/******************************************************************************

* Remote Debugging Module - Frame Functions

*

* This file contains functions for parsing interpreter frames and

* managing stack chunks from remote process memory.

******************************************************************************/

#include "_remote_debugging.h"

/* ============================================================================

* STACK CHUNK MANAGEMENT FUNCTIONS

* ============================================================================ */

void

cleanup_stack_chunks(StackChunkList *chunks)

{

for (size_t i = 0; i < chunks->count; ++i) {

PyMem_RawFree(chunks->chunks[i].local_copy);

}

PyMem_RawFree(chunks->chunks);

}

static int

process_single_stack_chunk(

RemoteUnwinderObject *unwinder,

uintptr_t chunk_addr,

StackChunkInfo *chunk_info

) {

// Start with default size assumption

size_t current_size = _PY_DATA_STACK_CHUNK_SIZE;

char *this_chunk = PyMem_RawMalloc(current_size);

if (!this_chunk) {

PyErr_NoMemory();

set_exception_cause(unwinder, PyExc_MemoryError, "Failed to allocate stack chunk buffer");

return -1;

}

if (_Py_RemoteDebug_PagedReadRemoteMemory(&unwinder->handle, chunk_addr, current_size, this_chunk) < 0) {

PyMem_RawFree(this_chunk);

set_exception_cause(unwinder, PyExc_RuntimeError, "Failed to read stack chunk");

return -1;

}

// Check actual size and reread if necessary

size_t actual_size = GET_MEMBER(size_t, this_chunk, offsetof(_PyStackChunk, size));

if (actual_size != current_size) {

// Validate size: reject garbage (too small or unreasonably large)

// Size must be at least enough for the header and reasonably bounded

if (actual_size <= offsetof(_PyStackChunk, data) || actual_size > MAX_STACK_CHUNK_SIZE) {

PyMem_RawFree(this_chunk);

PyErr_Format(PyExc_RuntimeError,

"Invalid stack chunk size %zu (corrupted remote memory)", actual_size);

set_exception_cause(unwinder, PyExc_RuntimeError,

"Invalid stack chunk size (corrupted remote memory)");

return -1;

}

this_chunk = PyMem_RawRealloc(this_chunk, actual_size);

if (!this_chunk) {

PyErr_NoMemory();

set_exception_cause(unwinder, PyExc_MemoryError, "Failed to reallocate stack chunk buffer");

return -1;

}

if (_Py_RemoteDebug_PagedReadRemoteMemory(&unwinder->handle, chunk_addr, actual_size, this_chunk) < 0) {

PyMem_RawFree(this_chunk);

set_exception_cause(unwinder, PyExc_RuntimeError, "Failed to reread stack chunk with correct size");

return -1;

}

current_size = actual_size;

}

chunk_info->remote_addr = chunk_addr;

chunk_info->size = current_size;

chunk_info->local_copy = this_chunk;

return 0;

}

int

copy_stack_chunks(RemoteUnwinderObject *unwinder,

uintptr_t tstate_addr,

StackChunkList *out_chunks)

{

uintptr_t chunk_addr;

StackChunkInfo *chunks = NULL;

size_t count = 0;

size_t max_chunks = 16;

if (read_ptr(unwinder, tstate_addr + (uintptr_t)unwinder->debug_offsets.thread_state.datastack_chunk, &chunk_addr)) {

set_exception_cause(unwinder, PyExc_RuntimeError, "Failed to read initial stack chunk address");

return -1;

}

chunks = PyMem_RawMalloc(max_chunks * sizeof(StackChunkInfo));

if (!chunks) {

PyErr_NoMemory();

set_exception_cause(unwinder, PyExc_MemoryError, "Failed to allocate stack chunks array");

return -1;

}

const size_t MAX_STACK_CHUNKS = 4096;

while (chunk_addr != 0 && count < MAX_STACK_CHUNKS) {

// Grow array if needed

if (count >= max_chunks) {

max_chunks *= 2;

StackChunkInfo *new_chunks = PyMem_RawRealloc(chunks, max_chunks * sizeof(StackChunkInfo));

if (!new_chunks) {

PyErr_NoMemory();

set_exception_cause(unwinder, PyExc_MemoryError, "Failed to grow stack chunks array");

goto error;

}

chunks = new_chunks;

}

// Process this chunk

if (process_single_stack_chunk(unwinder, chunk_addr, &chunks[count]) < 0) {

set_exception_cause(unwinder, PyExc_RuntimeError, "Failed to process stack chunk");

goto error;

}

// Get next chunk address and increment count

chunk_addr = GET_MEMBER(uintptr_t, chunks[count].local_copy, offsetof(_PyStackChunk, previous));

count++;

}

out_chunks->chunks = chunks;

out_chunks->count = count;

return 0;

error:

for (size_t i = 0; i < count; ++i) {

PyMem_RawFree(chunks[i].local_copy);

}

PyMem_RawFree(chunks);

return -1;

}

void *

find_frame_in_chunks(StackChunkList *chunks, uintptr_t remote_ptr)

{

for (size_t i = 0; i < chunks->count; ++i) {

// Validate size: reject garbage that would cause underflow

if (chunks->chunks[i].size <= offsetof(_PyStackChunk, data)) {

// Skip this chunk - corrupted size from remote memory

continue;

}

uintptr_t base = chunks->chunks[i].remote_addr + offsetof(_PyStackChunk, data);

size_t payload = chunks->chunks[i].size - offsetof(_PyStackChunk, data);

if (payload >= SIZEOF_INTERP_FRAME &&

remote_ptr >= base &&

remote_ptr <= base + payload - SIZEOF_INTERP_FRAME) {

return (char *)chunks->chunks[i].local_copy + (remote_ptr - chunks->chunks[i].remote_addr);

}

}

return NULL;

}

/* ============================================================================

* FRAME PARSING FUNCTIONS

* ============================================================================ */

int

is_frame_valid(

RemoteUnwinderObject *unwinder,

uintptr_t frame_addr,

uintptr_t code_object_addr

) {

if ((void*)code_object_addr == NULL) {

return 0;

}

void* frame = (void*)frame_addr;

char owner = GET_MEMBER(char, frame, unwinder->debug_offsets.interpreter_frame.owner);

if (owner == FRAME_OWNED_BY_INTERPRETER) {

return 0; // C frame or sentinel base frame

}

if (owner != FRAME_OWNED_BY_GENERATOR && owner != FRAME_OWNED_BY_THREAD) {

PyErr_Format(PyExc_RuntimeError, "Unhandled frame owner %d.\n", owner);

set_exception_cause(unwinder, PyExc_RuntimeError, "Unhandled frame owner type in async frame");

return -1;

}

return 1;

}

int

parse_frame_object(

RemoteUnwinderObject *unwinder,

PyObject** result,

uintptr_t address,

uintptr_t* address_of_code_object,

uintptr_t* previous_frame

) {

char frame[SIZEOF_INTERP_FRAME];

*address_of_code_object = 0;

Py_ssize_t bytes_read = _Py_RemoteDebug_PagedReadRemoteMemory(

&unwinder->handle,

address,

SIZEOF_INTERP_FRAME,

frame

);

if (bytes_read < 0) {

set_exception_cause(unwinder, PyExc_RuntimeError, "Failed to read interpreter frame");

return -1;

}

STATS_INC(unwinder, memory_reads);

STATS_ADD(unwinder, memory_bytes_read, SIZEOF_INTERP_FRAME);

*previous_frame = GET_MEMBER(uintptr_t, frame, unwinder->debug_offsets.interpreter_frame.previous);

uintptr_t code_object = GET_MEMBER_NO_TAG(uintptr_t, frame, unwinder->debug_offsets.interpreter_frame.executable);

int frame_valid = is_frame_valid(unwinder, (uintptr_t)frame, code_object);

if (frame_valid != 1) {

return frame_valid;

}

uintptr_t instruction_pointer = GET_MEMBER(uintptr_t, frame, unwinder->debug_offsets.interpreter_frame.instr_ptr);

// Get tlbc_index for free threading builds

int32_t tlbc_index = 0;

#ifdef Py_GIL_DISABLED

if (unwinder->debug_offsets.interpreter_frame.tlbc_index != 0) {

tlbc_index = GET_MEMBER(int32_t, frame, unwinder->debug_offsets.interpreter_frame.tlbc_index);

}

#endif

*address_of_code_object = code_object;

CodeObjectContext code_ctx = {

.code_addr = code_object,

.instruction_pointer = instruction_pointer,

.tlbc_index = tlbc_index,

};

return parse_code_object(unwinder, result, &code_ctx);

}

int

parse_frame_from_chunks(

RemoteUnwinderObject *unwinder,

PyObject **result,

uintptr_t address,

uintptr_t *previous_frame,

uintptr_t *stackpointer,

StackChunkList *chunks

) {

void *frame_ptr = find_frame_in_chunks(chunks, address);

if (!frame_ptr) {

PyErr_Format(PyExc_RuntimeError, "Frame at address 0x%lx not found in stack chunks", address);

set_exception_cause(unwinder, PyExc_RuntimeError, "Frame not found in stack chunks");

return -1;

}

char *frame = (char *)frame_ptr;

*previous_frame = GET_MEMBER(uintptr_t, frame, unwinder->debug_offsets.interpreter_frame.previous);

*stackpointer = GET_MEMBER(uintptr_t, frame, unwinder->debug_offsets.interpreter_frame.stackpointer);

uintptr_t code_object = GET_MEMBER_NO_TAG(uintptr_t, frame_ptr, unwinder->debug_offsets.interpreter_frame.executable);

int frame_valid = is_frame_valid(unwinder, (uintptr_t)frame, code_object);

if (frame_valid != 1) {

return frame_valid;

}

uintptr_t instruction_pointer = GET_MEMBER(uintptr_t, frame, unwinder->debug_offsets.interpreter_frame.instr_ptr);

// Get tlbc_index for free threading builds

int32_t tlbc_index = 0;

#ifdef Py_GIL_DISABLED

if (unwinder->debug_offsets.interpreter_frame.tlbc_index != 0) {

tlbc_index = GET_MEMBER(int32_t, frame, unwinder->debug_offsets.interpreter_frame.tlbc_index);

}

#endif

CodeObjectContext code_ctx = {

.code_addr = code_object,

.instruction_pointer = instruction_pointer,

.tlbc_index = tlbc_index,

};

return parse_code_object(unwinder, result, &code_ctx);

}

/* ============================================================================

* FRAME CHAIN PROCESSING

* ============================================================================ */

int

process_frame_chain(

RemoteUnwinderObject *unwinder,

FrameWalkContext *ctx)

{

uintptr_t frame_addr = ctx->frame_addr;

uintptr_t prev_frame_addr = 0;

uintptr_t last_frame_addr = 0;

const size_t MAX_FRAMES = 1024 + 512;

size_t frame_count = 0;

assert(MAX_FRAMES > 0 && MAX_FRAMES < 10000);

ctx->stopped_at_cached_frame = 0;

ctx->last_frame_visited = 0;

while ((void*)frame_addr != NULL) {

PyObject *frame = NULL;

uintptr_t next_frame_addr = 0;

uintptr_t stackpointer = 0;

last_frame_addr = frame_addr;

if (++frame_count > MAX_FRAMES) {

PyErr_SetString(PyExc_RuntimeError, "Too many stack frames (possible infinite loop)");

set_exception_cause(unwinder, PyExc_RuntimeError, "Frame chain iteration limit exceeded");

return -1;

}

assert(frame_count <= MAX_FRAMES);

if (parse_frame_from_chunks(unwinder, &frame, frame_addr, &next_frame_addr, &stackpointer, ctx->chunks) < 0) {

PyErr_Clear();

uintptr_t address_of_code_object = 0;

if (parse_frame_object(unwinder, &frame, frame_addr, &address_of_code_object, &next_frame_addr) < 0) {

set_exception_cause(unwinder, PyExc_RuntimeError, "Failed to parse frame object in chain");

return -1;

}

}

// Skip first frame if requested (used for cache miss continuation)

if (ctx->skip_first_frame && frame_count == 1) {

Py_XDECREF(frame);

frame_addr = next_frame_addr;

continue;

}

if (frame == NULL && PyList_GET_SIZE(ctx->frame_info) == 0) {

const char *e = "Failed to parse initial frame in chain";

PyErr_SetString(PyExc_RuntimeError, e);

return -1;

}

PyObject *extra_frame = NULL;

if (unwinder->gc && frame_addr == ctx->gc_frame) {

_Py_DECLARE_STR(gc, "<GC>");

extra_frame = &_Py_STR(gc);

}

else if (unwinder->native &&

frame == NULL &&

next_frame_addr &&

!(unwinder->gc && next_frame_addr == ctx->gc_frame))

{

_Py_DECLARE_STR(native, "<native>");

extra_frame = &_Py_STR(native);

}

if (extra_frame) {

PyObject *extra_frame_info = make_frame_info(

unwinder, _Py_LATIN1_CHR('~'), Py_None, extra_frame, Py_None);

if (extra_frame_info == NULL) {

Py_XDECREF(frame);

return -1;

}

if (PyList_Append(ctx->frame_info, extra_frame_info) < 0) {

Py_DECREF(extra_frame_info);

Py_XDECREF(frame);

set_exception_cause(unwinder, PyExc_RuntimeError, "Failed to append extra frame");

return -1;

}

if (ctx->frame_addrs && ctx->num_addrs < ctx->max_addrs) {

assert(ctx->num_addrs >= 0);

ctx->frame_addrs[ctx->num_addrs++] = 0;

}

Py_DECREF(extra_frame_info);

}

if (frame) {

if (prev_frame_addr && frame_addr != prev_frame_addr) {

const char *f = "Broken frame chain: expected frame at 0x%lx, got 0x%lx";

PyErr_Format(PyExc_RuntimeError, f, prev_frame_addr, frame_addr);

Py_DECREF(frame);

set_exception_cause(unwinder, PyExc_RuntimeError, "Frame chain consistency check failed");

return -1;

}

if (PyList_Append(ctx->frame_info, frame) < 0) {

Py_DECREF(frame);

set_exception_cause(unwinder, PyExc_RuntimeError, "Failed to append frame");

return -1;

}

if (ctx->frame_addrs && ctx->num_addrs < ctx->max_addrs) {

assert(ctx->num_addrs >= 0);

ctx->frame_addrs[ctx->num_addrs++] = frame_addr;

}

Py_DECREF(frame);

}

if (ctx->last_profiled_frame != 0 && frame_addr == ctx->last_profiled_frame) {

ctx->stopped_at_cached_frame = 1;

break;

}

prev_frame_addr = next_frame_addr;

frame_addr = next_frame_addr;

}

if (!ctx->stopped_at_cached_frame && ctx->base_frame_addr != 0 && last_frame_addr != ctx->base_frame_addr) {

PyErr_Format(PyExc_RuntimeError,

"Incomplete sample: did not reach base frame (expected 0x%lx, got 0x%lx)",

ctx->base_frame_addr, last_frame_addr);

return -1;

}

ctx->last_frame_visited = last_frame_addr;

return 0;

}

// Clear last_profiled_frame for all threads in the target process.

// This must be called at the start of profiling to avoid stale values

// from previous profilers causing us to stop frame walking early.

int

clear_last_profiled_frames(RemoteUnwinderObject *unwinder)

{

uintptr_t current_interp = unwinder->interpreter_addr;

uintptr_t zero = 0;

const size_t MAX_INTERPRETERS = 256;

size_t interp_count = 0;

while (current_interp != 0 && interp_count < MAX_INTERPRETERS) {

interp_count++;

// Get first thread in this interpreter

uintptr_t tstate_addr;

if (_Py_RemoteDebug_PagedReadRemoteMemory(

&unwinder->handle,

current_interp + unwinder->debug_offsets.interpreter_state.threads_head,

sizeof(void*),

&tstate_addr) < 0) {

// Non-fatal: just skip clearing

PyErr_Clear();

return 0;

}

// Iterate all threads in this interpreter

const size_t MAX_THREADS_PER_INTERP = 8192;

size_t thread_count = 0;

while (tstate_addr != 0 && thread_count < MAX_THREADS_PER_INTERP) {

thread_count++;

// Clear last_profiled_frame

uintptr_t lpf_addr = tstate_addr + unwinder->debug_offsets.thread_state.last_profiled_frame;

if (_Py_RemoteDebug_WriteRemoteMemory(&unwinder->handle, lpf_addr,

sizeof(uintptr_t), &zero) < 0) {

// Non-fatal: just continue

PyErr_Clear();

}

// Move to next thread

if (_Py_RemoteDebug_PagedReadRemoteMemory(

&unwinder->handle,

tstate_addr + unwinder->debug_offsets.thread_state.next,

sizeof(void*),

&tstate_addr) < 0) {

PyErr_Clear();

break;

}

}

// Move to next interpreter

if (_Py_RemoteDebug_PagedReadRemoteMemory(

&unwinder->handle,

current_interp + unwinder->debug_offsets.interpreter_state.next,

sizeof(void*),

&current_interp) < 0) {

PyErr_Clear();

break;

}

}

return 0;

}

// Fast path: check if we have a full cache hit (parent stack unchanged)

// A "full hit" means current frame == last profiled frame, so we can reuse

// cached parent frames. We always read the current frame from memory to get

// updated line numbers (the line within a frame can change between samples).

// Returns: 1 if full hit (frame_info populated with current frame + cached parents),

// 0 if miss, -1 on error

static int

try_full_cache_hit(

RemoteUnwinderObject *unwinder,

const FrameWalkContext *ctx,

uint64_t thread_id)

{

if (!unwinder->frame_cache || ctx->last_profiled_frame == 0) {

return 0;

}

if (ctx->frame_addr != ctx->last_profiled_frame) {

return 0;

}

FrameCacheEntry *entry = frame_cache_find(unwinder, thread_id);

if (!entry || !entry->frame_list) {

return 0;

}

if (entry->num_addrs == 0 || entry->addrs[0] != ctx->frame_addr) {

return 0;

}

PyObject *current_frame = NULL;

uintptr_t code_object_addr = 0;

uintptr_t previous_frame = 0;

int parse_result = parse_frame_object(unwinder, &current_frame, ctx->frame_addr,

&code_object_addr, &previous_frame);

if (parse_result < 0) {

return -1;

}

Py_ssize_t cached_size = PyList_GET_SIZE(entry->frame_list);

PyObject *parent_slice = NULL;

if (cached_size > 1) {

parent_slice = PyList_GetSlice(entry->frame_list, 1, cached_size);

if (!parent_slice) {

Py_XDECREF(current_frame);

return -1;

}

}

if (current_frame != NULL) {

if (PyList_Append(ctx->frame_info, current_frame) < 0) {

Py_DECREF(current_frame);

Py_XDECREF(parent_slice);

return -1;

}

Py_DECREF(current_frame);

STATS_ADD(unwinder, frames_read_from_memory, 1);

}

if (parent_slice) {

Py_ssize_t cur_size = PyList_GET_SIZE(ctx->frame_info);

int result = PyList_SetSlice(ctx->frame_info, cur_size, cur_size, parent_slice);

Py_DECREF(parent_slice);

if (result < 0) {

return -1;

}

STATS_ADD(unwinder, frames_read_from_cache, cached_size - 1);

}

STATS_INC(unwinder, frame_cache_hits);

return 1;

}

// High-level helper: collect frames with cache optimization

// Returns complete frame_info list, handling all cache logic internally

int

collect_frames_with_cache(

RemoteUnwinderObject *unwinder,

FrameWalkContext *ctx,

uint64_t thread_id)

{

int full_hit = try_full_cache_hit(unwinder, ctx, thread_id);

if (full_hit != 0) {

return full_hit < 0 ? -1 : 0;

}

Py_ssize_t frames_before = PyList_GET_SIZE(ctx->frame_info);

if (process_frame_chain(unwinder, ctx) < 0) {

return -1;

}

STATS_ADD(unwinder, frames_read_from_memory, PyList_GET_SIZE(ctx->frame_info) - frames_before);

if (ctx->stopped_at_cached_frame) {

Py_ssize_t frames_before_cache = PyList_GET_SIZE(ctx->frame_info);

int cache_result = frame_cache_lookup_and_extend(unwinder, thread_id, ctx->last_profiled_frame,

ctx->frame_info, ctx->frame_addrs, &ctx->num_addrs,

ctx->max_addrs);

if (cache_result < 0) {

return -1;

}

if (cache_result == 0) {

STATS_INC(unwinder, frame_cache_misses);

// Continue walking from last_profiled_frame, skipping it (already processed)

Py_ssize_t frames_before_walk = PyList_GET_SIZE(ctx->frame_info);

FrameWalkContext continue_ctx = {

.frame_addr = ctx->last_profiled_frame,

.base_frame_addr = ctx->base_frame_addr,

.gc_frame = ctx->gc_frame,

.chunks = ctx->chunks,

.skip_first_frame = 1,

.frame_info = ctx->frame_info,

.frame_addrs = ctx->frame_addrs,

.num_addrs = ctx->num_addrs,

.max_addrs = ctx->max_addrs,

};

if (process_frame_chain(unwinder, &continue_ctx) < 0) {

return -1;

}

ctx->num_addrs = continue_ctx.num_addrs;

ctx->last_frame_visited = continue_ctx.last_frame_visited;

STATS_ADD(unwinder, frames_read_from_memory, PyList_GET_SIZE(ctx->frame_info) - frames_before_walk);

} else {

// Partial cache hit - cached stack was validated as complete when stored,

// so set last_frame_visited to base_frame_addr for validation in frame_cache_store

ctx->last_frame_visited = ctx->base_frame_addr;

STATS_INC(unwinder, frame_cache_partial_hits);

STATS_ADD(unwinder, frames_read_from_cache, PyList_GET_SIZE(ctx->frame_info) - frames_before_cache);

}

} else {

if (ctx->last_profiled_frame == 0) {

STATS_INC(unwinder, frame_cache_misses);

}

}

if (frame_cache_store(unwinder, thread_id, ctx->frame_info, ctx->frame_addrs, ctx->num_addrs,

ctx->base_frame_addr, ctx->last_frame_visited) < 0) {

return -1;

}

return 0;

}