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llvm-project/llvm/lib/CodeGen/AsmPrinter/DwarfException.cpp

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//===-- CodeGen/AsmPrinter/DwarfException.cpp - Dwarf Exception Impl ------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains support for writing DWARF exception info into asm files.
//
//===----------------------------------------------------------------------===//
#include "DwarfException.h"
#include "llvm/Module.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineLocation.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetFrameInfo.h"
#include "llvm/Target/TargetLoweringObjectFile.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Support/Dwarf.h"
#include "llvm/Support/Mangler.h"
#include "llvm/Support/Timer.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringExtras.h"
using namespace llvm;
static TimerGroup &getDwarfTimerGroup() {
static TimerGroup DwarfTimerGroup("DWARF Exception");
return DwarfTimerGroup;
}
DwarfException::DwarfException(raw_ostream &OS, AsmPrinter *A,
const MCAsmInfo *T)
: Dwarf(OS, A, T, "eh"), shouldEmitTable(false), shouldEmitMoves(false),
shouldEmitTableModule(false), shouldEmitMovesModule(false),
ExceptionTimer(0) {
if (TimePassesIsEnabled)
ExceptionTimer = new Timer("DWARF Exception Writer",
getDwarfTimerGroup());
}
DwarfException::~DwarfException() {
delete ExceptionTimer;
}
/// SizeOfEncodedValue - Return the size of the encoding in bytes.
unsigned DwarfException::SizeOfEncodedValue(unsigned Encoding) {
if (Encoding == dwarf::DW_EH_PE_omit)
return 0;
switch (Encoding & 0x07) {
case dwarf::DW_EH_PE_absptr:
return TD->getPointerSize();
case dwarf::DW_EH_PE_udata2:
return 2;
case dwarf::DW_EH_PE_udata4:
return 4;
case dwarf::DW_EH_PE_udata8:
return 8;
}
assert(0 && "Invalid encoded value.");
return 0;
}
/// EmitCIE - Emit a Common Information Entry (CIE). This holds information that
/// is shared among many Frame Description Entries. There is at least one CIE
/// in every non-empty .debug_frame section.
void DwarfException::EmitCIE(const Function *PersonalityFn, unsigned Index) {
// Size and sign of stack growth.
int stackGrowth =
Asm->TM.getFrameInfo()->getStackGrowthDirection() ==
TargetFrameInfo::StackGrowsUp ?
TD->getPointerSize() : -TD->getPointerSize();
const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
// Begin eh frame section.
Asm->OutStreamer.SwitchSection(TLOF.getEHFrameSection());
if (MAI->is_EHSymbolPrivate())
O << MAI->getPrivateGlobalPrefix();
O << "EH_frame" << Index << ":\n";
EmitLabel("section_eh_frame", Index);
// Define base labels.
EmitLabel("eh_frame_common", Index);
// Define the eh frame length.
EmitDifference("eh_frame_common_end", Index,
"eh_frame_common_begin", Index, true);
Asm->EOL("Length of Common Information Entry");
// EH frame header.
EmitLabel("eh_frame_common_begin", Index);
Asm->EmitInt32((int)0);
Asm->EOL("CIE Identifier Tag");
Asm->EmitInt8(dwarf::DW_CIE_VERSION);
Asm->EOL("CIE Version");
// The personality presence indicates that language specific information will
// show up in the eh frame. Find out how we are supposed to lower the
// personality function reference:
const MCExpr *PersonalityRef = 0;
bool IsPersonalityIndirect = false, IsPersonalityPCRel = false;
if (PersonalityFn) {
// FIXME: HANDLE STATIC CODEGEN MODEL HERE.
// In non-static mode, ask the object file how to represent this reference.
PersonalityRef =
TLOF.getSymbolForDwarfGlobalReference(PersonalityFn, Asm->Mang,
Asm->MMI,
IsPersonalityIndirect,
IsPersonalityPCRel);
}
unsigned PerEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
if (IsPersonalityIndirect)
PerEncoding |= dwarf::DW_EH_PE_indirect;
unsigned LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
unsigned FDEEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
char Augmentation[5] = { 0 };
unsigned AugmentationSize = 0;
char *APtr = Augmentation + 1;
if (PersonalityRef) {
// There is a personality function.
*APtr++ = 'P';
AugmentationSize += 1 + SizeOfEncodedValue(PerEncoding);
}
if (UsesLSDA[Index]) {
// An LSDA pointer is in the FDE augmentation.
*APtr++ = 'L';
++AugmentationSize;
}
if (FDEEncoding != dwarf::DW_EH_PE_absptr) {
// A non-default pointer encoding for the FDE.
*APtr++ = 'R';
++AugmentationSize;
}
if (APtr != Augmentation + 1)
Augmentation[0] = 'z';
Asm->EmitString(Augmentation);
Asm->EOL("CIE Augmentation");
// Round out reader.
Asm->EmitULEB128Bytes(1);
Asm->EOL("CIE Code Alignment Factor");
Asm->EmitSLEB128Bytes(stackGrowth);
Asm->EOL("CIE Data Alignment Factor");
Asm->EmitInt8(RI->getDwarfRegNum(RI->getRARegister(), true));
Asm->EOL("CIE Return Address Column");
Asm->EmitULEB128Bytes(AugmentationSize);
Asm->EOL("Augmentation Size");
Asm->EmitInt8(PerEncoding);
Asm->EOL("Personality", PerEncoding);
// If there is a personality, we need to indicate the function's location.
if (PersonalityRef) {
// If the reference to the personality function symbol is not already
// pc-relative, then we need to subtract our current address from it. Do
// this by emitting a label and subtracting it from the expression we
// already have. This is equivalent to emitting "foo - .", but we have to
// emit the label for "." directly.
if (!IsPersonalityPCRel) {
SmallString<64> Name;
raw_svector_ostream(Name) << MAI->getPrivateGlobalPrefix()
<< "personalityref_addr" << Asm->getFunctionNumber() << "_" << Index;
MCSymbol *DotSym = Asm->OutContext.GetOrCreateSymbol(Name.str());
Asm->OutStreamer.EmitLabel(DotSym);
PersonalityRef =
MCBinaryExpr::CreateSub(PersonalityRef,
MCSymbolRefExpr::Create(DotSym,Asm->OutContext),
Asm->OutContext);
}
O << MAI->getData32bitsDirective();
PersonalityRef->print(O, MAI);
Asm->EOL("Personality");
Asm->EmitInt8(LSDAEncoding);
Asm->EOL("LSDA Encoding", LSDAEncoding);
Asm->EmitInt8(FDEEncoding);
Asm->EOL("FDE Encoding", FDEEncoding);
}
// Indicate locations of general callee saved registers in frame.
std::vector<MachineMove> Moves;
RI->getInitialFrameState(Moves);
EmitFrameMoves(NULL, 0, Moves, true);
// On Darwin the linker honors the alignment of eh_frame, which means it must
// be 8-byte on 64-bit targets to match what gcc does. Otherwise you get
// holes which confuse readers of eh_frame.
Asm->EmitAlignment(TD->getPointerSize() == 4 ? 2 : 3, 0, 0, false);
EmitLabel("eh_frame_common_end", Index);
Asm->EOL();
}
/// EmitFDE - Emit the Frame Description Entry (FDE) for the function.
void DwarfException::EmitFDE(const FunctionEHFrameInfo &EHFrameInfo) {
assert(!EHFrameInfo.function->hasAvailableExternallyLinkage() &&
"Should not emit 'available externally' functions at all");
const Function *TheFunc = EHFrameInfo.function;
Asm->OutStreamer.SwitchSection(Asm->getObjFileLowering().getEHFrameSection());
// Externally visible entry into the functions eh frame info. If the
// corresponding function is static, this should not be externally visible.
if (!TheFunc->hasLocalLinkage())
if (const char *GlobalEHDirective = MAI->getGlobalEHDirective())
O << GlobalEHDirective << EHFrameInfo.FnName << "\n";
// If corresponding function is weak definition, this should be too.
if (TheFunc->isWeakForLinker() && MAI->getWeakDefDirective())
O << MAI->getWeakDefDirective() << EHFrameInfo.FnName << "\n";
// If there are no calls then you can't unwind. This may mean we can omit the
// EH Frame, but some environments do not handle weak absolute symbols. If
// UnwindTablesMandatory is set we cannot do this optimization; the unwind
// info is to be available for non-EH uses.
if (!EHFrameInfo.hasCalls && !UnwindTablesMandatory &&
(!TheFunc->isWeakForLinker() ||
!MAI->getWeakDefDirective() ||
MAI->getSupportsWeakOmittedEHFrame())) {
O << EHFrameInfo.FnName << " = 0\n";
// This name has no connection to the function, so it might get
// dead-stripped when the function is not, erroneously. Prohibit
// dead-stripping unconditionally.
if (const char *UsedDirective = MAI->getUsedDirective())
O << UsedDirective << EHFrameInfo.FnName << "\n\n";
} else {
O << EHFrameInfo.FnName << ":\n";
// EH frame header.
EmitDifference("eh_frame_end", EHFrameInfo.Number,
"eh_frame_begin", EHFrameInfo.Number, true);
Asm->EOL("Length of Frame Information Entry");
EmitLabel("eh_frame_begin", EHFrameInfo.Number);
EmitSectionOffset("eh_frame_begin", "eh_frame_common",
EHFrameInfo.Number, EHFrameInfo.PersonalityIndex,
true, true, false);
Asm->EOL("FDE CIE offset");
EmitReference("eh_func_begin", EHFrameInfo.Number, true, true);
Asm->EOL("FDE initial location");
EmitDifference("eh_func_end", EHFrameInfo.Number,
"eh_func_begin", EHFrameInfo.Number, true);
Asm->EOL("FDE address range");
// If there is a personality and landing pads then point to the language
// specific data area in the exception table.
if (MMI->getPersonalities()[0] != NULL) {
bool is4Byte = TD->getPointerSize() == sizeof(int32_t);
Asm->EmitULEB128Bytes(is4Byte ? 4 : 8);
Asm->EOL("Augmentation size");
if (EHFrameInfo.hasLandingPads)
EmitReference("exception", EHFrameInfo.Number, true, false);
else {
if (is4Byte)
Asm->EmitInt32((int)0);
else
Asm->EmitInt64((int)0);
}
Asm->EOL("Language Specific Data Area");
} else {
Asm->EmitULEB128Bytes(0);
Asm->EOL("Augmentation size");
}
// Indicate locations of function specific callee saved registers in frame.
EmitFrameMoves("eh_func_begin", EHFrameInfo.Number, EHFrameInfo.Moves,
true);
// On Darwin the linker honors the alignment of eh_frame, which means it
// must be 8-byte on 64-bit targets to match what gcc does. Otherwise you
// get holes which confuse readers of eh_frame.
Asm->EmitAlignment(TD->getPointerSize() == sizeof(int32_t) ? 2 : 3,
0, 0, false);
EmitLabel("eh_frame_end", EHFrameInfo.Number);
// If the function is marked used, this table should be also. We cannot
// make the mark unconditional in this case, since retaining the table also
// retains the function in this case, and there is code around that depends
// on unused functions (calling undefined externals) being dead-stripped to
// link correctly. Yes, there really is.
if (MMI->isUsedFunction(EHFrameInfo.function))
if (const char *UsedDirective = MAI->getUsedDirective())
O << UsedDirective << EHFrameInfo.FnName << "\n\n";
}
Asm->EOL();
}
/// SharedTypeIds - How many leading type ids two landing pads have in common.
unsigned DwarfException::SharedTypeIds(const LandingPadInfo *L,
const LandingPadInfo *R) {
const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
unsigned LSize = LIds.size(), RSize = RIds.size();
unsigned MinSize = LSize < RSize ? LSize : RSize;
unsigned Count = 0;
for (; Count != MinSize; ++Count)
if (LIds[Count] != RIds[Count])
return Count;
return Count;
}
/// PadLT - Order landing pads lexicographically by type id.
bool DwarfException::PadLT(const LandingPadInfo *L, const LandingPadInfo *R) {
const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
unsigned LSize = LIds.size(), RSize = RIds.size();
unsigned MinSize = LSize < RSize ? LSize : RSize;
for (unsigned i = 0; i != MinSize; ++i)
if (LIds[i] != RIds[i])
return LIds[i] < RIds[i];
return LSize < RSize;
}
/// ComputeActionsTable - Compute the actions table and gather the first action
/// index for each landing pad site.
unsigned DwarfException::
ComputeActionsTable(const SmallVectorImpl<const LandingPadInfo*> &LandingPads,
SmallVectorImpl<ActionEntry> &Actions,
SmallVectorImpl<unsigned> &FirstActions) {
// The action table follows the call-site table in the LSDA. The individual
// records are of two types:
//
// * Catch clause
// * Exception specification
//
// The two record kinds have the same format, with only small differences.
// They are distinguished by the "switch value" field: Catch clauses
// (TypeInfos) have strictly positive switch values, and exception
// specifications (FilterIds) have strictly negative switch values. Value 0
// indicates a catch-all clause.
//
// Negative type IDs index into FilterIds. Positive type IDs index into
// TypeInfos. The value written for a positive type ID is just the type ID
// itself. For a negative type ID, however, the value written is the
// (negative) byte offset of the corresponding FilterIds entry. The byte
// offset is usually equal to the type ID (because the FilterIds entries are
// written using a variable width encoding, which outputs one byte per entry
// as long as the value written is not too large) but can differ. This kind
// of complication does not occur for positive type IDs because type infos are
// output using a fixed width encoding. FilterOffsets[i] holds the byte
// offset corresponding to FilterIds[i].
const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
SmallVector<int, 16> FilterOffsets;
FilterOffsets.reserve(FilterIds.size());
int Offset = -1;
for (std::vector<unsigned>::const_iterator
I = FilterIds.begin(), E = FilterIds.end(); I != E; ++I) {
FilterOffsets.push_back(Offset);
Offset -= MCAsmInfo::getULEB128Size(*I);
}
FirstActions.reserve(LandingPads.size());
int FirstAction = 0;
unsigned SizeActions = 0;
const LandingPadInfo *PrevLPI = 0;
for (SmallVectorImpl<const LandingPadInfo *>::const_iterator
I = LandingPads.begin(), E = LandingPads.end(); I != E; ++I) {
const LandingPadInfo *LPI = *I;
const std::vector<int> &TypeIds = LPI->TypeIds;
const unsigned NumShared = PrevLPI ? SharedTypeIds(LPI, PrevLPI) : 0;
unsigned SizeSiteActions = 0;
if (NumShared < TypeIds.size()) {
unsigned SizeAction = 0;
ActionEntry *PrevAction = 0;
if (NumShared) {
const unsigned SizePrevIds = PrevLPI->TypeIds.size();
assert(Actions.size());
PrevAction = &Actions.back();
SizeAction = MCAsmInfo::getSLEB128Size(PrevAction->NextAction) +
MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
for (unsigned j = NumShared; j != SizePrevIds; ++j) {
SizeAction -=
MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
SizeAction += -PrevAction->NextAction;
PrevAction = PrevAction->Previous;
}
}
// Compute the actions.
for (unsigned J = NumShared, M = TypeIds.size(); J != M; ++J) {
int TypeID = TypeIds[J];
assert(-1 - TypeID < (int)FilterOffsets.size() && "Unknown filter id!");
int ValueForTypeID = TypeID < 0 ? FilterOffsets[-1 - TypeID] : TypeID;
unsigned SizeTypeID = MCAsmInfo::getSLEB128Size(ValueForTypeID);
int NextAction = SizeAction ? -(SizeAction + SizeTypeID) : 0;
SizeAction = SizeTypeID + MCAsmInfo::getSLEB128Size(NextAction);
SizeSiteActions += SizeAction;
ActionEntry Action = { ValueForTypeID, NextAction, PrevAction };
Actions.push_back(Action);
PrevAction = &Actions.back();
}
// Record the first action of the landing pad site.
FirstAction = SizeActions + SizeSiteActions - SizeAction + 1;
} // else identical - re-use previous FirstAction
// Information used when created the call-site table. The action record
// field of the call site record is the offset of the first associated
// action record, relative to the start of the actions table. This value is
// biased by 1 (1 in dicating the start of the actions table), and 0
// indicates that there are no actions.
FirstActions.push_back(FirstAction);
// Compute this sites contribution to size.
SizeActions += SizeSiteActions;
PrevLPI = LPI;
}
return SizeActions;
}
/// ComputeCallSiteTable - Compute the call-site table. The entry for an invoke
/// has a try-range containing the call, a non-zero landing pad, and an
/// appropriate action. The entry for an ordinary call has a try-range
/// containing the call and zero for the landing pad and the action. Calls
/// marked 'nounwind' have no entry and must not be contained in the try-range
/// of any entry - they form gaps in the table. Entries must be ordered by
/// try-range address.
void DwarfException::
ComputeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
const RangeMapType &PadMap,
const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
const SmallVectorImpl<unsigned> &FirstActions) {
// The end label of the previous invoke or nounwind try-range.
unsigned LastLabel = 0;
// Whether there is a potentially throwing instruction (currently this means
// an ordinary call) between the end of the previous try-range and now.
bool SawPotentiallyThrowing = false;
// Whether the last CallSite entry was for an invoke.
bool PreviousIsInvoke = false;
// Visit all instructions in order of address.
for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
I != E; ++I) {
for (MachineBasicBlock::const_iterator MI = I->begin(), E = I->end();
MI != E; ++MI) {
if (!MI->isLabel()) {
SawPotentiallyThrowing |= MI->getDesc().isCall();
continue;
}
unsigned BeginLabel = MI->getOperand(0).getImm();
assert(BeginLabel && "Invalid label!");
// End of the previous try-range?
if (BeginLabel == LastLabel)
SawPotentiallyThrowing = false;
// Beginning of a new try-range?
RangeMapType::iterator L = PadMap.find(BeginLabel);
if (L == PadMap.end())
// Nope, it was just some random label.
continue;
const PadRange &P = L->second;
const LandingPadInfo *LandingPad = LandingPads[P.PadIndex];
assert(BeginLabel == LandingPad->BeginLabels[P.RangeIndex] &&
"Inconsistent landing pad map!");
// For Dwarf exception handling (SjLj handling doesn't use this). If some
// instruction between the previous try-range and this one may throw,
// create a call-site entry with no landing pad for the region between the
// try-ranges.
if (SawPotentiallyThrowing &&
MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
CallSiteEntry Site = { LastLabel, BeginLabel, 0, 0 };
CallSites.push_back(Site);
PreviousIsInvoke = false;
}
LastLabel = LandingPad->EndLabels[P.RangeIndex];
assert(BeginLabel && LastLabel && "Invalid landing pad!");
if (LandingPad->LandingPadLabel) {
// This try-range is for an invoke.
CallSiteEntry Site = {
BeginLabel,
LastLabel,
LandingPad->LandingPadLabel,
FirstActions[P.PadIndex]
};
// Try to merge with the previous call-site. SJLJ doesn't do this
if (PreviousIsInvoke &&
MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
CallSiteEntry &Prev = CallSites.back();
if (Site.PadLabel == Prev.PadLabel && Site.Action == Prev.Action) {
// Extend the range of the previous entry.
Prev.EndLabel = Site.EndLabel;
continue;
}
}
// Otherwise, create a new call-site.
CallSites.push_back(Site);
PreviousIsInvoke = true;
} else {
// Create a gap.
PreviousIsInvoke = false;
}
}
}
// If some instruction between the previous try-range and the end of the
// function may throw, create a call-site entry with no landing pad for the
// region following the try-range.
if (SawPotentiallyThrowing &&
MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
CallSiteEntry Site = { LastLabel, 0, 0, 0 };
CallSites.push_back(Site);
}
}
/// EmitExceptionTable - Emit landing pads and actions.
///
/// The general organization of the table is complex, but the basic concepts are
/// easy. First there is a header which describes the location and organization
/// of the three components that follow.
///
/// 1. The landing pad site information describes the range of code covered by
/// the try. In our case it's an accumulation of the ranges covered by the
/// invokes in the try. There is also a reference to the landing pad that
/// handles the exception once processed. Finally an index into the actions
/// table.
/// 2. The action table, in our case, is composed of pairs of type IDs and next
/// action offset. Starting with the action index from the landing pad
/// site, each type ID is checked for a match to the current exception. If
/// it matches then the exception and type id are passed on to the landing
/// pad. Otherwise the next action is looked up. This chain is terminated
/// with a next action of zero. If no type id is found then the frame is
/// unwound and handling continues.
/// 3. Type ID table contains references to all the C++ typeinfo for all
/// catches in the function. This tables is reverse indexed base 1.
void DwarfException::EmitExceptionTable() {
const std::vector<GlobalVariable *> &TypeInfos = MMI->getTypeInfos();
const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
const std::vector<LandingPadInfo> &PadInfos = MMI->getLandingPads();
if (PadInfos.empty()) return;
// Sort the landing pads in order of their type ids. This is used to fold
// duplicate actions.
SmallVector<const LandingPadInfo *, 64> LandingPads;
LandingPads.reserve(PadInfos.size());
for (unsigned i = 0, N = PadInfos.size(); i != N; ++i)
LandingPads.push_back(&PadInfos[i]);
std::sort(LandingPads.begin(), LandingPads.end(), PadLT);
// Compute the actions table and gather the first action index for each
// landing pad site.
SmallVector<ActionEntry, 32> Actions;
SmallVector<unsigned, 64> FirstActions;
unsigned SizeActions = ComputeActionsTable(LandingPads, Actions,
FirstActions);
// Invokes and nounwind calls have entries in PadMap (due to being bracketed
// by try-range labels when lowered). Ordinary calls do not, so appropriate
// try-ranges for them need be deduced when using DWARF exception handling.
RangeMapType PadMap;
for (unsigned i = 0, N = LandingPads.size(); i != N; ++i) {
const LandingPadInfo *LandingPad = LandingPads[i];
for (unsigned j = 0, E = LandingPad->BeginLabels.size(); j != E; ++j) {
unsigned BeginLabel = LandingPad->BeginLabels[j];
assert(!PadMap.count(BeginLabel) && "Duplicate landing pad labels!");
PadRange P = { i, j };
PadMap[BeginLabel] = P;
}
}
// Compute the call-site table.
SmallVector<CallSiteEntry, 64> CallSites;
ComputeCallSiteTable(CallSites, PadMap, LandingPads, FirstActions);
// Final tallies.
// Call sites.
const unsigned SiteStartSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
const unsigned SiteLengthSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
const unsigned LandingPadSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
bool IsSJLJ = MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
bool HaveTTData = IsSJLJ ? (!TypeInfos.empty() || !FilterIds.empty()) : true;
unsigned SizeSites;
if (IsSJLJ)
SizeSites = 0;
else
SizeSites = CallSites.size() *
(SiteStartSize + SiteLengthSize + LandingPadSize);
for (unsigned i = 0, e = CallSites.size(); i < e; ++i) {
SizeSites += MCAsmInfo::getULEB128Size(CallSites[i].Action);
if (IsSJLJ)
SizeSites += MCAsmInfo::getULEB128Size(i);
}
// Type infos.
const MCSection *LSDASection = Asm->getObjFileLowering().getLSDASection();
unsigned TTypeFormat;
unsigned TypeFormatSize;
if (!HaveTTData) {
// For SjLj exceptions, if there is no TypeInfo, then we just explicitly say
// that we're omitting that bit.
TTypeFormat = dwarf::DW_EH_PE_omit;
TypeFormatSize = SizeOfEncodedValue(dwarf::DW_EH_PE_absptr);
} else {
// Okay, we have actual filters or typeinfos to emit. As such, we need to
// pick a type encoding for them. We're about to emit a list of pointers to
// typeinfo objects at the end of the LSDA. However, unless we're in static
// mode, this reference will require a relocation by the dynamic linker.
//
// Because of this, we have a couple of options:
//
// 1) If we are in -static mode, we can always use an absolute reference
// from the LSDA, because the static linker will resolve it.
//
// 2) Otherwise, if the LSDA section is writable, we can output the direct
// reference to the typeinfo and allow the dynamic linker to relocate
// it. Since it is in a writable section, the dynamic linker won't
// have a problem.
//
// 3) Finally, if we're in PIC mode and the LDSA section isn't writable,
// we need to use some form of indirection. For example, on Darwin,
// we can output a statically-relocatable reference to a dyld stub. The
// offset to the stub is constant, but the contents are in a section
// that is updated by the dynamic linker. This is easy enough, but we
// need to tell the personality function of the unwinder to indirect
// through the dyld stub.
//
// FIXME: When (3) is actually implemented, we'll have to emit the stubs
// somewhere. This predicate should be moved to a shared location that is
// in target-independent code.
//
if (LSDASection->getKind().isWriteable() ||
Asm->TM.getRelocationModel() == Reloc::Static)
TTypeFormat = dwarf::DW_EH_PE_absptr;
else
TTypeFormat = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4;
TypeFormatSize = SizeOfEncodedValue(TTypeFormat);
}
// Begin the exception table.
Asm->OutStreamer.SwitchSection(LSDASection);
Asm->EmitAlignment(2, 0, 0, false);
O << "GCC_except_table" << SubprogramCount << ":\n";
// The type infos need to be aligned. GCC does this by inserting padding just
// before the type infos. However, this changes the size of the exception
// table, so you need to take this into account when you output the exception
// table size. However, the size is output using a variable length encoding.
// So by increasing the size by inserting padding, you may increase the number
// of bytes used for writing the size. If it increases, say by one byte, then
// you now need to output one less byte of padding to get the type infos
// aligned. However this decreases the size of the exception table. This
// changes the value you have to output for the exception table size. Due to
// the variable length encoding, the number of bytes used for writing the
// length may decrease. If so, you then have to increase the amount of
// padding. And so on. If you look carefully at the GCC code you will see that
// it indeed does this in a loop, going on and on until the values stabilize.
// We chose another solution: don't output padding inside the table like GCC
// does, instead output it before the table.
unsigned SizeTypes = TypeInfos.size() * TypeFormatSize;
unsigned TyOffset = sizeof(int8_t) + // Call site format
MCAsmInfo::getULEB128Size(SizeSites) + // Call-site table length
SizeSites + SizeActions + SizeTypes;
unsigned TotalSize = sizeof(int8_t) + // LPStart format
sizeof(int8_t) + // TType format
(HaveTTData ?
MCAsmInfo::getULEB128Size(TyOffset) : 0) + // TType base offset
TyOffset;
unsigned SizeAlign = (4 - TotalSize) & 3;
for (unsigned i = 0; i != SizeAlign; ++i) {
Asm->EmitInt8(0);
Asm->EOL("Padding");
}
EmitLabel("exception", SubprogramCount);
if (IsSJLJ) {
SmallString<16> LSDAName;
raw_svector_ostream(LSDAName) << MAI->getPrivateGlobalPrefix() <<
"_LSDA_" << Asm->getFunctionNumber();
O << LSDAName.str() << ":\n";
}
// Emit the header.
Asm->EmitInt8(dwarf::DW_EH_PE_omit);
Asm->EOL("@LPStart format", dwarf::DW_EH_PE_omit);
Asm->EmitInt8(TTypeFormat);
Asm->EOL("@TType format", TTypeFormat);
if (HaveTTData) {
Asm->EmitULEB128Bytes(TyOffset);
Asm->EOL("@TType base offset");
}
// SjLj Exception handling
if (IsSJLJ) {
Asm->EmitInt8(dwarf::DW_EH_PE_udata4);
Asm->EOL("Call site format", dwarf::DW_EH_PE_udata4);
Asm->EmitULEB128Bytes(SizeSites);
Asm->EOL("Call site table length");
// Emit the landing pad site information.
unsigned idx = 0;
for (SmallVectorImpl<CallSiteEntry>::const_iterator
I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) {
const CallSiteEntry &S = *I;
// Offset of the landing pad, counted in 16-byte bundles relative to the
// @LPStart address.
Asm->EmitULEB128Bytes(idx);
Asm->EOL("Landing pad");
// Offset of the first associated action record, relative to the start of
// the action table. This value is biased by 1 (1 indicates the start of
// the action table), and 0 indicates that there are no actions.
Asm->EmitULEB128Bytes(S.Action);
Asm->EOL("Action");
}
} else {
// DWARF Exception handling
assert(MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf);
// The call-site table is a list of all call sites that may throw an
// exception (including C++ 'throw' statements) in the procedure
// fragment. It immediately follows the LSDA header. Each entry indicates,
// for a given call, the first corresponding action record and corresponding
// landing pad.
//
// The table begins with the number of bytes, stored as an LEB128
// compressed, unsigned integer. The records immediately follow the record
// count. They are sorted in increasing call-site address. Each record
// indicates:
//
// * The position of the call-site.
// * The position of the landing pad.
// * The first action record for that call site.
//
// A missing entry in the call-site table indicates that a call is not
// supposed to throw.
// Emit the landing pad call site table.
Asm->EmitInt8(dwarf::DW_EH_PE_udata4);
Asm->EOL("Call site format", dwarf::DW_EH_PE_udata4);
Asm->EmitULEB128Bytes(SizeSites);
Asm->EOL("Call site table size");
for (SmallVectorImpl<CallSiteEntry>::const_iterator
I = CallSites.begin(), E = CallSites.end(); I != E; ++I) {
const CallSiteEntry &S = *I;
const char *BeginTag;
unsigned BeginNumber;
if (!S.BeginLabel) {
BeginTag = "eh_func_begin";
BeginNumber = SubprogramCount;
} else {
BeginTag = "label";
BeginNumber = S.BeginLabel;
}
// Offset of the call site relative to the previous call site, counted in
// number of 16-byte bundles. The first call site is counted relative to
// the start of the procedure fragment.
EmitSectionOffset(BeginTag, "eh_func_begin", BeginNumber, SubprogramCount,
true, true);
Asm->EOL("Region start");
if (!S.EndLabel)
EmitDifference("eh_func_end", SubprogramCount, BeginTag, BeginNumber,
true);
else
EmitDifference("label", S.EndLabel, BeginTag, BeginNumber, true);
Asm->EOL("Region length");
// Offset of the landing pad, counted in 16-byte bundles relative to the
// @LPStart address.
if (!S.PadLabel)
Asm->EmitInt32(0);
else
EmitSectionOffset("label", "eh_func_begin", S.PadLabel, SubprogramCount,
true, true);
Asm->EOL("Landing pad");
// Offset of the first associated action record, relative to the start of
// the action table. This value is biased by 1 (1 indicates the start of
// the action table), and 0 indicates that there are no actions.
Asm->EmitULEB128Bytes(S.Action);
Asm->EOL("Action");
}
}
// Emit the Action Table.
for (SmallVectorImpl<ActionEntry>::const_iterator
I = Actions.begin(), E = Actions.end(); I != E; ++I) {
const ActionEntry &Action = *I;
// Type Filter
//
// Used by the runtime to match the type of the thrown exception to the
// type of the catch clauses or the types in the exception specification.
Asm->EmitSLEB128Bytes(Action.ValueForTypeID);
Asm->EOL("TypeInfo index");
// Action Record
//
// Self-relative signed displacement in bytes of the next action record,
// or 0 if there is no next action record.
Asm->EmitSLEB128Bytes(Action.NextAction);
Asm->EOL("Next action");
}
// Emit the Catch TypeInfos.
for (std::vector<GlobalVariable *>::const_reverse_iterator
I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I) {
const GlobalVariable *GV = *I;
PrintRelDirective();
if (GV) {
O << Asm->Mang->getMangledName(GV);
} else {
O << "0x0";
}
Asm->EOL("TypeInfo");
}
// Emit the Exception Specifications.
for (std::vector<unsigned>::const_iterator
I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) {
unsigned TypeID = *I;
Asm->EmitULEB128Bytes(TypeID);
if (TypeID != 0)
Asm->EOL("Exception specification");
else
Asm->EOL();
}
Asm->EmitAlignment(2, 0, 0, false);
}
/// EndModule - Emit all exception information that should come after the
/// content.
void DwarfException::EndModule() {
if (MAI->getExceptionHandlingType() != ExceptionHandling::Dwarf)
return;
if (!shouldEmitMovesModule && !shouldEmitTableModule)
return;
if (TimePassesIsEnabled)
ExceptionTimer->startTimer();
const std::vector<Function *> Personalities = MMI->getPersonalities();
for (unsigned I = 0, E = Personalities.size(); I < E; ++I)
EmitCIE(Personalities[I], I);
for (std::vector<FunctionEHFrameInfo>::iterator
I = EHFrames.begin(), E = EHFrames.end(); I != E; ++I)
EmitFDE(*I);
if (TimePassesIsEnabled)
ExceptionTimer->stopTimer();
}
/// BeginFunction - Gather pre-function exception information. Assumes it's
/// being emitted immediately after the function entry point.
void DwarfException::BeginFunction(MachineFunction *MF) {
if (!MMI || !MAI->doesSupportExceptionHandling()) return;
if (TimePassesIsEnabled)
ExceptionTimer->startTimer();
this->MF = MF;
shouldEmitTable = shouldEmitMoves = false;
// Map all labels and get rid of any dead landing pads.
MMI->TidyLandingPads();
// If any landing pads survive, we need an EH table.
if (!MMI->getLandingPads().empty())
shouldEmitTable = true;
// See if we need frame move info.
if (!MF->getFunction()->doesNotThrow() || UnwindTablesMandatory)
shouldEmitMoves = true;
if (shouldEmitMoves || shouldEmitTable)
// Assumes in correct section after the entry point.
EmitLabel("eh_func_begin", ++SubprogramCount);
shouldEmitTableModule |= shouldEmitTable;
shouldEmitMovesModule |= shouldEmitMoves;
if (TimePassesIsEnabled)
ExceptionTimer->stopTimer();
}
/// EndFunction - Gather and emit post-function exception information.
///
void DwarfException::EndFunction() {
if (!shouldEmitMoves && !shouldEmitTable) return;
if (TimePassesIsEnabled)
ExceptionTimer->startTimer();
EmitLabel("eh_func_end", SubprogramCount);
EmitExceptionTable();
std::string FunctionEHName =
Asm->Mang->getMangledName(MF->getFunction(), ".eh",
Asm->MAI->is_EHSymbolPrivate());
// Save EH frame information
EHFrames.push_back(FunctionEHFrameInfo(FunctionEHName, SubprogramCount,
MMI->getPersonalityIndex(),
MF->getFrameInfo()->hasCalls(),
!MMI->getLandingPads().empty(),
MMI->getFrameMoves(),
MF->getFunction()));
// Record if this personality index uses a landing pad.
UsesLSDA[MMI->getPersonalityIndex()] |= !MMI->getLandingPads().empty();
if (TimePassesIsEnabled)
ExceptionTimer->stopTimer();
}
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