LLVM  15.0.0git
WasmException.cpp
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1 //===-- CodeGen/AsmPrinter/WasmException.cpp - Wasm Exception Impl --------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file contains support for writing WebAssembly exception info into asm
10 // files.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "WasmException.h"
17 #include "llvm/IR/Mangler.h"
18 #include "llvm/MC/MCContext.h"
19 #include "llvm/MC/MCStreamer.h"
20 using namespace llvm;
21 
23  // These are symbols used to throw/catch C++ exceptions and C longjmps. These
24  // symbols have to be emitted somewhere once in the module. Check if each of
25  // the symbols has already been created, i.e., we have at least one 'throw' or
26  // 'catch' instruction with the symbol in the module, and emit the symbol only
27  // if so.
28  //
29  // But in dynamic linking, it is in general not possible to come up with a
30  // module instantiating order in which tag-defining modules are loaded before
31  // the importing modules. So we make them undefined symbols here, define tags
32  // in the JS side, and feed them to each importing module.
33  if (!Asm->isPositionIndependent()) {
34  for (const char *SymName : {"__cpp_exception", "__c_longjmp"}) {
35  SmallString<60> NameStr;
36  Mangler::getNameWithPrefix(NameStr, SymName, Asm->getDataLayout());
37  if (Asm->OutContext.lookupSymbol(NameStr)) {
38  MCSymbol *ExceptionSym = Asm->GetExternalSymbolSymbol(SymName);
39  Asm->OutStreamer->emitLabel(ExceptionSym);
40  }
41  }
42  }
43 }
44 
46  // Get rid of any dead landing pads.
47  if (!Asm->MF->getLandingPads().empty()) {
48  auto *NonConstMF = const_cast<MachineFunction *>(Asm->MF);
49  // Wasm does not set BeginLabel and EndLabel information for landing pads,
50  // so we should set the second argument false.
51  NonConstMF->tidyLandingPads(nullptr, /* TidyIfNoBeginLabels */ false);
52  }
53 }
54 
56  bool ShouldEmitExceptionTable = false;
57  for (const LandingPadInfo &Info : MF->getLandingPads()) {
58  if (MF->hasWasmLandingPadIndex(Info.LandingPadBlock)) {
59  ShouldEmitExceptionTable = true;
60  break;
61  }
62  }
63  if (!ShouldEmitExceptionTable)
64  return;
65  MCSymbol *LSDALabel = emitExceptionTable();
66  assert(LSDALabel && ".GCC_exception_table has not been emitted!");
67 
68  // Wasm requires every data section symbol to have a .size set. So we emit an
69  // end marker and set the size as the difference between the start end the end
70  // marker.
71  MCSymbol *LSDAEndLabel = Asm->createTempSymbol("GCC_except_table_end");
72  Asm->OutStreamer->emitLabel(LSDAEndLabel);
73  MCContext &OutContext = Asm->OutStreamer->getContext();
74  const MCExpr *SizeExp = MCBinaryExpr::createSub(
75  MCSymbolRefExpr::create(LSDAEndLabel, OutContext),
76  MCSymbolRefExpr::create(LSDALabel, OutContext), OutContext);
77  Asm->OutStreamer->emitELFSize(LSDALabel, SizeExp);
78 }
79 
80 // Compute the call-site table for wasm EH. Even though we use the same function
81 // name to share the common routines, a call site entry in the table corresponds
82 // to not a call site for possibly-throwing functions but a landing pad. In wasm
83 // EH the VM is responsible for stack unwinding. After an exception occurs and
84 // the stack is unwound, the control flow is transferred to wasm 'catch'
85 // instruction by the VM, after which the personality function is called from
86 // the compiler-generated code. Refer to WasmEHPrepare pass for more
87 // information.
90  SmallVectorImpl<CallSiteRange> &CallSiteRanges,
91  const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
92  const SmallVectorImpl<unsigned> &FirstActions) {
93  MachineFunction &MF = *Asm->MF;
94  for (unsigned I = 0, N = LandingPads.size(); I < N; ++I) {
95  const LandingPadInfo *Info = LandingPads[I];
96  MachineBasicBlock *LPad = Info->LandingPadBlock;
97  // We don't emit LSDA for single catch (...).
98  if (!MF.hasWasmLandingPadIndex(LPad))
99  continue;
100  // Wasm EH must maintain the EH pads in the order assigned to them by the
101  // WasmEHPrepare pass.
102  unsigned LPadIndex = MF.getWasmLandingPadIndex(LPad);
103  CallSiteEntry Site = {nullptr, nullptr, Info, FirstActions[I]};
104  if (CallSites.size() < LPadIndex + 1)
105  CallSites.resize(LPadIndex + 1);
106  CallSites[LPadIndex] = Site;
107  }
108 }
AsmPrinter.h
llvm::AsmPrinter::isPositionIndependent
bool isPositionIndependent() const
Definition: AsmPrinter.cpp:373
llvm
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:17
llvm::MCSymbol
MCSymbol - Instances of this class represent a symbol name in the MC file, and MCSymbols are created ...
Definition: MCSymbol.h:41
llvm::AsmPrinter::createTempSymbol
MCSymbol * createTempSymbol(const Twine &Name) const
Definition: AsmPrinter.cpp:3316
llvm::MCContext
Context object for machine code objects.
Definition: MCContext.h:74
llvm::MCContext::lookupSymbol
MCSymbol * lookupSymbol(const Twine &Name) const
Get the symbol for Name, or null.
Definition: MCContext.cpp:362
llvm::WasmException::computeCallSiteTable
void computeCallSiteTable(SmallVectorImpl< CallSiteEntry > &CallSites, SmallVectorImpl< CallSiteRange > &CallSiteRanges, const SmallVectorImpl< const LandingPadInfo * > &LandingPads, const SmallVectorImpl< unsigned > &FirstActions) override
Compute the call-site table and the call-site ranges.
Definition: WasmException.cpp:88
WasmException.h
llvm::AsmPrinter::OutStreamer
std::unique_ptr< MCStreamer > OutStreamer
This is the MCStreamer object for the file we are generating.
Definition: AsmPrinter.h:96
MCContext.h
llvm::EHStreamer::emitExceptionTable
MCSymbol * emitExceptionTable()
Emit landing pads and actions.
Definition: EHStreamer.cpp:375
llvm::Mangler::getNameWithPrefix
void getNameWithPrefix(raw_ostream &OS, const GlobalValue *GV, bool CannotUsePrivateLabel) const
Print the appropriate prefix and the specified global variable's name.
Definition: Mangler.cpp:119
llvm::SmallVectorImpl::resize
void resize(size_type N)
Definition: SmallVector.h:619
Info
Analysis containing CSE Info
Definition: CSEInfo.cpp:27
llvm::MachineFunction::tidyLandingPads
void tidyLandingPads(DenseMap< MCSymbol *, uintptr_t > *LPMap=nullptr, bool TidyIfNoBeginLabels=true)
Remap landing pad labels and remove any deleted landing pads.
Definition: MachineFunction.cpp:810
llvm::MachineBasicBlock
Definition: MachineBasicBlock.h:94
llvm::SmallString
SmallString - A SmallString is just a SmallVector with methods and accessors that make it work better...
Definition: SmallString.h:26
llvm::WasmException::endModule
void endModule() override
Emit all sections that should come after the content.
Definition: WasmException.cpp:22
I
#define I(x, y, z)
Definition: MD5.cpp:58
assert
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
llvm::MCBinaryExpr::createSub
static const MCBinaryExpr * createSub(const MCExpr *LHS, const MCExpr *RHS, MCContext &Ctx)
Definition: MCExpr.h:610
llvm::AsmPrinter::MF
MachineFunction * MF
The current machine function.
Definition: AsmPrinter.h:99
llvm::MachineFunction::getLandingPads
const std::vector< LandingPadInfo > & getLandingPads() const
Return a reference to the landing pad info for the current function.
Definition: MachineFunction.h:1078
llvm::AsmPrinter::OutContext
MCContext & OutContext
This is the context for the output file that we are streaming.
Definition: AsmPrinter.h:91
llvm::WasmException::markFunctionEnd
virtual void markFunctionEnd() override
Definition: WasmException.cpp:45
llvm::MachineFunction
Definition: MachineFunction.h:241
Mangler.h
llvm::AsmPrinter::GetExternalSymbolSymbol
MCSymbol * GetExternalSymbolSymbol(StringRef Sym) const
Return the MCSymbol for the specified ExternalSymbol.
Definition: AsmPrinter.cpp:3377
llvm::EHStreamer::CallSiteEntry
Structure describing an entry in the call-site table.
Definition: EHStreamer.h:61
llvm::EHStreamer::Asm
AsmPrinter * Asm
Target of directive emission.
Definition: EHStreamer.h:33
llvm::MCSymbolRefExpr::create
static const MCSymbolRefExpr * create(const MCSymbol *Symbol, MCContext &Ctx)
Definition: MCExpr.h:386
llvm::MachineFunction::hasWasmLandingPadIndex
bool hasWasmLandingPadIndex(const MachineBasicBlock *LPad) const
Returns true if the landing pad has an associate index in wasm EH.
Definition: MachineFunction.h:1129
N
#define N
MCStreamer.h
llvm::WasmException::endFunction
void endFunction(const MachineFunction *MF) override
Gather post-function debug information.
Definition: WasmException.cpp:55
llvm::AsmPrinter::getDataLayout
const DataLayout & getDataLayout() const
Return information about data layout.
Definition: AsmPrinter.cpp:386
llvm::SmallVectorImpl
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: APFloat.h:42
llvm::LandingPadInfo
This structure is used to retain landing pad info for the current function.
Definition: MachineFunction.h:229
llvm::MachineFunction::getWasmLandingPadIndex
unsigned getWasmLandingPadIndex(const MachineBasicBlock *LPad) const
Get the index in wasm EH for a given landing pad.
Definition: MachineFunction.h:1134
MachineFunction.h
llvm::MCExpr
Base class for the full range of assembler expressions which are needed for parsing.
Definition: MCExpr.h:35