llvm/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/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() {}