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authorMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
committerMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
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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 http://mozilla.org/MPL/2.0/. */
+
+#ifndef LulMain_h
+#define LulMain_h
+
+#include "LulPlatformMacros.h"
+#include "mozilla/Atomics.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 {
+public:
+ // RUNS IN NO-MALLOC CONTEXT
+ // Construct a valid one.
+ explicit TaggedUWord(uintptr_t w)
+ : mValue(w)
+ , mValid(true)
+ {}
+
+ // RUNS IN NO-MALLOC CONTEXT
+ // Construct an invalid one.
+ TaggedUWord()
+ : mValue(0)
+ , mValid(false)
+ {}
+
+ // RUNS IN NO-MALLOC CONTEXT
+ TaggedUWord operator+(TaggedUWord rhs) const {
+ return (Valid() && rhs.Valid()) ? TaggedUWord(Value() + rhs.Value())
+ : TaggedUWord();
+ }
+
+ // RUNS IN NO-MALLOC CONTEXT
+ TaggedUWord operator-(TaggedUWord rhs) const {
+ return (Valid() && rhs.Valid()) ? TaggedUWord(Value() - rhs.Value())
+ : TaggedUWord();
+ }
+
+ // RUNS IN NO-MALLOC CONTEXT
+ TaggedUWord operator&(TaggedUWord rhs) const {
+ return (Valid() && rhs.Valid()) ? TaggedUWord(Value() & rhs.Value())
+ : TaggedUWord();
+ }
+
+ // RUNS IN NO-MALLOC CONTEXT
+ TaggedUWord operator|(TaggedUWord rhs) const {
+ return (Valid() && rhs.Valid()) ? TaggedUWord(Value() | rhs.Value())
+ : TaggedUWord();
+ }
+
+ // RUNS IN NO-MALLOC CONTEXT
+ 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();
+ }
+
+ // RUNS IN NO-MALLOC CONTEXT
+ 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();
+ }
+
+ // RUNS IN NO-MALLOC CONTEXT
+ // Is equal? Note: non-validity on either side gives non-equality.
+ bool operator==(TaggedUWord other) const {
+ return (mValid && other.Valid()) ? (mValue == other.Value()) : false;
+ }
+
+ // RUNS IN NO-MALLOC CONTEXT
+ // Is it word-aligned?
+ bool IsAligned() const {
+ return mValid && (mValue & (sizeof(uintptr_t)-1)) == 0;
+ }
+
+ // RUNS IN NO-MALLOC CONTEXT
+ uintptr_t Value() const { return mValue; }
+
+ // RUNS IN NO-MALLOC CONTEXT
+ bool Valid() const { return mValid; }
+
+private:
+ uintptr_t mValue;
+ bool mValid;
+};
+
+
+// The registers, with validity tags, that will be unwound.
+
+struct UnwindRegs {
+#if defined(LUL_ARCH_arm)
+ TaggedUWord r7;
+ TaggedUWord r11;
+ TaggedUWord r12;
+ TaggedUWord r13;
+ TaggedUWord r14;
+ TaggedUWord r15;
+#elif defined(LUL_ARCH_x64) || defined(LUL_ARCH_x86)
+ TaggedUWord xbp;
+ TaggedUWord xsp;
+ TaggedUWord xip;
+#else
+# error "Unknown plat"
+#endif
+};
+
+
+// The maximum number of bytes in a stack snapshot. This can be
+// increased if necessary, but larger values cost performance, since a
+// stack snapshot needs to be copied between sampling and worker
+// threads for each snapshot. In practice 32k seems to be enough
+// to get good backtraces.
+static const size_t N_STACK_BYTES = 32768;
+
+// 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 {
+public:
+ LULStats()
+ : mContext(0)
+ , mCFI(0)
+ , mScanned(0)
+ {}
+
+ template <typename S>
+ explicit LULStats(const LULStats<S>& aOther)
+ : mContext(aOther.mContext)
+ , mCFI(aOther.mCFI)
+ , mScanned(aOther.mScanned)
+ {}
+
+ template <typename S>
+ LULStats<T>& operator=(const LULStats<S>& aOther)
+ {
+ mContext = aOther.mContext;
+ mCFI = aOther.mCFI;
+ mScanned = aOther.mScanned;
+ return *this;
+ }
+
+ template <typename S>
+ uint32_t operator-(const LULStats<S>& aOther) {
+ return (mContext - aOther.mContext) +
+ (mCFI - aOther.mCFI) + (mScanned - aOther.mScanned);
+ }
+
+ T mContext; // Number of context frames
+ T mCFI; // Number of CFI/EXIDX frames
+ T mScanned; // Number of scanned 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 {
+public:
+ // 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.
+ ~LUL();
+
+ // 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.
+ //
+ // Unwinding may optionally use stack scanning. The maximum number
+ // of frames that may be recovered by stack scanning is
+ // |aScannedFramesAllowed| and the actual number recovered is
+ // written into *aScannedFramesAcquired. |aScannedFramesAllowed|
+ // must be less than or equal to |aFramesAvail|.
+ //
+ // 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.
+ //
+ // Up to aScannedFramesAllowed stack-scanned frames may be recovered.
+ //
+ // 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* aScannedFramesAcquired,
+ size_t aFramesAvail,
+ size_t aScannedFramesAllowed,
+ 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();
+
+private:
+ // 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.
+ int 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, LUL* aLUL);
+
+} // namespace lul
+
+#endif // LulMain_h