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llvm-project/llvm/lib/MC/MCWin64EH.cpp

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//===- lib/MC/MCWin64EH.cpp - MCWin64EH implementation --------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/MCWin64EH.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCObjectFileInfo.h"
#include "llvm/MC/MCObjectStreamer.h"
#include "llvm/MC/MCSectionCOFF.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/Support/Win64EH.h"
using namespace llvm;
// NOTE: All relocations generated here are 4-byte image-relative.
static uint8_t CountOfUnwindCodes(std::vector<WinEH::Instruction> &Insns) {
uint8_t Count = 0;
for (const auto &I : Insns) {
switch (static_cast<Win64EH::UnwindOpcodes>(I.Operation)) {
default:
llvm_unreachable("Unsupported unwind code");
case Win64EH::UOP_PushNonVol:
case Win64EH::UOP_AllocSmall:
case Win64EH::UOP_SetFPReg:
case Win64EH::UOP_PushMachFrame:
Count += 1;
break;
case Win64EH::UOP_SaveNonVol:
case Win64EH::UOP_SaveXMM128:
Count += 2;
break;
case Win64EH::UOP_SaveNonVolBig:
case Win64EH::UOP_SaveXMM128Big:
Count += 3;
break;
case Win64EH::UOP_AllocLarge:
Count += (I.Offset > 512 * 1024 - 8) ? 3 : 2;
break;
}
}
return Count;
}
static void EmitAbsDifference(MCStreamer &Streamer, const MCSymbol *LHS,
const MCSymbol *RHS) {
MCContext &Context = Streamer.getContext();
const MCExpr *Diff =
MCBinaryExpr::createSub(MCSymbolRefExpr::create(LHS, Context),
MCSymbolRefExpr::create(RHS, Context), Context);
Streamer.emitValue(Diff, 1);
}
static void EmitUnwindCode(MCStreamer &streamer, const MCSymbol *begin,
WinEH::Instruction &inst) {
uint8_t b2;
uint16_t w;
b2 = (inst.Operation & 0x0F);
switch (static_cast<Win64EH::UnwindOpcodes>(inst.Operation)) {
default:
llvm_unreachable("Unsupported unwind code");
case Win64EH::UOP_PushNonVol:
EmitAbsDifference(streamer, inst.Label, begin);
b2 |= (inst.Register & 0x0F) << 4;
streamer.emitInt8(b2);
break;
case Win64EH::UOP_AllocLarge:
EmitAbsDifference(streamer, inst.Label, begin);
if (inst.Offset > 512 * 1024 - 8) {
b2 |= 0x10;
streamer.emitInt8(b2);
w = inst.Offset & 0xFFF8;
streamer.emitInt16(w);
w = inst.Offset >> 16;
} else {
streamer.emitInt8(b2);
w = inst.Offset >> 3;
}
streamer.emitInt16(w);
break;
case Win64EH::UOP_AllocSmall:
b2 |= (((inst.Offset - 8) >> 3) & 0x0F) << 4;
EmitAbsDifference(streamer, inst.Label, begin);
streamer.emitInt8(b2);
break;
case Win64EH::UOP_SetFPReg:
EmitAbsDifference(streamer, inst.Label, begin);
streamer.emitInt8(b2);
break;
case Win64EH::UOP_SaveNonVol:
case Win64EH::UOP_SaveXMM128:
b2 |= (inst.Register & 0x0F) << 4;
EmitAbsDifference(streamer, inst.Label, begin);
streamer.emitInt8(b2);
w = inst.Offset >> 3;
if (inst.Operation == Win64EH::UOP_SaveXMM128)
w >>= 1;
streamer.emitInt16(w);
break;
case Win64EH::UOP_SaveNonVolBig:
case Win64EH::UOP_SaveXMM128Big:
b2 |= (inst.Register & 0x0F) << 4;
EmitAbsDifference(streamer, inst.Label, begin);
streamer.emitInt8(b2);
if (inst.Operation == Win64EH::UOP_SaveXMM128Big)
w = inst.Offset & 0xFFF0;
else
w = inst.Offset & 0xFFF8;
streamer.emitInt16(w);
w = inst.Offset >> 16;
streamer.emitInt16(w);
break;
case Win64EH::UOP_PushMachFrame:
if (inst.Offset == 1)
b2 |= 0x10;
EmitAbsDifference(streamer, inst.Label, begin);
streamer.emitInt8(b2);
break;
}
}
static void EmitSymbolRefWithOfs(MCStreamer &streamer,
const MCSymbol *Base,
const MCSymbol *Other) {
MCContext &Context = streamer.getContext();
const MCSymbolRefExpr *BaseRef = MCSymbolRefExpr::create(Base, Context);
const MCSymbolRefExpr *OtherRef = MCSymbolRefExpr::create(Other, Context);
const MCExpr *Ofs = MCBinaryExpr::createSub(OtherRef, BaseRef, Context);
const MCSymbolRefExpr *BaseRefRel = MCSymbolRefExpr::create(Base,
MCSymbolRefExpr::VK_COFF_IMGREL32,
Context);
streamer.emitValue(MCBinaryExpr::createAdd(BaseRefRel, Ofs, Context), 4);
}
static void EmitRuntimeFunction(MCStreamer &streamer,
const WinEH::FrameInfo *info) {
MCContext &context = streamer.getContext();
streamer.emitValueToAlignment(4);
EmitSymbolRefWithOfs(streamer, info->Function, info->Begin);
EmitSymbolRefWithOfs(streamer, info->Function, info->End);
streamer.emitValue(MCSymbolRefExpr::create(info->Symbol,
MCSymbolRefExpr::VK_COFF_IMGREL32,
context), 4);
}
static void EmitUnwindInfo(MCStreamer &streamer, WinEH::FrameInfo *info) {
// If this UNWIND_INFO already has a symbol, it's already been emitted.
if (info->Symbol)
return;
MCContext &context = streamer.getContext();
MCSymbol *Label = context.createTempSymbol();
streamer.emitValueToAlignment(4);
streamer.emitLabel(Label);
info->Symbol = Label;
// Upper 3 bits are the version number (currently 1).
uint8_t flags = 0x01;
if (info->ChainedParent)
flags |= Win64EH::UNW_ChainInfo << 3;
else {
if (info->HandlesUnwind)
flags |= Win64EH::UNW_TerminateHandler << 3;
if (info->HandlesExceptions)
flags |= Win64EH::UNW_ExceptionHandler << 3;
}
streamer.emitInt8(flags);
if (info->PrologEnd)
EmitAbsDifference(streamer, info->PrologEnd, info->Begin);
else
streamer.emitInt8(0);
uint8_t numCodes = CountOfUnwindCodes(info->Instructions);
streamer.emitInt8(numCodes);
uint8_t frame = 0;
if (info->LastFrameInst >= 0) {
WinEH::Instruction &frameInst = info->Instructions[info->LastFrameInst];
assert(frameInst.Operation == Win64EH::UOP_SetFPReg);
frame = (frameInst.Register & 0x0F) | (frameInst.Offset & 0xF0);
}
streamer.emitInt8(frame);
// Emit unwind instructions (in reverse order).
uint8_t numInst = info->Instructions.size();
for (uint8_t c = 0; c < numInst; ++c) {
WinEH::Instruction inst = info->Instructions.back();
info->Instructions.pop_back();
EmitUnwindCode(streamer, info->Begin, inst);
}
// For alignment purposes, the instruction array will always have an even
// number of entries, with the final entry potentially unused (in which case
// the array will be one longer than indicated by the count of unwind codes
// field).
if (numCodes & 1) {
streamer.emitInt16(0);
}
if (flags & (Win64EH::UNW_ChainInfo << 3))
EmitRuntimeFunction(streamer, info->ChainedParent);
else if (flags &
((Win64EH::UNW_TerminateHandler|Win64EH::UNW_ExceptionHandler) << 3))
streamer.emitValue(MCSymbolRefExpr::create(info->ExceptionHandler,
MCSymbolRefExpr::VK_COFF_IMGREL32,
context), 4);
else if (numCodes == 0) {
// The minimum size of an UNWIND_INFO struct is 8 bytes. If we're not
// a chained unwind info, if there is no handler, and if there are fewer
// than 2 slots used in the unwind code array, we have to pad to 8 bytes.
streamer.emitInt32(0);
}
}
void llvm::Win64EH::UnwindEmitter::Emit(MCStreamer &Streamer) const {
// Emit the unwind info structs first.
for (const auto &CFI : Streamer.getWinFrameInfos()) {
MCSection *XData = Streamer.getAssociatedXDataSection(CFI->TextSection);
Streamer.SwitchSection(XData);
::EmitUnwindInfo(Streamer, CFI.get());
}
// Now emit RUNTIME_FUNCTION entries.
for (const auto &CFI : Streamer.getWinFrameInfos()) {
MCSection *PData = Streamer.getAssociatedPDataSection(CFI->TextSection);
Streamer.SwitchSection(PData);
EmitRuntimeFunction(Streamer, CFI.get());
}
}
void llvm::Win64EH::UnwindEmitter::EmitUnwindInfo(
MCStreamer &Streamer, WinEH::FrameInfo *info) const {
// Switch sections (the static function above is meant to be called from
// here and from Emit().
MCSection *XData = Streamer.getAssociatedXDataSection(info->TextSection);
Streamer.SwitchSection(XData);
::EmitUnwindInfo(Streamer, info);
}
static int64_t GetAbsDifference(MCStreamer &Streamer, const MCSymbol *LHS,
const MCSymbol *RHS) {
MCContext &Context = Streamer.getContext();
const MCExpr *Diff =
MCBinaryExpr::createSub(MCSymbolRefExpr::create(LHS, Context),
MCSymbolRefExpr::create(RHS, Context), Context);
MCObjectStreamer *OS = (MCObjectStreamer *)(&Streamer);
// It should normally be possible to calculate the length of a function
// at this point, but it might not be possible in the presence of certain
// unusual constructs, like an inline asm with an alignment directive.
int64_t value;
if (!Diff->evaluateAsAbsolute(value, OS->getAssembler()))
report_fatal_error("Failed to evaluate function length in SEH unwind info");
return value;
}
static uint32_t ARM64CountOfUnwindCodes(ArrayRef<WinEH::Instruction> Insns) {
uint32_t Count = 0;
for (const auto &I : Insns) {
switch (static_cast<Win64EH::UnwindOpcodes>(I.Operation)) {
default:
llvm_unreachable("Unsupported ARM64 unwind code");
case Win64EH::UOP_AllocSmall:
Count += 1;
break;
case Win64EH::UOP_AllocMedium:
Count += 2;
break;
case Win64EH::UOP_AllocLarge:
Count += 4;
break;
case Win64EH::UOP_SaveR19R20X:
Count += 1;
break;
case Win64EH::UOP_SaveFPLRX:
Count += 1;
break;
case Win64EH::UOP_SaveFPLR:
Count += 1;
break;
case Win64EH::UOP_SaveReg:
Count += 2;
break;
case Win64EH::UOP_SaveRegP:
Count += 2;
break;
case Win64EH::UOP_SaveRegPX:
Count += 2;
break;
case Win64EH::UOP_SaveRegX:
Count += 2;
break;
case Win64EH::UOP_SaveLRPair:
Count += 2;
break;
case Win64EH::UOP_SaveFReg:
Count += 2;
break;
case Win64EH::UOP_SaveFRegP:
Count += 2;
break;
case Win64EH::UOP_SaveFRegX:
Count += 2;
break;
case Win64EH::UOP_SaveFRegPX:
Count += 2;
break;
case Win64EH::UOP_SetFP:
Count += 1;
break;
case Win64EH::UOP_AddFP:
Count += 2;
break;
case Win64EH::UOP_Nop:
Count += 1;
break;
case Win64EH::UOP_End:
Count += 1;
break;
case Win64EH::UOP_SaveNext:
Count += 1;
break;
case Win64EH::UOP_TrapFrame:
Count += 1;
break;
case Win64EH::UOP_PushMachFrame:
Count += 1;
break;
case Win64EH::UOP_Context:
Count += 1;
break;
case Win64EH::UOP_ClearUnwoundToCall:
Count += 1;
break;
}
}
return Count;
}
// Unwind opcode encodings and restrictions are documented at
// https://docs.microsoft.com/en-us/cpp/build/arm64-exception-handling
static void ARM64EmitUnwindCode(MCStreamer &streamer, const MCSymbol *begin,
WinEH::Instruction &inst) {
uint8_t b, reg;
switch (static_cast<Win64EH::UnwindOpcodes>(inst.Operation)) {
default:
llvm_unreachable("Unsupported ARM64 unwind code");
case Win64EH::UOP_AllocSmall:
b = (inst.Offset >> 4) & 0x1F;
streamer.emitInt8(b);
break;
case Win64EH::UOP_AllocMedium: {
uint16_t hw = (inst.Offset >> 4) & 0x7FF;
b = 0xC0;
b |= (hw >> 8);
streamer.emitInt8(b);
b = hw & 0xFF;
streamer.emitInt8(b);
break;
}
case Win64EH::UOP_AllocLarge: {
uint32_t w;
b = 0xE0;
streamer.emitInt8(b);
w = inst.Offset >> 4;
b = (w & 0x00FF0000) >> 16;
streamer.emitInt8(b);
b = (w & 0x0000FF00) >> 8;
streamer.emitInt8(b);
b = w & 0x000000FF;
streamer.emitInt8(b);
break;
}
case Win64EH::UOP_SetFP:
b = 0xE1;
streamer.emitInt8(b);
break;
case Win64EH::UOP_AddFP:
b = 0xE2;
streamer.emitInt8(b);
b = (inst.Offset >> 3);
streamer.emitInt8(b);
break;
case Win64EH::UOP_Nop:
b = 0xE3;
streamer.emitInt8(b);
break;
case Win64EH::UOP_SaveR19R20X:
b = 0x20;
b |= (inst.Offset >> 3) & 0x1F;
streamer.emitInt8(b);
break;
case Win64EH::UOP_SaveFPLRX:
b = 0x80;
b |= ((inst.Offset - 1) >> 3) & 0x3F;
streamer.emitInt8(b);
break;
case Win64EH::UOP_SaveFPLR:
b = 0x40;
b |= (inst.Offset >> 3) & 0x3F;
streamer.emitInt8(b);
break;
case Win64EH::UOP_SaveReg:
assert(inst.Register >= 19 && "Saved reg must be >= 19");
reg = inst.Register - 19;
b = 0xD0 | ((reg & 0xC) >> 2);
streamer.emitInt8(b);
b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
streamer.emitInt8(b);
break;
case Win64EH::UOP_SaveRegX:
assert(inst.Register >= 19 && "Saved reg must be >= 19");
reg = inst.Register - 19;
b = 0xD4 | ((reg & 0x8) >> 3);
streamer.emitInt8(b);
b = ((reg & 0x7) << 5) | ((inst.Offset >> 3) - 1);
streamer.emitInt8(b);
break;
case Win64EH::UOP_SaveRegP:
assert(inst.Register >= 19 && "Saved registers must be >= 19");
reg = inst.Register - 19;
b = 0xC8 | ((reg & 0xC) >> 2);
streamer.emitInt8(b);
b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
streamer.emitInt8(b);
break;
case Win64EH::UOP_SaveRegPX:
assert(inst.Register >= 19 && "Saved registers must be >= 19");
reg = inst.Register - 19;
b = 0xCC | ((reg & 0xC) >> 2);
streamer.emitInt8(b);
b = ((reg & 0x3) << 6) | ((inst.Offset >> 3) - 1);
streamer.emitInt8(b);
break;
case Win64EH::UOP_SaveLRPair:
assert(inst.Register >= 19 && "Saved reg must be >= 19");
reg = inst.Register - 19;
assert((reg % 2) == 0 && "Saved reg must be 19+2*X");
reg /= 2;
b = 0xD6 | ((reg & 0x7) >> 2);
streamer.emitInt8(b);
b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
streamer.emitInt8(b);
break;
case Win64EH::UOP_SaveFReg:
assert(inst.Register >= 8 && "Saved dreg must be >= 8");
reg = inst.Register - 8;
b = 0xDC | ((reg & 0x4) >> 2);
streamer.emitInt8(b);
b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
streamer.emitInt8(b);
break;
case Win64EH::UOP_SaveFRegX:
assert(inst.Register >= 8 && "Saved dreg must be >= 8");
reg = inst.Register - 8;
b = 0xDE;
streamer.emitInt8(b);
b = ((reg & 0x7) << 5) | ((inst.Offset >> 3) - 1);
streamer.emitInt8(b);
break;
case Win64EH::UOP_SaveFRegP:
assert(inst.Register >= 8 && "Saved dregs must be >= 8");
reg = inst.Register - 8;
b = 0xD8 | ((reg & 0x4) >> 2);
streamer.emitInt8(b);
b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
streamer.emitInt8(b);
break;
case Win64EH::UOP_SaveFRegPX:
assert(inst.Register >= 8 && "Saved dregs must be >= 8");
reg = inst.Register - 8;
b = 0xDA | ((reg & 0x4) >> 2);
streamer.emitInt8(b);
b = ((reg & 0x3) << 6) | ((inst.Offset >> 3) - 1);
streamer.emitInt8(b);
break;
case Win64EH::UOP_End:
b = 0xE4;
streamer.emitInt8(b);
break;
case Win64EH::UOP_SaveNext:
b = 0xE6;
streamer.emitInt8(b);
break;
case Win64EH::UOP_TrapFrame:
b = 0xE8;
streamer.emitInt8(b);
break;
case Win64EH::UOP_PushMachFrame:
b = 0xE9;
streamer.emitInt8(b);
break;
case Win64EH::UOP_Context:
b = 0xEA;
streamer.emitInt8(b);
break;
case Win64EH::UOP_ClearUnwoundToCall:
b = 0xEC;
streamer.emitInt8(b);
break;
}
}
// Returns the epilog symbol of an epilog with the exact same unwind code
// sequence, if it exists. Otherwise, returns nulltpr.
// EpilogInstrs - Unwind codes for the current epilog.
// Epilogs - Epilogs that potentialy match the current epilog.
static MCSymbol*
FindMatchingEpilog(const std::vector<WinEH::Instruction>& EpilogInstrs,
const std::vector<MCSymbol *>& Epilogs,
const WinEH::FrameInfo *info) {
for (auto *EpilogStart : Epilogs) {
auto InstrsIter = info->EpilogMap.find(EpilogStart);
assert(InstrsIter != info->EpilogMap.end() &&
"Epilog not found in EpilogMap");
const auto &Instrs = InstrsIter->second;
if (Instrs.size() != EpilogInstrs.size())
continue;
bool Match = true;
for (unsigned i = 0; i < Instrs.size(); ++i)
if (Instrs[i].Operation != EpilogInstrs[i].Operation ||
Instrs[i].Offset != EpilogInstrs[i].Offset ||
Instrs[i].Register != EpilogInstrs[i].Register) {
Match = false;
break;
}
if (Match)
return EpilogStart;
}
return nullptr;
}
static void simplifyOpcodes(std::vector<WinEH::Instruction> &Instructions,
bool Reverse) {
unsigned PrevOffset = -1;
unsigned PrevRegister = -1;
auto VisitInstruction = [&](WinEH::Instruction &Inst) {
// Convert 2-byte opcodes into equivalent 1-byte ones.
if (Inst.Operation == Win64EH::UOP_SaveRegP && Inst.Register == 29) {
Inst.Operation = Win64EH::UOP_SaveFPLR;
Inst.Register = -1;
} else if (Inst.Operation == Win64EH::UOP_SaveRegPX &&
Inst.Register == 29) {
Inst.Operation = Win64EH::UOP_SaveFPLRX;
Inst.Register = -1;
} else if (Inst.Operation == Win64EH::UOP_SaveRegPX &&
Inst.Register == 19 && Inst.Offset <= 248) {
Inst.Operation = Win64EH::UOP_SaveR19R20X;
Inst.Register = -1;
} else if (Inst.Operation == Win64EH::UOP_AddFP && Inst.Offset == 0) {
Inst.Operation = Win64EH::UOP_SetFP;
} else if (Inst.Operation == Win64EH::UOP_SaveRegP &&
Inst.Register == PrevRegister + 2 &&
Inst.Offset == PrevOffset + 16) {
Inst.Operation = Win64EH::UOP_SaveNext;
Inst.Register = -1;
Inst.Offset = 0;
// Intentionally not creating UOP_SaveNext for float register pairs,
// as current versions of Windows (up to at least 20.04) is buggy
// regarding SaveNext for float pairs.
}
// Update info about the previous instruction, for detecting if
// the next one can be made a UOP_SaveNext
if (Inst.Operation == Win64EH::UOP_SaveR19R20X) {
PrevOffset = 0;
PrevRegister = 19;
} else if (Inst.Operation == Win64EH::UOP_SaveRegPX) {
PrevOffset = 0;
PrevRegister = Inst.Register;
} else if (Inst.Operation == Win64EH::UOP_SaveRegP) {
PrevOffset = Inst.Offset;
PrevRegister = Inst.Register;
} else if (Inst.Operation == Win64EH::UOP_SaveNext) {
PrevRegister += 2;
PrevOffset += 16;
} else {
PrevRegister = -1;
PrevOffset = -1;
}
};
// Iterate over instructions in a forward order (for prologues),
// backwards for epilogues (i.e. always reverse compared to how the
// opcodes are stored).
if (Reverse) {
for (auto It = Instructions.rbegin(); It != Instructions.rend(); It++)
VisitInstruction(*It);
} else {
for (WinEH::Instruction &Inst : Instructions)
VisitInstruction(Inst);
}
}
static int checkPackedEpilog(MCStreamer &streamer, WinEH::FrameInfo *info,
int PrologCodeBytes) {
// Can only pack if there's one single epilog
if (info->EpilogMap.size() != 1)
return -1;
const std::vector<WinEH::Instruction> &Epilog =
info->EpilogMap.begin()->second;
// Can pack if the epilog is a subset of the prolog but not vice versa
if (Epilog.size() > info->Instructions.size())
return -1;
// Check that the epilog actually is a perfect match for the end (backwrds)
// of the prolog.
for (int I = Epilog.size() - 1; I >= 0; I--) {
if (info->Instructions[I] != Epilog[Epilog.size() - 1 - I])
return -1;
}
// Check that the epilog actually is at the very end of the function,
// otherwise it can't be packed.
uint32_t DistanceFromEnd = (uint32_t)GetAbsDifference(
streamer, info->FuncletOrFuncEnd, info->EpilogMap.begin()->first);
if (DistanceFromEnd / 4 != Epilog.size())
return -1;
int Offset = Epilog.size() == info->Instructions.size()
? 0
: ARM64CountOfUnwindCodes(ArrayRef<WinEH::Instruction>(
&info->Instructions[Epilog.size()],
info->Instructions.size() - Epilog.size()));
// Check that the offset and prolog size fits in the first word; it's
// unclear whether the epilog count in the extension word can be taken
// as packed epilog offset.
if (Offset > 31 || PrologCodeBytes > 124)
return -1;
info->EpilogMap.clear();
return Offset;
}
static bool tryPackedUnwind(WinEH::FrameInfo *info, uint32_t FuncLength,
int PackedEpilogOffset) {
if (PackedEpilogOffset == 0) {
// Fully symmetric prolog and epilog, should be ok for packed format.
// For CR=3, the corresponding synthesized epilog actually lacks the
// SetFP opcode, but unwinding should work just fine despite that
// (if at the SetFP opcode, the unwinder considers it as part of the
// function body and just unwinds the full prolog instead).
} else if (PackedEpilogOffset == 1) {
// One single case of differences between prolog and epilog is allowed:
// The epilog can lack a single SetFP that is the last opcode in the
// prolog, for the CR=3 case.
if (info->Instructions.back().Operation != Win64EH::UOP_SetFP)
return false;
} else {
// Too much difference between prolog and epilog.
return false;
}
unsigned RegI = 0, RegF = 0;
int Predecrement = 0;
enum {
Start,
Start2,
IntRegs,
FloatRegs,
InputArgs,
StackAdjust,
FrameRecord,
End
} Location = Start;
bool StandaloneLR = false, FPLRPair = false;
int StackOffset = 0;
int Nops = 0;
// Iterate over the prolog and check that all opcodes exactly match
// the canonical order and form. A more lax check could verify that
// all saved registers are in the expected locations, but not enforce
// the order - that would work fine when unwinding from within
// functions, but not be exactly right if unwinding happens within
// prologs/epilogs.
for (const WinEH::Instruction &Inst : info->Instructions) {
switch (Inst.Operation) {
case Win64EH::UOP_End:
if (Location != Start)
return false;
Location = Start2;
break;
case Win64EH::UOP_SaveR19R20X:
if (Location != Start2)
return false;
Predecrement = Inst.Offset;
RegI = 2;
Location = IntRegs;
break;
case Win64EH::UOP_SaveRegX:
if (Location != Start2)
return false;
Predecrement = Inst.Offset;
if (Inst.Register == 19)
RegI += 1;
else if (Inst.Register == 30)
StandaloneLR = true;
else
return false;
// Odd register; can't be any further int registers.
Location = FloatRegs;
break;
case Win64EH::UOP_SaveRegPX:
// Can't have this in a canonical prologue. Either this has been
// canonicalized into SaveR19R20X or SaveFPLRX, or it's an unsupported
// register pair.
// It can't be canonicalized into SaveR19R20X if the offset is
// larger than 248 bytes, but even with the maximum case with
// RegI=10/RegF=8/CR=1/H=1, we end up with SavSZ = 216, which should
// fit into SaveR19R20X.
// The unwinding opcodes can't describe the otherwise seemingly valid
// case for RegI=1 CR=1, that would start with a
// "stp x19, lr, [sp, #-...]!" as that fits neither SaveRegPX nor
// SaveLRPair.
return false;
case Win64EH::UOP_SaveRegP:
if (Location != IntRegs || Inst.Offset != 8 * RegI ||
Inst.Register != 19 + RegI)
return false;
RegI += 2;
break;
case Win64EH::UOP_SaveReg:
if (Location != IntRegs || Inst.Offset != 8 * RegI)
return false;
if (Inst.Register == 19 + RegI)
RegI += 1;
else if (Inst.Register == 30)
StandaloneLR = true;
else
return false;
// Odd register; can't be any further int registers.
Location = FloatRegs;
break;
case Win64EH::UOP_SaveLRPair:
if (Location != IntRegs || Inst.Offset != 8 * RegI ||
Inst.Register != 19 + RegI)
return false;
RegI += 1;
StandaloneLR = true;
Location = FloatRegs;
break;
case Win64EH::UOP_SaveFRegX:
// Packed unwind can't handle prologs that only save one single
// float register.
return false;
case Win64EH::UOP_SaveFReg:
if (Location != FloatRegs || RegF == 0 || Inst.Register != 8 + RegF ||
Inst.Offset != 8 * (RegI + (StandaloneLR ? 1 : 0) + RegF))
return false;
RegF += 1;
Location = InputArgs;
break;
case Win64EH::UOP_SaveFRegPX:
if (Location != Start2 || Inst.Register != 8)
return false;
Predecrement = Inst.Offset;
RegF = 2;
Location = FloatRegs;
break;
case Win64EH::UOP_SaveFRegP:
if ((Location != IntRegs && Location != FloatRegs) ||
Inst.Register != 8 + RegF ||
Inst.Offset != 8 * (RegI + (StandaloneLR ? 1 : 0) + RegF))
return false;
RegF += 2;
Location = FloatRegs;
break;
case Win64EH::UOP_SaveNext:
if (Location == IntRegs)
RegI += 2;
else if (Location == FloatRegs)
RegF += 2;
else
return false;
break;
case Win64EH::UOP_Nop:
if (Location != IntRegs && Location != FloatRegs && Location != InputArgs)
return false;
Location = InputArgs;
Nops++;
break;
case Win64EH::UOP_AllocSmall:
case Win64EH::UOP_AllocMedium:
if (Location != Start2 && Location != IntRegs && Location != FloatRegs &&
Location != InputArgs && Location != StackAdjust)
return false;
// Can have either a single decrement, or a pair of decrements with
// 4080 and another decrement.
if (StackOffset == 0)
StackOffset = Inst.Offset;
else if (StackOffset != 4080)
return false;
else
StackOffset += Inst.Offset;
Location = StackAdjust;
break;
case Win64EH::UOP_SaveFPLRX:
// Not allowing FPLRX after StackAdjust; if a StackAdjust is used, it
// should be followed by a FPLR instead.
if (Location != Start2 && Location != IntRegs && Location != FloatRegs &&
Location != InputArgs)
return false;
StackOffset = Inst.Offset;
Location = FrameRecord;
FPLRPair = true;
break;
case Win64EH::UOP_SaveFPLR:
// This can only follow after a StackAdjust
if (Location != StackAdjust || Inst.Offset != 0)
return false;
Location = FrameRecord;
FPLRPair = true;
break;
case Win64EH::UOP_SetFP:
if (Location != FrameRecord)
return false;
Location = End;
break;
}
}
if (RegI > 10 || RegF > 8)
return false;
if (StandaloneLR && FPLRPair)
return false;
if (FPLRPair && Location != End)
return false;
if (Nops != 0 && Nops != 4)
return false;
int H = Nops == 4;
int IntSZ = 8 * RegI;
if (StandaloneLR)
IntSZ += 8;
int FpSZ = 8 * RegF; // RegF not yet decremented
int SavSZ = (IntSZ + FpSZ + 8 * 8 * H + 0xF) & ~0xF;
if (Predecrement != SavSZ)
return false;
if (FPLRPair && StackOffset < 16)
return false;
if (StackOffset % 16)
return false;
uint32_t FrameSize = (StackOffset + SavSZ) / 16;
if (FrameSize > 0x1FF)
return false;
assert(RegF != 1 && "One single float reg not allowed");
if (RegF > 0)
RegF--; // Convert from actual number of registers, to value stored
assert(FuncLength <= 0x7FF && "FuncLength should have been checked earlier");
int Flag = 0x01; // Function segments not supported yet
int CR = FPLRPair ? 3 : StandaloneLR ? 1 : 0;
info->PackedInfo |= Flag << 0;
info->PackedInfo |= (FuncLength & 0x7FF) << 2;
info->PackedInfo |= (RegF & 0x7) << 13;
info->PackedInfo |= (RegI & 0xF) << 16;
info->PackedInfo |= (H & 0x1) << 20;
info->PackedInfo |= (CR & 0x3) << 21;
info->PackedInfo |= (FrameSize & 0x1FF) << 23;
return true;
}
// Populate the .xdata section. The format of .xdata on ARM64 is documented at
// https://docs.microsoft.com/en-us/cpp/build/arm64-exception-handling
static void ARM64EmitUnwindInfo(MCStreamer &streamer, WinEH::FrameInfo *info,
bool TryPacked = true) {
// If this UNWIND_INFO already has a symbol, it's already been emitted.
if (info->Symbol)
return;
// If there's no unwind info here (not even a terminating UOP_End), the
// unwind info is considered bogus and skipped. If this was done in
// response to an explicit .seh_handlerdata, the associated trailing
// handler data is left orphaned in the xdata section.
if (info->empty()) {
info->EmitAttempted = true;
return;
}
if (info->EmitAttempted) {
// If we tried to emit unwind info before (due to an explicit
// .seh_handlerdata directive), but skipped it (because there was no
// valid information to emit at the time), and it later got valid unwind
// opcodes, we can't emit it here, because the trailing handler data
// was already emitted elsewhere in the xdata section.
streamer.getContext().reportError(
SMLoc(), "Earlier .seh_handlerdata for " + info->Function->getName() +
" skipped due to no unwind info at the time "
"(.seh_handlerdata too early?), but the function later "
"did get unwind info that can't be emitted");
return;
}
simplifyOpcodes(info->Instructions, false);
for (auto &I : info->EpilogMap)
simplifyOpcodes(I.second, true);
MCContext &context = streamer.getContext();
MCSymbol *Label = context.createTempSymbol();
streamer.emitValueToAlignment(4);
streamer.emitLabel(Label);
info->Symbol = Label;
int64_t RawFuncLength;
if (!info->FuncletOrFuncEnd) {
report_fatal_error("FuncletOrFuncEnd not set");
} else {
// FIXME: GetAbsDifference tries to compute the length of the function
// immediately, before the whole file is emitted, but in general
// that's impossible: the size in bytes of certain assembler directives
// like .align and .fill is not known until the whole file is parsed and
// relaxations are applied. Currently, GetAbsDifference fails with a fatal
// error in that case. (We mostly don't hit this because inline assembly
// specifying those directives is rare, and we don't normally try to
// align loops on AArch64.)
//
// There are two potential approaches to delaying the computation. One,
// we could emit something like ".word (endfunc-beginfunc)/4+0x10800000",
// as long as we have some conservative estimate we could use to prove
// that we don't need to split the unwind data. Emitting the constant
// is straightforward, but there's no existing code for estimating the
// size of the function.
//
// The other approach would be to use a dedicated, relaxable fragment,
// which could grow to accommodate splitting the unwind data if
// necessary. This is more straightforward, since it automatically works
// without any new infrastructure, and it's consistent with how we handle
// relaxation in other contexts. But it would require some refactoring
// to move parts of the pdata/xdata emission into the implementation of
// a fragment. We could probably continue to encode the unwind codes
// here, but we'd have to emit the pdata, the xdata header, and the
// epilogue scopes later, since they depend on whether the we need to
// split the unwind data.
RawFuncLength = GetAbsDifference(streamer, info->FuncletOrFuncEnd,
info->Begin);
}
if (RawFuncLength > 0xFFFFF)
report_fatal_error("SEH unwind data splitting not yet implemented");
uint32_t FuncLength = (uint32_t)RawFuncLength / 4;
uint32_t PrologCodeBytes = ARM64CountOfUnwindCodes(info->Instructions);
uint32_t TotalCodeBytes = PrologCodeBytes;
int PackedEpilogOffset = checkPackedEpilog(streamer, info, PrologCodeBytes);
if (PackedEpilogOffset >= 0 && !info->HandlesExceptions &&
FuncLength <= 0x7ff && TryPacked) {
// Matching prolog/epilog and no exception handlers; check if the
// prolog matches the patterns that can be described by the packed
// format.
// info->Symbol was already set even if we didn't actually write any
// unwind info there. Keep using that as indicator that this unwind
// info has been generated already.
if (tryPackedUnwind(info, FuncLength, PackedEpilogOffset))
return;
}
// Process epilogs.
MapVector<MCSymbol *, uint32_t> EpilogInfo;
// Epilogs processed so far.
std::vector<MCSymbol *> AddedEpilogs;
for (auto &I : info->EpilogMap) {
MCSymbol *EpilogStart = I.first;
auto &EpilogInstrs = I.second;
uint32_t CodeBytes = ARM64CountOfUnwindCodes(EpilogInstrs);
MCSymbol* MatchingEpilog =
FindMatchingEpilog(EpilogInstrs, AddedEpilogs, info);
if (MatchingEpilog) {
assert(EpilogInfo.find(MatchingEpilog) != EpilogInfo.end() &&
"Duplicate epilog not found");
EpilogInfo[EpilogStart] = EpilogInfo.lookup(MatchingEpilog);
// Clear the unwind codes in the EpilogMap, so that they don't get output
// in the logic below.
EpilogInstrs.clear();
} else {
EpilogInfo[EpilogStart] = TotalCodeBytes;
TotalCodeBytes += CodeBytes;
AddedEpilogs.push_back(EpilogStart);
}
}
// Code Words, Epilog count, E, X, Vers, Function Length
uint32_t row1 = 0x0;
uint32_t CodeWords = TotalCodeBytes / 4;
uint32_t CodeWordsMod = TotalCodeBytes % 4;
if (CodeWordsMod)
CodeWords++;
uint32_t EpilogCount =
PackedEpilogOffset >= 0 ? PackedEpilogOffset : info->EpilogMap.size();
bool ExtensionWord = EpilogCount > 31 || TotalCodeBytes > 124;
if (!ExtensionWord) {
row1 |= (EpilogCount & 0x1F) << 22;
row1 |= (CodeWords & 0x1F) << 27;
}
if (info->HandlesExceptions) // X
row1 |= 1 << 20;
if (PackedEpilogOffset >= 0) // E
row1 |= 1 << 21;
row1 |= FuncLength & 0x3FFFF;
streamer.emitInt32(row1);
// Extended Code Words, Extended Epilog Count
if (ExtensionWord) {
// FIXME: We should be able to split unwind info into multiple sections.
// FIXME: We should share epilog codes across epilogs, where possible,
// which would make this issue show up less frequently.
if (CodeWords > 0xFF || EpilogCount > 0xFFFF)
report_fatal_error("SEH unwind data splitting not yet implemented");
uint32_t row2 = 0x0;
row2 |= (CodeWords & 0xFF) << 16;
row2 |= (EpilogCount & 0xFFFF);
streamer.emitInt32(row2);
}
// Epilog Start Index, Epilog Start Offset
for (auto &I : EpilogInfo) {
MCSymbol *EpilogStart = I.first;
uint32_t EpilogIndex = I.second;
uint32_t EpilogOffset =
(uint32_t)GetAbsDifference(streamer, EpilogStart, info->Begin);
if (EpilogOffset)
EpilogOffset /= 4;
uint32_t row3 = EpilogOffset;
row3 |= (EpilogIndex & 0x3FF) << 22;
streamer.emitInt32(row3);
}
// Emit prolog unwind instructions (in reverse order).
uint8_t numInst = info->Instructions.size();
for (uint8_t c = 0; c < numInst; ++c) {
WinEH::Instruction inst = info->Instructions.back();
info->Instructions.pop_back();
ARM64EmitUnwindCode(streamer, info->Begin, inst);
}
// Emit epilog unwind instructions
for (auto &I : info->EpilogMap) {
auto &EpilogInstrs = I.second;
for (uint32_t i = 0; i < EpilogInstrs.size(); i++) {
WinEH::Instruction inst = EpilogInstrs[i];
ARM64EmitUnwindCode(streamer, info->Begin, inst);
}
}
int32_t BytesMod = CodeWords * 4 - TotalCodeBytes;
assert(BytesMod >= 0);
for (int i = 0; i < BytesMod; i++)
streamer.emitInt8(0xE3);
if (info->HandlesExceptions)
streamer.emitValue(
MCSymbolRefExpr::create(info->ExceptionHandler,
MCSymbolRefExpr::VK_COFF_IMGREL32, context),
4);
}
static void ARM64EmitRuntimeFunction(MCStreamer &streamer,
const WinEH::FrameInfo *info) {
MCContext &context = streamer.getContext();
streamer.emitValueToAlignment(4);
EmitSymbolRefWithOfs(streamer, info->Function, info->Begin);
if (info->PackedInfo)
streamer.emitInt32(info->PackedInfo);
else
streamer.emitValue(
MCSymbolRefExpr::create(info->Symbol, MCSymbolRefExpr::VK_COFF_IMGREL32,
context),
4);
}
void llvm::Win64EH::ARM64UnwindEmitter::Emit(MCStreamer &Streamer) const {
// Emit the unwind info structs first.
for (const auto &CFI : Streamer.getWinFrameInfos()) {
WinEH::FrameInfo *Info = CFI.get();
if (Info->empty())
continue;
MCSection *XData = Streamer.getAssociatedXDataSection(CFI->TextSection);
Streamer.SwitchSection(XData);
ARM64EmitUnwindInfo(Streamer, Info);
}
// Now emit RUNTIME_FUNCTION entries.
for (const auto &CFI : Streamer.getWinFrameInfos()) {
WinEH::FrameInfo *Info = CFI.get();
// ARM64EmitUnwindInfo above clears the info struct, so we can't check
// empty here. But if a Symbol is set, we should create the corresponding
// pdata entry.
if (!Info->Symbol)
continue;
MCSection *PData = Streamer.getAssociatedPDataSection(CFI->TextSection);
Streamer.SwitchSection(PData);
ARM64EmitRuntimeFunction(Streamer, Info);
}
}
void llvm::Win64EH::ARM64UnwindEmitter::EmitUnwindInfo(
MCStreamer &Streamer, WinEH::FrameInfo *info) const {
// Called if there's an .seh_handlerdata directive before the end of the
// function. This forces writing the xdata record already here - and
// in this case, the function isn't actually ended already, but the xdata
// record needs to know the function length. In these cases, if the funclet
// end hasn't been marked yet, the xdata function length won't cover the
// whole function, only up to this point.
if (!info->FuncletOrFuncEnd) {
Streamer.SwitchSection(info->TextSection);
info->FuncletOrFuncEnd = Streamer.emitCFILabel();
}
// Switch sections (the static function above is meant to be called from
// here and from Emit().
MCSection *XData = Streamer.getAssociatedXDataSection(info->TextSection);
Streamer.SwitchSection(XData);
ARM64EmitUnwindInfo(Streamer, info, false);
}
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