1 //===- ErlangGCPrinter.cpp - Erlang/OTP frametable emitter ----------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file implements the compiler plugin that is used in order to emit 11 // garbage collection information in a convenient layout for parsing and 12 // loading in the Erlang/OTP runtime. 13 // 14 //===----------------------------------------------------------------------===// 15 16 #include "llvm/BinaryFormat/ELF.h" 17 #include "llvm/CodeGen/AsmPrinter.h" 18 #include "llvm/CodeGen/GCMetadata.h" 19 #include "llvm/CodeGen/GCMetadataPrinter.h" 20 #include "llvm/CodeGen/GCStrategy.h" 21 #include "llvm/CodeGen/GCs.h" 22 #include "llvm/IR/DataLayout.h" 23 #include "llvm/IR/Function.h" 24 #include "llvm/IR/Module.h" 25 #include "llvm/MC/MCContext.h" 26 #include "llvm/MC/MCSectionELF.h" 27 #include "llvm/MC/MCStreamer.h" 28 #include "llvm/MC/MCSymbol.h" 29 #include "llvm/Target/TargetLoweringObjectFile.h" 30 31 using namespace llvm; 32 33 namespace { 34 35 class ErlangGCPrinter : public GCMetadataPrinter { 36 public: 37 void finishAssembly(Module &M, GCModuleInfo &Info, AsmPrinter &AP) override; 38 }; 39 40 } // end anonymous namespace 41 42 static GCMetadataPrinterRegistry::Add<ErlangGCPrinter> 43 X("erlang", "erlang-compatible garbage collector"); 44 45 void ErlangGCPrinter::finishAssembly(Module &M, GCModuleInfo &Info, 46 AsmPrinter &AP) { 47 MCStreamer &OS = *AP.OutStreamer; 48 unsigned IntPtrSize = M.getDataLayout().getPointerSize(); 49 50 // Put this in a custom .note section. 51 OS.SwitchSection( 52 AP.getObjFileLowering().getContext().getELFSection(".note.gc", 53 ELF::SHT_PROGBITS, 0)); 54 55 // For each function... 56 for (GCModuleInfo::FuncInfoVec::iterator FI = Info.funcinfo_begin(), 57 IE = Info.funcinfo_end(); 58 FI != IE; ++FI) { 59 GCFunctionInfo &MD = **FI; 60 if (MD.getStrategy().getName() != getStrategy().getName()) 61 // this function is managed by some other GC 62 continue; 63 /** A compact GC layout. Emit this data structure: 64 * 65 * struct { 66 * int16_t PointCount; 67 * void *SafePointAddress[PointCount]; 68 * int16_t StackFrameSize; (in words) 69 * int16_t StackArity; 70 * int16_t LiveCount; 71 * int16_t LiveOffsets[LiveCount]; 72 * } __gcmap_<FUNCTIONNAME>; 73 **/ 74 75 // Align to address width. 76 AP.EmitAlignment(IntPtrSize == 4 ? 2 : 3); 77 78 // Emit PointCount. 79 OS.AddComment("safe point count"); 80 AP.emitInt16(MD.size()); 81 82 // And each safe point... 83 for (GCFunctionInfo::iterator PI = MD.begin(), PE = MD.end(); PI != PE; 84 ++PI) { 85 // Emit the address of the safe point. 86 OS.AddComment("safe point address"); 87 MCSymbol *Label = PI->Label; 88 AP.EmitLabelPlusOffset(Label /*Hi*/, 0 /*Offset*/, 4 /*Size*/); 89 } 90 91 // Stack information never change in safe points! Only print info from the 92 // first call-site. 93 GCFunctionInfo::iterator PI = MD.begin(); 94 95 // Emit the stack frame size. 96 OS.AddComment("stack frame size (in words)"); 97 AP.emitInt16(MD.getFrameSize() / IntPtrSize); 98 99 // Emit stack arity, i.e. the number of stacked arguments. 100 unsigned RegisteredArgs = IntPtrSize == 4 ? 5 : 6; 101 unsigned StackArity = MD.getFunction().arg_size() > RegisteredArgs 102 ? MD.getFunction().arg_size() - RegisteredArgs 103 : 0; 104 OS.AddComment("stack arity"); 105 AP.emitInt16(StackArity); 106 107 // Emit the number of live roots in the function. 108 OS.AddComment("live root count"); 109 AP.emitInt16(MD.live_size(PI)); 110 111 // And for each live root... 112 for (GCFunctionInfo::live_iterator LI = MD.live_begin(PI), 113 LE = MD.live_end(PI); 114 LI != LE; ++LI) { 115 // Emit live root's offset within the stack frame. 116 OS.AddComment("stack index (offset / wordsize)"); 117 AP.emitInt16(LI->StackOffset / IntPtrSize); 118 } 119 } 120 } 121 122 void llvm::linkErlangGCPrinter() {} 123