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