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
33using namespace llvm;
34
35namespace {
36
37class ErlangGCPrinter : public GCMetadataPrinter {
38public:
39  void finishAssembly(Module &M, GCModuleInfo &Info, AsmPrinter &AP) override;
40};
41}
42
43static GCMetadataPrinterRegistry::Add<ErlangGCPrinter>
44    X("erlang", "erlang-compatible garbage collector");
45
46void llvm::linkErlangGCPrinter() {}
47
48void 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