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cpython/Python/assemble.c

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#include <stdbool.h>
#include "Python.h"
#include "pycore_code.h" // write_location_entry_start()
#include "pycore_compile.h"
#include "pycore_instruction_sequence.h"
#include "pycore_opcode_utils.h" // IS_BACKWARDS_JUMP_OPCODE
#include "pycore_opcode_metadata.h" // is_pseudo_target, _PyOpcode_Caches
#include "pycore_symtable.h" // _Py_SourceLocation
#define DEFAULT_CODE_SIZE 128
#define DEFAULT_LNOTAB_SIZE 16
#define DEFAULT_CNOTAB_SIZE 32
#undef SUCCESS
#undef ERROR
#define SUCCESS 0
#define ERROR -1
#define RETURN_IF_ERROR(X) \
if ((X) < 0) { \
return ERROR; \
}
typedef _Py_SourceLocation location;
typedef _PyInstruction instruction;
typedef _PyInstructionSequence instr_sequence;
static inline bool
same_location(location a, location b)
{
return a.lineno == b.lineno &&
a.end_lineno == b.end_lineno &&
a.col_offset == b.col_offset &&
a.end_col_offset == b.end_col_offset;
}
static int
instr_size(instruction *instr)
{
int opcode = instr->i_opcode;
int oparg = instr->i_oparg;
assert(!IS_PSEUDO_INSTR(opcode));
assert(OPCODE_HAS_ARG(opcode) || oparg == 0);
int extended_args = (0xFFFFFF < oparg) + (0xFFFF < oparg) + (0xFF < oparg);
int caches = _PyOpcode_Caches[opcode];
return extended_args + 1 + caches;
}
struct assembler {
PyObject *a_bytecode; /* bytes containing bytecode */
int a_offset; /* offset into bytecode */
PyObject *a_except_table; /* bytes containing exception table */
int a_except_table_off; /* offset into exception table */
/* Location Info */
int a_lineno; /* lineno of last emitted instruction */
PyObject* a_linetable; /* bytes containing location info */
int a_location_off; /* offset of last written location info frame */
};
static int
assemble_init(struct assembler *a, int firstlineno)
{
memset(a, 0, sizeof(struct assembler));
a->a_lineno = firstlineno;
a->a_linetable = NULL;
a->a_location_off = 0;
a->a_except_table = NULL;
a->a_bytecode = PyBytes_FromStringAndSize(NULL, DEFAULT_CODE_SIZE);
if (a->a_bytecode == NULL) {
goto error;
}
a->a_linetable = PyBytes_FromStringAndSize(NULL, DEFAULT_CNOTAB_SIZE);
if (a->a_linetable == NULL) {
goto error;
}
a->a_except_table = PyBytes_FromStringAndSize(NULL, DEFAULT_LNOTAB_SIZE);
if (a->a_except_table == NULL) {
goto error;
}
return SUCCESS;
error:
Py_XDECREF(a->a_bytecode);
Py_XDECREF(a->a_linetable);
Py_XDECREF(a->a_except_table);
return ERROR;
}
static void
assemble_free(struct assembler *a)
{
Py_XDECREF(a->a_bytecode);
Py_XDECREF(a->a_linetable);
Py_XDECREF(a->a_except_table);
}
static inline void
write_except_byte(struct assembler *a, int byte) {
unsigned char *p = (unsigned char *) PyBytes_AS_STRING(a->a_except_table);
p[a->a_except_table_off++] = byte;
}
#define CONTINUATION_BIT 64
static void
assemble_emit_exception_table_item(struct assembler *a, int value, int msb)
{
assert ((msb | 128) == 128);
assert(value >= 0 && value < (1 << 30));
if (value >= 1 << 24) {
write_except_byte(a, (value >> 24) | CONTINUATION_BIT | msb);
msb = 0;
}
if (value >= 1 << 18) {
write_except_byte(a, ((value >> 18)&0x3f) | CONTINUATION_BIT | msb);
msb = 0;
}
if (value >= 1 << 12) {
write_except_byte(a, ((value >> 12)&0x3f) | CONTINUATION_BIT | msb);
msb = 0;
}
if (value >= 1 << 6) {
write_except_byte(a, ((value >> 6)&0x3f) | CONTINUATION_BIT | msb);
msb = 0;
}
write_except_byte(a, (value&0x3f) | msb);
}
/* See Objects/exception_handling_notes.txt for details of layout */
#define MAX_SIZE_OF_ENTRY 20
static int
assemble_emit_exception_table_entry(struct assembler *a, int start, int end,
int handler_offset,
_PyExceptHandlerInfo *handler)
{
Py_ssize_t len = PyBytes_GET_SIZE(a->a_except_table);
if (a->a_except_table_off + MAX_SIZE_OF_ENTRY >= len) {
RETURN_IF_ERROR(_PyBytes_Resize(&a->a_except_table, len * 2));
}
int size = end-start;
assert(end > start);
int target = handler_offset;
int depth = handler->h_startdepth - 1;
if (handler->h_preserve_lasti > 0) {
depth -= 1;
}
assert(depth >= 0);
int depth_lasti = (depth<<1) | handler->h_preserve_lasti;
assemble_emit_exception_table_item(a, start, (1<<7));
assemble_emit_exception_table_item(a, size, 0);
assemble_emit_exception_table_item(a, target, 0);
assemble_emit_exception_table_item(a, depth_lasti, 0);
return SUCCESS;
}
static int
assemble_exception_table(struct assembler *a, instr_sequence *instrs)
{
int ioffset = 0;
_PyExceptHandlerInfo handler;
handler.h_label = -1;
handler.h_startdepth = -1;
handler.h_preserve_lasti = -1;
int start = -1;
for (int i = 0; i < instrs->s_used; i++) {
instruction *instr = &instrs->s_instrs[i];
if (instr->i_except_handler_info.h_label != handler.h_label) {
if (handler.h_label >= 0) {
int handler_offset = instrs->s_instrs[handler.h_label].i_offset;
RETURN_IF_ERROR(
assemble_emit_exception_table_entry(a, start, ioffset,
handler_offset,
&handler));
}
start = ioffset;
handler = instr->i_except_handler_info;
}
ioffset += instr_size(instr);
}
if (handler.h_label >= 0) {
int handler_offset = instrs->s_instrs[handler.h_label].i_offset;
RETURN_IF_ERROR(assemble_emit_exception_table_entry(a, start, ioffset,
handler_offset,
&handler));
}
return SUCCESS;
}
/* Code location emitting code. See locations.md for a description of the format. */
#define MSB 0x80
static void
write_location_byte(struct assembler* a, int val)
{
PyBytes_AS_STRING(a->a_linetable)[a->a_location_off] = val&255;
a->a_location_off++;
}
static uint8_t *
location_pointer(struct assembler* a)
{
return (uint8_t *)PyBytes_AS_STRING(a->a_linetable) +
a->a_location_off;
}
static void
write_location_first_byte(struct assembler* a, int code, int length)
{
a->a_location_off += write_location_entry_start(
location_pointer(a), code, length);
}
static void
write_location_varint(struct assembler* a, unsigned int val)
{
uint8_t *ptr = location_pointer(a);
a->a_location_off += write_varint(ptr, val);
}
static void
write_location_signed_varint(struct assembler* a, int val)
{
uint8_t *ptr = location_pointer(a);
a->a_location_off += write_signed_varint(ptr, val);
}
static void
write_location_info_short_form(struct assembler* a, int length, int column, int end_column)
{
assert(length > 0 && length <= 8);
int column_low_bits = column & 7;
int column_group = column >> 3;
assert(column < 80);
assert(end_column >= column);
assert(end_column - column < 16);
write_location_first_byte(a, PY_CODE_LOCATION_INFO_SHORT0 + column_group, length);
write_location_byte(a, (column_low_bits << 4) | (end_column - column));
}
static void
write_location_info_oneline_form(struct assembler* a, int length, int line_delta, int column, int end_column)
{
assert(length > 0 && length <= 8);
assert(line_delta >= 0 && line_delta < 3);
assert(column < 128);
assert(end_column < 128);
write_location_first_byte(a, PY_CODE_LOCATION_INFO_ONE_LINE0 + line_delta, length);
write_location_byte(a, column);
write_location_byte(a, end_column);
}
static void
write_location_info_long_form(struct assembler* a, location loc, int length)
{
assert(length > 0 && length <= 8);
write_location_first_byte(a, PY_CODE_LOCATION_INFO_LONG, length);
write_location_signed_varint(a, loc.lineno - a->a_lineno);
assert(loc.end_lineno >= loc.lineno);
write_location_varint(a, loc.end_lineno - loc.lineno);
write_location_varint(a, loc.col_offset + 1);
write_location_varint(a, loc.end_col_offset + 1);
}
static void
write_location_info_none(struct assembler* a, int length)
{
write_location_first_byte(a, PY_CODE_LOCATION_INFO_NONE, length);
}
static void
write_location_info_no_column(struct assembler* a, int length, int line_delta)
{
write_location_first_byte(a, PY_CODE_LOCATION_INFO_NO_COLUMNS, length);
write_location_signed_varint(a, line_delta);
}
#define THEORETICAL_MAX_ENTRY_SIZE 25 /* 1 + 6 + 6 + 6 + 6 */
static int
write_location_info_entry(struct assembler* a, location loc, int isize)
{
Py_ssize_t len = PyBytes_GET_SIZE(a->a_linetable);
if (a->a_location_off + THEORETICAL_MAX_ENTRY_SIZE >= len) {
assert(len > THEORETICAL_MAX_ENTRY_SIZE);
RETURN_IF_ERROR(_PyBytes_Resize(&a->a_linetable, len*2));
}
if (loc.lineno < 0) {
write_location_info_none(a, isize);
return SUCCESS;
}
int line_delta = loc.lineno - a->a_lineno;
int column = loc.col_offset;
int end_column = loc.end_col_offset;
assert(column >= -1);
assert(end_column >= -1);
if (column < 0 || end_column < 0) {
if (loc.end_lineno == loc.lineno || loc.end_lineno == -1) {
write_location_info_no_column(a, isize, line_delta);
a->a_lineno = loc.lineno;
return SUCCESS;
}
}
else if (loc.end_lineno == loc.lineno) {
if (line_delta == 0 && column < 80 && end_column - column < 16 && end_column >= column) {
write_location_info_short_form(a, isize, column, end_column);
return SUCCESS;
}
if (line_delta >= 0 && line_delta < 3 && column < 128 && end_column < 128) {
write_location_info_oneline_form(a, isize, line_delta, column, end_column);
a->a_lineno = loc.lineno;
return SUCCESS;
}
}
write_location_info_long_form(a, loc, isize);
a->a_lineno = loc.lineno;
return SUCCESS;
}
static int
assemble_emit_location(struct assembler* a, location loc, int isize)
{
if (isize == 0) {
return SUCCESS;
}
while (isize > 8) {
RETURN_IF_ERROR(write_location_info_entry(a, loc, 8));
isize -= 8;
}
return write_location_info_entry(a, loc, isize);
}
static int
assemble_location_info(struct assembler *a, instr_sequence *instrs,
int firstlineno)
{
a->a_lineno = firstlineno;
location loc = NO_LOCATION;
int size = 0;
for (int i = 0; i < instrs->s_used; i++) {
instruction *instr = &instrs->s_instrs[i];
if (!same_location(loc, instr->i_loc)) {
RETURN_IF_ERROR(assemble_emit_location(a, loc, size));
loc = instr->i_loc;
size = 0;
}
size += instr_size(instr);
}
RETURN_IF_ERROR(assemble_emit_location(a, loc, size));
return SUCCESS;
}
static void
write_instr(_Py_CODEUNIT *codestr, instruction *instr, int ilen)
{
int opcode = instr->i_opcode;
assert(!IS_PSEUDO_INSTR(opcode));
int oparg = instr->i_oparg;
assert(OPCODE_HAS_ARG(opcode) || oparg == 0);
int caches = _PyOpcode_Caches[opcode];
switch (ilen - caches) {
case 4:
codestr->op.code = EXTENDED_ARG;
codestr->op.arg = (oparg >> 24) & 0xFF;
codestr++;
_Py_FALLTHROUGH;
case 3:
codestr->op.code = EXTENDED_ARG;
codestr->op.arg = (oparg >> 16) & 0xFF;
codestr++;
_Py_FALLTHROUGH;
case 2:
codestr->op.code = EXTENDED_ARG;
codestr->op.arg = (oparg >> 8) & 0xFF;
codestr++;
_Py_FALLTHROUGH;
case 1:
codestr->op.code = opcode;
codestr->op.arg = oparg & 0xFF;
codestr++;
break;
default:
Py_UNREACHABLE();
}
while (caches--) {
codestr->op.code = CACHE;
codestr->op.arg = 0;
codestr++;
}
}
/* assemble_emit_instr()
Extend the bytecode with a new instruction.
Update lnotab if necessary.
*/
static int
assemble_emit_instr(struct assembler *a, instruction *instr)
{
Py_ssize_t len = PyBytes_GET_SIZE(a->a_bytecode);
_Py_CODEUNIT *code;
int size = instr_size(instr);
if (a->a_offset + size >= len / (int)sizeof(_Py_CODEUNIT)) {
if (len > PY_SSIZE_T_MAX / 2) {
return ERROR;
}
RETURN_IF_ERROR(_PyBytes_Resize(&a->a_bytecode, len * 2));
}
code = (_Py_CODEUNIT *)PyBytes_AS_STRING(a->a_bytecode) + a->a_offset;
a->a_offset += size;
write_instr(code, instr, size);
return SUCCESS;
}
static int
assemble_emit(struct assembler *a, instr_sequence *instrs,
int first_lineno, PyObject *const_cache)
{
RETURN_IF_ERROR(assemble_init(a, first_lineno));
for (int i = 0; i < instrs->s_used; i++) {
instruction *instr = &instrs->s_instrs[i];
RETURN_IF_ERROR(assemble_emit_instr(a, instr));
}
RETURN_IF_ERROR(assemble_location_info(a, instrs, a->a_lineno));
RETURN_IF_ERROR(assemble_exception_table(a, instrs));
RETURN_IF_ERROR(_PyBytes_Resize(&a->a_except_table, a->a_except_table_off));
RETURN_IF_ERROR(_PyCompile_ConstCacheMergeOne(const_cache, &a->a_except_table));
RETURN_IF_ERROR(_PyBytes_Resize(&a->a_linetable, a->a_location_off));
RETURN_IF_ERROR(_PyCompile_ConstCacheMergeOne(const_cache, &a->a_linetable));
RETURN_IF_ERROR(_PyBytes_Resize(&a->a_bytecode, a->a_offset * sizeof(_Py_CODEUNIT)));
RETURN_IF_ERROR(_PyCompile_ConstCacheMergeOne(const_cache, &a->a_bytecode));
return SUCCESS;
}
static PyObject *
dict_keys_inorder(PyObject *dict, Py_ssize_t offset)
{
PyObject *tuple, *k, *v;
Py_ssize_t pos = 0, size = PyDict_GET_SIZE(dict);
tuple = PyTuple_New(size);
if (tuple == NULL)
return NULL;
while (PyDict_Next(dict, &pos, &k, &v)) {
Py_ssize_t i = PyLong_AsSsize_t(v);
if (i == -1 && PyErr_Occurred()) {
Py_DECREF(tuple);
return NULL;
}
assert((i - offset) < size);
assert((i - offset) >= 0);
PyTuple_SET_ITEM(tuple, i - offset, Py_NewRef(k));
}
return tuple;
}
// This is in codeobject.c.
extern void _Py_set_localsplus_info(int, PyObject *, unsigned char,
PyObject *, PyObject *);
static int
compute_localsplus_info(_PyCompile_CodeUnitMetadata *umd, int nlocalsplus,
PyObject *names, PyObject *kinds)
{
PyObject *k, *v;
Py_ssize_t pos = 0;
while (PyDict_Next(umd->u_varnames, &pos, &k, &v)) {
int offset = PyLong_AsInt(v);
if (offset == -1 && PyErr_Occurred()) {
return ERROR;
}
assert(offset >= 0);
assert(offset < nlocalsplus);
// For now we do not distinguish arg kinds.
_PyLocals_Kind kind = CO_FAST_LOCAL;
int has_key = PyDict_Contains(umd->u_fasthidden, k);
RETURN_IF_ERROR(has_key);
if (has_key) {
kind |= CO_FAST_HIDDEN;
}
has_key = PyDict_Contains(umd->u_cellvars, k);
RETURN_IF_ERROR(has_key);
if (has_key) {
kind |= CO_FAST_CELL;
}
_Py_set_localsplus_info(offset, k, kind, names, kinds);
}
int nlocals = (int)PyDict_GET_SIZE(umd->u_varnames);
// This counter mirrors the fix done in fix_cell_offsets().
int numdropped = 0;
pos = 0;
while (PyDict_Next(umd->u_cellvars, &pos, &k, &v)) {
int has_name = PyDict_Contains(umd->u_varnames, k);
RETURN_IF_ERROR(has_name);
if (has_name) {
// Skip cells that are already covered by locals.
numdropped += 1;
continue;
}
int offset = PyLong_AsInt(v);
if (offset == -1 && PyErr_Occurred()) {
return ERROR;
}
assert(offset >= 0);
offset += nlocals - numdropped;
assert(offset < nlocalsplus);
_Py_set_localsplus_info(offset, k, CO_FAST_CELL, names, kinds);
}
pos = 0;
while (PyDict_Next(umd->u_freevars, &pos, &k, &v)) {
int offset = PyLong_AsInt(v);
if (offset == -1 && PyErr_Occurred()) {
return ERROR;
}
assert(offset >= 0);
offset += nlocals - numdropped;
assert(offset < nlocalsplus);
_Py_set_localsplus_info(offset, k, CO_FAST_FREE, names, kinds);
}
return SUCCESS;
}
static PyCodeObject *
makecode(_PyCompile_CodeUnitMetadata *umd, struct assembler *a, PyObject *const_cache,
PyObject *constslist, int maxdepth, int nlocalsplus, int code_flags,
PyObject *filename)
{
PyCodeObject *co = NULL;
PyObject *names = NULL;
PyObject *consts = NULL;
PyObject *localsplusnames = NULL;
PyObject *localspluskinds = NULL;
names = dict_keys_inorder(umd->u_names, 0);
if (!names) {
goto error;
}
if (_PyCompile_ConstCacheMergeOne(const_cache, &names) < 0) {
goto error;
}
consts = PyList_AsTuple(constslist); /* PyCode_New requires a tuple */
if (consts == NULL) {
goto error;
}
if (_PyCompile_ConstCacheMergeOne(const_cache, &consts) < 0) {
goto error;
}
assert(umd->u_posonlyargcount < INT_MAX);
assert(umd->u_argcount < INT_MAX);
assert(umd->u_kwonlyargcount < INT_MAX);
int posonlyargcount = (int)umd->u_posonlyargcount;
int posorkwargcount = (int)umd->u_argcount;
assert(INT_MAX - posonlyargcount - posorkwargcount > 0);
int kwonlyargcount = (int)umd->u_kwonlyargcount;
localsplusnames = PyTuple_New(nlocalsplus);
if (localsplusnames == NULL) {
goto error;
}
localspluskinds = PyBytes_FromStringAndSize(NULL, nlocalsplus);
if (localspluskinds == NULL) {
goto error;
}
if (compute_localsplus_info(umd, nlocalsplus,
localsplusnames, localspluskinds) == ERROR) {
goto error;
}
struct _PyCodeConstructor con = {
.filename = filename,
.name = umd->u_name,
.qualname = umd->u_qualname ? umd->u_qualname : umd->u_name,
.flags = code_flags,
.code = a->a_bytecode,
.firstlineno = umd->u_firstlineno,
.linetable = a->a_linetable,
.consts = consts,
.names = names,
.localsplusnames = localsplusnames,
.localspluskinds = localspluskinds,
.argcount = posonlyargcount + posorkwargcount,
.posonlyargcount = posonlyargcount,
.kwonlyargcount = kwonlyargcount,
.stacksize = maxdepth,
.exceptiontable = a->a_except_table,
};
if (_PyCode_Validate(&con) < 0) {
goto error;
}
if (_PyCompile_ConstCacheMergeOne(const_cache, &localsplusnames) < 0) {
goto error;
}
con.localsplusnames = localsplusnames;
co = _PyCode_New(&con);
if (co == NULL) {
goto error;
}
error:
Py_XDECREF(names);
Py_XDECREF(consts);
Py_XDECREF(localsplusnames);
Py_XDECREF(localspluskinds);
return co;
}
static int
resolve_jump_offsets(instr_sequence *instrs)
{
/* Compute the size of each instruction and fixup jump args.
* Replace instruction index with position in bytecode.
*/
for (int i = 0; i < instrs->s_used; i++) {
instruction *instr = &instrs->s_instrs[i];
if (OPCODE_HAS_JUMP(instr->i_opcode)) {
instr->i_target = instr->i_oparg;
}
}
int extended_arg_recompile;
do {
int totsize = 0;
for (int i = 0; i < instrs->s_used; i++) {
instruction *instr = &instrs->s_instrs[i];
instr->i_offset = totsize;
int isize = instr_size(instr);
totsize += isize;
}
extended_arg_recompile = 0;
int offset = 0;
for (int i = 0; i < instrs->s_used; i++) {
instruction *instr = &instrs->s_instrs[i];
int isize = instr_size(instr);
/* jump offsets are computed relative to
* the instruction pointer after fetching
* the jump instruction.
*/
offset += isize;
if (OPCODE_HAS_JUMP(instr->i_opcode)) {
instruction *target = &instrs->s_instrs[instr->i_target];
instr->i_oparg = target->i_offset;
if (instr->i_oparg < offset) {
assert(IS_BACKWARDS_JUMP_OPCODE(instr->i_opcode));
instr->i_oparg = offset - instr->i_oparg;
}
else {
assert(!IS_BACKWARDS_JUMP_OPCODE(instr->i_opcode));
instr->i_oparg = instr->i_oparg - offset;
}
if (instr_size(instr) != isize) {
extended_arg_recompile = 1;
}
}
}
/* XXX: This is an awful hack that could hurt performance, but
on the bright side it should work until we come up
with a better solution.
The issue is that in the first loop instr_size() is
called, and it requires i_oparg be set appropriately.
There is a bootstrap problem because i_oparg is
calculated in the second loop above.
So we loop until we stop seeing new EXTENDED_ARGs.
The only EXTENDED_ARGs that could be popping up are
ones in jump instructions. So this should converge
fairly quickly.
*/
} while (extended_arg_recompile);
return SUCCESS;
}
static int
resolve_unconditional_jumps(instr_sequence *instrs)
{
/* Resolve directions of unconditional jumps */
for (int i = 0; i < instrs->s_used; i++) {
instruction *instr = &instrs->s_instrs[i];
bool is_forward = (instr->i_oparg > i);
switch(instr->i_opcode) {
case JUMP:
assert(is_pseudo_target(JUMP, JUMP_FORWARD));
assert(is_pseudo_target(JUMP, JUMP_BACKWARD));
instr->i_opcode = is_forward ? JUMP_FORWARD : JUMP_BACKWARD;
break;
case JUMP_NO_INTERRUPT:
assert(is_pseudo_target(JUMP_NO_INTERRUPT, JUMP_FORWARD));
assert(is_pseudo_target(JUMP_NO_INTERRUPT, JUMP_BACKWARD_NO_INTERRUPT));
instr->i_opcode = is_forward ?
JUMP_FORWARD : JUMP_BACKWARD_NO_INTERRUPT;
break;
default:
if (OPCODE_HAS_JUMP(instr->i_opcode) &&
IS_PSEUDO_INSTR(instr->i_opcode)) {
Py_UNREACHABLE();
}
}
}
return SUCCESS;
}
PyCodeObject *
_PyAssemble_MakeCodeObject(_PyCompile_CodeUnitMetadata *umd, PyObject *const_cache,
PyObject *consts, int maxdepth, instr_sequence *instrs,
int nlocalsplus, int code_flags, PyObject *filename)
{
if (_PyInstructionSequence_ApplyLabelMap(instrs) < 0) {
return NULL;
}
if (resolve_unconditional_jumps(instrs) < 0) {
return NULL;
}
if (resolve_jump_offsets(instrs) < 0) {
return NULL;
}
PyCodeObject *co = NULL;
struct assembler a;
int res = assemble_emit(&a, instrs, umd->u_firstlineno, const_cache);
if (res == SUCCESS) {
co = makecode(umd, &a, const_cache, consts, maxdepth, nlocalsplus,
code_flags, filename);
}
assemble_free(&a);
return co;
}
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