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      1 //===-- ErlangGCPrinter.cpp - Erlang/OTP frametable emitter -----*- C++ -*-===//
      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/CodeGen/AsmPrinter.h"
     17 #include "llvm/CodeGen/GCs.h"
     18 #include "llvm/CodeGen/GCMetadataPrinter.h"
     19 #include "llvm/IR/DataLayout.h"
     20 #include "llvm/IR/Function.h"
     21 #include "llvm/IR/Instruction.h"
     22 #include "llvm/IR/IntrinsicInst.h"
     23 #include "llvm/IR/Metadata.h"
     24 #include "llvm/MC/MCAsmInfo.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 #include "llvm/Target/TargetMachine.h"
     31 
     32 using namespace llvm;
     33 
     34 namespace {
     35 
     36   class ErlangGCPrinter : public GCMetadataPrinter {
     37   public:
     38     void beginAssembly(AsmPrinter &AP);
     39     void finishAssembly(AsmPrinter &AP);
     40   };
     41 
     42 }
     43 
     44 static GCMetadataPrinterRegistry::Add<ErlangGCPrinter>
     45 X("erlang", "erlang-compatible garbage collector");
     46 
     47 void llvm::linkErlangGCPrinter() { }
     48 
     49 void ErlangGCPrinter::beginAssembly(AsmPrinter &AP) { }
     50 
     51 void ErlangGCPrinter::finishAssembly(AsmPrinter &AP) {
     52   MCStreamer &OS = AP.OutStreamer;
     53   unsigned IntPtrSize = AP.TM.getDataLayout()->getPointerSize();
     54 
     55   // Put this in a custom .note section.
     56   AP.OutStreamer.SwitchSection(AP.getObjFileLowering().getContext()
     57     .getELFSection(".note.gc", ELF::SHT_PROGBITS, 0,
     58                    SectionKind::getDataRel()));
     59 
     60   // For each function...
     61   for (iterator FI = begin(), FE = end(); FI != FE; ++FI) {
     62     GCFunctionInfo &MD = **FI;
     63 
     64     /** A compact GC layout. Emit this data structure:
     65      *
     66      * struct {
     67      *   int16_t PointCount;
     68      *   void *SafePointAddress[PointCount];
     69      *   int16_t StackFrameSize; (in words)
     70      *   int16_t StackArity;
     71      *   int16_t LiveCount;
     72      *   int16_t LiveOffsets[LiveCount];
     73      * } __gcmap_<FUNCTIONNAME>;
     74      **/
     75 
     76     // Align to address width.
     77     AP.EmitAlignment(IntPtrSize == 4 ? 2 : 3);
     78 
     79     // Emit PointCount.
     80     OS.AddComment("safe point count");
     81     AP.EmitInt16(MD.size());
     82 
     83     // And each safe point...
     84     for (GCFunctionInfo::iterator PI = MD.begin(), PE = MD.end(); PI != PE;
     85          ++PI) {
     86       // Emit the address of the safe point.
     87       OS.AddComment("safe point address");
     88       MCSymbol *Label = PI->Label;
     89       AP.EmitLabelPlusOffset(Label/*Hi*/, 0/*Offset*/, 4/*Size*/);
     90     }
     91 
     92     // Stack information never change in safe points! Only print info from the
     93     // first call-site.
     94     GCFunctionInfo::iterator PI = MD.begin();
     95 
     96     // Emit the stack frame size.
     97     OS.AddComment("stack frame size (in words)");
     98     AP.EmitInt16(MD.getFrameSize() / IntPtrSize);
     99 
    100     // Emit stack arity, i.e. the number of stacked arguments.
    101     unsigned RegisteredArgs = IntPtrSize == 4 ? 5 : 6;
    102     unsigned StackArity = MD.getFunction().arg_size() > RegisteredArgs ?
    103                           MD.getFunction().arg_size() - RegisteredArgs : 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