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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/. */
+
+/*
+ * This is an implementation of stack unwinding according to a subset
+ * of the ARM Exception Handling ABI, as described in:
+ * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0038a/IHI0038A_ehabi.pdf
+ *
+ * This handles only the ARM-defined "personality routines" (chapter
+ * 9), and don't track the value of FP registers, because profiling
+ * needs only chain of PC/SP values.
+ *
+ * Because the exception handling info may not be accurate for all
+ * possible places where an async signal could occur (e.g., in a
+ * prologue or epilogue), this bounds-checks all stack accesses.
+ *
+ * This file uses "struct" for structures in the exception tables and
+ * "class" otherwise. We should avoid violating the C++11
+ * standard-layout rules in the former.
+ */
+
+#include "EHABIStackWalk.h"
+
+#include "shared-libraries.h"
+#include "platform.h"
+
+#include "mozilla/Atomics.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/EndianUtils.h"
+
+#include <algorithm>
+#include <elf.h>
+#include <stdint.h>
+#include <vector>
+#include <string>
+
+#ifndef PT_ARM_EXIDX
+# define PT_ARM_EXIDX 0x70000001
+#endif
+
+namespace mozilla {
+
+struct PRel31 {
+ uint32_t mBits;
+ bool topBit() const { return mBits & 0x80000000; }
+ uint32_t value() const { return mBits & 0x7fffffff; }
+ int32_t offset() const { return (static_cast<int32_t>(mBits) << 1) >> 1; }
+ const void* compute() const {
+ return reinterpret_cast<const char*>(this) + offset();
+ }
+
+ private:
+ PRel31(const PRel31& copied) = delete;
+ PRel31() = delete;
+};
+
+struct EHEntry {
+ PRel31 startPC;
+ PRel31 exidx;
+
+ private:
+ EHEntry(const EHEntry& copied) = delete;
+ EHEntry() = delete;
+};
+
+class EHState {
+ // Note that any core register can be used as a "frame pointer" to
+ // influence the unwinding process, so this must track all of them.
+ uint32_t mRegs[16];
+
+ public:
+ bool unwind(const EHEntry* aEntry, const void* stackBase);
+ uint32_t& operator[](int i) { return mRegs[i]; }
+ const uint32_t& operator[](int i) const { return mRegs[i]; }
+ explicit EHState(const mcontext_t&);
+};
+
+enum { R_SP = 13, R_LR = 14, R_PC = 15 };
+
+class EHTable {
+ uint32_t mStartPC;
+ uint32_t mEndPC;
+ uint32_t mBaseAddress;
+ const EHEntry* mEntriesBegin;
+ const EHEntry* mEntriesEnd;
+ std::string mName;
+
+ public:
+ EHTable(const void* aELF, size_t aSize, const std::string& aName);
+ const EHEntry* lookup(uint32_t aPC) const;
+ bool isValid() const { return mEntriesEnd != mEntriesBegin; }
+ const std::string& name() const { return mName; }
+ uint32_t startPC() const { return mStartPC; }
+ uint32_t endPC() const { return mEndPC; }
+ uint32_t baseAddress() const { return mBaseAddress; }
+};
+
+class EHAddrSpace {
+ std::vector<uint32_t> mStarts;
+ std::vector<EHTable> mTables;
+ static mozilla::Atomic<const EHAddrSpace*> sCurrent;
+
+ public:
+ explicit EHAddrSpace(const std::vector<EHTable>& aTables);
+ const EHTable* lookup(uint32_t aPC) const;
+ static void Update();
+ static const EHAddrSpace* Get();
+};
+
+void EHABIStackWalkInit() { EHAddrSpace::Update(); }
+
+size_t EHABIStackWalk(const mcontext_t& aContext, void* stackBase, void** aSPs,
+ void** aPCs, const size_t aNumFrames) {
+ const EHAddrSpace* space = EHAddrSpace::Get();
+ EHState state(aContext);
+ size_t count = 0;
+
+ while (count < aNumFrames) {
+ uint32_t pc = state[R_PC], sp = state[R_SP];
+
+ // ARM instructions are always aligned to 2 or 4 bytes.
+ // The last bit of the pc / lr indicates ARM or Thumb mode.
+ // We're only interested in the instruction address, so we mask off that
+ // bit.
+ constexpr uint32_t instrAddrMask = ~1;
+ uint32_t instrAddress = pc & instrAddrMask;
+
+ aPCs[count] = reinterpret_cast<void*>(instrAddress);
+ aSPs[count] = reinterpret_cast<void*>(sp);
+ count++;
+
+ if (!space) break;
+ // TODO: cache these lookups. Binary-searching libxul is
+ // expensive (possibly more expensive than doing the actual
+ // unwind), and even a small cache should help.
+ const EHTable* table = space->lookup(pc);
+ if (!table) break;
+ const EHEntry* entry = table->lookup(pc);
+ if (!entry) break;
+ if (!state.unwind(entry, stackBase)) break;
+ }
+
+ return count;
+}
+
+class EHInterp {
+ public:
+ // Note that stackLimit is exclusive and stackBase is inclusive
+ // (i.e, stackLimit < SP <= stackBase), following the convention
+ // set by the AAPCS spec.
+ EHInterp(EHState& aState, const EHEntry* aEntry, uint32_t aStackLimit,
+ uint32_t aStackBase)
+ : mState(aState),
+ mStackLimit(aStackLimit),
+ mStackBase(aStackBase),
+ mNextWord(0),
+ mWordsLeft(0),
+ mFailed(false) {
+ const PRel31& exidx = aEntry->exidx;
+ uint32_t firstWord;
+
+ if (exidx.mBits == 1) { // EXIDX_CANTUNWIND
+ mFailed = true;
+ return;
+ }
+ if (exidx.topBit()) {
+ firstWord = exidx.mBits;
+ } else {
+ mNextWord = reinterpret_cast<const uint32_t*>(exidx.compute());
+ firstWord = *mNextWord++;
+ }
+
+ switch (firstWord >> 24) {
+ case 0x80: // short
+ mWord = firstWord << 8;
+ mBytesLeft = 3;
+ break;
+ case 0x81:
+ case 0x82: // long; catch descriptor size ignored
+ mWord = firstWord << 16;
+ mBytesLeft = 2;
+ mWordsLeft = (firstWord >> 16) & 0xff;
+ break;
+ default:
+ // unknown personality
+ mFailed = true;
+ }
+ }
+
+ bool unwind();
+
+ private:
+ // TODO: GCC has been observed not CSEing repeated reads of
+ // mState[R_SP] with writes to mFailed between them, suggesting that
+ // it hasn't determined that they can't alias and is thus missing
+ // optimization opportunities. So, we may want to flatten EHState
+ // into this class; this may also make the code simpler.
+ EHState& mState;
+ uint32_t mStackLimit;
+ uint32_t mStackBase;
+ const uint32_t* mNextWord;
+ uint32_t mWord;
+ uint8_t mWordsLeft;
+ uint8_t mBytesLeft;
+ bool mFailed;
+
+ enum {
+ I_ADDSP = 0x00, // 0sxxxxxx (subtract if s)
+ M_ADDSP = 0x80,
+ I_POPMASK = 0x80, // 1000iiii iiiiiiii (if any i set)
+ M_POPMASK = 0xf0,
+ I_MOVSP = 0x90, // 1001nnnn
+ M_MOVSP = 0xf0,
+ I_POPN = 0xa0, // 1010lnnn
+ M_POPN = 0xf0,
+ I_FINISH = 0xb0, // 10110000
+ I_POPLO = 0xb1, // 10110001 0000iiii (if any i set)
+ I_ADDSPBIG = 0xb2, // 10110010 uleb128
+ I_POPFDX = 0xb3, // 10110011 sssscccc
+ I_POPFDX8 = 0xb8, // 10111nnn
+ M_POPFDX8 = 0xf8,
+ // "Intel Wireless MMX" extensions omitted.
+ I_POPFDD = 0xc8, // 1100100h sssscccc
+ M_POPFDD = 0xfe,
+ I_POPFDD8 = 0xd0, // 11010nnn
+ M_POPFDD8 = 0xf8
+ };
+
+ uint8_t next() {
+ if (mBytesLeft == 0) {
+ if (mWordsLeft == 0) {
+ return I_FINISH;
+ }
+ mWordsLeft--;
+ mWord = *mNextWord++;
+ mBytesLeft = 4;
+ }
+ mBytesLeft--;
+ mWord = (mWord << 8) | (mWord >> 24); // rotate
+ return mWord;
+ }
+
+ uint32_t& vSP() { return mState[R_SP]; }
+ uint32_t* ptrSP() { return reinterpret_cast<uint32_t*>(vSP()); }
+
+ void checkStackBase() {
+ if (vSP() > mStackBase) mFailed = true;
+ }
+ void checkStackLimit() {
+ if (vSP() <= mStackLimit) mFailed = true;
+ }
+ void checkStackAlign() {
+ if ((vSP() & 3) != 0) mFailed = true;
+ }
+ void checkStack() {
+ checkStackBase();
+ checkStackLimit();
+ checkStackAlign();
+ }
+
+ void popRange(uint8_t first, uint8_t last, uint16_t mask) {
+ bool hasSP = false;
+ uint32_t tmpSP;
+ if (mask == 0) mFailed = true;
+ for (uint8_t r = first; r <= last; ++r) {
+ if (mask & 1) {
+ if (r == R_SP) {
+ hasSP = true;
+ tmpSP = *ptrSP();
+ } else
+ mState[r] = *ptrSP();
+ vSP() += 4;
+ checkStackBase();
+ if (mFailed) return;
+ }
+ mask >>= 1;
+ }
+ if (hasSP) {
+ vSP() = tmpSP;
+ checkStack();
+ }
+ }
+};
+
+bool EHState::unwind(const EHEntry* aEntry, const void* stackBasePtr) {
+ // The unwinding program cannot set SP to less than the initial value.
+ uint32_t stackLimit = mRegs[R_SP] - 4;
+ uint32_t stackBase = reinterpret_cast<uint32_t>(stackBasePtr);
+ EHInterp interp(*this, aEntry, stackLimit, stackBase);
+ return interp.unwind();
+}
+
+bool EHInterp::unwind() {
+ mState[R_PC] = 0;
+ checkStack();
+ while (!mFailed) {
+ uint8_t insn = next();
+#if DEBUG_EHABI_UNWIND
+ LOG("unwind insn = %02x", (unsigned)insn);
+#endif
+ // Try to put the common cases first.
+
+ // 00xxxxxx: vsp = vsp + (xxxxxx << 2) + 4
+ // 01xxxxxx: vsp = vsp - (xxxxxx << 2) - 4
+ if ((insn & M_ADDSP) == I_ADDSP) {
+ uint32_t offset = ((insn & 0x3f) << 2) + 4;
+ if (insn & 0x40) {
+ vSP() -= offset;
+ checkStackLimit();
+ } else {
+ vSP() += offset;
+ checkStackBase();
+ }
+ continue;
+ }
+
+ // 10100nnn: Pop r4-r[4+nnn]
+ // 10101nnn: Pop r4-r[4+nnn], r14
+ if ((insn & M_POPN) == I_POPN) {
+ uint8_t n = (insn & 0x07) + 1;
+ bool lr = insn & 0x08;
+ uint32_t* ptr = ptrSP();
+ vSP() += (n + (lr ? 1 : 0)) * 4;
+ checkStackBase();
+ for (uint8_t r = 4; r < 4 + n; ++r) mState[r] = *ptr++;
+ if (lr) mState[R_LR] = *ptr++;
+ continue;
+ }
+
+ // 1011000: Finish
+ if (insn == I_FINISH) {
+ if (mState[R_PC] == 0) {
+ mState[R_PC] = mState[R_LR];
+ // Non-standard change (bug 916106): Prevent the caller from
+ // re-using LR. Since the caller is by definition not a leaf
+ // routine, it will have to restore LR from somewhere to
+ // return to its own caller, so we can safely zero it here.
+ // This makes a difference only if an error in unwinding
+ // (e.g., caused by starting from within a prologue/epilogue)
+ // causes us to load a pointer to a leaf routine as LR; if we
+ // don't do something, we'll go into an infinite loop of
+ // "returning" to that same function.
+ mState[R_LR] = 0;
+ }
+ return true;
+ }
+
+ // 1001nnnn: Set vsp = r[nnnn]
+ if ((insn & M_MOVSP) == I_MOVSP) {
+ vSP() = mState[insn & 0x0f];
+ checkStack();
+ continue;
+ }
+
+ // 11001000 sssscccc: Pop VFP regs D[16+ssss]-D[16+ssss+cccc] (as FLDMFDD)
+ // 11001001 sssscccc: Pop VFP regs D[ssss]-D[ssss+cccc] (as FLDMFDD)
+ if ((insn & M_POPFDD) == I_POPFDD) {
+ uint8_t n = (next() & 0x0f) + 1;
+ // Note: if the 16+ssss+cccc > 31, the encoding is reserved.
+ // As the space is currently unused, we don't try to check.
+ vSP() += 8 * n;
+ checkStackBase();
+ continue;
+ }
+
+ // 11010nnn: Pop VFP regs D[8]-D[8+nnn] (as FLDMFDD)
+ if ((insn & M_POPFDD8) == I_POPFDD8) {
+ uint8_t n = (insn & 0x07) + 1;
+ vSP() += 8 * n;
+ checkStackBase();
+ continue;
+ }
+
+ // 10110010 uleb128: vsp = vsp + 0x204 + (uleb128 << 2)
+ if (insn == I_ADDSPBIG) {
+ uint32_t acc = 0;
+ uint8_t shift = 0;
+ uint8_t byte;
+ do {
+ if (shift >= 32) return false;
+ byte = next();
+ acc |= (byte & 0x7f) << shift;
+ shift += 7;
+ } while (byte & 0x80);
+ uint32_t offset = 0x204 + (acc << 2);
+ // The calculations above could have overflowed.
+ // But the one we care about is this:
+ if (vSP() + offset < vSP()) mFailed = true;
+ vSP() += offset;
+ // ...so that this is the only other check needed:
+ checkStackBase();
+ continue;
+ }
+
+ // 1000iiii iiiiiiii (i not all 0): Pop under masks {r15-r12}, {r11-r4}
+ if ((insn & M_POPMASK) == I_POPMASK) {
+ popRange(4, 15, ((insn & 0x0f) << 8) | next());
+ continue;
+ }
+
+ // 1011001 0000iiii (i not all 0): Pop under mask {r3-r0}
+ if (insn == I_POPLO) {
+ popRange(0, 3, next() & 0x0f);
+ continue;
+ }
+
+ // 10110011 sssscccc: Pop VFP regs D[ssss]-D[ssss+cccc] (as FLDMFDX)
+ if (insn == I_POPFDX) {
+ uint8_t n = (next() & 0x0f) + 1;
+ vSP() += 8 * n + 4;
+ checkStackBase();
+ continue;
+ }
+
+ // 10111nnn: Pop VFP regs D[8]-D[8+nnn] (as FLDMFDX)
+ if ((insn & M_POPFDX8) == I_POPFDX8) {
+ uint8_t n = (insn & 0x07) + 1;
+ vSP() += 8 * n + 4;
+ checkStackBase();
+ continue;
+ }
+
+ // unhandled instruction
+#ifdef DEBUG_EHABI_UNWIND
+ LOG("Unhandled EHABI instruction 0x%02x", insn);
+#endif
+ mFailed = true;
+ }
+ return false;
+}
+
+bool operator<(const EHTable& lhs, const EHTable& rhs) {
+ return lhs.startPC() < rhs.startPC();
+}
+
+// Async signal unsafe.
+EHAddrSpace::EHAddrSpace(const std::vector<EHTable>& aTables)
+ : mTables(aTables) {
+ std::sort(mTables.begin(), mTables.end());
+ DebugOnly<uint32_t> lastEnd = 0;
+ for (std::vector<EHTable>::iterator i = mTables.begin(); i != mTables.end();
+ ++i) {
+ MOZ_ASSERT(i->startPC() >= lastEnd);
+ mStarts.push_back(i->startPC());
+ lastEnd = i->endPC();
+ }
+}
+
+const EHTable* EHAddrSpace::lookup(uint32_t aPC) const {
+ ptrdiff_t i = (std::upper_bound(mStarts.begin(), mStarts.end(), aPC) -
+ mStarts.begin()) -
+ 1;
+
+ if (i < 0 || aPC >= mTables[i].endPC()) return 0;
+ return &mTables[i];
+}
+
+const EHEntry* EHTable::lookup(uint32_t aPC) const {
+ MOZ_ASSERT(aPC >= mStartPC);
+ if (aPC >= mEndPC) return nullptr;
+
+ const EHEntry* begin = mEntriesBegin;
+ const EHEntry* end = mEntriesEnd;
+ MOZ_ASSERT(begin < end);
+ if (aPC < reinterpret_cast<uint32_t>(begin->startPC.compute()))
+ return nullptr;
+
+ while (end - begin > 1) {
+#ifdef EHABI_UNWIND_MORE_ASSERTS
+ if ((end - 1)->startPC.compute() < begin->startPC.compute()) {
+ MOZ_CRASH("unsorted exidx");
+ }
+#endif
+ const EHEntry* mid = begin + (end - begin) / 2;
+ if (aPC < reinterpret_cast<uint32_t>(mid->startPC.compute()))
+ end = mid;
+ else
+ begin = mid;
+ }
+ return begin;
+}
+
+#if MOZ_LITTLE_ENDIAN()
+static const unsigned char hostEndian = ELFDATA2LSB;
+#elif MOZ_BIG_ENDIAN()
+static const unsigned char hostEndian = ELFDATA2MSB;
+#else
+# error "No endian?"
+#endif
+
+// Async signal unsafe: std::vector::reserve, std::string copy ctor.
+EHTable::EHTable(const void* aELF, size_t aSize, const std::string& aName)
+ : mStartPC(~0), // largest uint32_t
+ mEndPC(0),
+ mEntriesBegin(nullptr),
+ mEntriesEnd(nullptr),
+ mName(aName) {
+ const uint32_t fileHeaderAddr = reinterpret_cast<uint32_t>(aELF);
+
+ if (aSize < sizeof(Elf32_Ehdr)) return;
+
+ const Elf32_Ehdr& file = *(reinterpret_cast<Elf32_Ehdr*>(fileHeaderAddr));
+ if (memcmp(&file.e_ident[EI_MAG0], ELFMAG, SELFMAG) != 0 ||
+ file.e_ident[EI_CLASS] != ELFCLASS32 ||
+ file.e_ident[EI_DATA] != hostEndian ||
+ file.e_ident[EI_VERSION] != EV_CURRENT || file.e_machine != EM_ARM ||
+ file.e_version != EV_CURRENT)
+ // e_flags?
+ return;
+
+ MOZ_ASSERT(file.e_phoff + file.e_phnum * file.e_phentsize <= aSize);
+ const Elf32_Phdr *exidxHdr = 0, *zeroHdr = 0;
+ for (unsigned i = 0; i < file.e_phnum; ++i) {
+ const Elf32_Phdr& phdr = *(reinterpret_cast<Elf32_Phdr*>(
+ fileHeaderAddr + file.e_phoff + i * file.e_phentsize));
+ if (phdr.p_type == PT_ARM_EXIDX) {
+ exidxHdr = &phdr;
+ } else if (phdr.p_type == PT_LOAD) {
+ if (phdr.p_offset == 0) {
+ zeroHdr = &phdr;
+ }
+ if (phdr.p_flags & PF_X) {
+ mStartPC = std::min(mStartPC, phdr.p_vaddr);
+ mEndPC = std::max(mEndPC, phdr.p_vaddr + phdr.p_memsz);
+ }
+ }
+ }
+ if (!exidxHdr) return;
+ if (!zeroHdr) return;
+ mBaseAddress = fileHeaderAddr - zeroHdr->p_vaddr;
+ mStartPC += mBaseAddress;
+ mEndPC += mBaseAddress;
+ mEntriesBegin =
+ reinterpret_cast<const EHEntry*>(mBaseAddress + exidxHdr->p_vaddr);
+ mEntriesEnd = reinterpret_cast<const EHEntry*>(
+ mBaseAddress + exidxHdr->p_vaddr + exidxHdr->p_memsz);
+}
+
+mozilla::Atomic<const EHAddrSpace*> EHAddrSpace::sCurrent(nullptr);
+
+// Async signal safe; can fail if Update() hasn't returned yet.
+const EHAddrSpace* EHAddrSpace::Get() { return sCurrent; }
+
+// Collect unwinding information from loaded objects. Calls after the
+// first have no effect. Async signal unsafe.
+void EHAddrSpace::Update() {
+ const EHAddrSpace* space = sCurrent;
+ if (space) return;
+
+ SharedLibraryInfo info = SharedLibraryInfo::GetInfoForSelf();
+ std::vector<EHTable> tables;
+
+ for (size_t i = 0; i < info.GetSize(); ++i) {
+ const SharedLibrary& lib = info.GetEntry(i);
+ // FIXME: This isn't correct if the start address isn't p_offset 0, because
+ // the start address will not point at the file header. But this is worked
+ // around by magic number checks in the EHTable constructor.
+ EHTable tab(reinterpret_cast<const void*>(lib.GetStart()),
+ lib.GetEnd() - lib.GetStart(), lib.GetNativeDebugPath());
+ if (tab.isValid()) tables.push_back(tab);
+ }
+ space = new EHAddrSpace(tables);
+
+ if (!sCurrent.compareExchange(nullptr, space)) {
+ delete space;
+ space = sCurrent;
+ }
+}
+
+EHState::EHState(const mcontext_t& context) {
+#ifdef linux
+ mRegs[0] = context.arm_r0;
+ mRegs[1] = context.arm_r1;
+ mRegs[2] = context.arm_r2;
+ mRegs[3] = context.arm_r3;
+ mRegs[4] = context.arm_r4;
+ mRegs[5] = context.arm_r5;
+ mRegs[6] = context.arm_r6;
+ mRegs[7] = context.arm_r7;
+ mRegs[8] = context.arm_r8;
+ mRegs[9] = context.arm_r9;
+ mRegs[10] = context.arm_r10;
+ mRegs[11] = context.arm_fp;
+ mRegs[12] = context.arm_ip;
+ mRegs[13] = context.arm_sp;
+ mRegs[14] = context.arm_lr;
+ mRegs[15] = context.arm_pc;
+#else
+# error "Unhandled OS for ARM EHABI unwinding"
+#endif
+}
+
+} // namespace mozilla
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