Home | History | Annotate | Download | only in AsmPrinter 
      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/GCMetadataPrinter.h"
     18 #include "llvm/CodeGen/GCs.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 #include "llvm/Target/TargetSubtargetInfo.h"
     32 
     33 using namespace llvm;
     34 
     35 namespace {
     36 
     37 class ErlangGCPrinter : public GCMetadataPrinter {
     38 public:
     39   void finishAssembly(Module &M, GCModuleInfo &Info, AsmPrinter &AP) override;
     40 };
     41 }
     42 
     43 static GCMetadataPrinterRegistry::Add<ErlangGCPrinter>
     44     X("erlang", "erlang-compatible garbage collector");
     45 
     46 void llvm::linkErlangGCPrinter() {}
     47 
     48 void ErlangGCPrinter::finishAssembly(Module &M, GCModuleInfo &Info,
     49                                      AsmPrinter &AP) {
     50   MCStreamer &OS = *AP.OutStreamer;
     51   unsigned IntPtrSize = M.getDataLayout().getPointerSize();
     52 
     53   // Put this in a custom .note section.
     54   OS.SwitchSection(
     55       AP.getObjFileLowering().getContext().getELFSection(".note.gc",
     56                                                          ELF::SHT_PROGBITS, 0));
     57 
     58   // For each function...
     59   for (GCModuleInfo::FuncInfoVec::iterator FI = Info.funcinfo_begin(),
     60                                            IE = Info.funcinfo_end();
     61        FI != IE; ++FI) {
     62     GCFunctionInfo &MD = **FI;
     63     if (MD.getStrategy().getName() != getStrategy().getName())
     64       // this function is managed by some other GC
     65       continue;
     66     /** A compact GC layout. Emit this data structure:
     67      *
     68      * struct {
     69      *   int16_t PointCount;
     70      *   void *SafePointAddress[PointCount];
     71      *   int16_t StackFrameSize; (in words)
     72      *   int16_t StackArity;
     73      *   int16_t LiveCount;
     74      *   int16_t LiveOffsets[LiveCount];
     75      * } __gcmap_<FUNCTIONNAME>;
     76      **/
     77 
     78     // Align to address width.
     79     AP.EmitAlignment(IntPtrSize == 4 ? 2 : 3);
     80 
     81     // Emit PointCount.
     82     OS.AddComment("safe point count");
     83     AP.EmitInt16(MD.size());
     84 
     85     // And each safe point...
     86     for (GCFunctionInfo::iterator PI = MD.begin(), PE = MD.end(); PI != PE;
     87          ++PI) {
     88       // Emit the address of the safe point.
     89       OS.AddComment("safe point address");
     90       MCSymbol *Label = PI->Label;
     91       AP.EmitLabelPlusOffset(Label /*Hi*/, 0 /*Offset*/, 4 /*Size*/);
     92     }
     93 
     94     // Stack information never change in safe points! Only print info from the
     95     // first call-site.
     96     GCFunctionInfo::iterator PI = MD.begin();
     97 
     98     // Emit the stack frame size.
     99     OS.AddComment("stack frame size (in words)");
    100     AP.EmitInt16(MD.getFrameSize() / IntPtrSize);
    101 
    102     // Emit stack arity, i.e. the number of stacked arguments.
    103     unsigned RegisteredArgs = IntPtrSize == 4 ? 5 : 6;
    104     unsigned StackArity = MD.getFunction().arg_size() > RegisteredArgs
    105                               ? MD.getFunction().arg_size() - RegisteredArgs
    106                               : 0;
    107     OS.AddComment("stack arity");
    108     AP.EmitInt16(StackArity);
    109 
    110     // Emit the number of live roots in the function.
    111     OS.AddComment("live root count");
    112     AP.EmitInt16(MD.live_size(PI));
    113 
    114     // And for each live root...
    115     for (GCFunctionInfo::live_iterator LI = MD.live_begin(PI),
    116                                        LE = MD.live_end(PI);
    117          LI != LE; ++LI) {
    118       // Emit live root's offset within the stack frame.
    119       OS.AddComment("stack index (offset / wordsize)");
    120       AP.EmitInt16(LI->StackOffset / IntPtrSize);
    121     }
    122   }
    123 }
    124