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ca752c9020
llvm/lib/CodeGen/AsmPrinter/DwarfException.cpp
Jim Grosbach ca752c9020 Update of 94055 to track the IR level call site information via an intrinsic. 
This allows code gen and the exception table writer to cooperate to make sure
landing pads are associated with the correct invoke locations.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94726 91177308-0d34-0410-b5e6-96231b3b80d8
2010-01-28 01:45:32 +00:00

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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/MC/MCSymbol.h"
#include "llvm/Target/Mangler.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/FormattedStream.h"
#include "llvm/Support/Timer.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringExtras.h"
using namespace llvm;
DwarfException::DwarfException(raw_ostream &OS, AsmPrinter *A,
const MCAsmInfo *T)
: DwarfPrinter(OS, A, T, "eh"), shouldEmitTable(false),shouldEmitMoves(false),
shouldEmitTableModule(false), shouldEmitMovesModule(false),
ExceptionTimer(0) {
if (TimePassesIsEnabled)
ExceptionTimer = new Timer("DWARF Exception Writer");
}
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;
}
/// CreateLabelDiff - Emit a label and subtract it from the expression we
/// already have. This is equivalent to emitting "foo - .", but we have to emit
/// the label for "." directly.
const MCExpr *DwarfException::CreateLabelDiff(const MCExpr *ExprRef,
const char *LabelName,
unsigned Index) {
SmallString<64> Name;
raw_svector_ostream(Name) << MAI->getPrivateGlobalPrefix()
<< LabelName << Asm->getFunctionNumber()
<< "_" << Index;
MCSymbol *DotSym = Asm->OutContext.GetOrCreateSymbol(Name.str());
Asm->OutStreamer.EmitLabel(DotSym);
return MCBinaryExpr::CreateSub(ExprRef,
MCSymbolRefExpr::Create(DotSym,
Asm->OutContext),
Asm->OutContext);
}
/// 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);
EOL("Length of Common Information Entry");
// EH frame header.
EmitLabel("eh_frame_common_begin", Index);
if (Asm->VerboseAsm) Asm->OutStreamer.AddComment("CIE Identifier Tag");
Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
if (Asm->VerboseAsm) Asm->OutStreamer.AddComment("DW_CIE_VERSION");
Asm->OutStreamer.EmitIntValue(dwarf::DW_CIE_VERSION, 1/*size*/, 0/*addr*/);
// 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[6] = { 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->OutStreamer.EmitBytes(StringRef(Augmentation, strlen(Augmentation)+1),0);
EOL("CIE Augmentation");
// Round out reader.
EmitULEB128(1, "CIE Code Alignment Factor");
EmitSLEB128(stackGrowth, "CIE Data Alignment Factor");
Asm->EmitInt8(RI->getDwarfRegNum(RI->getRARegister(), true));
EOL("CIE Return Address Column");
EmitULEB128(AugmentationSize, "Augmentation Size");
EmitEncodingByte(PerEncoding, "Personality");
// If there is a personality, we need to indicate the function's location.
if (PersonalityRef) {
if (!IsPersonalityPCRel)
PersonalityRef = CreateLabelDiff(PersonalityRef, "personalityref_addr",
Index);
O << MAI->getData32bitsDirective() << *PersonalityRef;
EOL("Personality");
EmitEncodingByte(LSDAEncoding, "LSDA");
EmitEncodingByte(FDEEncoding, "FDE");
}
// 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->O << '\n';
}
/// 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.FunctionEHSym << '\n';
// If corresponding function is weak definition, this should be too.
if (TheFunc->isWeakForLinker() && MAI->getWeakDefDirective())
O << MAI->getWeakDefDirective() << *EHFrameInfo.FunctionEHSym << '\n';
// If corresponding function is hidden, this should be too.
if (TheFunc->hasHiddenVisibility())
if (MCSymbolAttr HiddenAttr = MAI->getHiddenVisibilityAttr())
Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
HiddenAttr);
// 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.FunctionEHSym << " = 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 (MAI->hasNoDeadStrip())
Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
MCSA_NoDeadStrip);
} else {
O << *EHFrameInfo.FunctionEHSym << ":\n";
// EH frame header.
EmitDifference("eh_frame_end", EHFrameInfo.Number,
"eh_frame_begin", EHFrameInfo.Number, true);
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);
EOL("FDE CIE offset");
EmitReference("eh_func_begin", EHFrameInfo.Number, true, true);
EOL("FDE initial location");
EmitDifference("eh_func_end", EHFrameInfo.Number,
"eh_func_begin", EHFrameInfo.Number, true);
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) {
if (Asm->TM.getLSDAEncoding() != DwarfLSDAEncoding::EightByte) {
EmitULEB128(4, "Augmentation size");
if (EHFrameInfo.hasLandingPads)
EmitReference("exception", EHFrameInfo.Number, true, true);
else
Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
} else {
EmitULEB128(TD->getPointerSize(), "Augmentation size");
if (EHFrameInfo.hasLandingPads) {
EmitReference("exception", EHFrameInfo.Number, true, false);
} else {
Asm->OutStreamer.EmitIntValue(0, TD->getPointerSize(),
0/*addrspace*/);
}
}
EOL("Language Specific Data Area");
} else {
EmitULEB128(0, "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 (MAI->hasNoDeadStrip())
Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
MCSA_NoDeadStrip);
}
Asm->O << '\n';
}
/// 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;
}
/// CallToNoUnwindFunction - Return `true' if this is a call to a function
/// marked `nounwind'. Return `false' otherwise.
bool DwarfException::CallToNoUnwindFunction(const MachineInstr *MI) {
assert(MI->getDesc().isCall() && "This should be a call instruction!");
bool MarkedNoUnwind = false;
bool SawFunc = false;
for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
const MachineOperand &MO = MI->getOperand(I);
if (MO.isGlobal()) {
if (Function *F = dyn_cast<Function>(MO.getGlobal())) {
if (SawFunc) {
// Be conservative. If we have more than one function operand for this
// call, then we can't make the assumption that it's the callee and
// not a parameter to the call.
//
// FIXME: Determine if there's a way to say that `F' is the callee or
// parameter.
MarkedNoUnwind = false;
break;
}
MarkedNoUnwind = F->doesNotThrow();
SawFunc = true;
}
}
}
return MarkedNoUnwind;
}
/// 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()) {
if (MI->getDesc().isCall())
SawPotentiallyThrowing |= !CallToNoUnwindFunction(MI);
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::const_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.
if (MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf)
CallSites.push_back(Site);
else {
// SjLj EH must maintain the call sites in the order assigned
// to them by the SjLjPrepare pass.
unsigned SiteNo = MMI->getCallSiteBeginLabel(BeginLabel);
if (CallSites.size() < SiteNo)
CallSites.resize(SiteNo);
CallSites[SiteNo - 1] = 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);
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.
EmitEncodingByte(dwarf::DW_EH_PE_omit, "@LPStart");
EmitEncodingByte(TTypeFormat, "@TType");
if (HaveTTData)
EmitULEB128(TyOffset, "@TType base offset");
// SjLj Exception handling
if (IsSJLJ) {
EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
EmitULEB128(SizeSites, "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.
EmitULEB128(idx, "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.
EmitULEB128(S.Action, "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.
EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
EmitULEB128(SizeSites, "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);
EOL("Region start");
if (!S.EndLabel)
EmitDifference("eh_func_end", SubprogramCount, BeginTag, BeginNumber,
true);
else
EmitDifference("label", S.EndLabel, BeginTag, BeginNumber, true);
EOL("Region length");
// Offset of the landing pad, counted in 16-byte bundles relative to the
// @LPStart address.
if (!S.PadLabel)
Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
else
EmitSectionOffset("label", "eh_func_begin", S.PadLabel, SubprogramCount,
true, true);
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.
EmitULEB128(S.Action, "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.
EmitSLEB128(Action.ValueForTypeID, "TypeInfo index");
// Action Record
//
// Self-relative signed displacement in bytes of the next action record,
// or 0 if there is no next action record.
EmitSLEB128(Action.NextAction, "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->GetGlobalValueSymbol(GV);
else
O << "0x0";
EOL("TypeInfo");
}
// Emit the Exception Specifications.
for (std::vector<unsigned>::const_iterator
I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) {
unsigned TypeID = *I;
EmitULEB128(TypeID, TypeID != 0 ? "Exception specification" : 0);
}
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(const 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();
MCSymbol *FunctionEHSym =
Asm->GetSymbolWithGlobalValueBase(MF->getFunction(), ".eh",
Asm->MAI->is_EHSymbolPrivate());
// Save EH frame information
EHFrames.push_back(FunctionEHFrameInfo(FunctionEHSym, 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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