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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#ifndef LulMain_h
#define LulMain_h
#include "PlatformMacros.h"
#include "mozilla/Atomics.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/BaseProfilerUtils.h"
// LUL: A Lightweight Unwind Library.
// This file provides the end-user (external) interface for LUL.
// Some comments about naming in the implementation. These are safe
// to ignore if you are merely using LUL, but are important if you
// hack on its internals.
// Debuginfo readers in general have tended to use the word "address"
// to mean several different things. This sometimes makes them
// difficult to understand and maintain. LUL tries hard to avoid
// using the word "address" and instead uses the following more
// precise terms:
// * SVMA ("Stated Virtual Memory Address"): this is an address of a
// symbol (etc) as it is stated in the symbol table, or other
// metadata, of an object. Such values are typically small and
// start from zero or thereabouts, unless the object has been
// prelinked.
// * AVMA ("Actual Virtual Memory Address"): this is the address of a
// symbol (etc) in a running process, that is, once the associated
// object has been mapped into a process. Such values are typically
// much larger than SVMAs, since objects can get mapped arbitrarily
// far along the address space.
// * "Bias": the difference between AVMA and SVMA for a given symbol
// (specifically, AVMA - SVMA). The bias is always an integral
// number of pages. Once we know the bias for a given object's
// text section (for example), we can compute the AVMAs of all of
// its text symbols by adding the bias to their SVMAs.
// * "Image address": typically, to read debuginfo from an object we
// will temporarily mmap in the file so as to read symbol tables
// etc. Addresses in this temporary mapping are called "Image
// addresses". Note that the temporary mapping is entirely
// unrelated to the mappings of the file that the dynamic linker
// must perform merely in order to get the program to run. Hence
// image addresses are unrelated to either SVMAs or AVMAs.
namespace lul {
// A machine word plus validity tag.
class TaggedUWord {
// Construct a valid one.
explicit TaggedUWord(uintptr_t w) : mValue(w), mValid(true) {}
// Construct an invalid one.
TaggedUWord() : mValue(0), mValid(false) {}
TaggedUWord operator+(TaggedUWord rhs) const {
return (Valid() && rhs.Valid()) ? TaggedUWord(Value() + rhs.Value())
: TaggedUWord();
TaggedUWord operator-(TaggedUWord rhs) const {
return (Valid() && rhs.Valid()) ? TaggedUWord(Value() - rhs.Value())
: TaggedUWord();
TaggedUWord operator&(TaggedUWord rhs) const {
return (Valid() && rhs.Valid()) ? TaggedUWord(Value() & rhs.Value())
: TaggedUWord();
TaggedUWord operator|(TaggedUWord rhs) const {
return (Valid() && rhs.Valid()) ? TaggedUWord(Value() | rhs.Value())
: TaggedUWord();
TaggedUWord CmpGEs(TaggedUWord rhs) const {
if (Valid() && rhs.Valid()) {
intptr_t s1 = (intptr_t)Value();
intptr_t s2 = (intptr_t)rhs.Value();
return TaggedUWord(s1 >= s2 ? 1 : 0);
return TaggedUWord();
TaggedUWord operator<<(TaggedUWord rhs) const {
if (Valid() && rhs.Valid()) {
uintptr_t shift = rhs.Value();
if (shift < 8 * sizeof(uintptr_t)) return TaggedUWord(Value() << shift);
return TaggedUWord();
// Is equal? Note: non-validity on either side gives non-equality.
bool operator==(TaggedUWord other) const {
return (mValid && other.Valid()) ? (mValue == other.Value()) : false;
// Is it word-aligned?
bool IsAligned() const {
return mValid && (mValue & (sizeof(uintptr_t) - 1)) == 0;
uintptr_t Value() const { return mValue; }
bool Valid() const { return mValid; }
uintptr_t mValue;
bool mValid;
// The registers, with validity tags, that will be unwound.
struct UnwindRegs {
#if defined(GP_ARCH_arm)
TaggedUWord r7;
TaggedUWord r11;
TaggedUWord r12;
TaggedUWord r13;
TaggedUWord r14;
TaggedUWord r15;
#elif defined(GP_ARCH_arm64)
TaggedUWord x29;
TaggedUWord x30;
TaggedUWord sp;
TaggedUWord pc;
#elif defined(GP_ARCH_amd64) || defined(GP_ARCH_x86)
TaggedUWord xbp;
TaggedUWord xsp;
TaggedUWord xip;
#elif defined(GP_ARCH_mips64)
TaggedUWord sp;
TaggedUWord fp;
TaggedUWord pc;
# error "Unknown plat"
// The maximum number of bytes in a stack snapshot. This value can be increased
// if necessary, but testing showed that 160k is enough to obtain good
// backtraces on x86_64 Linux. Most backtraces fit comfortably into 4-8k of
// stack space, but we do have some very deep stacks occasionally. Please see
// the comments in DoNativeBacktrace as to why it's OK to have this value be so
// large.
static const size_t N_STACK_BYTES = 160 * 1024;
// The stack chunk image that will be unwound.
struct StackImage {
// [start_avma, +len) specify the address range in the buffer.
// Obviously we require 0 <= len <= N_STACK_BYTES.
uintptr_t mStartAvma;
size_t mLen;
uint8_t mContents[N_STACK_BYTES];
// Statistics collection for the unwinder.
template <typename T>
class LULStats {
LULStats() : mContext(0), mCFI(0), mFP(0) {}
template <typename S>
explicit LULStats(const LULStats<S>& aOther)
: mContext(aOther.mContext), mCFI(aOther.mCFI), mFP(aOther.mFP) {}
template <typename S>
LULStats<T>& operator=(const LULStats<S>& aOther) {
mContext = aOther.mContext;
mCFI = aOther.mCFI;
mFP = aOther.mFP;
return *this;
template <typename S>
uint32_t operator-(const LULStats<S>& aOther) {
return (mContext - aOther.mContext) + (mCFI - aOther.mCFI) +
(mFP - aOther.mFP);
T mContext; // Number of context frames
T mCFI; // Number of CFI/EXIDX frames
T mFP; // Number of frame-pointer recovered frames
// The core unwinder library class. Just one of these is needed, and
// it can be shared by multiple unwinder threads.
// The library operates in one of two modes.
// * Admin mode. The library is this state after creation. In Admin
// mode, no unwinding may be performed. It is however allowable to
// perform administrative tasks -- primarily, loading of unwind info
// -- in this mode. In particular, it is safe for the library to
// perform dynamic memory allocation in this mode. Safe in the
// sense that there is no risk of deadlock against unwinding threads
// that might -- because of where they have been sampled -- hold the
// system's malloc lock.
// * Unwind mode. In this mode, calls to ::Unwind may be made, but
// nothing else. ::Unwind guarantees not to make any dynamic memory
// requests, so as to guarantee that the calling thread won't
// deadlock in the case where it already holds the system's malloc lock.
// The library is created in Admin mode. After debuginfo is loaded,
// the caller must switch it into Unwind mode by calling
// ::EnableUnwinding. There is no way to switch it back to Admin mode
// after that. To safely switch back to Admin mode would require the
// caller (or other external agent) to guarantee that there are no
// pending ::Unwind calls.
class PriMap;
class SegArray;
class UniqueStringUniverse;
class LUL {
// Create; supply a logging sink. Sets the object in Admin mode.
explicit LUL(void (*aLog)(const char*));
// Destroy. Caller is responsible for ensuring that no other
// threads are in Unwind calls. All resources are freed and all
// registered unwinder threads are deregistered. Can be called
// either in Admin or Unwind mode.
// Notify the library that unwinding is now allowed and so
// admin-mode calls are no longer allowed. The object is initially
// created in admin mode. The only possible transition is
// admin->unwinding, therefore.
void EnableUnwinding();
// Notify of a new r-x mapping, and load the associated unwind info.
// The filename is strdup'd and used for debug printing. If
// aMappedImage is NULL, this function will mmap/munmap the file
// itself, so as to be able to read the unwind info. If
// aMappedImage is non-NULL then it is assumed to point to a
// called-supplied and caller-managed mapped image of the file.
// May only be called in Admin mode.
void NotifyAfterMap(uintptr_t aRXavma, size_t aSize, const char* aFileName,
const void* aMappedImage);
// In rare cases we know an executable area exists but don't know
// what the associated file is. This call notifies LUL of such
// areas. This is important for correct functioning of stack
// scanning and of the x86-{linux,android} special-case
// __kernel_syscall function handling.
// This must be called only after the code area in
// question really has been mapped.
// May only be called in Admin mode.
void NotifyExecutableArea(uintptr_t aRXavma, size_t aSize);
// Notify that a mapped area has been unmapped; discard any
// associated unwind info. Acquires mRWlock for writing. Note that
// to avoid segfaulting the stack-scan unwinder, which inspects code
// areas, this must be called before the code area in question is
// really unmapped. Note that, unlike NotifyAfterMap(), this
// function takes the start and end addresses of the range to be
// unmapped, rather than a start and a length parameter. This is so
// as to make it possible to notify an unmap for the entire address
// space using a single call.
// May only be called in Admin mode.
void NotifyBeforeUnmap(uintptr_t aAvmaMin, uintptr_t aAvmaMax);
// Apply NotifyBeforeUnmap to the entire address space. This causes
// LUL to discard all unwind and executable-area information for the
// entire address space.
// May only be called in Admin mode.
void NotifyBeforeUnmapAll() { NotifyBeforeUnmap(0, UINTPTR_MAX); }
// Returns the number of mappings currently registered.
// May only be called in Admin mode.
size_t CountMappings();
// Unwind |aStackImg| starting with the context in |aStartRegs|.
// Write the number of frames recovered in *aFramesUsed. Put
// the PC values in aFramePCs[0 .. *aFramesUsed-1] and
// the SP values in aFrameSPs[0 .. *aFramesUsed-1].
// |aFramesAvail| is the size of the two output arrays and hence the
// largest possible value of *aFramesUsed. PC values are always
// valid, and the unwind will stop when the PC becomes invalid, but
// the SP values might be invalid, in which case the value zero will
// be written in the relevant frameSPs[] slot.
// This function assumes that the SP values increase as it unwinds
// away from the innermost frame -- that is, that the stack grows
// down. It monitors SP values as it unwinds to check they
// decrease, so as to avoid looping on corrupted stacks.
// May only be called in Unwind mode. Multiple threads may unwind
// at once. LUL user is responsible for ensuring that no thread makes
// any Admin calls whilst in Unwind mode.
// MOZ_CRASHes if the calling thread is not registered for unwinding.
// The calling thread must previously have been registered via a call to
// RegisterSampledThread.
void Unwind(/*OUT*/ uintptr_t* aFramePCs,
/*OUT*/ uintptr_t* aFrameSPs,
/*OUT*/ size_t* aFramesUsed,
/*OUT*/ size_t* aFramePointerFramesAcquired, size_t aFramesAvail,
UnwindRegs* aStartRegs, StackImage* aStackImg);
// The logging sink. Call to send debug strings to the caller-
// specified destination. Can only be called by the Admin thread.
void (*mLog)(const char*);
// Statistics relating to unwinding. These have to be atomic since
// unwinding can occur on different threads simultaneously.
LULStats<mozilla::Atomic<uint32_t>> mStats;
// Possibly show the statistics. This may not be called from any
// registered sampling thread, since it involves I/O.
void MaybeShowStats();
size_t SizeOfIncludingThis(mozilla::MallocSizeOf) const;
// The statistics counters at the point where they were last printed.
LULStats<uint32_t> mStatsPrevious;
// Are we in admin mode? Initially |true| but changes to |false|
// once unwinding begins.
bool mAdminMode;
// The thread ID associated with admin mode. This is the only thread
// that is allowed do perform non-Unwind calls on this object. Conversely,
// no registered Unwinding thread may be the admin thread. This is so
// as to clearly partition the one thread that may do dynamic memory
// allocation from the threads that are being sampled, since the latter
// absolutely may not do dynamic memory allocation.
mozilla::baseprofiler::BaseProfilerThreadId mAdminThreadId;
// The top level mapping from code address ranges to postprocessed
// unwind info. Basically a sorted array of (addr, len, info)
// records. This field is updated by NotifyAfterMap and NotifyBeforeUnmap.
PriMap* mPriMap;
// An auxiliary structure that records which address ranges are
// mapped r-x, for the benefit of the stack scanner.
SegArray* mSegArray;
// A UniqueStringUniverse that holds all the strdup'd strings created
// whilst reading unwind information. This is included so as to make
// it possible to free them in ~LUL.
UniqueStringUniverse* mUSU;
// Run unit tests on an initialised, loaded-up LUL instance, and print
// summary results on |aLUL|'s logging sink. Also return the number
// of tests run in *aNTests and the number that passed in
// *aNTestsPassed.
void RunLulUnitTests(/*OUT*/ int* aNTests, /*OUT*/ int* aNTestsPassed,
} // namespace lul
#endif // LulMain_h