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