Source code

Revision control

Other Tools

/* -*- 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 LulMainInt_h
#define LulMainInt_h
#include "PlatformMacros.h"
#include "LulMain.h" // for TaggedUWord
#include "mozilla/Assertions.h"
#include <string>
#include <vector>
// This file is provides internal interface inside LUL. If you are an
// end-user of LUL, do not include it in your code. The end-user
// interface is in LulMain.h.
namespace lul {
using std::vector;
// DW_REG_ constants //
// These are the Dwarf CFI register numbers, as (presumably) defined
// in the ELF ABI supplements for each architecture.
// No real register has this number. It's convenient to be able to
// treat the CFA (Canonical Frame Address) as "just another
// register", though.
DW_REG_CFA = -1,
#if defined(GP_ARCH_arm)
// ARM registers
DW_REG_ARM_R7 = 7,
DW_REG_ARM_R11 = 11,
DW_REG_ARM_R12 = 12,
DW_REG_ARM_R13 = 13,
DW_REG_ARM_R14 = 14,
DW_REG_ARM_R15 = 15,
#elif defined(GP_ARCH_arm64)
// aarch64 registers
DW_REG_AARCH64_X29 = 29,
DW_REG_AARCH64_X30 = 30,
#elif defined(GP_ARCH_amd64)
// Because the X86 (32 bit) and AMD64 (64 bit) summarisers are
// combined, a merged set of register constants is needed.
#elif defined(GP_ARCH_x86)
#elif defined(GP_ARCH_mips64)
# error "Unknown arch"
// PfxExpr //
enum PfxExprOp {
// meaning of mOperand effect on stack
PX_Start, // bool start-with-CFA? start, with CFA on stack, or not
PX_End, // none stop; result is at top of stack
PX_SImm32, // int32 push signed int32
PX_DwReg, // DW_REG_NUMBER push value of the specified reg
PX_Deref, // none pop X ; push *X
PX_Add, // none pop X ; pop Y ; push Y + X
PX_Sub, // none pop X ; pop Y ; push Y - X
PX_And, // none pop X ; pop Y ; push Y & X
PX_Or, // none pop X ; pop Y ; push Y | X
PX_CmpGES, // none pop X ; pop Y ; push (Y >=s X) ? 1 : 0
PX_Shl // none pop X ; pop Y ; push Y << X
struct PfxInstr {
PfxInstr(PfxExprOp opcode, int32_t operand)
: mOpcode(opcode), mOperand(operand) {}
explicit PfxInstr(PfxExprOp opcode) : mOpcode(opcode), mOperand(0) {}
bool operator==(const PfxInstr& other) const {
return mOpcode == other.mOpcode && mOperand == other.mOperand;
PfxExprOp mOpcode;
int32_t mOperand;
static_assert(sizeof(PfxInstr) <= 8, "PfxInstr size changed unexpectedly");
// Evaluate the prefix expression whose PfxInstrs start at aPfxInstrs[start].
// In the case of any mishap (stack over/underflow, running off the end of
// the instruction vector, obviously malformed sequences),
// return an invalid TaggedUWord.
TaggedUWord EvaluatePfxExpr(int32_t start, const UnwindRegs* aOldRegs,
TaggedUWord aCFA, const StackImage* aStackImg,
const vector<PfxInstr>& aPfxInstrs);
// LExpr //
// An expression -- very primitive. Denotes either "register +
// offset", a dereferenced version of the same, or a reference to a
// prefix expression stored elsewhere. So as to allow convenient
// handling of Dwarf-derived unwind info, the register may also denote
// the CFA. A large number of these need to be stored, so we ensure
// it fits into 8 bytes. See comment below on RuleSet to see how
// expressions fit into the bigger picture.
enum LExprHow {
UNKNOWN = 0, // This LExpr denotes no value.
NODEREF, // Value is (mReg + mOffset).
DEREF, // Value is *(mReg + mOffset).
PFXEXPR // Value is EvaluatePfxExpr(secMap->mPfxInstrs[mOffset])
inline static const char* NameOf_LExprHow(LExprHow how) {
switch (how) {
return "UNKNOWN";
return "NODEREF";
case DEREF:
return "DEREF";
return "PFXEXPR";
return "LExpr-??";
struct LExpr {
// Denotes an expression with no value.
LExpr() : mHow(UNKNOWN), mReg(0), mOffset(0) {}
// Denotes any expressible expression.
LExpr(LExprHow how, int16_t reg, int32_t offset)
: mHow(how), mReg(reg), mOffset(offset) {
switch (how) {
MOZ_ASSERT(reg == 0 && offset == 0);
case DEREF:
MOZ_ASSERT(reg == 0 && offset >= 0);
MOZ_ASSERT(0, "LExpr::LExpr: invalid how");
// Change the offset for an expression that references memory.
LExpr add_delta(long delta) {
// If this is a non-debug build and the above assertion would have
// failed, at least return LExpr() so that the machinery that uses
// the resulting expression fails in a repeatable way.
return (mHow == NODEREF) ? LExpr(mHow, mReg, mOffset + delta)
: LExpr(); // Gone bad
// Dereference an expression that denotes a memory address.
LExpr deref() {
// Same rationale as for add_delta().
return (mHow == NODEREF) ? LExpr(DEREF, mReg, mOffset)
: LExpr(); // Gone bad
// Print a rule for recovery of |aNewReg| whose recovered value
// is this LExpr.
std::string ShowRule(const char* aNewReg) const;
// Evaluate this expression, producing a TaggedUWord. |aOldRegs|
// holds register values that may be referred to by the expression.
// |aCFA| holds the CFA value, if any, that applies. |aStackImg|
// contains a chuck of stack that will be consulted if the expression
// references memory. |aPfxInstrs| holds the vector of PfxInstrs
// that will be consulted if this is a PFXEXPR.
TaggedUWord EvaluateExpr(const UnwindRegs* aOldRegs, TaggedUWord aCFA,
const StackImage* aStackImg,
const vector<PfxInstr>* aPfxInstrs) const;
// Representation of expressions. If |mReg| is DW_REG_CFA (-1) then
// it denotes the CFA. All other allowed values for |mReg| are
// nonnegative and are DW_REG_ values.
LExprHow mHow : 8;
int16_t mReg; // A DW_REG_ value
int32_t mOffset; // 32-bit signed offset should be more than enough.
static_assert(sizeof(LExpr) <= 8, "LExpr size changed unexpectedly");
// RuleSet //
// This is platform-dependent. For some address range, describes how
// to recover the CFA and then how to recover the registers for the
// previous frame.
// The set of LExprs contained in a given RuleSet describe a DAG which
// says how to compute the caller's registers ("new registers") from
// the callee's registers ("old registers"). The DAG can contain a
// single internal node, which is the value of the CFA for the callee.
// It would be possible to construct a DAG that omits the CFA, but
// including it makes the summarisers simpler, and the Dwarf CFI spec
// has the CFA as a central concept.
// For this to make sense, |mCfaExpr| can't have
// |mReg| == DW_REG_CFA since we have no previous value for the CFA.
// All of the other |Expr| fields can -- and usually do -- specify
// |mReg| == DW_REG_CFA.
// With that in place, the unwind algorithm proceeds as follows.
// (0) Initially: we have values for the old registers, and a memory
// image.
// (1) Compute the CFA by evaluating |mCfaExpr|. Add the computed
// value to the set of "old registers".
// (2) Compute values for the registers by evaluating all of the other
// |Expr| fields in the RuleSet. These can depend on both the old
// register values and the just-computed CFA.
// If we are unwinding without computing a CFA, perhaps because the
// RuleSets are derived from EXIDX instead of Dwarf, then
// |mCfaExpr.mHow| will be LExpr::UNKNOWN, so the computed value will
// be invalid -- that is, TaggedUWord() -- and so any attempt to use
// that will result in the same value. But that's OK because the
// RuleSet would make no sense if depended on the CFA but specified no
// way to compute it.
// A RuleSet is not allowed to cover zero address range. Having zero
// length would break binary searching in SecMaps and PriMaps.
class RuleSet {
void Print(void (*aLog)(const char*)) const;
// Find the LExpr* for a given DW_REG_ value in this class.
LExpr* ExprForRegno(DW_REG_NUMBER aRegno);
uintptr_t mAddr;
uintptr_t mLen;
// How to compute the CFA.
LExpr mCfaExpr;
// How to compute caller register values. These may reference the
// value defined by |mCfaExpr|.
#if defined(GP_ARCH_amd64) || defined(GP_ARCH_x86)
LExpr mXipExpr; // return address
LExpr mXspExpr;
LExpr mXbpExpr;
#elif defined(GP_ARCH_arm)
LExpr mR15expr; // return address
LExpr mR14expr;
LExpr mR13expr;
LExpr mR12expr;
LExpr mR11expr;
LExpr mR7expr;
#elif defined(GP_ARCH_arm64)
LExpr mX29expr; // frame pointer register
LExpr mX30expr; // link register
LExpr mSPexpr;
#elif defined(GP_ARCH_mips64)
LExpr mPCexpr;
LExpr mFPexpr;
LExpr mSPexpr;
# error "Unknown arch"
// Returns |true| for Dwarf register numbers which are members
// of the set of registers that LUL unwinds on this target.
static inline bool registerIsTracked(DW_REG_NUMBER reg) {
switch (reg) {
#if defined(GP_ARCH_amd64) || defined(GP_ARCH_x86)
return true;
#elif defined(GP_ARCH_arm)
case DW_REG_ARM_R7:
case DW_REG_ARM_R11:
case DW_REG_ARM_R12:
case DW_REG_ARM_R13:
case DW_REG_ARM_R14:
case DW_REG_ARM_R15:
return true;
#elif defined(GP_ARCH_arm64)
case DW_REG_AARCH64_X29:
case DW_REG_AARCH64_X30:
return true;
#elif defined(GP_ARCH_mips64)
return true;
# error "Unknown arch"
return false;
// SecMap //
// A SecMap may have zero address range, temporarily, whilst RuleSets
// are being added to it. But adding a zero-range SecMap to a PriMap
// will make it impossible to maintain the total order of the PriMap
// entries, and so that can't be allowed to happen.
class SecMap {
// These summarise the contained mRuleSets, in that they give
// exactly the lowest and highest addresses that any of the entries
// in this SecMap cover. Hence invariants:
// mRuleSets is nonempty
// <=> mSummaryMinAddr <= mSummaryMaxAddr
// && mSummaryMinAddr == mRuleSets[0].mAddr
// && mSummaryMaxAddr == mRuleSets[#rulesets-1].mAddr
// + mRuleSets[#rulesets-1].mLen - 1;
// This requires that no RuleSet has zero length.
// mRuleSets is empty
// <=> mSummaryMinAddr > mSummaryMaxAddr
// This doesn't constrain mSummaryMinAddr and mSummaryMaxAddr uniquely,
// so let's use mSummaryMinAddr == 1 and mSummaryMaxAddr == 0 to denote
// this case.
explicit SecMap(void (*aLog)(const char*));
// Binary search mRuleSets to find one that brackets |ia|, or nullptr
// if none is found. It's not allowable to do this until PrepareRuleSets
// has been called first.
RuleSet* FindRuleSet(uintptr_t ia);
// Add a RuleSet to the collection. The rule is copied in. Calling
// this makes the map non-searchable.
void AddRuleSet(const RuleSet* rs);
// Add a PfxInstr to the vector of such instrs, and return the index
// in the vector. Calling this makes the map non-searchable.
uint32_t AddPfxInstr(PfxInstr pfxi);
// Returns the entire vector of PfxInstrs.
const vector<PfxInstr>* GetPfxInstrs() { return &mPfxInstrs; }
// Prepare the map for searching. Also, remove any rules for code
// address ranges which don't fall inside [start, +len). |len| may
// not be zero.
void PrepareRuleSets(uintptr_t start, size_t len);
bool IsEmpty();
size_t Size() { return mRuleSets.size(); }
size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
// The min and max addresses of the addresses in the contained
// RuleSets. See comment above for invariants.
uintptr_t mSummaryMinAddr;
uintptr_t mSummaryMaxAddr;
// False whilst adding entries; true once it is safe to call FindRuleSet.
// Transition (false->true) is caused by calling PrepareRuleSets().
bool mUsable;
// A vector of RuleSets, sorted, nonoverlapping (post Prepare()).
vector<RuleSet> mRuleSets;
// A vector of PfxInstrs, which are referred to by the RuleSets.
// These are provided as a representation of Dwarf expressions
// (DW_CFA_val_expression, DW_CFA_expression, DW_CFA_def_cfa_expression),
// are relatively expensive to evaluate, and and are therefore
// expected to be used only occasionally.
// The vector holds a bunch of separate PfxInstr programs, each one
// starting with a PX_Start and terminated by a PX_End, all
// concatenated together. When a RuleSet can't recover a value
// using a self-contained LExpr, it uses a PFXEXPR whose mOffset is
// the index in this vector of start of the necessary PfxInstr program.
vector<PfxInstr> mPfxInstrs;
// A logging sink, for debugging.
void (*mLog)(const char*);
} // namespace lul
#endif // ndef LulMainInt_h