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,
40                         AsmPrinter &AP) override;
41   };
42 
43 }
44 
45 static GCMetadataPrinterRegistry::Add<ErlangGCPrinter>
46 X("erlang", "erlang-compatible garbage collector");
47 
48 void llvm::linkErlangGCPrinter() { }
49 
50 void ErlangGCPrinter::finishAssembly(Module &M, GCModuleInfo &Info,
51                                      AsmPrinter &AP) {
52   MCStreamer &OS = AP.OutStreamer;
53   unsigned IntPtrSize =
54       AP.TM.getSubtargetImpl()->getDataLayout()->getPointerSize();
55 
56   // Put this in a custom .note section.
57   AP.OutStreamer.SwitchSection(AP.getObjFileLowering().getContext()
58     .getELFSection(".note.gc", ELF::SHT_PROGBITS, 0,
59                    SectionKind::getDataRel()));
60 
61   // For each function...
62   for (GCModuleInfo::FuncInfoVec::iterator FI = Info.funcinfo_begin(),
63          IE = Info.funcinfo_end();
64        FI != IE; ++FI) {
65     GCFunctionInfo &MD = **FI;
66     if (MD.getStrategy().getName() != getStrategy().getName())
67       // this function is managed by some other GC
68       continue;
69     /** A compact GC layout. Emit this data structure:
70      *
71      * struct {
72      *   int16_t PointCount;
73      *   void *SafePointAddress[PointCount];
74      *   int16_t StackFrameSize; (in words)
75      *   int16_t StackArity;
76      *   int16_t LiveCount;
77      *   int16_t LiveOffsets[LiveCount];
78      * } __gcmap_<FUNCTIONNAME>;
79      **/
80 
81     // Align to address width.
82     AP.EmitAlignment(IntPtrSize == 4 ? 2 : 3);
83 
84     // Emit PointCount.
85     OS.AddComment("safe point count");
86     AP.EmitInt16(MD.size());
87 
88     // And each safe point...
89     for (GCFunctionInfo::iterator PI = MD.begin(), PE = MD.end(); PI != PE;
90          ++PI) {
91       // Emit the address of the safe point.
92       OS.AddComment("safe point address");
93       MCSymbol *Label = PI->Label;
94       AP.EmitLabelPlusOffset(Label/*Hi*/, 0/*Offset*/, 4/*Size*/);
95     }
96 
97     // Stack information never change in safe points! Only print info from the
98     // first call-site.
99     GCFunctionInfo::iterator PI = MD.begin();
100 
101     // Emit the stack frame size.
102     OS.AddComment("stack frame size (in words)");
103     AP.EmitInt16(MD.getFrameSize() / IntPtrSize);
104 
105     // Emit stack arity, i.e. the number of stacked arguments.
106     unsigned RegisteredArgs = IntPtrSize == 4 ? 5 : 6;
107     unsigned StackArity = MD.getFunction().arg_size() > RegisteredArgs ?
108                           MD.getFunction().arg_size() - RegisteredArgs : 0;
109     OS.AddComment("stack arity");
110     AP.EmitInt16(StackArity);
111 
112     // Emit the number of live roots in the function.
113     OS.AddComment("live root count");
114     AP.EmitInt16(MD.live_size(PI));
115 
116     // And for each live root...
117     for (GCFunctionInfo::live_iterator LI = MD.live_begin(PI),
118                                        LE = MD.live_end(PI);
119                                        LI != LE; ++LI) {
120       // Emit live root's offset within the stack frame.
121       OS.AddComment("stack index (offset / wordsize)");
122       AP.EmitInt16(LI->StackOffset / IntPtrSize);
123     }
124   }
125 }
126