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llvm-project/bolt/lib/Rewrite/LinuxKernelRewriter.cpp
Maksim Panchenko b8d3efa189
[BOLT][Linux] Fix linux_banner lookup (#144962) 
While detecting the Linux kernel version, look for `linux_banner` symbol
with local visibility if the global one was not found.

Fixes #144847
2025-06-19 23:09:34 -07:00

2017 lines
73 KiB
C++
Raw Blame History

//===- bolt/Rewrite/LinuxKernelRewriter.cpp -------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Support for updating Linux Kernel metadata.
//
//===----------------------------------------------------------------------===//
#include "bolt/Core/BinaryFunction.h"
#include "bolt/Rewrite/MetadataRewriter.h"
#include "bolt/Rewrite/MetadataRewriters.h"
#include "bolt/Utils/CommandLineOpts.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/MC/MCDisassembler/MCDisassembler.h"
#include "llvm/Support/BinaryStreamWriter.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/ErrorOr.h"
#include <regex>
#define DEBUG_TYPE "bolt-linux"
using namespace llvm;
using namespace bolt;
namespace opts {
static cl::opt<bool>
AltInstHasPadLen("alt-inst-has-padlen",
cl::desc("specify that .altinstructions has padlen field"),
cl::init(false), cl::Hidden, cl::cat(BoltCategory));
static cl::opt<uint32_t>
AltInstFeatureSize("alt-inst-feature-size",
cl::desc("size of feature field in .altinstructions"),
cl::init(2), cl::Hidden, cl::cat(BoltCategory));
static cl::opt<bool>
DumpAltInstructions("dump-alt-instructions",
cl::desc("dump Linux alternative instructions info"),
cl::init(false), cl::Hidden, cl::cat(BoltCategory));
static cl::opt<bool>
DumpExceptions("dump-linux-exceptions",
cl::desc("dump Linux kernel exception table"),
cl::init(false), cl::Hidden, cl::cat(BoltCategory));
static cl::opt<bool>
DumpORC("dump-orc", cl::desc("dump raw ORC unwind information (sorted)"),
cl::init(false), cl::Hidden, cl::cat(BoltCategory));
static cl::opt<bool> DumpParavirtualPatchSites(
"dump-para-sites", cl::desc("dump Linux kernel paravitual patch sites"),
cl::init(false), cl::Hidden, cl::cat(BoltCategory));
static cl::opt<bool>
DumpPCIFixups("dump-pci-fixups",
cl::desc("dump Linux kernel PCI fixup table"),
cl::init(false), cl::Hidden, cl::cat(BoltCategory));
static cl::opt<bool> DumpSMPLocks("dump-smp-locks",
cl::desc("dump Linux kernel SMP locks"),
cl::init(false), cl::Hidden,
cl::cat(BoltCategory));
static cl::opt<bool> DumpStaticCalls("dump-static-calls",
cl::desc("dump Linux kernel static calls"),
cl::init(false), cl::Hidden,
cl::cat(BoltCategory));
static cl::opt<bool>
DumpStaticKeys("dump-static-keys",
cl::desc("dump Linux kernel static keys jump table"),
cl::init(false), cl::Hidden, cl::cat(BoltCategory));
static cl::opt<bool> LongJumpLabels(
"long-jump-labels",
cl::desc("always use long jumps/nops for Linux kernel static keys"),
cl::init(false), cl::Hidden, cl::cat(BoltCategory));
static cl::opt<bool>
PrintORC("print-orc",
cl::desc("print ORC unwind information for instructions"),
cl::init(true), cl::Hidden, cl::cat(BoltCategory));
} // namespace opts
/// Linux kernel version
struct LKVersion {
LKVersion() {}
LKVersion(unsigned Major, unsigned Minor, unsigned Rev)
: Major(Major), Minor(Minor), Rev(Rev) {}
bool operator<(const LKVersion &Other) const {
return std::make_tuple(Major, Minor, Rev) <
std::make_tuple(Other.Major, Other.Minor, Other.Rev);
}
bool operator>(const LKVersion &Other) const { return Other < *this; }
bool operator<=(const LKVersion &Other) const { return !(*this > Other); }
bool operator>=(const LKVersion &Other) const { return !(*this < Other); }
bool operator==(const LKVersion &Other) const {
return Major == Other.Major && Minor == Other.Minor && Rev == Other.Rev;
}
bool operator!=(const LKVersion &Other) const { return !(*this == Other); }
unsigned Major{0};
unsigned Minor{0};
unsigned Rev{0};
};
/// Linux Kernel supports stack unwinding using ORC (oops rewind capability).
/// ORC state at every IP can be described by the following data structure.
struct ORCState {
int16_t SPOffset;
int16_t BPOffset;
int16_t Info;
bool operator==(const ORCState &Other) const {
return SPOffset == Other.SPOffset && BPOffset == Other.BPOffset &&
Info == Other.Info;
}
bool operator!=(const ORCState &Other) const { return !(*this == Other); }
};
/// Section terminator ORC entry.
static ORCState NullORC = {0, 0, 0};
/// Basic printer for ORC entry. It does not provide the same level of
/// information as objtool (for now).
inline raw_ostream &operator<<(raw_ostream &OS, const ORCState &E) {
if (!opts::PrintORC)
return OS;
if (E != NullORC)
OS << format("{sp: %d, bp: %d, info: 0x%x}", E.SPOffset, E.BPOffset,
E.Info);
else
OS << "{terminator}";
return OS;
}
namespace {
/// Extension to DataExtractor that supports reading addresses stored in
/// PC-relative format.
class AddressExtractor : public DataExtractor {
uint64_t DataAddress;
public:
AddressExtractor(StringRef Data, uint64_t DataAddress, bool IsLittleEndian,
uint8_t AddressSize)
: DataExtractor(Data, IsLittleEndian, AddressSize),
DataAddress(DataAddress) {}
/// Extract 32-bit PC-relative address/pointer.
uint64_t getPCRelAddress32(Cursor &C) {
const uint64_t Base = DataAddress + C.tell();
return Base + (int32_t)getU32(C);
}
/// Extract 64-bit PC-relative address/pointer.
uint64_t getPCRelAddress64(Cursor &C) {
const uint64_t Base = DataAddress + C.tell();
return Base + (int64_t)getU64(C);
}
};
class LinuxKernelRewriter final : public MetadataRewriter {
LKVersion LinuxKernelVersion;
/// Information required for updating metadata referencing an instruction.
struct InstructionFixup {
BinarySection &Section; // Section referencing the instruction.
uint64_t Offset; // Offset in the section above.
BinaryFunction &BF; // Function containing the instruction.
MCSymbol &Label; // Label marking the instruction.
bool IsPCRelative; // If the reference type is relative.
};
std::vector<InstructionFixup> Fixups;
/// Size of an entry in .smp_locks section.
static constexpr size_t SMP_LOCKS_ENTRY_SIZE = 4;
/// Linux ORC sections.
ErrorOr<BinarySection &> ORCUnwindSection = std::errc::bad_address;
ErrorOr<BinarySection &> ORCUnwindIPSection = std::errc::bad_address;
/// Size of entries in ORC sections.
static constexpr size_t ORC_UNWIND_ENTRY_SIZE = 6;
static constexpr size_t ORC_UNWIND_IP_ENTRY_SIZE = 4;
struct ORCListEntry {
uint64_t IP; /// Instruction address.
BinaryFunction *BF; /// Binary function corresponding to the entry.
ORCState ORC; /// Stack unwind info in ORC format.
/// ORC entries are sorted by their IPs. Terminator entries (NullORC)
/// should precede other entries with the same address.
bool operator<(const ORCListEntry &Other) const {
if (IP < Other.IP)
return 1;
if (IP > Other.IP)
return 0;
return ORC == NullORC && Other.ORC != NullORC;
}
};
using ORCListType = std::vector<ORCListEntry>;
ORCListType ORCEntries;
/// Number of entries in the input file ORC sections.
uint64_t NumORCEntries = 0;
/// Section containing static keys jump table.
ErrorOr<BinarySection &> StaticKeysJumpSection = std::errc::bad_address;
uint64_t StaticKeysJumpTableAddress = 0;
static constexpr size_t STATIC_KEYS_JUMP_ENTRY_SIZE = 8;
struct JumpInfoEntry {
bool Likely;
bool InitValue;
};
SmallVector<JumpInfoEntry, 16> JumpInfo;
/// Static key entries that need nop conversion.
DenseSet<uint32_t> NopIDs;
/// Section containing static call table.
ErrorOr<BinarySection &> StaticCallSection = std::errc::bad_address;
uint64_t StaticCallTableAddress = 0;
static constexpr size_t STATIC_CALL_ENTRY_SIZE = 8;
struct StaticCallInfo {
uint32_t ID; /// Identifier of the entry in the table.
BinaryFunction *Function; /// Function containing associated call.
MCSymbol *Label; /// Label attached to the call.
};
using StaticCallListType = std::vector<StaticCallInfo>;
StaticCallListType StaticCallEntries;
/// Section containing the Linux exception table.
ErrorOr<BinarySection &> ExceptionsSection = std::errc::bad_address;
static constexpr size_t EXCEPTION_TABLE_ENTRY_SIZE = 12;
/// Functions with exception handling code.
DenseSet<BinaryFunction *> FunctionsWithExceptions;
/// Section with paravirtual patch sites.
ErrorOr<BinarySection &> ParavirtualPatchSection = std::errc::bad_address;
/// Alignment of paravirtual patch structures.
static constexpr size_t PARA_PATCH_ALIGN = 8;
/// .altinstructions section.
ErrorOr<BinarySection &> AltInstrSection = std::errc::bad_address;
/// Section containing Linux bug table.
ErrorOr<BinarySection &> BugTableSection = std::errc::bad_address;
/// Size of bug_entry struct.
static constexpr size_t BUG_TABLE_ENTRY_SIZE = 12;
/// List of bug entries per function.
using FunctionBugListType =
DenseMap<BinaryFunction *, SmallVector<uint32_t, 2>>;
FunctionBugListType FunctionBugList;
/// .pci_fixup section.
ErrorOr<BinarySection &> PCIFixupSection = std::errc::bad_address;
static constexpr size_t PCI_FIXUP_ENTRY_SIZE = 16;
Error detectLinuxKernelVersion();
/// Process linux kernel special sections and their relocations.
void processLKSections();
/// Process __ksymtab and __ksymtab_gpl.
void processLKKSymtab(bool IsGPL = false);
// Create relocations in sections requiring fixups.
//
// Make sure functions that will not be emitted are marked as such before this
// function is executed.
void processInstructionFixups();
/// Process .smp_locks section.
Error processSMPLocks();
/// Read ORC unwind information and annotate instructions.
Error readORCTables();
/// Update ORC for functions once CFG is constructed.
Error processORCPostCFG();
/// Update ORC data in the binary.
Error rewriteORCTables();
/// Validate written ORC tables after binary emission.
Error validateORCTables();
/// Static call table handling.
Error readStaticCalls();
Error rewriteStaticCalls();
Error readExceptionTable();
Error rewriteExceptionTable();
/// Paravirtual instruction patch sites.
Error readParaInstructions();
Error rewriteParaInstructions();
/// __bug_table section handling.
Error readBugTable();
Error rewriteBugTable();
/// Do no process functions containing instruction annotated with
/// \p Annotation.
void skipFunctionsWithAnnotation(StringRef Annotation) const;
/// Handle alternative instruction info from .altinstructions.
Error readAltInstructions();
void processAltInstructionsPostCFG();
Error tryReadAltInstructions(uint32_t AltInstFeatureSize,
bool AltInstHasPadLen, bool ParseOnly);
/// Read .pci_fixup
Error readPCIFixupTable();
/// Handle static keys jump table.
Error readStaticKeysJumpTable();
Error rewriteStaticKeysJumpTable();
Error updateStaticKeysJumpTablePostEmit();
public:
LinuxKernelRewriter(BinaryContext &BC)
: MetadataRewriter("linux-kernel-rewriter", BC) {}
Error preCFGInitializer() override {
if (Error E = detectLinuxKernelVersion())
return E;
processLKSections();
if (Error E = processSMPLocks())
return E;
if (Error E = readStaticCalls())
return E;
if (Error E = readExceptionTable())
return E;
if (Error E = readParaInstructions())
return E;
if (Error E = readBugTable())
return E;
if (Error E = readAltInstructions())
return E;
// Some ORC entries could be linked to alternative instruction
// sequences. Hence, we read ORC after .altinstructions.
if (Error E = readORCTables())
return E;
if (Error E = readPCIFixupTable())
return E;
if (Error E = readStaticKeysJumpTable())
return E;
return Error::success();
}
Error postCFGInitializer() override {
if (Error E = processORCPostCFG())
return E;
processAltInstructionsPostCFG();
return Error::success();
}
Error preEmitFinalizer() override {
// Since rewriteExceptionTable() can mark functions as non-simple, run it
// before other rewriters that depend on simple/emit status.
if (Error E = rewriteExceptionTable())
return E;
if (Error E = rewriteParaInstructions())
return E;
if (Error E = rewriteORCTables())
return E;
if (Error E = rewriteStaticCalls())
return E;
if (Error E = rewriteStaticKeysJumpTable())
return E;
if (Error E = rewriteBugTable())
return E;
processInstructionFixups();
return Error::success();
}
Error postEmitFinalizer() override {
if (Error E = updateStaticKeysJumpTablePostEmit())
return E;
if (Error E = validateORCTables())
return E;
return Error::success();
}
};
Error LinuxKernelRewriter::detectLinuxKernelVersion() {
// Check for global and local linux_banner symbol.
BinaryData *BD = BC.getBinaryDataByName("linux_banner");
if (!BD)
BD = BC.getBinaryDataByName("linux_banner/1");
if (!BD)
return createStringError(errc::executable_format_error,
"unable to locate linux_banner");
const BinarySection &Section = BD->getSection();
const std::string S =
Section.getContents().substr(BD->getOffset(), BD->getSize()).str();
const std::regex Re(R"---(Linux version ((\d+)\.(\d+)(\.(\d+))?))---");
std::smatch Match;
if (std::regex_search(S, Match, Re)) {
const unsigned Major = std::stoi(Match[2].str());
const unsigned Minor = std::stoi(Match[3].str());
const unsigned Rev = Match[5].matched ? std::stoi(Match[5].str()) : 0;
LinuxKernelVersion = LKVersion(Major, Minor, Rev);
BC.outs() << "BOLT-INFO: Linux kernel version is " << Match[1].str()
<< "\n";
return Error::success();
}
return createStringError(errc::executable_format_error,
"Linux kernel version is unknown: " + S);
}
void LinuxKernelRewriter::processLKSections() {
processLKKSymtab();
processLKKSymtab(true);
}
/// Process __ksymtab[_gpl] sections of Linux Kernel.
/// This section lists all the vmlinux symbols that kernel modules can access.
///
/// All the entries are 4 bytes each and hence we can read them by one by one
/// and ignore the ones that are not pointing to the .text section. All pointers
/// are PC relative offsets. Always, points to the beginning of the function.
void LinuxKernelRewriter::processLKKSymtab(bool IsGPL) {
StringRef SectionName = "__ksymtab";
if (IsGPL)
SectionName = "__ksymtab_gpl";
ErrorOr<BinarySection &> SectionOrError =
BC.getUniqueSectionByName(SectionName);
assert(SectionOrError &&
"__ksymtab[_gpl] section not found in Linux Kernel binary");
const uint64_t SectionSize = SectionOrError->getSize();
const uint64_t SectionAddress = SectionOrError->getAddress();
assert((SectionSize % 4) == 0 &&
"The size of the __ksymtab[_gpl] section should be a multiple of 4");
for (uint64_t I = 0; I < SectionSize; I += 4) {
const uint64_t EntryAddress = SectionAddress + I;
ErrorOr<int64_t> Offset = BC.getSignedValueAtAddress(EntryAddress, 4);
assert(Offset && "Reading valid PC-relative offset for a ksymtab entry");
const int32_t SignedOffset = *Offset;
const uint64_t RefAddress = EntryAddress + SignedOffset;
BinaryFunction *BF = BC.getBinaryFunctionAtAddress(RefAddress);
if (!BF)
continue;
BC.addRelocation(EntryAddress, BF->getSymbol(), Relocation::getPC32(), 0,
*Offset);
}
}
/// .smp_locks section contains PC-relative references to instructions with LOCK
/// prefix. The prefix can be converted to NOP at boot time on non-SMP systems.
Error LinuxKernelRewriter::processSMPLocks() {
ErrorOr<BinarySection &> SMPLocksSection =
BC.getUniqueSectionByName(".smp_locks");
if (!SMPLocksSection)
return Error::success();
const uint64_t SectionSize = SMPLocksSection->getSize();
const uint64_t SectionAddress = SMPLocksSection->getAddress();
if (SectionSize % SMP_LOCKS_ENTRY_SIZE)
return createStringError(errc::executable_format_error,
"bad size of .smp_locks section");
AddressExtractor AE(SMPLocksSection->getContents(), SectionAddress,
BC.AsmInfo->isLittleEndian(),
BC.AsmInfo->getCodePointerSize());
AddressExtractor::Cursor Cursor(0);
while (Cursor && Cursor.tell() < SectionSize) {
const uint64_t Offset = Cursor.tell();
const uint64_t IP = AE.getPCRelAddress32(Cursor);
// Consume the status of the cursor.
if (!Cursor)
return createStringError(errc::executable_format_error,
"error while reading .smp_locks: %s",
toString(Cursor.takeError()).c_str());
if (opts::DumpSMPLocks)
BC.outs() << "SMP lock at 0x: " << Twine::utohexstr(IP) << '\n';
BinaryFunction *BF = BC.getBinaryFunctionContainingAddress(IP);
if (!BF || !BC.shouldEmit(*BF))
continue;
MCInst *Inst = BF->getInstructionAtOffset(IP - BF->getAddress());
if (!Inst)
return createStringError(errc::executable_format_error,
"no instruction matches lock at 0x%" PRIx64, IP);
// Check for duplicate entries.
if (BC.MIB->hasAnnotation(*Inst, "SMPLock"))
return createStringError(errc::executable_format_error,
"duplicate SMP lock at 0x%" PRIx64, IP);
BC.MIB->addAnnotation(*Inst, "SMPLock", true);
MCSymbol *Label =
BC.MIB->getOrCreateInstLabel(*Inst, "__SMPLock_", BC.Ctx.get());
Fixups.push_back({*SMPLocksSection, Offset, *BF, *Label,
/*IsPCRelative*/ true});
}
const uint64_t NumEntries = SectionSize / SMP_LOCKS_ENTRY_SIZE;
BC.outs() << "BOLT-INFO: parsed " << NumEntries << " SMP lock entries\n";
return Error::success();
}
void LinuxKernelRewriter::processInstructionFixups() {
for (InstructionFixup &Fixup : Fixups) {
if (!BC.shouldEmit(Fixup.BF))
continue;
Fixup.Section.addRelocation(Fixup.Offset, &Fixup.Label,
Fixup.IsPCRelative ? ELF::R_X86_64_PC32
: ELF::R_X86_64_64,
/*Addend*/ 0);
}
}
Error LinuxKernelRewriter::readORCTables() {
// NOTE: we should ignore relocations for orc tables as the tables are sorted
// post-link time and relocations are not updated.
ORCUnwindSection = BC.getUniqueSectionByName(".orc_unwind");
ORCUnwindIPSection = BC.getUniqueSectionByName(".orc_unwind_ip");
if (!ORCUnwindSection && !ORCUnwindIPSection)
return Error::success();
if (!ORCUnwindSection || !ORCUnwindIPSection)
return createStringError(errc::executable_format_error,
"missing ORC section");
NumORCEntries = ORCUnwindIPSection->getSize() / ORC_UNWIND_IP_ENTRY_SIZE;
if (ORCUnwindSection->getSize() != NumORCEntries * ORC_UNWIND_ENTRY_SIZE ||
ORCUnwindIPSection->getSize() != NumORCEntries * ORC_UNWIND_IP_ENTRY_SIZE)
return createStringError(errc::executable_format_error,
"ORC entries number mismatch detected");
DataExtractor OrcDE(ORCUnwindSection->getContents(),
BC.AsmInfo->isLittleEndian(),
BC.AsmInfo->getCodePointerSize());
AddressExtractor IPAE(
ORCUnwindIPSection->getContents(), ORCUnwindIPSection->getAddress(),
BC.AsmInfo->isLittleEndian(), BC.AsmInfo->getCodePointerSize());
DataExtractor::Cursor ORCCursor(0);
DataExtractor::Cursor IPCursor(0);
uint64_t PrevIP = 0;
for (uint32_t Index = 0; Index < NumORCEntries; ++Index) {
const uint64_t IP = IPAE.getPCRelAddress32(IPCursor);
// Consume the status of the cursor.
if (!IPCursor)
return createStringError(errc::executable_format_error,
"out of bounds while reading ORC IP table: %s",
toString(IPCursor.takeError()).c_str());
if (IP < PrevIP && opts::Verbosity)
BC.errs() << "BOLT-WARNING: out of order IP 0x" << Twine::utohexstr(IP)
<< " detected while reading ORC\n";
PrevIP = IP;
// Store all entries, includes those we are not going to update as the
// tables need to be sorted globally before being written out.
ORCEntries.push_back(ORCListEntry());
ORCListEntry &Entry = ORCEntries.back();
Entry.IP = IP;
Entry.ORC.SPOffset = (int16_t)OrcDE.getU16(ORCCursor);
Entry.ORC.BPOffset = (int16_t)OrcDE.getU16(ORCCursor);
Entry.ORC.Info = (int16_t)OrcDE.getU16(ORCCursor);
Entry.BF = nullptr;
// Consume the status of the cursor.
if (!ORCCursor)
return createStringError(errc::executable_format_error,
"out of bounds while reading ORC: %s",
toString(ORCCursor.takeError()).c_str());
if (Entry.ORC == NullORC)
continue;
BinaryFunction *&BF = Entry.BF;
BF = BC.getBinaryFunctionContainingAddress(IP, /*CheckPastEnd*/ true);
// If the entry immediately pointing past the end of the function is not
// the terminator entry, then it does not belong to this function.
if (BF && BF->getAddress() + BF->getSize() == IP)
BF = 0;
if (!BF) {
if (opts::Verbosity)
BC.errs() << "BOLT-WARNING: no binary function found matching ORC 0x"
<< Twine::utohexstr(IP) << ": " << Entry.ORC << '\n';
continue;
}
BF->setHasORC(true);
if (!BF->hasInstructions())
continue;
const uint64_t Offset = IP - BF->getAddress();
MCInst *Inst = BF->getInstructionAtOffset(Offset);
if (!Inst) {
// Check if there is an alternative instruction(s) at this IP. Multiple
// alternative instructions can take a place of a single original
// instruction and each alternative can have a separate ORC entry.
// Since ORC table is shared between all alternative sequences, there's
// a requirement that only one (out of many) sequences can have an
// instruction from the ORC table to avoid ambiguities/conflicts.
//
// For now, we have limited support for alternatives. I.e. we still print
// functions with them, but will not change the code in the output binary.
// As such, we can ignore alternative ORC entries. They will be preserved
// in the binary, but will not get printed in the instruction stream.
Inst = BF->getInstructionContainingOffset(Offset);
if (Inst || BC.MIB->hasAnnotation(*Inst, "AltInst"))
continue;
return createStringError(
errc::executable_format_error,
"no instruction at address 0x%" PRIx64 " in .orc_unwind_ip", IP);
}
// Some addresses will have two entries associated with them. The first
// one being a "weak" section terminator. Since we ignore the terminator,
// we should only assign one entry per instruction.
if (BC.MIB->hasAnnotation(*Inst, "ORC"))
return createStringError(
errc::executable_format_error,
"duplicate non-terminal ORC IP 0x%" PRIx64 " in .orc_unwind_ip", IP);
BC.MIB->addAnnotation(*Inst, "ORC", Entry.ORC);
}
BC.outs() << "BOLT-INFO: parsed " << NumORCEntries << " ORC entries\n";
if (opts::DumpORC) {
BC.outs() << "BOLT-INFO: ORC unwind information:\n";
for (const ORCListEntry &E : ORCEntries) {
BC.outs() << "0x" << Twine::utohexstr(E.IP) << ": " << E.ORC;
if (E.BF)
BC.outs() << ": " << *E.BF;
BC.outs() << '\n';
}
}
// Add entries for functions that don't have explicit ORC info at the start.
// We'll have the correct info for them even if ORC for the preceding function
// changes.
ORCListType NewEntries;
for (BinaryFunction &BF : llvm::make_second_range(BC.getBinaryFunctions())) {
auto It = llvm::partition_point(ORCEntries, [&](const ORCListEntry &E) {
return E.IP <= BF.getAddress();
});
if (It != ORCEntries.begin())
--It;
if (It->BF == &BF)
continue;
if (It->ORC == NullORC && It->IP == BF.getAddress()) {
assert(!It->BF);
It->BF = &BF;
continue;
}
NewEntries.push_back({BF.getAddress(), &BF, It->ORC});
if (It->ORC != NullORC)
BF.setHasORC(true);
}
llvm::copy(NewEntries, std::back_inserter(ORCEntries));
llvm::sort(ORCEntries);
if (opts::DumpORC) {
BC.outs() << "BOLT-INFO: amended ORC unwind information:\n";
for (const ORCListEntry &E : ORCEntries) {
BC.outs() << "0x" << Twine::utohexstr(E.IP) << ": " << E.ORC;
if (E.BF)
BC.outs() << ": " << *E.BF;
BC.outs() << '\n';
}
}
return Error::success();
}
Error LinuxKernelRewriter::processORCPostCFG() {
if (!NumORCEntries)
return Error::success();
// Propagate ORC to the rest of the function. We can annotate every
// instruction in every function, but to minimize the overhead, we annotate
// the first instruction in every basic block to reflect the state at the
// entry. This way, the ORC state can be calculated based on annotations
// regardless of the basic block layout. Note that if we insert/delete
// instructions, we must take care to attach ORC info to the new/deleted ones.
for (BinaryFunction &BF : llvm::make_second_range(BC.getBinaryFunctions())) {
std::optional<ORCState> CurrentState;
for (BinaryBasicBlock &BB : BF) {
for (MCInst &Inst : BB) {
ErrorOr<ORCState> State =
BC.MIB->tryGetAnnotationAs<ORCState>(Inst, "ORC");
if (State) {
CurrentState = *State;
continue;
}
// Get state for the start of the function.
if (!CurrentState) {
// A terminator entry (NullORC) can match the function address. If
// there's also a non-terminator entry, it will be placed after the
// terminator. Hence, we are looking for the last ORC entry that
// matches the address.
auto It =
llvm::partition_point(ORCEntries, [&](const ORCListEntry &E) {
return E.IP <= BF.getAddress();
});
if (It != ORCEntries.begin())
--It;
assert(It->IP == BF.getAddress() && (!It->BF || It->BF == &BF) &&
"ORC info at function entry expected.");
if (It->ORC == NullORC && BF.hasORC()) {
BC.errs() << "BOLT-WARNING: ORC unwind info excludes prologue for "
<< BF << '\n';
}
It->BF = &BF;
CurrentState = It->ORC;
if (It->ORC != NullORC)
BF.setHasORC(true);
}
// While printing ORC, attach info to every instruction for convenience.
if (opts::PrintORC || &Inst == &BB.front())
BC.MIB->addAnnotation(Inst, "ORC", *CurrentState);
}
}
}
return Error::success();
}
Error LinuxKernelRewriter::rewriteORCTables() {
if (!NumORCEntries)
return Error::success();
// Update ORC sections in-place. As we change the code, the number of ORC
// entries may increase for some functions. However, as we remove terminator
// redundancy (see below), more space is freed up and we should always be able
// to fit new ORC tables in the reserved space.
auto createInPlaceWriter = [&](BinarySection &Section) -> BinaryStreamWriter {
const size_t Size = Section.getSize();
uint8_t *NewContents = new uint8_t[Size];
Section.updateContents(NewContents, Size);
Section.setOutputFileOffset(Section.getInputFileOffset());
return BinaryStreamWriter({NewContents, Size}, BC.AsmInfo->isLittleEndian()
? endianness::little
: endianness::big);
};
BinaryStreamWriter UnwindWriter = createInPlaceWriter(*ORCUnwindSection);
BinaryStreamWriter UnwindIPWriter = createInPlaceWriter(*ORCUnwindIPSection);
uint64_t NumEmitted = 0;
std::optional<ORCState> LastEmittedORC;
auto emitORCEntry = [&](const uint64_t IP, const ORCState &ORC,
MCSymbol *Label = 0, bool Force = false) -> Error {
if (LastEmittedORC && ORC == *LastEmittedORC && !Force)
return Error::success();
LastEmittedORC = ORC;
if (++NumEmitted > NumORCEntries)
return createStringError(errc::executable_format_error,
"exceeded the number of allocated ORC entries");
if (Label)
ORCUnwindIPSection->addRelocation(UnwindIPWriter.getOffset(), Label,
Relocation::getPC32(), /*Addend*/ 0);
const int32_t IPValue =
IP - ORCUnwindIPSection->getAddress() - UnwindIPWriter.getOffset();
if (Error E = UnwindIPWriter.writeInteger(IPValue))
return E;
if (Error E = UnwindWriter.writeInteger(ORC.SPOffset))
return E;
if (Error E = UnwindWriter.writeInteger(ORC.BPOffset))
return E;
if (Error E = UnwindWriter.writeInteger(ORC.Info))
return E;
return Error::success();
};
// Emit new ORC entries for the emitted function.
auto emitORC = [&](const FunctionFragment &FF) -> Error {
ORCState CurrentState = NullORC;
for (BinaryBasicBlock *BB : FF) {
for (MCInst &Inst : *BB) {
ErrorOr<ORCState> ErrorOrState =
BC.MIB->tryGetAnnotationAs<ORCState>(Inst, "ORC");
if (!ErrorOrState || *ErrorOrState == CurrentState)
continue;
// Issue label for the instruction.
MCSymbol *Label =
BC.MIB->getOrCreateInstLabel(Inst, "__ORC_", BC.Ctx.get());
if (Error E = emitORCEntry(0, *ErrorOrState, Label))
return E;
CurrentState = *ErrorOrState;
}
}
return Error::success();
};
// Emit ORC entries for cold fragments. We assume that these fragments are
// emitted contiguously in memory using reserved space in the kernel. This
// assumption is validated in post-emit pass validateORCTables() where we
// check that ORC entries are sorted by their addresses.
auto emitColdORC = [&]() -> Error {
for (BinaryFunction &BF :
llvm::make_second_range(BC.getBinaryFunctions())) {
if (!BC.shouldEmit(BF))
continue;
for (FunctionFragment &FF : BF.getLayout().getSplitFragments())
if (Error E = emitORC(FF))
return E;
}
return Error::success();
};
bool ShouldEmitCold = !BC.BOLTReserved.empty();
for (ORCListEntry &Entry : ORCEntries) {
if (ShouldEmitCold && Entry.IP > BC.BOLTReserved.start()) {
if (Error E = emitColdORC())
return E;
// Emit terminator entry at the end of the reserved region.
if (Error E = emitORCEntry(BC.BOLTReserved.end(), NullORC))
return E;
ShouldEmitCold = false;
}
// Emit original entries for functions that we haven't modified.
if (!Entry.BF || !BC.shouldEmit(*Entry.BF)) {
// Emit terminator only if it marks the start of a function.
if (Entry.ORC == NullORC && !Entry.BF)
continue;
if (Error E = emitORCEntry(Entry.IP, Entry.ORC))
return E;
continue;
}
// Emit all ORC entries for a function referenced by an entry and skip over
// the rest of entries for this function by resetting its ORC attribute.
if (Entry.BF->hasORC()) {
if (Error E = emitORC(Entry.BF->getLayout().getMainFragment()))
return E;
Entry.BF->setHasORC(false);
}
}
LLVM_DEBUG(dbgs() << "BOLT-DEBUG: emitted " << NumEmitted
<< " ORC entries\n");
// Populate ORC tables with a terminator entry with max address to match the
// original table sizes.
const uint64_t LastIP = std::numeric_limits<uint64_t>::max();
while (UnwindWriter.bytesRemaining()) {
if (Error E = emitORCEntry(LastIP, NullORC, nullptr, /*Force*/ true))
return E;
}
return Error::success();
}
Error LinuxKernelRewriter::validateORCTables() {
if (!ORCUnwindIPSection)
return Error::success();
AddressExtractor IPAE(
ORCUnwindIPSection->getOutputContents(), ORCUnwindIPSection->getAddress(),
BC.AsmInfo->isLittleEndian(), BC.AsmInfo->getCodePointerSize());
AddressExtractor::Cursor IPCursor(0);
uint64_t PrevIP = 0;
for (uint32_t Index = 0; Index < NumORCEntries; ++Index) {
const uint64_t IP = IPAE.getPCRelAddress32(IPCursor);
if (!IPCursor)
return createStringError(errc::executable_format_error,
"out of bounds while reading ORC IP table: %s",
toString(IPCursor.takeError()).c_str());
assert(IP >= PrevIP && "Unsorted ORC table detected");
(void)PrevIP;
PrevIP = IP;
}
return Error::success();
}
/// The static call site table is created by objtool and contains entries in the
/// following format:
///
/// struct static_call_site {
/// s32 addr;
/// s32 key;
/// };
///
Error LinuxKernelRewriter::readStaticCalls() {
const BinaryData *StaticCallTable =
BC.getBinaryDataByName("__start_static_call_sites");
if (!StaticCallTable)
return Error::success();
StaticCallTableAddress = StaticCallTable->getAddress();
const BinaryData *Stop = BC.getBinaryDataByName("__stop_static_call_sites");
if (!Stop)
return createStringError(errc::executable_format_error,
"missing __stop_static_call_sites symbol");
ErrorOr<BinarySection &> ErrorOrSection =
BC.getSectionForAddress(StaticCallTableAddress);
if (!ErrorOrSection)
return createStringError(errc::executable_format_error,
"no section matching __start_static_call_sites");
StaticCallSection = *ErrorOrSection;
if (!StaticCallSection->containsAddress(Stop->getAddress() - 1))
return createStringError(errc::executable_format_error,
"__stop_static_call_sites not in the same section "
"as __start_static_call_sites");
if ((Stop->getAddress() - StaticCallTableAddress) % STATIC_CALL_ENTRY_SIZE)
return createStringError(errc::executable_format_error,
"static call table size error");
const uint64_t SectionAddress = StaticCallSection->getAddress();
AddressExtractor AE(StaticCallSection->getContents(), SectionAddress,
BC.AsmInfo->isLittleEndian(),
BC.AsmInfo->getCodePointerSize());
AddressExtractor::Cursor Cursor(StaticCallTableAddress - SectionAddress);
uint32_t EntryID = 0;
while (Cursor && Cursor.tell() < Stop->getAddress() - SectionAddress) {
const uint64_t CallAddress = AE.getPCRelAddress32(Cursor);
const uint64_t KeyAddress = AE.getPCRelAddress32(Cursor);
// Consume the status of the cursor.
if (!Cursor)
return createStringError(errc::executable_format_error,
"out of bounds while reading static calls: %s",
toString(Cursor.takeError()).c_str());
++EntryID;
if (opts::DumpStaticCalls) {
BC.outs() << "Static Call Site: " << EntryID << '\n';
BC.outs() << "\tCallAddress: 0x" << Twine::utohexstr(CallAddress)
<< "\n\tKeyAddress: 0x" << Twine::utohexstr(KeyAddress)
<< '\n';
}
BinaryFunction *BF = BC.getBinaryFunctionContainingAddress(CallAddress);
if (!BF)
continue;
if (!BC.shouldEmit(*BF))
continue;
if (!BF->hasInstructions())
continue;
MCInst *Inst = BF->getInstructionAtOffset(CallAddress - BF->getAddress());
if (!Inst)
return createStringError(errc::executable_format_error,
"no instruction at call site address 0x%" PRIx64,
CallAddress);
// Check for duplicate entries.
if (BC.MIB->hasAnnotation(*Inst, "StaticCall"))
return createStringError(errc::executable_format_error,
"duplicate static call site at 0x%" PRIx64,
CallAddress);
BC.MIB->addAnnotation(*Inst, "StaticCall", EntryID);
MCSymbol *Label =
BC.MIB->getOrCreateInstLabel(*Inst, "__SC_", BC.Ctx.get());
StaticCallEntries.push_back({EntryID, BF, Label});
}
BC.outs() << "BOLT-INFO: parsed " << StaticCallEntries.size()
<< " static call entries\n";
return Error::success();
}
/// The static call table is sorted during boot time in
/// static_call_sort_entries(). This makes it possible to update existing
/// entries in-place ignoring their relative order.
Error LinuxKernelRewriter::rewriteStaticCalls() {
if (!StaticCallTableAddress || !StaticCallSection)
return Error::success();
for (auto &Entry : StaticCallEntries) {
if (!Entry.Function)
continue;
BinaryFunction &BF = *Entry.Function;
if (!BC.shouldEmit(BF))
continue;
// Create a relocation against the label.
const uint64_t EntryOffset = StaticCallTableAddress -
StaticCallSection->getAddress() +
(Entry.ID - 1) * STATIC_CALL_ENTRY_SIZE;
StaticCallSection->addRelocation(EntryOffset, Entry.Label,
ELF::R_X86_64_PC32, /*Addend*/ 0);
}
return Error::success();
}
/// Instructions that access user-space memory can cause page faults. These
/// faults will be handled by the kernel and execution will resume at the fixup
/// code location if the address was invalid. The kernel uses the exception
/// table to match the faulting instruction to its fixup. The table consists of
/// the following entries:
///
/// struct exception_table_entry {
/// int insn;
/// int fixup;
/// int data;
/// };
///
/// More info at:
/// https://www.kernel.org/doc/Documentation/x86/exception-tables.txt
Error LinuxKernelRewriter::readExceptionTable() {
ExceptionsSection = BC.getUniqueSectionByName("__ex_table");
if (!ExceptionsSection)
return Error::success();
if (ExceptionsSection->getSize() % EXCEPTION_TABLE_ENTRY_SIZE)
return createStringError(errc::executable_format_error,
"exception table size error");
AddressExtractor AE(
ExceptionsSection->getContents(), ExceptionsSection->getAddress(),
BC.AsmInfo->isLittleEndian(), BC.AsmInfo->getCodePointerSize());
AddressExtractor::Cursor Cursor(0);
uint32_t EntryID = 0;
while (Cursor && Cursor.tell() < ExceptionsSection->getSize()) {
const uint64_t InstAddress = AE.getPCRelAddress32(Cursor);
const uint64_t FixupAddress = AE.getPCRelAddress32(Cursor);
const uint64_t Data = AE.getU32(Cursor);
// Consume the status of the cursor.
if (!Cursor)
return createStringError(
errc::executable_format_error,
"out of bounds while reading exception table: %s",
toString(Cursor.takeError()).c_str());
++EntryID;
if (opts::DumpExceptions) {
BC.outs() << "Exception Entry: " << EntryID << '\n';
BC.outs() << "\tInsn: 0x" << Twine::utohexstr(InstAddress) << '\n'
<< "\tFixup: 0x" << Twine::utohexstr(FixupAddress) << '\n'
<< "\tData: 0x" << Twine::utohexstr(Data) << '\n';
}
MCInst *Inst = nullptr;
MCSymbol *FixupLabel = nullptr;
BinaryFunction *InstBF = BC.getBinaryFunctionContainingAddress(InstAddress);
if (InstBF && BC.shouldEmit(*InstBF)) {
Inst = InstBF->getInstructionAtOffset(InstAddress - InstBF->getAddress());
if (!Inst)
return createStringError(errc::executable_format_error,
"no instruction at address 0x%" PRIx64
" in exception table",
InstAddress);
BC.MIB->addAnnotation(*Inst, "ExceptionEntry", EntryID);
FunctionsWithExceptions.insert(InstBF);
}
if (!InstBF && opts::Verbosity) {
BC.outs() << "BOLT-INFO: no function matches instruction at 0x"
<< Twine::utohexstr(InstAddress)
<< " referenced by Linux exception table\n";
}
BinaryFunction *FixupBF =
BC.getBinaryFunctionContainingAddress(FixupAddress);
if (FixupBF && BC.shouldEmit(*FixupBF)) {
const uint64_t Offset = FixupAddress - FixupBF->getAddress();
if (!FixupBF->getInstructionAtOffset(Offset))
return createStringError(errc::executable_format_error,
"no instruction at fixup address 0x%" PRIx64
" in exception table",
FixupAddress);
FixupLabel = Offset ? FixupBF->addEntryPointAtOffset(Offset)
: FixupBF->getSymbol();
if (Inst)
BC.MIB->addAnnotation(*Inst, "Fixup", FixupLabel->getName());
FunctionsWithExceptions.insert(FixupBF);
}
if (!FixupBF && opts::Verbosity) {
BC.outs() << "BOLT-INFO: no function matches fixup code at 0x"
<< Twine::utohexstr(FixupAddress)
<< " referenced by Linux exception table\n";
}
}
BC.outs() << "BOLT-INFO: parsed "
<< ExceptionsSection->getSize() / EXCEPTION_TABLE_ENTRY_SIZE
<< " exception table entries\n";
return Error::success();
}
/// Depending on the value of CONFIG_BUILDTIME_TABLE_SORT, the kernel expects
/// the exception table to be sorted. Hence we have to sort it after code
/// reordering.
Error LinuxKernelRewriter::rewriteExceptionTable() {
// Disable output of functions with exceptions before rewrite support is
// added.
for (BinaryFunction *BF : FunctionsWithExceptions)
BF->setSimple(false);
return Error::success();
}
/// .parainsrtuctions section contains information for patching parvirtual call
/// instructions during runtime. The entries in the section are in the form:
///
/// struct paravirt_patch_site {
/// u8 *instr; /* original instructions */
/// u8 type; /* type of this instruction */
/// u8 len; /* length of original instruction */
/// };
///
/// Note that the structures are aligned at 8-byte boundary.
Error LinuxKernelRewriter::readParaInstructions() {
ParavirtualPatchSection = BC.getUniqueSectionByName(".parainstructions");
if (!ParavirtualPatchSection)
return Error::success();
DataExtractor DE(ParavirtualPatchSection->getContents(),
BC.AsmInfo->isLittleEndian(),
BC.AsmInfo->getCodePointerSize());
uint32_t EntryID = 0;
DataExtractor::Cursor Cursor(0);
while (Cursor && !DE.eof(Cursor)) {
const uint64_t NextOffset = alignTo(Cursor.tell(), Align(PARA_PATCH_ALIGN));
if (!DE.isValidOffset(NextOffset))
break;
Cursor.seek(NextOffset);
const uint64_t InstrLocation = DE.getU64(Cursor);
const uint8_t Type = DE.getU8(Cursor);
const uint8_t Len = DE.getU8(Cursor);
if (!Cursor)
return createStringError(
errc::executable_format_error,
"out of bounds while reading .parainstructions: %s",
toString(Cursor.takeError()).c_str());
++EntryID;
if (opts::DumpParavirtualPatchSites) {
BC.outs() << "Paravirtual patch site: " << EntryID << '\n';
BC.outs() << "\tInstr: 0x" << Twine::utohexstr(InstrLocation)
<< "\n\tType: 0x" << Twine::utohexstr(Type) << "\n\tLen: 0x"
<< Twine::utohexstr(Len) << '\n';
}
BinaryFunction *BF = BC.getBinaryFunctionContainingAddress(InstrLocation);
if (!BF && opts::Verbosity) {
BC.outs() << "BOLT-INFO: no function matches address 0x"
<< Twine::utohexstr(InstrLocation)
<< " referenced by paravirutal patch site\n";
}
if (BF && BC.shouldEmit(*BF)) {
MCInst *Inst =
BF->getInstructionAtOffset(InstrLocation - BF->getAddress());
if (!Inst)
return createStringError(errc::executable_format_error,
"no instruction at address 0x%" PRIx64
" in paravirtual call site %d",
InstrLocation, EntryID);
BC.MIB->addAnnotation(*Inst, "ParaSite", EntryID);
}
}
BC.outs() << "BOLT-INFO: parsed " << EntryID << " paravirtual patch sites\n";
return Error::success();
}
void LinuxKernelRewriter::skipFunctionsWithAnnotation(
StringRef Annotation) const {
for (BinaryFunction &BF : llvm::make_second_range(BC.getBinaryFunctions())) {
if (!BC.shouldEmit(BF))
continue;
for (const BinaryBasicBlock &BB : BF) {
const bool HasAnnotation = llvm::any_of(BB, [&](const MCInst &Inst) {
return BC.MIB->hasAnnotation(Inst, Annotation);
});
if (HasAnnotation) {
BF.setSimple(false);
break;
}
}
}
}
Error LinuxKernelRewriter::rewriteParaInstructions() {
// Disable output of functions with paravirtual instructions before the
// rewrite support is complete.
skipFunctionsWithAnnotation("ParaSite");
return Error::success();
}
/// Process __bug_table section.
/// This section contains information useful for kernel debugging, mostly
/// utilized by WARN()/WARN_ON() macros and deprecated BUG()/BUG_ON().
///
/// Each entry in the section is a struct bug_entry that contains a pointer to
/// the ud2 instruction corresponding to the bug, corresponding file name (both
/// pointers use PC relative offset addressing), line number, and flags.
/// The definition of the struct bug_entry can be found in
/// `include/asm-generic/bug.h`. The first entry in the struct is an instruction
/// address encoded as a PC-relative offset. In theory, it could be an absolute
/// address if CONFIG_GENERIC_BUG_RELATIVE_POINTERS is not set, but in practice
/// the kernel code relies on it being a relative offset on x86-64.
Error LinuxKernelRewriter::readBugTable() {
BugTableSection = BC.getUniqueSectionByName("__bug_table");
if (!BugTableSection)
return Error::success();
if (BugTableSection->getSize() % BUG_TABLE_ENTRY_SIZE)
return createStringError(errc::executable_format_error,
"bug table size error");
AddressExtractor AE(
BugTableSection->getContents(), BugTableSection->getAddress(),
BC.AsmInfo->isLittleEndian(), BC.AsmInfo->getCodePointerSize());
AddressExtractor::Cursor Cursor(0);
uint32_t EntryID = 0;
while (Cursor && Cursor.tell() < BugTableSection->getSize()) {
const uint64_t Pos = Cursor.tell();
const uint64_t InstAddress = AE.getPCRelAddress32(Cursor);
Cursor.seek(Pos + BUG_TABLE_ENTRY_SIZE);
if (!Cursor)
return createStringError(errc::executable_format_error,
"out of bounds while reading __bug_table: %s",
toString(Cursor.takeError()).c_str());
++EntryID;
BinaryFunction *BF = BC.getBinaryFunctionContainingAddress(InstAddress);
if (!BF && opts::Verbosity) {
BC.outs() << "BOLT-INFO: no function matches address 0x"
<< Twine::utohexstr(InstAddress)
<< " referenced by bug table\n";
}
if (BF && BC.shouldEmit(*BF)) {
MCInst *Inst = BF->getInstructionAtOffset(InstAddress - BF->getAddress());
if (!Inst)
return createStringError(errc::executable_format_error,
"no instruction at address 0x%" PRIx64
" referenced by bug table entry %d",
InstAddress, EntryID);
BC.MIB->addAnnotation(*Inst, "BugEntry", EntryID);
FunctionBugList[BF].push_back(EntryID);
}
}
BC.outs() << "BOLT-INFO: parsed " << EntryID << " bug table entries\n";
return Error::success();
}
/// find_bug() uses linear search to match an address to an entry in the bug
/// table. Hence, there is no need to sort entries when rewriting the table.
/// When we need to erase an entry, we set its instruction address to zero.
Error LinuxKernelRewriter::rewriteBugTable() {
if (!BugTableSection)
return Error::success();
for (BinaryFunction &BF : llvm::make_second_range(BC.getBinaryFunctions())) {
if (!BC.shouldEmit(BF))
continue;
if (!FunctionBugList.count(&BF))
continue;
// Bugs that will be emitted for this function.
DenseSet<uint32_t> EmittedIDs;
for (BinaryBasicBlock &BB : BF) {
for (MCInst &Inst : BB) {
if (!BC.MIB->hasAnnotation(Inst, "BugEntry"))
continue;
const uint32_t ID = BC.MIB->getAnnotationAs<uint32_t>(Inst, "BugEntry");
EmittedIDs.insert(ID);
// Create a relocation entry for this bug entry.
MCSymbol *Label =
BC.MIB->getOrCreateInstLabel(Inst, "__BUG_", BC.Ctx.get());
const uint64_t EntryOffset = (ID - 1) * BUG_TABLE_ENTRY_SIZE;
BugTableSection->addRelocation(EntryOffset, Label, ELF::R_X86_64_PC32,
/*Addend*/ 0);
}
}
// Clear bug entries that were not emitted for this function, e.g. as a
// result of DCE, but setting their instruction address to zero.
for (const uint32_t ID : FunctionBugList[&BF]) {
if (!EmittedIDs.count(ID)) {
const uint64_t EntryOffset = (ID - 1) * BUG_TABLE_ENTRY_SIZE;
BugTableSection->addRelocation(EntryOffset, nullptr, ELF::R_X86_64_PC32,
/*Addend*/ 0);
}
}
}
return Error::success();
}
/// The kernel can replace certain instruction sequences depending on hardware
/// it is running on and features specified during boot time. The information
/// about alternative instruction sequences is stored in .altinstructions
/// section. The format of entries in this section is defined in
/// arch/x86/include/asm/alternative.h:
///
/// struct alt_instr {
/// s32 instr_offset;
/// s32 repl_offset;
/// uXX feature;
/// u8 instrlen;
/// u8 replacementlen;
/// u8 padlen; // present in older kernels
/// } __packed;
///
/// Note that the structure is packed.
///
/// Since the size of the "feature" field could be either u16 or u32, and
/// "padlen" presence is unknown, we attempt to parse .altinstructions section
/// using all possible combinations (four at this time). Since we validate the
/// contents of the section and its size, the detection works quite well.
/// Still, we leave the user the opportunity to specify these features on the
/// command line and skip the guesswork.
Error LinuxKernelRewriter::readAltInstructions() {
AltInstrSection = BC.getUniqueSectionByName(".altinstructions");
if (!AltInstrSection)
return Error::success();
// Presence of "padlen" field.
std::vector<bool> PadLenVariants;
if (opts::AltInstHasPadLen.getNumOccurrences())
PadLenVariants.push_back(opts::AltInstHasPadLen);
else
PadLenVariants = {false, true};
// Size (in bytes) variants of "feature" field.
std::vector<uint32_t> FeatureSizeVariants;
if (opts::AltInstFeatureSize.getNumOccurrences())
FeatureSizeVariants.push_back(opts::AltInstFeatureSize);
else
FeatureSizeVariants = {2, 4};
for (bool AltInstHasPadLen : PadLenVariants) {
for (uint32_t AltInstFeatureSize : FeatureSizeVariants) {
LLVM_DEBUG({
dbgs() << "BOLT-DEBUG: trying AltInstHasPadLen = " << AltInstHasPadLen
<< "; AltInstFeatureSize = " << AltInstFeatureSize << ";\n";
});
if (Error E = tryReadAltInstructions(AltInstFeatureSize, AltInstHasPadLen,
/*ParseOnly*/ true)) {
consumeError(std::move(E));
continue;
}
LLVM_DEBUG(dbgs() << "Matched .altinstructions format\n");
if (!opts::AltInstHasPadLen.getNumOccurrences())
BC.outs() << "BOLT-INFO: setting --" << opts::AltInstHasPadLen.ArgStr
<< '=' << AltInstHasPadLen << '\n';
if (!opts::AltInstFeatureSize.getNumOccurrences())
BC.outs() << "BOLT-INFO: setting --" << opts::AltInstFeatureSize.ArgStr
<< '=' << AltInstFeatureSize << '\n';
return tryReadAltInstructions(AltInstFeatureSize, AltInstHasPadLen,
/*ParseOnly*/ false);
}
}
// We couldn't match the format. Read again to properly propagate the error
// to the user.
return tryReadAltInstructions(opts::AltInstFeatureSize,
opts::AltInstHasPadLen, /*ParseOnly*/ false);
}
Error LinuxKernelRewriter::tryReadAltInstructions(uint32_t AltInstFeatureSize,
bool AltInstHasPadLen,
bool ParseOnly) {
AddressExtractor AE(
AltInstrSection->getContents(), AltInstrSection->getAddress(),
BC.AsmInfo->isLittleEndian(), BC.AsmInfo->getCodePointerSize());
AddressExtractor::Cursor Cursor(0);
uint64_t EntryID = 0;
while (Cursor && !AE.eof(Cursor)) {
const uint64_t OrgInstAddress = AE.getPCRelAddress32(Cursor);
const uint64_t AltInstAddress = AE.getPCRelAddress32(Cursor);
const uint64_t Feature = AE.getUnsigned(Cursor, AltInstFeatureSize);
const uint8_t OrgSize = AE.getU8(Cursor);
const uint8_t AltSize = AE.getU8(Cursor);
// Older kernels may have the padlen field.
const uint8_t PadLen = AltInstHasPadLen ? AE.getU8(Cursor) : 0;
if (!Cursor)
return createStringError(
errc::executable_format_error,
"out of bounds while reading .altinstructions: %s",
toString(Cursor.takeError()).c_str());
++EntryID;
if (opts::DumpAltInstructions) {
BC.outs() << "Alternative instruction entry: " << EntryID
<< "\n\tOrg: 0x" << Twine::utohexstr(OrgInstAddress)
<< "\n\tAlt: 0x" << Twine::utohexstr(AltInstAddress)
<< "\n\tFeature: 0x" << Twine::utohexstr(Feature)
<< "\n\tOrgSize: " << (int)OrgSize
<< "\n\tAltSize: " << (int)AltSize << '\n';
if (AltInstHasPadLen)
BC.outs() << "\tPadLen: " << (int)PadLen << '\n';
}
if (AltSize > OrgSize)
return createStringError(errc::executable_format_error,
"error reading .altinstructions");
BinaryFunction *BF = BC.getBinaryFunctionContainingAddress(OrgInstAddress);
if (!BF && opts::Verbosity) {
BC.outs() << "BOLT-INFO: no function matches address 0x"
<< Twine::utohexstr(OrgInstAddress)
<< " of instruction from .altinstructions\n";
}
BinaryFunction *AltBF =
BC.getBinaryFunctionContainingAddress(AltInstAddress);
if (!ParseOnly && AltBF && BC.shouldEmit(*AltBF)) {
BC.errs()
<< "BOLT-WARNING: alternative instruction sequence found in function "
<< *AltBF << '\n';
AltBF->setIgnored();
}
if (!BF || !BF->hasInstructions())
continue;
if (OrgInstAddress + OrgSize > BF->getAddress() + BF->getSize())
return createStringError(errc::executable_format_error,
"error reading .altinstructions");
MCInst *Inst =
BF->getInstructionAtOffset(OrgInstAddress - BF->getAddress());
if (!Inst)
return createStringError(errc::executable_format_error,
"no instruction at address 0x%" PRIx64
" referenced by .altinstructions entry %d",
OrgInstAddress, EntryID);
if (ParseOnly)
continue;
// There could be more than one alternative instruction sequences for the
// same original instruction. Annotate each alternative separately.
std::string AnnotationName = "AltInst";
unsigned N = 2;
while (BC.MIB->hasAnnotation(*Inst, AnnotationName))
AnnotationName = "AltInst" + std::to_string(N++);
BC.MIB->addAnnotation(*Inst, AnnotationName, EntryID);
// Annotate all instructions from the original sequence. Note that it's not
// the most efficient way to look for instructions in the address range,
// but since alternative instructions are uncommon, it will do for now.
for (uint32_t Offset = 1; Offset < OrgSize; ++Offset) {
Inst = BF->getInstructionAtOffset(OrgInstAddress + Offset -
BF->getAddress());
if (Inst)
BC.MIB->addAnnotation(*Inst, AnnotationName, EntryID);
}
}
if (!ParseOnly)
BC.outs() << "BOLT-INFO: parsed " << EntryID
<< " alternative instruction entries\n";
return Error::success();
}
void LinuxKernelRewriter::processAltInstructionsPostCFG() {
// Disable optimization and output of functions with alt instructions before
// the rewrite support is complete. Alt instructions can modify the control
// flow, hence we may end up deleting seemingly unreachable code.
skipFunctionsWithAnnotation("AltInst");
}
/// When the Linux kernel needs to handle an error associated with a given PCI
/// device, it uses a table stored in .pci_fixup section to locate a fixup code
/// specific to the vendor and the problematic device. The section contains a
/// list of the following structures defined in include/linux/pci.h:
///
/// struct pci_fixup {
/// u16 vendor; /* Or PCI_ANY_ID */
/// u16 device; /* Or PCI_ANY_ID */
/// u32 class; /* Or PCI_ANY_ID */
/// unsigned int class_shift; /* should be 0, 8, 16 */
/// int hook_offset;
/// };
///
/// Normally, the hook will point to a function start and we don't have to
/// update the pointer if we are not relocating functions. Hence, while reading
/// the table we validate this assumption. If a function has a fixup code in the
/// middle of its body, we issue a warning and ignore it.
Error LinuxKernelRewriter::readPCIFixupTable() {
PCIFixupSection = BC.getUniqueSectionByName(".pci_fixup");
if (!PCIFixupSection)
return Error::success();
if (PCIFixupSection->getSize() % PCI_FIXUP_ENTRY_SIZE)
return createStringError(errc::executable_format_error,
"PCI fixup table size error");
AddressExtractor AE(
PCIFixupSection->getContents(), PCIFixupSection->getAddress(),
BC.AsmInfo->isLittleEndian(), BC.AsmInfo->getCodePointerSize());
AddressExtractor::Cursor Cursor(0);
uint64_t EntryID = 0;
while (Cursor && !AE.eof(Cursor)) {
const uint16_t Vendor = AE.getU16(Cursor);
const uint16_t Device = AE.getU16(Cursor);
const uint32_t Class = AE.getU32(Cursor);
const uint32_t ClassShift = AE.getU32(Cursor);
const uint64_t HookAddress = AE.getPCRelAddress32(Cursor);
if (!Cursor)
return createStringError(errc::executable_format_error,
"out of bounds while reading .pci_fixup: %s",
toString(Cursor.takeError()).c_str());
++EntryID;
if (opts::DumpPCIFixups) {
BC.outs() << "PCI fixup entry: " << EntryID << "\n\tVendor 0x"
<< Twine::utohexstr(Vendor) << "\n\tDevice: 0x"
<< Twine::utohexstr(Device) << "\n\tClass: 0x"
<< Twine::utohexstr(Class) << "\n\tClassShift: 0x"
<< Twine::utohexstr(ClassShift) << "\n\tHookAddress: 0x"
<< Twine::utohexstr(HookAddress) << '\n';
}
BinaryFunction *BF = BC.getBinaryFunctionContainingAddress(HookAddress);
if (!BF && opts::Verbosity) {
BC.outs() << "BOLT-INFO: no function matches address 0x"
<< Twine::utohexstr(HookAddress)
<< " of hook from .pci_fixup\n";
}
if (!BF || !BC.shouldEmit(*BF))
continue;
if (const uint64_t Offset = HookAddress - BF->getAddress()) {
BC.errs() << "BOLT-WARNING: PCI fixup detected in the middle of function "
<< *BF << " at offset 0x" << Twine::utohexstr(Offset) << '\n';
BF->setSimple(false);
}
}
BC.outs() << "BOLT-INFO: parsed " << EntryID << " PCI fixup entries\n";
return Error::success();
}
/// Runtime code modification used by static keys is the most ubiquitous
/// self-modifying feature of the Linux kernel. The idea is to eliminate the
/// condition check and associated conditional jump on a hot path if that
/// condition (based on a boolean value of a static key) does not change often.
/// Whenever the condition changes, the kernel runtime modifies all code paths
/// associated with that key flipping the code between nop and (unconditional)
/// jump. The information about the code is stored in a static key jump table
/// and contains the list of entries of the following type from
/// include/linux/jump_label.h:
//
/// struct jump_entry {
/// s32 code;
/// s32 target;
/// long key; // key may be far away from the core kernel under KASLR
/// };
///
/// The list does not have to be stored in any sorted way, but it is sorted at
/// boot time (or module initialization time) first by "key" and then by "code".
/// jump_label_sort_entries() is responsible for sorting the table.
///
/// The key in jump_entry structure uses lower two bits of the key address
/// (which itself is aligned) to store extra information. We are interested in
/// the lower bit which indicates if the key is likely to be set on the code
/// path associated with this jump_entry.
///
/// static_key_{enable,disable}() functions modify the code based on key and
/// jump table entries.
///
/// jump_label_update() updates all code entries for a given key. Batch mode is
/// used for x86.
///
/// The actual patching happens in text_poke_bp_batch() that overrides the first
/// byte of the sequence with int3 before proceeding with actual code
/// replacement.
Error LinuxKernelRewriter::readStaticKeysJumpTable() {
const BinaryData *StaticKeysJumpTable =
BC.getBinaryDataByName("__start___jump_table");
if (!StaticKeysJumpTable)
return Error::success();
StaticKeysJumpTableAddress = StaticKeysJumpTable->getAddress();
const BinaryData *Stop = BC.getBinaryDataByName("__stop___jump_table");
if (!Stop)
return createStringError(errc::executable_format_error,
"missing __stop___jump_table symbol");
ErrorOr<BinarySection &> ErrorOrSection =
BC.getSectionForAddress(StaticKeysJumpTableAddress);
if (!ErrorOrSection)
return createStringError(errc::executable_format_error,
"no section matching __start___jump_table");
StaticKeysJumpSection = *ErrorOrSection;
if (!StaticKeysJumpSection->containsAddress(Stop->getAddress() - 1))
return createStringError(errc::executable_format_error,
"__stop___jump_table not in the same section "
"as __start___jump_table");
if ((Stop->getAddress() - StaticKeysJumpTableAddress) %
STATIC_KEYS_JUMP_ENTRY_SIZE)
return createStringError(errc::executable_format_error,
"static keys jump table size error");
const uint64_t SectionAddress = StaticKeysJumpSection->getAddress();
AddressExtractor AE(StaticKeysJumpSection->getContents(), SectionAddress,
BC.AsmInfo->isLittleEndian(),
BC.AsmInfo->getCodePointerSize());
AddressExtractor::Cursor Cursor(StaticKeysJumpTableAddress - SectionAddress);
uint32_t EntryID = 0;
while (Cursor && Cursor.tell() < Stop->getAddress() - SectionAddress) {
const uint64_t JumpAddress = AE.getPCRelAddress32(Cursor);
const uint64_t TargetAddress = AE.getPCRelAddress32(Cursor);
const uint64_t KeyAddress = AE.getPCRelAddress64(Cursor);
// Consume the status of the cursor.
if (!Cursor)
return createStringError(
errc::executable_format_error,
"out of bounds while reading static keys jump table: %s",
toString(Cursor.takeError()).c_str());
++EntryID;
JumpInfo.push_back(JumpInfoEntry());
JumpInfoEntry &Info = JumpInfo.back();
Info.Likely = KeyAddress & 1;
if (opts::DumpStaticKeys) {
BC.outs() << "Static key jump entry: " << EntryID
<< "\n\tJumpAddress: 0x" << Twine::utohexstr(JumpAddress)
<< "\n\tTargetAddress: 0x" << Twine::utohexstr(TargetAddress)
<< "\n\tKeyAddress: 0x" << Twine::utohexstr(KeyAddress)
<< "\n\tIsLikely: " << Info.Likely << '\n';
}
BinaryFunction *BF = BC.getBinaryFunctionContainingAddress(JumpAddress);
if (!BF && opts::Verbosity) {
BC.outs()
<< "BOLT-INFO: no function matches address 0x"
<< Twine::utohexstr(JumpAddress)
<< " of jump instruction referenced from static keys jump table\n";
}
if (!BF || !BC.shouldEmit(*BF))
continue;
MCInst *Inst = BF->getInstructionAtOffset(JumpAddress - BF->getAddress());
if (!Inst)
return createStringError(
errc::executable_format_error,
"no instruction at static keys jump site address 0x%" PRIx64,
JumpAddress);
if (!BF->containsAddress(TargetAddress))
return createStringError(
errc::executable_format_error,
"invalid target of static keys jump at 0x%" PRIx64 " : 0x%" PRIx64,
JumpAddress, TargetAddress);
const bool IsBranch = BC.MIB->isBranch(*Inst);
if (!IsBranch && !BC.MIB->isNoop(*Inst))
return createStringError(errc::executable_format_error,
"jump or nop expected at address 0x%" PRIx64,
JumpAddress);
const uint64_t Size = BC.computeInstructionSize(*Inst);
if (Size != 2 && Size != 5) {
return createStringError(
errc::executable_format_error,
"unexpected static keys jump size at address 0x%" PRIx64,
JumpAddress);
}
MCSymbol *Target = BF->registerBranch(JumpAddress, TargetAddress);
MCInst StaticKeyBranch;
// Create a conditional branch instruction. The actual conditional code type
// should not matter as long as it's a valid code. The instruction should be
// treated as a conditional branch for control-flow purposes. Before we emit
// the code, it will be converted to a different instruction in
// rewriteStaticKeysJumpTable().
//
// NB: for older kernels, under LongJumpLabels option, we create long
// conditional branch to guarantee that code size estimation takes
// into account the extra bytes needed for long branch that will be used
// by the kernel patching code. Newer kernels can work with both short
// and long branches. The code for long conditional branch is larger
// than unconditional one, so we are pessimistic in our estimations.
if (opts::LongJumpLabels)
BC.MIB->createLongCondBranch(StaticKeyBranch, Target, 0, BC.Ctx.get());
else
BC.MIB->createCondBranch(StaticKeyBranch, Target, 0, BC.Ctx.get());
BC.MIB->moveAnnotations(std::move(*Inst), StaticKeyBranch);
BC.MIB->setDynamicBranch(StaticKeyBranch, EntryID);
*Inst = StaticKeyBranch;
// IsBranch = InitialValue ^ LIKELY
//
// 0 0 0
// 1 0 1
// 1 1 0
// 0 1 1
//
// => InitialValue = IsBranch ^ LIKELY
Info.InitValue = IsBranch ^ Info.Likely;
// Add annotations to facilitate manual code analysis.
BC.MIB->addAnnotation(*Inst, "Likely", Info.Likely);
BC.MIB->addAnnotation(*Inst, "InitValue", Info.InitValue);
if (!BC.MIB->getSize(*Inst))
BC.MIB->setSize(*Inst, Size);
if (!BC.MIB->getOffset(*Inst))
BC.MIB->setOffset(*Inst, JumpAddress - BF->getAddress());
if (opts::LongJumpLabels)
BC.MIB->setSize(*Inst, 5);
}
BC.outs() << "BOLT-INFO: parsed " << EntryID << " static keys jump entries\n";
return Error::success();
}
// Pre-emit pass. Convert dynamic branch instructions into jumps that could be
// relaxed. In post-emit pass we will convert those jumps into nops when
// necessary. We do the unconditional conversion into jumps so that the jumps
// can be relaxed and the optimal size of jump/nop instruction is selected.
Error LinuxKernelRewriter::rewriteStaticKeysJumpTable() {
if (!StaticKeysJumpSection)
return Error::success();
uint64_t NumShort = 0;
uint64_t NumLong = 0;
for (BinaryFunction &BF : llvm::make_second_range(BC.getBinaryFunctions())) {
if (!BC.shouldEmit(BF))
continue;
for (BinaryBasicBlock &BB : BF) {
for (MCInst &Inst : BB) {
if (!BC.MIB->isDynamicBranch(Inst))
continue;
const uint32_t EntryID = *BC.MIB->getDynamicBranchID(Inst);
MCSymbol *Target =
const_cast<MCSymbol *>(BC.MIB->getTargetSymbol(Inst));
assert(Target && "Target symbol should be set.");
const JumpInfoEntry &Info = JumpInfo[EntryID - 1];
const bool IsBranch = Info.Likely ^ Info.InitValue;
uint32_t Size = *BC.MIB->getSize(Inst);
if (Size == 2)
++NumShort;
else if (Size == 5)
++NumLong;
else
llvm_unreachable("Wrong size for static keys jump instruction.");
MCInst NewInst;
// Replace the instruction with unconditional jump even if it needs to
// be nop in the binary.
if (opts::LongJumpLabels) {
BC.MIB->createLongUncondBranch(NewInst, Target, BC.Ctx.get());
} else {
// Newer kernels can handle short and long jumps for static keys.
// Optimistically, emit short jump and check if it gets relaxed into
// a long one during post-emit. Only then convert the jump to a nop.
BC.MIB->createUncondBranch(NewInst, Target, BC.Ctx.get());
}
BC.MIB->moveAnnotations(std::move(Inst), NewInst);
Inst = NewInst;
// Mark the instruction for nop conversion.
if (!IsBranch)
NopIDs.insert(EntryID);
MCSymbol *Label =
BC.MIB->getOrCreateInstLabel(Inst, "__SK_", BC.Ctx.get());
// Create a relocation against the label.
const uint64_t EntryOffset = StaticKeysJumpTableAddress -
StaticKeysJumpSection->getAddress() +
(EntryID - 1) * 16;
StaticKeysJumpSection->addRelocation(EntryOffset, Label,
ELF::R_X86_64_PC32,
/*Addend*/ 0);
StaticKeysJumpSection->addRelocation(EntryOffset + 4, Target,
ELF::R_X86_64_PC32, /*Addend*/ 0);
}
}
}
BC.outs() << "BOLT-INFO: the input contains " << NumShort << " short and "
<< NumLong << " long static keys jumps in optimized functions\n";
return Error::success();
}
// Post-emit pass of static keys jump section. Convert jumps to nops.
Error LinuxKernelRewriter::updateStaticKeysJumpTablePostEmit() {
if (!StaticKeysJumpSection || !StaticKeysJumpSection->isFinalized())
return Error::success();
const uint64_t SectionAddress = StaticKeysJumpSection->getAddress();
AddressExtractor AE(StaticKeysJumpSection->getOutputContents(),
SectionAddress, BC.AsmInfo->isLittleEndian(),
BC.AsmInfo->getCodePointerSize());
AddressExtractor::Cursor Cursor(StaticKeysJumpTableAddress - SectionAddress);
const BinaryData *Stop = BC.getBinaryDataByName("__stop___jump_table");
uint32_t EntryID = 0;
uint64_t NumShort = 0;
uint64_t NumLong = 0;
while (Cursor && Cursor.tell() < Stop->getAddress() - SectionAddress) {
const uint64_t JumpAddress = AE.getPCRelAddress32(Cursor);
const uint64_t TargetAddress = AE.getPCRelAddress32(Cursor);
const uint64_t KeyAddress = AE.getPCRelAddress64(Cursor);
// Consume the status of the cursor.
if (!Cursor)
return createStringError(errc::executable_format_error,
"out of bounds while updating static keys: %s",
toString(Cursor.takeError()).c_str());
++EntryID;
LLVM_DEBUG({
dbgs() << "\n\tJumpAddress: 0x" << Twine::utohexstr(JumpAddress)
<< "\n\tTargetAddress: 0x" << Twine::utohexstr(TargetAddress)
<< "\n\tKeyAddress: 0x" << Twine::utohexstr(KeyAddress) << '\n';
});
(void)TargetAddress;
(void)KeyAddress;
BinaryFunction *BF =
BC.getBinaryFunctionContainingAddress(JumpAddress,
/*CheckPastEnd*/ false,
/*UseMaxSize*/ true);
assert(BF && "Cannot get function for modified static key.");
if (!BF->isEmitted())
continue;
// Disassemble instruction to collect stats even if nop-conversion is
// unnecessary.
MutableArrayRef<uint8_t> Contents = MutableArrayRef<uint8_t>(
reinterpret_cast<uint8_t *>(BF->getImageAddress()), BF->getImageSize());
assert(Contents.size() && "Non-empty function image expected.");
MCInst Inst;
uint64_t Size;
const uint64_t JumpOffset = JumpAddress - BF->getAddress();
if (!BC.DisAsm->getInstruction(Inst, Size, Contents.slice(JumpOffset), 0,
nulls())) {
llvm_unreachable("Unable to disassemble jump instruction.");
}
assert(BC.MIB->isBranch(Inst) && "Branch instruction expected.");
if (Size == 2)
++NumShort;
else if (Size == 5)
++NumLong;
else
llvm_unreachable("Unexpected size for static keys jump instruction.");
// Check if we need to convert jump instruction into a nop.
if (!NopIDs.contains(EntryID))
continue;
SmallString<15> NopCode;
raw_svector_ostream VecOS(NopCode);
BC.MAB->writeNopData(VecOS, Size, BC.STI.get());
for (uint64_t I = 0; I < Size; ++I)
Contents[JumpOffset + I] = NopCode[I];
}
BC.outs() << "BOLT-INFO: written " << NumShort << " short and " << NumLong
<< " long static keys jumps in optimized functions\n";
return Error::success();
}
} // namespace
std::unique_ptr<MetadataRewriter>
llvm::bolt::createLinuxKernelRewriter(BinaryContext &BC) {
return std::make_unique<LinuxKernelRewriter>(BC);
}
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