Reland "[WebAssembly] LSDA info generation"
Summary:
This adds support for LSDA (exception table) generation for wasm EH.
Wasm EH mostly follows the structure of Itanium-style exception tables,
with one exception: a call site table entry in wasm EH corresponds to
not a call site but a landing pad.
In wasm EH, the VM is responsible for stack unwinding. After an
exception occurs and the stack is unwound, the control flow is
transferred to wasm 'catch' instruction by the VM, after which the
personality function is called from the compiler-generated code. (Refer
to WasmEHPrepare pass for more information on this part.)
This patch:
- Changes wasm.landingpad.index intrinsic to take a token argument, to
make this 1:1 match with a catchpad instruction
- Stores landingpad index info and catch type info MachineFunction in
before instruction selection
- Lowers wasm.lsda intrinsic to an MCSymbol pointing to the start of an
exception table
- Adds WasmException class with overridden methods for table generation
- Adds support for LSDA section in Wasm object writer
Reviewers: dschuff, sbc100, rnk
Subscribers: mgorny, jgravelle-google, sunfish, llvm-commits
Differential Revision: https://reviews.llvm.org/D52748
llvm-svn: 345345
diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 63c5b26..526f7ce 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -16,6 +16,7 @@
#include "CodeViewDebug.h"
#include "DwarfDebug.h"
#include "DwarfException.h"
+#include "WasmException.h"
#include "WinCFGuard.h"
#include "WinException.h"
#include "llvm/ADT/APFloat.h"
@@ -356,7 +357,7 @@
}
break;
case ExceptionHandling::Wasm:
- // TODO to prevent warning
+ ES = new WasmException(this);
break;
}
if (ES)
diff --git a/llvm/lib/CodeGen/AsmPrinter/CMakeLists.txt b/llvm/lib/CodeGen/AsmPrinter/CMakeLists.txt
index 6cba4a0..3fb088a 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CMakeLists.txt
+++ b/llvm/lib/CodeGen/AsmPrinter/CMakeLists.txt
@@ -23,6 +23,7 @@
WinCFGuard.cpp
WinException.cpp
CodeViewDebug.cpp
+ WasmException.cpp
DEPENDS
intrinsics_gen
diff --git a/llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp b/llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp
index be04b9a..7599121 100644
--- a/llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp
@@ -345,7 +345,9 @@
/// 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 EHStreamer::emitExceptionTable() {
+///
+/// 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();
@@ -375,6 +377,7 @@
computeCallSiteTable(CallSites, LandingPads, FirstActions);
bool IsSJLJ = Asm->MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
+ bool IsWasm = Asm->MAI->getExceptionHandlingType() == ExceptionHandling::Wasm;
unsigned CallSiteEncoding =
IsSJLJ ? dwarf::DW_EH_PE_udata4 : dwarf::DW_EH_PE_uleb128;
bool HaveTTData = !TypeInfos.empty() || !FilterIds.empty();
@@ -457,8 +460,8 @@
Asm->EmitLabelDifferenceAsULEB128(CstEndLabel, CstBeginLabel);
Asm->OutStreamer->EmitLabel(CstBeginLabel);
- // SjLj Exception handling
- if (IsSJLJ) {
+ // SjLj / Wasm Exception handling
+ if (IsSJLJ || IsWasm) {
unsigned idx = 0;
for (SmallVectorImpl<CallSiteEntry>::const_iterator
I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) {
@@ -604,6 +607,7 @@
}
Asm->EmitAlignment(2);
+ return GCCETSym;
}
void EHStreamer::emitTypeInfos(unsigned TTypeEncoding, MCSymbol *TTBaseLabel) {
diff --git a/llvm/lib/CodeGen/AsmPrinter/EHStreamer.h b/llvm/lib/CodeGen/AsmPrinter/EHStreamer.h
index b89421a..e3a6f8e9 100644
--- a/llvm/lib/CodeGen/AsmPrinter/EHStreamer.h
+++ b/llvm/lib/CodeGen/AsmPrinter/EHStreamer.h
@@ -85,9 +85,10 @@
/// 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 computeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
- const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
- const SmallVectorImpl<unsigned> &FirstActions);
+ virtual void computeCallSiteTable(
+ SmallVectorImpl<CallSiteEntry> &CallSites,
+ const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
+ const SmallVectorImpl<unsigned> &FirstActions);
/// Emit landing pads and actions.
///
@@ -108,7 +109,9 @@
/// found 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 reversed indexed base 1.
- void emitExceptionTable();
+ ///
+ /// Returns the starting symbol of an exception table.
+ MCSymbol *emitExceptionTable();
virtual void emitTypeInfos(unsigned TTypeEncoding, MCSymbol *TTBaseLabel);
diff --git a/llvm/lib/CodeGen/AsmPrinter/WasmException.cpp b/llvm/lib/CodeGen/AsmPrinter/WasmException.cpp
new file mode 100644
index 0000000..46745d0
--- /dev/null
+++ b/llvm/lib/CodeGen/AsmPrinter/WasmException.cpp
@@ -0,0 +1,81 @@
+//===-- CodeGen/AsmPrinter/WasmException.cpp - Wasm 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 WebAssembly exception info into asm
+// files.
+//
+//===----------------------------------------------------------------------===//
+
+#include "WasmException.h"
+#include "llvm/MC/MCStreamer.h"
+using namespace llvm;
+
+void WasmException::markFunctionEnd() {
+ // Get rid of any dead landing pads.
+ if (!Asm->MF->getLandingPads().empty()) {
+ auto *NonConstMF = const_cast<MachineFunction *>(Asm->MF);
+ // Wasm does not set BeginLabel and EndLabel information for landing pads,
+ // so we should set the second argument false.
+ NonConstMF->tidyLandingPads(nullptr, /* TidyIfNoBeginLabels */ false);
+ }
+}
+
+void WasmException::endFunction(const MachineFunction *MF) {
+ bool ShouldEmitExceptionTable = false;
+ for (const LandingPadInfo &Info : MF->getLandingPads()) {
+ if (MF->hasWasmLandingPadIndex(Info.LandingPadBlock)) {
+ ShouldEmitExceptionTable = true;
+ break;
+ }
+ }
+ if (!ShouldEmitExceptionTable)
+ return;
+ MCSymbol *LSDALabel = emitExceptionTable();
+ assert(LSDALabel && ".GCC_exception_table has not been emitted!");
+
+ // Wasm requires every data section symbol to have a .size set. So we emit an
+ // end marker and set the size as the difference between the start end the end
+ // marker.
+ MCSymbol *LSDAEndLabel = Asm->createTempSymbol("GCC_except_table_end");
+ Asm->OutStreamer->EmitLabel(LSDAEndLabel);
+ MCContext &OutContext = Asm->OutStreamer->getContext();
+ const MCExpr *SizeExp = MCBinaryExpr::createSub(
+ MCSymbolRefExpr::create(LSDAEndLabel, OutContext),
+ MCSymbolRefExpr::create(LSDALabel, OutContext), OutContext);
+ Asm->OutStreamer->emitELFSize(LSDALabel, SizeExp);
+}
+
+// Compute the call-site table for wasm EH. Even though we use the same function
+// name to share the common routines, a call site entry in the table corresponds
+// to not a call site for possibly-throwing functions but a landing pad. In wasm
+// EH the VM is responsible for stack unwinding. After an exception occurs and
+// the stack is unwound, the control flow is transferred to wasm 'catch'
+// instruction by the VM, after which the personality function is called from
+// the compiler-generated code. Refer to WasmEHPrepare pass for more
+// information.
+void WasmException::computeCallSiteTable(
+ SmallVectorImpl<CallSiteEntry> &CallSites,
+ const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
+ const SmallVectorImpl<unsigned> &FirstActions) {
+ MachineFunction &MF = *Asm->MF;
+ for (unsigned I = 0, N = LandingPads.size(); I < N; ++I) {
+ const LandingPadInfo *Info = LandingPads[I];
+ MachineBasicBlock *LPad = Info->LandingPadBlock;
+ // We don't emit LSDA for single catch (...).
+ if (!MF.hasWasmLandingPadIndex(LPad))
+ continue;
+ // Wasm EH must maintain the EH pads in the order assigned to them by the
+ // WasmEHPrepare pass.
+ unsigned LPadIndex = MF.getWasmLandingPadIndex(LPad);
+ CallSiteEntry Site = {nullptr, nullptr, Info, FirstActions[I]};
+ if (CallSites.size() < LPadIndex + 1)
+ CallSites.resize(LPadIndex + 1);
+ CallSites[LPadIndex] = Site;
+ }
+}
diff --git a/llvm/lib/CodeGen/AsmPrinter/WasmException.h b/llvm/lib/CodeGen/AsmPrinter/WasmException.h
new file mode 100644
index 0000000..09a9a25
--- /dev/null
+++ b/llvm/lib/CodeGen/AsmPrinter/WasmException.h
@@ -0,0 +1,42 @@
+//===-- WasmException.h - Wasm Exception Framework -------------*- C++ -*--===//
+//
+// 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 WebAssembly exception info into asm
+// files.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_CODEGEN_ASMPRINTER_WASMEXCEPTION_H
+#define LLVM_LIB_CODEGEN_ASMPRINTER_WASMEXCEPTION_H
+
+#include "EHStreamer.h"
+#include "llvm/CodeGen/AsmPrinter.h"
+
+namespace llvm {
+
+class LLVM_LIBRARY_VISIBILITY WasmException : public EHStreamer {
+public:
+ WasmException(AsmPrinter *A) : EHStreamer(A) {}
+
+ void endModule() override {}
+ void beginFunction(const MachineFunction *MF) override {}
+ virtual void markFunctionEnd() override;
+ void endFunction(const MachineFunction *MF) override;
+
+protected:
+ // Compute the call site table for wasm EH.
+ void computeCallSiteTable(
+ SmallVectorImpl<CallSiteEntry> &CallSites,
+ const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
+ const SmallVectorImpl<unsigned> &FirstActions) override;
+};
+
+} // End of namespace llvm
+
+#endif