adjust(Buffer *buf, word adjust) {
if (adjust < 0) {
Emit_sub_reg_imm32(buf, kRsp, -adjust);
} else if (adjust > 0) {
Emit_add_reg_imm32(buf, kRsp, adjust);
}