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

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//===- CodeGen/AsmPrinter/EHStreamer.cpp - Exception Directive Streamer ---===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file contains support for writing exception info into assembly files.
//
//===----------------------------------------------------------------------===//
#include "EHStreamer.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Twine.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/CodeGen/AsmPrinter.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Function.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCTargetOptions.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Target/TargetLoweringObjectFile.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <vector>
using namespace llvm;
EHStreamer::EHStreamer(AsmPrinter *A) : Asm(A), MMI(Asm->MMI) {}
EHStreamer::~EHStreamer() = default;
/// How many leading type ids two landing pads have in common.
unsigned EHStreamer::sharedTypeIDs(const LandingPadInfo *L,
const LandingPadInfo *R) {
const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
return std::mismatch(LIds.begin(), LIds.end(), RIds.begin(), RIds.end())
.first -
LIds.begin();
}
/// Compute the actions table and gather the first action index for each landing
/// pad site.
void EHStreamer::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 = Asm->MF->getFilterIds();
SmallVector<int, 16> FilterOffsets;
FilterOffsets.reserve(FilterIds.size());
int Offset = -1;
for (unsigned FilterId : FilterIds) {
FilterOffsets.push_back(Offset);
Offset -= getULEB128Size(FilterId);
}
FirstActions.reserve(LandingPads.size());
int FirstAction = 0;
unsigned SizeActions = 0; // Total size of all action entries for a function
const LandingPadInfo *PrevLPI = nullptr;
for (const LandingPadInfo *LPI : LandingPads) {
const std::vector<int> &TypeIds = LPI->TypeIds;
unsigned NumShared = PrevLPI ? sharedTypeIDs(LPI, PrevLPI) : 0;
unsigned SizeSiteActions = 0; // Total size of all entries for a landingpad
if (NumShared < TypeIds.size()) {
// Size of one action entry (typeid + next action)
unsigned SizeActionEntry = 0;
unsigned PrevAction = (unsigned)-1;
if (NumShared) {
unsigned SizePrevIds = PrevLPI->TypeIds.size();
assert(Actions.size());
PrevAction = Actions.size() - 1;
SizeActionEntry = getSLEB128Size(Actions[PrevAction].NextAction) +
getSLEB128Size(Actions[PrevAction].ValueForTypeID);
for (unsigned j = NumShared; j != SizePrevIds; ++j) {
assert(PrevAction != (unsigned)-1 && "PrevAction is invalid!");
SizeActionEntry -= getSLEB128Size(Actions[PrevAction].ValueForTypeID);
SizeActionEntry += -Actions[PrevAction].NextAction;
PrevAction = Actions[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 =
isFilterEHSelector(TypeID) ? FilterOffsets[-1 - TypeID] : TypeID;
unsigned SizeTypeID = getSLEB128Size(ValueForTypeID);
int NextAction = SizeActionEntry ? -(SizeActionEntry + SizeTypeID) : 0;
SizeActionEntry = SizeTypeID + getSLEB128Size(NextAction);
SizeSiteActions += SizeActionEntry;
ActionEntry Action = { ValueForTypeID, NextAction, PrevAction };
Actions.push_back(Action);
PrevAction = Actions.size() - 1;
}
// Record the first action of the landing pad site.
FirstAction = SizeActions + SizeSiteActions - SizeActionEntry + 1;
} // else identical - re-use previous FirstAction
// Information used when creating 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 indicating 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 `true' if this is a call to a function marked `nounwind'. Return
/// `false' otherwise.
bool EHStreamer::callToNoUnwindFunction(const MachineInstr *MI) {
assert(MI->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()) continue;
const Function *F = dyn_cast<Function>(MO.getGlobal());
if (!F) continue;
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;
}
void EHStreamer::computePadMap(
const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
RangeMapType &PadMap) {
// 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 so we can put them in the LSDA.
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) {
MCSymbol *BeginLabel = LandingPad->BeginLabels[j];
assert(!PadMap.count(BeginLabel) && "Duplicate landing pad labels!");
PadRange P = { i, j };
PadMap[BeginLabel] = P;
}
}
}
/// 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.
///
/// Call-sites are split into one or more call-site ranges associated with
/// different sections of the function.
///
/// - Without -basic-block-sections, all call-sites are grouped into one
/// call-site-range corresponding to the function section.
///
/// - With -basic-block-sections, one call-site range is created for each
/// section, with its FragmentBeginLabel and FragmentEndLabel respectively
// set to the beginning and ending of the corresponding section and its
// ExceptionLabel set to the exception symbol dedicated for this section.
// Later, one LSDA header will be emitted for each call-site range with its
// call-sites following. The action table and type info table will be
// shared across all ranges.
void EHStreamer::computeCallSiteTable(
SmallVectorImpl<CallSiteEntry> &CallSites,
SmallVectorImpl<CallSiteRange> &CallSiteRanges,
const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
const SmallVectorImpl<unsigned> &FirstActions) {
RangeMapType PadMap;
computePadMap(LandingPads, PadMap);
// The end label of the previous invoke or nounwind try-range.
MCSymbol *LastLabel = Asm->getFunctionBegin();
// 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;
bool IsSJLJ = Asm->MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
// Visit all instructions in order of address.
for (const auto &MBB : *Asm->MF) {
if (&MBB == &Asm->MF->front() || MBB.isBeginSection()) {
// We start a call-site range upon function entry and at the beginning of
// every basic block section.
CallSiteRanges.push_back(
{Asm->MBBSectionRanges[MBB.getSectionIDNum()].BeginLabel,
Asm->MBBSectionRanges[MBB.getSectionIDNum()].EndLabel,
Asm->getMBBExceptionSym(MBB), CallSites.size()});
PreviousIsInvoke = false;
SawPotentiallyThrowing = false;
LastLabel = nullptr;
}
if (MBB.isEHPad())
CallSiteRanges.back().IsLPRange = true;
for (const auto &MI : MBB) {
if (!MI.isEHLabel()) {
if (MI.isCall())
SawPotentiallyThrowing |= !callToNoUnwindFunction(&MI);
continue;
}
// End of the previous try-range?
MCSymbol *BeginLabel = MI.getOperand(0).getMCSymbol();
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 and AIX 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 &&
(Asm->MAI->usesCFIForEH() ||
Asm->MAI->getExceptionHandlingType() == ExceptionHandling::AIX)) {
CallSites.push_back({LastLabel, BeginLabel, nullptr, 0});
PreviousIsInvoke = false;
}
LastLabel = LandingPad->EndLabels[P.RangeIndex];
assert(BeginLabel && LastLabel && "Invalid landing pad!");
if (!LandingPad->LandingPadLabel) {
// Create a gap.
PreviousIsInvoke = false;
} else {
// This try-range is for an invoke.
CallSiteEntry Site = {
BeginLabel,
LastLabel,
LandingPad,
FirstActions[P.PadIndex]
};
// Try to merge with the previous call-site. SJLJ doesn't do this
if (PreviousIsInvoke && !IsSJLJ) {
CallSiteEntry &Prev = CallSites.back();
if (Site.LPad == Prev.LPad && Site.Action == Prev.Action) {
// Extend the range of the previous entry.
Prev.EndLabel = Site.EndLabel;
continue;
}
}
// Otherwise, create a new call-site.
if (!IsSJLJ)
CallSites.push_back(Site);
else {
// SjLj EH must maintain the call sites in the order assigned
// to them by the SjLjPrepare pass.
unsigned SiteNo = Asm->MF->getCallSiteBeginLabel(BeginLabel);
if (CallSites.size() < SiteNo)
CallSites.resize(SiteNo);
CallSites[SiteNo - 1] = Site;
}
PreviousIsInvoke = true;
}
}
// We end the call-site range upon function exit and at the end of every
// basic block section.
if (&MBB == &Asm->MF->back() || MBB.isEndSection()) {
// 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 && !IsSJLJ) {
CallSiteEntry Site = {LastLabel, CallSiteRanges.back().FragmentEndLabel,
nullptr, 0};
CallSites.push_back(Site);
SawPotentiallyThrowing = false;
}
CallSiteRanges.back().CallSiteEndIdx = CallSites.size();
}
}
}
/// 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.
///
/// Returns the starting symbol of an exception table.
MCSymbol *EHStreamer::emitExceptionTable() {
const MachineFunction *MF = Asm->MF;
const std::vector<const GlobalValue *> &TypeInfos = MF->getTypeInfos();
const std::vector<unsigned> &FilterIds = MF->getFilterIds();
const std::vector<LandingPadInfo> &PadInfos = MF->getLandingPads();
// 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]);
// Order landing pads lexicographically by type id.
llvm::sort(LandingPads, [](const LandingPadInfo *L, const LandingPadInfo *R) {
return L->TypeIds < R->TypeIds;
});
// Compute the actions table and gather the first action index for each
// landing pad site.
SmallVector<ActionEntry, 32> Actions;
SmallVector<unsigned, 64> FirstActions;
computeActionsTable(LandingPads, Actions, FirstActions);
// Compute the call-site table and call-site ranges. Normally, there is only
// one call-site-range which covers the whole funciton. With
// -basic-block-sections, there is one call-site-range per basic block
// section.
SmallVector<CallSiteEntry, 64> CallSites;
SmallVector<CallSiteRange, 4> CallSiteRanges;
computeCallSiteTable(CallSites, CallSiteRanges, LandingPads, FirstActions);
bool IsSJLJ = Asm->MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
bool IsWasm = Asm->MAI->getExceptionHandlingType() == ExceptionHandling::Wasm;
bool HasLEB128Directives = Asm->MAI->hasLEB128Directives();
unsigned CallSiteEncoding =
IsSJLJ ? static_cast<unsigned>(dwarf::DW_EH_PE_udata4) :
Asm->getObjFileLowering().getCallSiteEncoding();
bool HaveTTData = !TypeInfos.empty() || !FilterIds.empty();
// Type infos.
MCSection *LSDASection = Asm->getObjFileLowering().getSectionForLSDA(
MF->getFunction(), *Asm->CurrentFnSym, Asm->TM);
unsigned TTypeEncoding;
if (!HaveTTData) {
// If there is no TypeInfo, then we just explicitly say that we're omitting
// that bit.
TTypeEncoding = dwarf::DW_EH_PE_omit;
} 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.
//
TTypeEncoding = Asm->getObjFileLowering().getTTypeEncoding();
}
// Begin the exception table.
// Sometimes we want not to emit the data into separate section (e.g. ARM
// EHABI). In this case LSDASection will be NULL.
if (LSDASection)
Asm->OutStreamer->SwitchSection(LSDASection);
Asm->emitAlignment(Align(4));
// Emit the LSDA.
MCSymbol *GCCETSym =
Asm->OutContext.getOrCreateSymbol(Twine("GCC_except_table")+
Twine(Asm->getFunctionNumber()));
Asm->OutStreamer->emitLabel(GCCETSym);
MCSymbol *CstEndLabel = Asm->createTempSymbol(
CallSiteRanges.size() > 1 ? "action_table_base" : "cst_end");
MCSymbol *TTBaseLabel = nullptr;
if (HaveTTData)
TTBaseLabel = Asm->createTempSymbol("ttbase");
const bool VerboseAsm = Asm->OutStreamer->isVerboseAsm();
// Helper for emitting references (offsets) for type table and the end of the
// call-site table (which marks the beginning of the action table).
// * For Itanium, these references will be emitted for every callsite range.
// * For SJLJ and Wasm, they will be emitted only once in the LSDA header.
auto EmitTypeTableRefAndCallSiteTableEndRef = [&]() {
Asm->emitEncodingByte(TTypeEncoding, "@TType");
if (HaveTTData) {
// N.B.: There is a dependency loop between the size of the TTBase uleb128
// here and the amount of padding before the aligned type table. The
// assembler must sometimes pad this uleb128 or insert extra padding
// before the type table. See PR35809 or GNU as bug 4029.
MCSymbol *TTBaseRefLabel = Asm->createTempSymbol("ttbaseref");
Asm->emitLabelDifferenceAsULEB128(TTBaseLabel, TTBaseRefLabel);
Asm->OutStreamer->emitLabel(TTBaseRefLabel);
}
// The Action table follows the call-site table. So we emit the
// label difference from here (start of the call-site table for SJLJ and
// Wasm, and start of a call-site range for Itanium) to the end of the
// whole call-site table (end of the last call-site range for Itanium).
MCSymbol *CstBeginLabel = Asm->createTempSymbol("cst_begin");
Asm->emitEncodingByte(CallSiteEncoding, "Call site");
Asm->emitLabelDifferenceAsULEB128(CstEndLabel, CstBeginLabel);
Asm->OutStreamer->emitLabel(CstBeginLabel);
};
// An alternative path to EmitTypeTableRefAndCallSiteTableEndRef.
// For some platforms, the system assembler does not accept the form of
// `.uleb128 label2 - label1`. In those situations, we would need to calculate
// the size between label1 and label2 manually.
// In this case, we would need to calculate the LSDA size and the call
// site table size.
auto EmitTypeTableOffsetAndCallSiteTableOffset = [&]() {
assert(CallSiteEncoding == dwarf::DW_EH_PE_udata4 && !HasLEB128Directives &&
"Targets supporting .uleb128 do not need to take this path.");
if (CallSiteRanges.size() > 1)
report_fatal_error(
"-fbasic-block-sections is not yet supported on "
"platforms that do not have general LEB128 directive support.");
uint64_t CallSiteTableSize = 0;
const CallSiteRange &CSRange = CallSiteRanges.back();
for (size_t CallSiteIdx = CSRange.CallSiteBeginIdx;
CallSiteIdx < CSRange.CallSiteEndIdx; ++CallSiteIdx) {
const CallSiteEntry &S = CallSites[CallSiteIdx];
// Each call site entry consists of 3 udata4 fields (12 bytes) and
// 1 ULEB128 field.
CallSiteTableSize += 12 + getULEB128Size(S.Action);
assert(isUInt<32>(CallSiteTableSize) && "CallSiteTableSize overflows.");
}
Asm->emitEncodingByte(TTypeEncoding, "@TType");
if (HaveTTData) {
const unsigned ByteSizeOfCallSiteOffset =
getULEB128Size(CallSiteTableSize);
uint64_t ActionTableSize = 0;
for (const ActionEntry &Action : Actions) {
// Each action entry consists of two SLEB128 fields.
ActionTableSize += getSLEB128Size(Action.ValueForTypeID) +
getSLEB128Size(Action.NextAction);
assert(isUInt<32>(ActionTableSize) && "ActionTableSize overflows.");
}
const unsigned TypeInfoSize =
Asm->GetSizeOfEncodedValue(TTypeEncoding) * MF->getTypeInfos().size();
const uint64_t LSDASizeBeforeAlign =
1 // Call site encoding byte.
+ ByteSizeOfCallSiteOffset // ULEB128 encoding of CallSiteTableSize.
+ CallSiteTableSize // Call site table content.
+ ActionTableSize; // Action table content.
const uint64_t LSDASizeWithoutAlign = LSDASizeBeforeAlign + TypeInfoSize;
const unsigned ByteSizeOfLSDAWithoutAlign =
getULEB128Size(LSDASizeWithoutAlign);
const uint64_t DisplacementBeforeAlign =
2 // LPStartEncoding and TypeTableEncoding.
+ ByteSizeOfLSDAWithoutAlign + LSDASizeBeforeAlign;
// The type info area starts with 4 byte alignment.
const unsigned NeedAlignVal = (4 - DisplacementBeforeAlign % 4) % 4;
uint64_t LSDASizeWithAlign = LSDASizeWithoutAlign + NeedAlignVal;
const unsigned ByteSizeOfLSDAWithAlign =
getULEB128Size(LSDASizeWithAlign);
// The LSDASizeWithAlign could use 1 byte less padding for alignment
// when the data we use to represent the LSDA Size "needs" to be 1 byte
// larger than the one previously calculated without alignment.
if (ByteSizeOfLSDAWithAlign > ByteSizeOfLSDAWithoutAlign)
LSDASizeWithAlign -= 1;
Asm->OutStreamer->emitULEB128IntValue(LSDASizeWithAlign,
ByteSizeOfLSDAWithAlign);
}
Asm->emitEncodingByte(CallSiteEncoding, "Call site");
Asm->OutStreamer->emitULEB128IntValue(CallSiteTableSize);
};
// SjLj / Wasm Exception handling
if (IsSJLJ || IsWasm) {
Asm->OutStreamer->emitLabel(Asm->getMBBExceptionSym(Asm->MF->front()));
// emit the LSDA header.
Asm->emitEncodingByte(dwarf::DW_EH_PE_omit, "@LPStart");
EmitTypeTableRefAndCallSiteTableEndRef();
unsigned idx = 0;
for (SmallVectorImpl<CallSiteEntry>::const_iterator
I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) {
const CallSiteEntry &S = *I;
// Index of the call site entry.
if (VerboseAsm) {
Asm->OutStreamer->AddComment(">> Call Site " + Twine(idx) + " <<");
Asm->OutStreamer->AddComment(" On exception at call site "+Twine(idx));
}
Asm->emitULEB128(idx);
// 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.
if (VerboseAsm) {
if (S.Action == 0)
Asm->OutStreamer->AddComment(" Action: cleanup");
else
Asm->OutStreamer->AddComment(" Action: " +
Twine((S.Action - 1) / 2 + 1));
}
Asm->emitULEB128(S.Action);
}
Asm->OutStreamer->emitLabel(CstEndLabel);
} else {
// Itanium LSDA exception handling
// 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.
assert(CallSiteRanges.size() != 0 && "No call-site ranges!");
// There should be only one call-site range which includes all the landing
// pads. Find that call-site range here.
const CallSiteRange *LandingPadRange = nullptr;
for (const CallSiteRange &CSRange : CallSiteRanges) {
if (CSRange.IsLPRange) {
assert(LandingPadRange == nullptr &&
"All landing pads must be in a single callsite range.");
LandingPadRange = &CSRange;
}
}
// The call-site table is split into its call-site ranges, each being
// emitted as:
// [ LPStartEncoding | LPStart ]
// [ TypeTableEncoding | TypeTableOffset ]
// [ CallSiteEncoding | CallSiteTableEndOffset ]
// cst_begin -> { call-site entries contained in this range }
//
// and is followed by the next call-site range.
//
// For each call-site range, CallSiteTableEndOffset is computed as the
// difference between cst_begin of that range and the last call-site-table's
// end label. This offset is used to find the action table.
unsigned Entry = 0;
for (const CallSiteRange &CSRange : CallSiteRanges) {
if (CSRange.CallSiteBeginIdx != 0) {
// Align the call-site range for all ranges except the first. The
// first range is already aligned due to the exception table alignment.
Asm->emitAlignment(Align(4));
}
Asm->OutStreamer->emitLabel(CSRange.ExceptionLabel);
// Emit the LSDA header.
// If only one call-site range exists, LPStart is omitted as it is the
// same as the function entry.
if (CallSiteRanges.size() == 1) {
Asm->emitEncodingByte(dwarf::DW_EH_PE_omit, "@LPStart");
} else if (!Asm->isPositionIndependent()) {
// For more than one call-site ranges, LPStart must be explicitly
// specified.
// For non-PIC we can simply use the absolute value.
Asm->emitEncodingByte(dwarf::DW_EH_PE_absptr, "@LPStart");
Asm->OutStreamer->emitSymbolValue(LandingPadRange->FragmentBeginLabel,
Asm->MAI->getCodePointerSize());
} else {
// For PIC mode, we Emit a PC-relative address for LPStart.
Asm->emitEncodingByte(dwarf::DW_EH_PE_pcrel, "@LPStart");
MCContext &Context = Asm->OutStreamer->getContext();
MCSymbol *Dot = Context.createTempSymbol();
Asm->OutStreamer->emitLabel(Dot);
Asm->OutStreamer->emitValue(
MCBinaryExpr::createSub(
MCSymbolRefExpr::create(LandingPadRange->FragmentBeginLabel,
Context),
MCSymbolRefExpr::create(Dot, Context), Context),
Asm->MAI->getCodePointerSize());
}
if (HasLEB128Directives)
EmitTypeTableRefAndCallSiteTableEndRef();
else
EmitTypeTableOffsetAndCallSiteTableOffset();
for (size_t CallSiteIdx = CSRange.CallSiteBeginIdx;
CallSiteIdx != CSRange.CallSiteEndIdx; ++CallSiteIdx) {
const CallSiteEntry &S = CallSites[CallSiteIdx];
MCSymbol *EHFuncBeginSym = CSRange.FragmentBeginLabel;
MCSymbol *EHFuncEndSym = CSRange.FragmentEndLabel;
MCSymbol *BeginLabel = S.BeginLabel;
if (!BeginLabel)
BeginLabel = EHFuncBeginSym;
MCSymbol *EndLabel = S.EndLabel;
if (!EndLabel)
EndLabel = EHFuncEndSym;
// Offset of the call site relative to the start of the procedure.
if (VerboseAsm)
Asm->OutStreamer->AddComment(">> Call Site " + Twine(++Entry) +
" <<");
Asm->emitCallSiteOffset(BeginLabel, EHFuncBeginSym, CallSiteEncoding);
if (VerboseAsm)
Asm->OutStreamer->AddComment(Twine(" Call between ") +
BeginLabel->getName() + " and " +
EndLabel->getName());
Asm->emitCallSiteOffset(EndLabel, BeginLabel, CallSiteEncoding);
// Offset of the landing pad relative to the start of the landing pad
// fragment.
if (!S.LPad) {
if (VerboseAsm)
Asm->OutStreamer->AddComment(" has no landing pad");
Asm->emitCallSiteValue(0, CallSiteEncoding);
} else {
if (VerboseAsm)
Asm->OutStreamer->AddComment(Twine(" jumps to ") +
S.LPad->LandingPadLabel->getName());
Asm->emitCallSiteOffset(S.LPad->LandingPadLabel,
LandingPadRange->FragmentBeginLabel,
CallSiteEncoding);
}
// 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.
if (VerboseAsm) {
if (S.Action == 0)
Asm->OutStreamer->AddComment(" On action: cleanup");
else
Asm->OutStreamer->AddComment(" On action: " +
Twine((S.Action - 1) / 2 + 1));
}
Asm->emitULEB128(S.Action);
}
}
Asm->OutStreamer->emitLabel(CstEndLabel);
}
// Emit the Action Table.
int Entry = 0;
for (const ActionEntry &Action : Actions) {
if (VerboseAsm) {
// Emit comments that decode the action table.
Asm->OutStreamer->AddComment(">> Action Record " + Twine(++Entry) + " <<");
}
// 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.
if (VerboseAsm) {
if (Action.ValueForTypeID > 0)
Asm->OutStreamer->AddComment(" Catch TypeInfo " +
Twine(Action.ValueForTypeID));
else if (Action.ValueForTypeID < 0)
Asm->OutStreamer->AddComment(" Filter TypeInfo " +
Twine(Action.ValueForTypeID));
else
Asm->OutStreamer->AddComment(" Cleanup");
}
Asm->emitSLEB128(Action.ValueForTypeID);
// Action Record
if (VerboseAsm) {
if (Action.Previous == unsigned(-1)) {
Asm->OutStreamer->AddComment(" No further actions");
} else {
Asm->OutStreamer->AddComment(" Continue to action " +
Twine(Action.Previous + 1));
}
}
Asm->emitSLEB128(Action.NextAction);
}
if (HaveTTData) {
Asm->emitAlignment(Align(4));
emitTypeInfos(TTypeEncoding, TTBaseLabel);
}
Asm->emitAlignment(Align(4));
return GCCETSym;
}
void EHStreamer::emitTypeInfos(unsigned TTypeEncoding, MCSymbol *TTBaseLabel) {
const MachineFunction *MF = Asm->MF;
const std::vector<const GlobalValue *> &TypeInfos = MF->getTypeInfos();
const std::vector<unsigned> &FilterIds = MF->getFilterIds();
const bool VerboseAsm = Asm->OutStreamer->isVerboseAsm();
int Entry = 0;
// Emit the Catch TypeInfos.
if (VerboseAsm && !TypeInfos.empty()) {
Asm->OutStreamer->AddComment(">> Catch TypeInfos <<");
Asm->OutStreamer->AddBlankLine();
Entry = TypeInfos.size();
}
for (const GlobalValue *GV : llvm::reverse(TypeInfos)) {
if (VerboseAsm)
Asm->OutStreamer->AddComment("TypeInfo " + Twine(Entry--));
Asm->emitTTypeReference(GV, TTypeEncoding);
}
Asm->OutStreamer->emitLabel(TTBaseLabel);
// Emit the Exception Specifications.
if (VerboseAsm && !FilterIds.empty()) {
Asm->OutStreamer->AddComment(">> Filter TypeInfos <<");
Asm->OutStreamer->AddBlankLine();
Entry = 0;
}
for (std::vector<unsigned>::const_iterator
I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) {
unsigned TypeID = *I;
if (VerboseAsm) {
--Entry;
if (isFilterEHSelector(TypeID))
Asm->OutStreamer->AddComment("FilterInfo " + Twine(Entry));
}
Asm->emitULEB128(TypeID);
}
}
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