daScript/src/misc/alloc_tracker_fast_stack.cpp at master · PushoN/daScript · GitHub

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#include "daScript/misc/platform.h"

// Fast Win64 stack unwinder for the heap-leak tracker. Replaces the

// per-allocation call to CaptureStackBackTrace (which takes a spinlock inside

// RtlLookupFunctionEntry) with:

// 1) A cached PE .pdata table -- binary-searched, no OS locks.

// 2) A lightweight UNWIND_INFO interpreter that avoids RtlVirtualUnwind for

// the common opcodes.

// 3) A single-level "landmark" RAII that fully walks once, stores the

// remaining chain, and lets later captures tail-memoize from a known

// frame (matched by RSP).

// Non-Win64 platforms fall through to the generic path in alloc_tracker.cpp.

// Ported from Gaijin's dag_fastStackCapture.cpp.

#if DAS_TRACK_ALLOC && defined(_MSC_VER) && defined(_M_X64)

#include <windows.h>

#include <winnt.h>

#include <tlhelp32.h>

#include <intrin.h>

#include <atomic>

#include <mutex>

#include <new> // placement new for the immortal mutex storage

#include <algorithm>

#include <cstring>

#include <cstdint>

namespace das {

// ---------------------------------------------------------------------------

// Module cache

// ---------------------------------------------------------------------------

struct CachedModule {

ULONG64 base;

ULONG64 end;

PRUNTIME_FUNCTION pdata;

ULONG pdataLast;

};

static constexpr int MAX_CACHED_MODULES = 512;

static CachedModule g_modules[MAX_CACHED_MODULES];

static std::atomic<int> g_moduleCount{0};

static std::atomic<bool> g_cacheReady{false};

static std::mutex & getCacheMutex() {

alignas(std::mutex) static unsigned char storage[sizeof(std::mutex)];

static std::mutex *m = ::new (storage) std::mutex();

return *m;

}

// Negative cache for PCs that don't belong to any module (JIT code, etc).

// Direct-mapped, lossy on collisions; page granularity is 64KB.

static constexpr int NEG_CACHE_BITS = 6;

static constexpr int NEG_CACHE_SIZE = 1 << NEG_CACHE_BITS;

static std::atomic<uint64_t> g_negCache[NEG_CACHE_SIZE];

static __forceinline bool isNegCached(ULONG64 pc) {

uint64_t page = pc >> 16;

return g_negCache[page & (NEG_CACHE_SIZE - 1)].load(std::memory_order_relaxed) == page;

}

static __forceinline void addNegCache(ULONG64 pc) {

uint64_t page = pc >> 16;

g_negCache[page & (NEG_CACHE_SIZE - 1)].store(page, std::memory_order_relaxed);

}

static void buildModuleCache() noexcept {

HANDLE snap = CreateToolhelp32Snapshot(TH32CS_SNAPMODULE, 0);

if (snap == INVALID_HANDLE_VALUE) return;

MODULEENTRY32W me;

me.dwSize = sizeof(me);

int count = 0;

BOOL ok = Module32FirstW(snap, &me);

while (ok && count < MAX_CACHED_MODULES) {

const BYTE *dllBase = me.modBaseAddr;

if (dllBase && me.modBaseSize) {

__try {

const IMAGE_DOS_HEADER *dos = (const IMAGE_DOS_HEADER*)dllBase;

if (dos->e_magic == IMAGE_DOS_SIGNATURE) {

const IMAGE_NT_HEADERS64 *nt = (const IMAGE_NT_HEADERS64*)(dllBase + dos->e_lfanew);

if (nt->Signature == IMAGE_NT_SIGNATURE &&

nt->OptionalHeader.NumberOfRvaAndSizes > IMAGE_DIRECTORY_ENTRY_EXCEPTION) {

const IMAGE_DATA_DIRECTORY &excDir =

nt->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXCEPTION];

if (excDir.VirtualAddress && excDir.Size >= sizeof(RUNTIME_FUNCTION)) {

CachedModule &m = g_modules[count];

m.base = (ULONG64)dllBase;

m.end = (ULONG64)dllBase + me.modBaseSize;

m.pdata = (PRUNTIME_FUNCTION)(dllBase + excDir.VirtualAddress);

m.pdataLast = (excDir.Size / sizeof(RUNTIME_FUNCTION)) - 1;

++count;

}

} __except (EXCEPTION_EXECUTE_HANDLER) {}

}

ok = Module32NextW(snap, &me);

}

CloseHandle(snap);

std::sort(g_modules, g_modules + count,

[](const CachedModule &a, const CachedModule &b) { return a.base < b.base; });

g_moduleCount.store(count, std::memory_order_release);

}

static __declspec(noinline) void ensureCacheReady() noexcept {

if (g_cacheReady.load(std::memory_order_acquire)) return;

std::lock_guard<std::mutex> lock(getCacheMutex());

if (g_cacheReady.load(std::memory_order_relaxed)) return;

buildModuleCache();

g_cacheReady.store(true, std::memory_order_release);

}

static __forceinline bool findModule(ULONG64 pc, const CachedModule *&lastModule, ULONG64 &imageBase) {

if (lastModule && pc >= imageBase && pc < lastModule->end)

return true;

lastModule = nullptr;

int count = g_moduleCount.load(std::memory_order_acquire);

int lo = 0, hi = count - 1;

while (lo <= hi) {

int mid = (lo + hi) >> 1;

const CachedModule &mod = g_modules[mid];

if (pc < mod.base) hi = mid - 1;

else if (pc >= mod.end) lo = mid + 1;

else { lastModule = &mod; imageBase = mod.base; return true; }

}

return false;

}

static __forceinline PRUNTIME_FUNCTION findFunctionEntry(const CachedModule *mod, DWORD rva, int &hint) {

PRUNTIME_FUNCTION table = mod->pdata;

int lo = 0, hi = (int)mod->pdataLast;

int mid = hint;

goto first_check;

do {

mid = (lo + hi) >> 1;

first_check:

if (rva < table[mid].BeginAddress) hi = mid - 1;

else if (rva >= table[mid].EndAddress) lo = mid + 1;

else { hint = mid; return &table[mid]; }

} while (lo <= hi);

return nullptr;

}

static __forceinline PRUNTIME_FUNCTION cachedLookupOnly(ULONG64 pc, const CachedModule *&lastModule,

ULONG64 &imageBase, int &pdataHint) {

const CachedModule *prev = lastModule;

if (findModule(pc, lastModule, imageBase)) {

if (lastModule != prev) pdataHint = (int)(lastModule->pdataLast) >> 1;

return findFunctionEntry(lastModule, (DWORD)(pc - imageBase), pdataHint);

}

return nullptr;

}

// SEH-wrapped PE parse: reads from dllBase may fault on unmapped pages during

// module teardown. Returns true if newMod was populated. Kept free of C++

// objects with destructors so MSVC allows the __try/__except (C2712).

static bool parseModuleHeader(ULONG64 pc, const BYTE *dllBase, CachedModule &newMod) noexcept {

__try {

const IMAGE_DOS_HEADER *dos = (const IMAGE_DOS_HEADER*)dllBase;

if (dos->e_magic != IMAGE_DOS_SIGNATURE) { addNegCache(pc); return false; }

const IMAGE_NT_HEADERS64 *nt = (const IMAGE_NT_HEADERS64*)(dllBase + dos->e_lfanew);

if (nt->Signature != IMAGE_NT_SIGNATURE ||

nt->OptionalHeader.NumberOfRvaAndSizes <= IMAGE_DIRECTORY_ENTRY_EXCEPTION) {

addNegCache(pc); return false;

}

const IMAGE_DATA_DIRECTORY &excDir =

nt->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXCEPTION];

if (!excDir.VirtualAddress || excDir.Size < sizeof(RUNTIME_FUNCTION)) {

addNegCache(pc); return false;

}

newMod.base = (ULONG64)dllBase;

newMod.end = (ULONG64)dllBase + nt->OptionalHeader.SizeOfImage;

newMod.pdata = (PRUNTIME_FUNCTION)(dllBase + excDir.VirtualAddress);

newMod.pdataLast = (excDir.Size / sizeof(RUNTIME_FUNCTION)) - 1;

return true;

} __except (EXCEPTION_EXECUTE_HANDLER) {

addNegCache(pc);

return false;

}

// Incremental add for late-loaded DLLs via GetModuleHandleExW — avoids full snapshot reinit.

// Concurrency: writers serialize through getCacheMutex(); readers in findModule()

// load g_modules[] without locking. The memmove below shifts existing entries

// in place, so a concurrent reader's binary search may briefly observe torn

// base/end/pdataLast values from an in-flight shift. Possible outcomes:

// 1. Mis-comparison → findModule returns nullptr → caller falls into

// tryAddAndLookup again, which re-acquires the writer lock and finds the

// module already present. Wasted work, no functional damage.

// 2. Garbage pdataLast or pdata → findFunctionEntry walks an invalid table →

// access violation → outer __try/__except in walk_from_context catches it

// and we return a partial stack.

// The race window is the duration of one memmove (≤256 entries × 24 bytes,

// micro-second scale) and only opens when a DLL is loaded after the initial

// snapshot — i.e. fio::register_dynamic_module, JIT codegen, or transitive

// LoadLibrary. Net effect at the diagnostic level is rare truncated frames,

// no crashes, which matches the trade-off in the upstream Gaijin source.

static bool tryAddModuleForPC(ULONG64 pc) noexcept {

if (isNegCached(pc)) return false;

HMODULE hMod = nullptr;

if (!GetModuleHandleExW(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS | GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT,

(LPCWSTR)(uintptr_t)pc, &hMod) || !hMod) {

addNegCache(pc);

return false;

}

CachedModule newMod{};

if (!parseModuleHeader(pc, (const BYTE*)hMod, newMod)) return false;

std::lock_guard<std::mutex> lock(getCacheMutex());

int count = g_moduleCount.load(std::memory_order_relaxed);

if (count >= MAX_CACHED_MODULES) return false;

// sorted insert

int lo = 0, hi = count - 1, insertPos = count;

while (lo <= hi) {

int mid = (lo + hi) >> 1;

if (newMod.base < g_modules[mid].base) { insertPos = mid; hi = mid - 1; }

else if (newMod.base > g_modules[mid].base) { lo = mid + 1; }

else { return true; } // already added by other thread

}

memmove(&g_modules[insertPos + 1], &g_modules[insertPos],

(count - insertPos) * sizeof(CachedModule));

g_modules[insertPos] = newMod;

g_moduleCount.store(count + 1, std::memory_order_release);

return true;

}

static __declspec(noinline) PRUNTIME_FUNCTION tryAddAndLookup(ULONG64 pc, const CachedModule *&lastMod,

ULONG64 &imageBase, int &pdataHint) noexcept {

return tryAddModuleForPC(pc) ? cachedLookupOnly(pc, lastMod, imageBase, pdataHint) : nullptr;

}

// ---------------------------------------------------------------------------

// Lightweight UNWIND_INFO interpreter

// ---------------------------------------------------------------------------

#define UNW_UWOP_PUSH_NONVOL 0

#define UNW_UWOP_ALLOC_LARGE 1

#define UNW_UWOP_ALLOC_SMALL 2

#define UNW_UWOP_SET_FPREG 3

#define UNW_UWOP_SAVE_NONVOL 4

#define UNW_UWOP_SAVE_NONVOL_FAR 5

#define UNW_UWOP_SAVE_XMM128 8

#define UNW_UWOP_SAVE_XMM128_FAR 9

#define UNW_UWOP_PUSH_MACHFRAME 10

struct UNWIND_CODE_ENTRY_X {

BYTE CodeOffset;

BYTE UnwindOp : 4;

BYTE OpInfo : 4;

};

struct UNWIND_INFO_HEADER_X {

BYTE VersionAndFlags;

BYTE SizeOfProlog;

BYTE CountOfCodes;

BYTE FrameRegAndOffset;

UNWIND_CODE_ENTRY_X UnwindCode[1]; // variable length

};

static __forceinline DWORD64 &contextGpReg(CONTEXT &ctx, unsigned regNum) {

return (&ctx.Rax)[regNum];

}

static __forceinline bool lightweightVirtualUnwind(PRUNTIME_FUNCTION func, ULONG64 imageBase, CONTEXT &ctx) {

struct ChainEntry {

const UNWIND_INFO_HEADER_X *info;

PRUNTIME_FUNCTION func;

};

constexpr int MAX_CHAIN = 8;

ChainEntry chain[MAX_CHAIN];

int chainLen = 0;

{

const UNWIND_INFO_HEADER_X *cur = (const UNWIND_INFO_HEADER_X*)(imageBase + func->UnwindData);

PRUNTIME_FUNCTION curFunc = func;

while (chainLen < MAX_CHAIN) {

chain[chainLen++] = { cur, curFunc };

if (!(cur->VersionAndFlags & 0x20)) break; // UNW_FLAG_CHAININFO

unsigned codeSlots = (cur->CountOfCodes + 1) & ~1u;

curFunc = (PRUNTIME_FUNCTION)&cur->UnwindCode[codeSlots];

cur = (const UNWIND_INFO_HEADER_X*)(imageBase + curFunc->UnwindData);

}

const UNWIND_INFO_HEADER_X *primaryInfo = chain[0].info;

unsigned frameReg = primaryInfo->FrameRegAndOffset & 0x0F;

if (frameReg != 0) {

unsigned frameOffset = (primaryInfo->FrameRegAndOffset >> 4) & 0x0F;

ctx.Rsp = contextGpReg(ctx, frameReg) - (DWORD64)frameOffset * 16;

}

DWORD64 initialRsp = ctx.Rsp;

DWORD ripRva = (DWORD)(ctx.Rip - imageBase);

for (int c = 0; c < chainLen; ++c) {

const UNWIND_INFO_HEADER_X *info = chain[c].info;

DWORD funcBegin = chain[c].func->BeginAddress;

int count = info->CountOfCodes;

for (int i = 0; i < count;) {

const UNWIND_CODE_ENTRY_X &code = info->UnwindCode[i];

bool executed = (c > 0) || (ripRva >= (DWORD)(funcBegin + code.CodeOffset));

switch (code.UnwindOp) {

case UNW_UWOP_PUSH_NONVOL:

if (executed) {

contextGpReg(ctx, code.OpInfo) = *(DWORD64*)ctx.Rsp;

ctx.Rsp += 8;

}

i += 1; break;

case UNW_UWOP_ALLOC_LARGE:

if (code.OpInfo == 0) {

if (executed && (i + 1) < count)

ctx.Rsp += *(const USHORT*)&info->UnwindCode[i + 1] * 8;

i += 2;

} else {

if (executed && (i + 2) < count)

ctx.Rsp += *(const ULONG*)&info->UnwindCode[i + 1];

i += 3;

}

break;

case UNW_UWOP_ALLOC_SMALL:

if (executed) ctx.Rsp += code.OpInfo * 8 + 8;

i += 1; break;

case UNW_UWOP_SET_FPREG: i += 1; break;

case UNW_UWOP_SAVE_NONVOL:

if (executed && (i + 1) < count) {

ULONG offset = *(const USHORT*)&info->UnwindCode[i + 1] * 8;

contextGpReg(ctx, code.OpInfo) = *(DWORD64*)(initialRsp + offset);

}

i += 2; break;

case UNW_UWOP_SAVE_NONVOL_FAR:

if (executed && (i + 2) < count) {

ULONG offset = *(const ULONG*)&info->UnwindCode[i + 1];

contextGpReg(ctx, code.OpInfo) = *(DWORD64*)(initialRsp + offset);

}

i += 3; break;

case UNW_UWOP_SAVE_XMM128: i += 2; break;

case UNW_UWOP_SAVE_XMM128_FAR: i += 3; break;

case UNW_UWOP_PUSH_MACHFRAME: return false;

default: return false;

}

ctx.Rip = *(DWORD64*)ctx.Rsp;

ctx.Rsp += 8;

return true;

}

// ---------------------------------------------------------------------------

// Landmark (tail-memoize cache)

// Tail-memoize matches by RSP, which is inherently per-thread, so the landmark

// is thread_local: each thread arms its own landmark on entry and consumes its

// own on subsequent captures. No cross-thread races, no atomics required.

// Before this was thread_local, enterCount was a plain int on a process-global

// landmark and concurrent enter/exit on different threads was a data race.

// ---------------------------------------------------------------------------

static constexpr int kLandmarkFrames = 32;

struct Landmark {

bool active = false;

DWORD64 rsp = 0;

int frameCount = 0;

void * frames[kLandmarkFrames] = {};

int enterCount = 0; // nested enters no-op; only outermost arms

};

static thread_local Landmark g_landmark;

// ---------------------------------------------------------------------------

// Walk inner: given a captured CONTEXT, fill `stack[]` by unwinding.

// Uses the landmark cache if armed and the match flag is set.

// ---------------------------------------------------------------------------

static __declspec(noinline) unsigned walk_from_context(void **stack, unsigned maxFrames,

CONTEXT &ctx, int skipFrames,

bool useLandmark) noexcept {

const CachedModule *lastMod = nullptr;

ULONG64 imageBase = 0;

int pdataHint = -1;

int frame = -skipFrames;

DWORD64 landmarkRsp = 0;

bool canMatch = false;

if (useLandmark && g_landmark.active) {

landmarkRsp = g_landmark.rsp;

canMatch = (landmarkRsp != 0);

}

__try {

while (ctx.Rip && frame < (int)maxFrames) {

// Try to tail-memoize from landmark before recording this frame.

if (canMatch && frame >= 0 && ctx.Rsp == landmarkRsp) {

int copy = g_landmark.frameCount;

int room = (int)maxFrames - frame;

if (copy > room) copy = room;

memcpy(&stack[frame], g_landmark.frames, copy * sizeof(void*));

return (unsigned)(frame + copy);

}

if (frame >= 0) stack[frame] = (void*)(uintptr_t)ctx.Rip;

PRUNTIME_FUNCTION pFunc = cachedLookupOnly(ctx.Rip, lastMod, imageBase, pdataHint);

if (!pFunc)

pFunc = tryAddAndLookup(ctx.Rip, lastMod, imageBase, pdataHint);

if (!pFunc) break;

if (!lightweightVirtualUnwind(pFunc, imageBase, ctx)) {

// PUSH_MACHFRAME or unknown opcode → fall back to OS.

PVOID handlerData = nullptr;

ULONG64 establisherFrame = 0;

RtlVirtualUnwind(UNW_FLAG_NHANDLER, imageBase, ctx.Rip, pFunc,

&ctx, &handlerData, &establisherFrame, nullptr);

}

++frame;

}

} __except (EXCEPTION_EXECUTE_HANDLER) {

// Partial result is fine for diagnostics.

}

return frame > 0 ? (unsigned)frame : 0;

}

// ---------------------------------------------------------------------------

// Public API (internal to this translation unit / alloc_tracker.cpp)

// ---------------------------------------------------------------------------

// Default skipFrames=2 drops this function's own frame AND the caller (the

// tracker hook, which is always track_alloc_hook and carries no signal). Both

// this function and track_alloc_hook are declared noinline so the skip count

// is stable across /Ob levels.

__declspec(noinline) unsigned das_fast_stack_capture(void **stack, unsigned maxFrames, int skipFrames) noexcept {

if (!stack || !maxFrames) return 0;

CONTEXT ctx;

RtlCaptureContext(&ctx);

ensureCacheReady();

return walk_from_context(stack, maxFrames, ctx, skipFrames, /*useLandmark*/ true);

}

// Arm/disarm the landmark. First enter fully walks the stack from the caller's

// frame and stores it; later captures matching the caller's RSP short-circuit

// with a memcpy. Nested enters are no-ops. disarm clears when refcount hits 0.

// SEH-wrapped: cachedLookupOnly / tryAddAndLookup / lightweightVirtualUnwind

// may AV on torn reads during the late-DLL-load race window or on freshly

// unmapped DLLs. Failure degrades to "landmark disabled" (active stays false

// and subsequent captures just walk fully), never a process crash.

__declspec(noinline) void das_fast_stack_landmark_enter() noexcept {

// Guard against nested enters (e.g. recursive compile_and_run).

if (g_landmark.enterCount++ != 0) return;

__try {

CONTEXT ctx;

RtlCaptureContext(&ctx);

ensureCacheReady();

// Unwind once to leave this function — ctx then describes the caller frame.

const CachedModule *lastMod = nullptr;

ULONG64 imageBase = 0;

int pdataHint = -1;

PRUNTIME_FUNCTION pFunc = cachedLookupOnly(ctx.Rip, lastMod, imageBase, pdataHint);

if (!pFunc) pFunc = tryAddAndLookup(ctx.Rip, lastMod, imageBase, pdataHint);

if (!pFunc) return; // give up; leave landmark disarmed

if (!lightweightVirtualUnwind(pFunc, imageBase, ctx)) {

PVOID handlerData = nullptr;

ULONG64 establisherFrame = 0;

RtlVirtualUnwind(UNW_FLAG_NHANDLER, imageBase, ctx.Rip, pFunc,

&ctx, &handlerData, &establisherFrame, nullptr);

}

DWORD64 landmarkRsp = ctx.Rsp;

// Walk the rest WITHOUT landmark match (we're building it). walk_from_context

// has its own __try/__except, so any fault inside it returns a partial frame

// count rather than escaping.

g_landmark.frameCount = (int)walk_from_context(g_landmark.frames, kLandmarkFrames, ctx,

/*skipFrames*/ 0, /*useLandmark*/ false);

g_landmark.rsp = landmarkRsp;

g_landmark.active = true;

} __except (EXCEPTION_EXECUTE_HANDLER) {

// Leave landmark disarmed; subsequent captures will walk without memoization.

}

__declspec(noinline) void das_fast_stack_landmark_exit() noexcept {

if (--g_landmark.enterCount != 0) return;

g_landmark.active = false;

g_landmark.rsp = 0;

g_landmark.frameCount = 0;

}

} // namespace das

#endif // DAS_TRACK_ALLOC && _MSC_VER && _M_X64

daScript/src/misc/alloc_tracker_fast_stack.cpp at master · PushoN/daScript · GitHub

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