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 
linkErlangGCPrinter()46 void llvm::linkErlangGCPrinter() {}
47 
finishAssembly(Module & M,GCModuleInfo & Info,AsmPrinter & AP)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