1 //===- ErlangGCPrinter.cpp - Erlang/OTP frametable emitter ----------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements the compiler plugin that is used in order to emit
10 // garbage collection information in a convenient layout for parsing and
11 // loading in the Erlang/OTP runtime.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "llvm/BinaryFormat/ELF.h"
16 #include "llvm/CodeGen/AsmPrinter.h"
17 #include "llvm/CodeGen/BuiltinGCs.h"
18 #include "llvm/CodeGen/GCMetadata.h"
19 #include "llvm/CodeGen/GCMetadataPrinter.h"
20 #include "llvm/CodeGen/GCStrategy.h"
21 #include "llvm/IR/DataLayout.h"
22 #include "llvm/IR/Function.h"
23 #include "llvm/IR/Module.h"
24 #include "llvm/MC/MCContext.h"
25 #include "llvm/MC/MCSectionELF.h"
26 #include "llvm/MC/MCStreamer.h"
27 #include "llvm/MC/MCSymbol.h"
28 #include "llvm/Target/TargetLoweringObjectFile.h"
29
30 using namespace llvm;
31
32 namespace {
33
34 class ErlangGCPrinter : public GCMetadataPrinter {
35 public:
36 void finishAssembly(Module &M, GCModuleInfo &Info, AsmPrinter &AP) override;
37 };
38
39 } // end anonymous namespace
40
41 static GCMetadataPrinterRegistry::Add<ErlangGCPrinter>
42 X("erlang", "erlang-compatible garbage collector");
43
finishAssembly(Module & M,GCModuleInfo & Info,AsmPrinter & AP)44 void ErlangGCPrinter::finishAssembly(Module &M, GCModuleInfo &Info,
45 AsmPrinter &AP) {
46 MCStreamer &OS = *AP.OutStreamer;
47 unsigned IntPtrSize = M.getDataLayout().getPointerSize();
48
49 // Put this in a custom .note section.
50 OS.SwitchSection(
51 AP.getObjFileLowering().getContext().getELFSection(".note.gc",
52 ELF::SHT_PROGBITS, 0));
53
54 // For each function...
55 for (GCModuleInfo::FuncInfoVec::iterator FI = Info.funcinfo_begin(),
56 IE = Info.funcinfo_end();
57 FI != IE; ++FI) {
58 GCFunctionInfo &MD = **FI;
59 if (MD.getStrategy().getName() != getStrategy().getName())
60 // this function is managed by some other GC
61 continue;
62 /** A compact GC layout. Emit this data structure:
63 *
64 * struct {
65 * int16_t PointCount;
66 * void *SafePointAddress[PointCount];
67 * int16_t StackFrameSize; (in words)
68 * int16_t StackArity;
69 * int16_t LiveCount;
70 * int16_t LiveOffsets[LiveCount];
71 * } __gcmap_<FUNCTIONNAME>;
72 **/
73
74 // Align to address width.
75 AP.emitAlignment(IntPtrSize == 4 ? Align(4) : Align(8));
76
77 // Emit PointCount.
78 OS.AddComment("safe point count");
79 AP.emitInt16(MD.size());
80
81 // And each safe point...
82 for (GCFunctionInfo::iterator PI = MD.begin(), PE = MD.end(); PI != PE;
83 ++PI) {
84 // Emit the address of the safe point.
85 OS.AddComment("safe point address");
86 MCSymbol *Label = PI->Label;
87 AP.emitLabelPlusOffset(Label /*Hi*/, 0 /*Offset*/, 4 /*Size*/);
88 }
89
90 // Stack information never change in safe points! Only print info from the
91 // first call-site.
92 GCFunctionInfo::iterator PI = MD.begin();
93
94 // Emit the stack frame size.
95 OS.AddComment("stack frame size (in words)");
96 AP.emitInt16(MD.getFrameSize() / IntPtrSize);
97
98 // Emit stack arity, i.e. the number of stacked arguments.
99 unsigned RegisteredArgs = IntPtrSize == 4 ? 5 : 6;
100 unsigned StackArity = MD.getFunction().arg_size() > RegisteredArgs
101 ? MD.getFunction().arg_size() - RegisteredArgs
102 : 0;
103 OS.AddComment("stack arity");
104 AP.emitInt16(StackArity);
105
106 // Emit the number of live roots in the function.
107 OS.AddComment("live root count");
108 AP.emitInt16(MD.live_size(PI));
109
110 // And for each live root...
111 for (GCFunctionInfo::live_iterator LI = MD.live_begin(PI),
112 LE = MD.live_end(PI);
113 LI != LE; ++LI) {
114 // Emit live root's offset within the stack frame.
115 OS.AddComment("stack index (offset / wordsize)");
116 AP.emitInt16(LI->StackOffset / IntPtrSize);
117 }
118 }
119 }
120
linkErlangGCPrinter()121 void llvm::linkErlangGCPrinter() {}
122