lib/CodeGen/AsmPrinter/ErlangGCPrinter.cpp

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