LulMainInt.h
/* -*- 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 LulMainInt_h
#define LulMainInt_h
#include "LulPlatformMacros.h"
#include <vector>
#include "mozilla/Assertions.h"
// 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 {
////////////////////////////////////////////////////////////////
// DW_REG_ constants //
////////////////////////////////////////////////////////////////
// These are the Dwarf CFI register numbers, as (presumably) defined
// in the ELF ABI supplements for each architecture.
enum DW_REG_NUMBER {
// 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(LUL_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(LUL_ARCH_x64)
// Because the X86 (32 bit) and AMD64 (64 bit) summarisers are
// combined, a merged set of register constants is needed.
DW_REG_INTEL_XBP = 6,
DW_REG_INTEL_XSP = 7,
DW_REG_INTEL_XIP = 16,
#elif defined(LUL_ARCH_x86)
DW_REG_INTEL_XBP = 5,
DW_REG_INTEL_XSP = 4,
DW_REG_INTEL_XIP = 8,
#else
# error "Unknown arch"
#endif
};
////////////////////////////////////////////////////////////////
// LExpr //
////////////////////////////////////////////////////////////////
// An expression -- very primitive. Denotes either "register +
// offset" or a dereferenced version of the same. 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.
struct LExpr {
// Denotes an expression with no value.
LExpr()
: mHow(UNKNOWN)
, mReg(0)
, mOffset(0)
{}
// Denotes any expressible expression.
LExpr(uint8_t how, int16_t reg, int32_t offset)
: mHow(how)
, mReg(reg)
, mOffset(offset)
{}
// Change the offset for an expression that references memory.
LExpr add_delta(long delta)
{
MOZ_ASSERT(mHow == NODEREF);
// 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()
{
MOZ_ASSERT(mHow == NODEREF);
// Same rationale as for add_delta().
return (mHow == NODEREF) ? LExpr(DEREF, mReg, mOffset)
: LExpr(); // Gone bad
}
// 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.
enum { UNKNOWN=0, // This LExpr denotes no value.
NODEREF, // Value is (mReg + mOffset).
DEREF }; // Value is *(mReg + mOffset).
uint8_t mHow; // UNKNOWN, NODEREF or DEREF
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 {
public:
RuleSet();
void Print(void(*aLog)(const char*));
// 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(LUL_ARCH_x64) || defined(LUL_ARCH_x86)
LExpr mXipExpr; // return address
LExpr mXspExpr;
LExpr mXbpExpr;
#elif defined(LUL_ARCH_arm)
LExpr mR15expr; // return address
LExpr mR14expr;
LExpr mR13expr;
LExpr mR12expr;
LExpr mR11expr;
LExpr mR7expr;
#else
# error "Unknown arch"
#endif
};
////////////////////////////////////////////////////////////////
// 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 {
public:
// 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.
SecMap(void(*aLog)(const char*));
~SecMap();
// 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(RuleSet* rs);
// 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(); }
// The min and max addresses of the addresses in the contained
// RuleSets. See comment above for invariants.
uintptr_t mSummaryMinAddr;
uintptr_t mSummaryMaxAddr;
private:
// 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()).
std::vector<RuleSet> mRuleSets;
// A logging sink, for debugging.
void (*mLog)(const char*);
};
} // namespace lul
#endif // ndef LulMainInt_h
