1 //===- OcamlGCPrinter.cpp - Ocaml frametable emitter ----------------------===// 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 implements printing the assembly code for an Ocaml frametable. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "llvm/ADT/STLExtras.h" 14 #include "llvm/ADT/SmallString.h" 15 #include "llvm/ADT/Twine.h" 16 #include "llvm/CodeGen/AsmPrinter.h" 17 #include "llvm/CodeGen/GCMetadata.h" 18 #include "llvm/CodeGen/GCMetadataPrinter.h" 19 #include "llvm/IR/BuiltinGCs.h" 20 #include "llvm/IR/DataLayout.h" 21 #include "llvm/IR/Function.h" 22 #include "llvm/IR/Mangler.h" 23 #include "llvm/IR/Module.h" 24 #include "llvm/MC/MCContext.h" 25 #include "llvm/MC/MCDirectives.h" 26 #include "llvm/MC/MCStreamer.h" 27 #include "llvm/Support/ErrorHandling.h" 28 #include "llvm/Target/TargetLoweringObjectFile.h" 29 #include <cctype> 30 #include <cstddef> 31 #include <cstdint> 32 #include <string> 33 34 using namespace llvm; 35 36 namespace { 37 38 class OcamlGCMetadataPrinter : public GCMetadataPrinter { 39 public: 40 void beginAssembly(Module &M, GCModuleInfo &Info, AsmPrinter &AP) override; 41 void finishAssembly(Module &M, GCModuleInfo &Info, AsmPrinter &AP) override; 42 }; 43 44 } // end anonymous namespace 45 46 static GCMetadataPrinterRegistry::Add<OcamlGCMetadataPrinter> 47 Y("ocaml", "ocaml 3.10-compatible collector"); 48 49 void llvm::linkOcamlGCPrinter() {} 50 51 static void EmitCamlGlobal(const Module &M, AsmPrinter &AP, const char *Id) { 52 const std::string &MId = M.getModuleIdentifier(); 53 54 std::string SymName; 55 SymName += "caml"; 56 size_t Letter = SymName.size(); 57 SymName.append(MId.begin(), llvm::find(MId, '.')); 58 SymName += "__"; 59 SymName += Id; 60 61 // Capitalize the first letter of the module name. 62 SymName[Letter] = toupper(SymName[Letter]); 63 64 SmallString<128> TmpStr; 65 Mangler::getNameWithPrefix(TmpStr, SymName, M.getDataLayout()); 66 67 MCSymbol *Sym = AP.OutContext.getOrCreateSymbol(TmpStr); 68 69 AP.OutStreamer->emitSymbolAttribute(Sym, MCSA_Global); 70 AP.OutStreamer->emitLabel(Sym); 71 } 72 73 void OcamlGCMetadataPrinter::beginAssembly(Module &M, GCModuleInfo &Info, 74 AsmPrinter &AP) { 75 AP.OutStreamer->switchSection(AP.getObjFileLowering().getTextSection()); 76 EmitCamlGlobal(M, AP, "code_begin"); 77 78 AP.OutStreamer->switchSection(AP.getObjFileLowering().getDataSection()); 79 EmitCamlGlobal(M, AP, "data_begin"); 80 } 81 82 /// emitAssembly - Print the frametable. The ocaml frametable format is thus: 83 /// 84 /// extern "C" struct align(sizeof(intptr_t)) { 85 /// uint16_t NumDescriptors; 86 /// struct align(sizeof(intptr_t)) { 87 /// void *ReturnAddress; 88 /// uint16_t FrameSize; 89 /// uint16_t NumLiveOffsets; 90 /// uint16_t LiveOffsets[NumLiveOffsets]; 91 /// } Descriptors[NumDescriptors]; 92 /// } caml${module}__frametable; 93 /// 94 /// Note that this precludes programs from stack frames larger than 64K 95 /// (FrameSize and LiveOffsets would overflow). FrameTablePrinter will abort if 96 /// either condition is detected in a function which uses the GC. 97 /// 98 void OcamlGCMetadataPrinter::finishAssembly(Module &M, GCModuleInfo &Info, 99 AsmPrinter &AP) { 100 unsigned IntPtrSize = M.getDataLayout().getPointerSize(); 101 102 AP.OutStreamer->switchSection(AP.getObjFileLowering().getTextSection()); 103 EmitCamlGlobal(M, AP, "code_end"); 104 105 AP.OutStreamer->switchSection(AP.getObjFileLowering().getDataSection()); 106 EmitCamlGlobal(M, AP, "data_end"); 107 108 // FIXME: Why does ocaml emit this?? 109 AP.OutStreamer->emitIntValue(0, IntPtrSize); 110 111 AP.OutStreamer->switchSection(AP.getObjFileLowering().getDataSection()); 112 EmitCamlGlobal(M, AP, "frametable"); 113 114 int NumDescriptors = 0; 115 for (std::unique_ptr<GCFunctionInfo> &FI : 116 llvm::make_range(Info.funcinfo_begin(), Info.funcinfo_end())) { 117 if (FI->getStrategy().getName() != getStrategy().getName()) 118 // this function is managed by some other GC 119 continue; 120 NumDescriptors += FI->size(); 121 } 122 123 if (NumDescriptors >= 1 << 16) { 124 // Very rude! 125 report_fatal_error(" Too much descriptor for ocaml GC"); 126 } 127 AP.emitInt16(NumDescriptors); 128 AP.emitAlignment(IntPtrSize == 4 ? Align(4) : Align(8)); 129 130 for (std::unique_ptr<GCFunctionInfo> &FI : 131 llvm::make_range(Info.funcinfo_begin(), Info.funcinfo_end())) { 132 if (FI->getStrategy().getName() != getStrategy().getName()) 133 // this function is managed by some other GC 134 continue; 135 136 uint64_t FrameSize = FI->getFrameSize(); 137 if (FrameSize >= 1 << 16) { 138 // Very rude! 139 report_fatal_error("Function '" + FI->getFunction().getName() + 140 "' is too large for the ocaml GC! " 141 "Frame size " + 142 Twine(FrameSize) + 143 ">= 65536.\n" 144 "(" + 145 Twine(reinterpret_cast<uintptr_t>(FI.get())) + ")"); 146 } 147 148 AP.OutStreamer->AddComment("live roots for " + 149 Twine(FI->getFunction().getName())); 150 AP.OutStreamer->addBlankLine(); 151 152 for (GCFunctionInfo::iterator J = FI->begin(), JE = FI->end(); J != JE; 153 ++J) { 154 size_t LiveCount = FI->live_size(J); 155 if (LiveCount >= 1 << 16) { 156 // Very rude! 157 report_fatal_error("Function '" + FI->getFunction().getName() + 158 "' is too large for the ocaml GC! " 159 "Live root count " + 160 Twine(LiveCount) + " >= 65536."); 161 } 162 163 AP.OutStreamer->emitSymbolValue(J->Label, IntPtrSize); 164 AP.emitInt16(FrameSize); 165 AP.emitInt16(LiveCount); 166 167 for (GCFunctionInfo::live_iterator K = FI->live_begin(J), 168 KE = FI->live_end(J); 169 K != KE; ++K) { 170 if (K->StackOffset >= 1 << 16) { 171 // Very rude! 172 report_fatal_error( 173 "GC root stack offset is outside of fixed stack frame and out " 174 "of range for ocaml GC!"); 175 } 176 AP.emitInt16(K->StackOffset); 177 } 178 179 AP.emitAlignment(IntPtrSize == 4 ? Align(4) : Align(8)); 180 } 181 } 182 } 183