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