1 //===-- OcamlGCPrinter.cpp - Ocaml frametable emitter ---------------------===//
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 printing the assembly code for an Ocaml frametable.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/CodeGen/GCs.h"
15 #include "llvm/CodeGen/AsmPrinter.h"
16 #include "llvm/CodeGen/GCMetadataPrinter.h"
17 #include "llvm/Module.h"
18 #include "llvm/Support/Compiler.h"
19 #include "llvm/Support/raw_ostream.h"
20 #include "llvm/Target/TargetAsmInfo.h"
21 #include "llvm/Target/TargetData.h"
22 #include "llvm/Target/TargetMachine.h"
23 
24 using namespace llvm;
25 
26 namespace {
27 
28   class VISIBILITY_HIDDEN OcamlGCMetadataPrinter : public GCMetadataPrinter {
29   public:
30     void beginAssembly(raw_ostream &OS, AsmPrinter &AP,
31                        const TargetAsmInfo &TAI);
32 
33     void finishAssembly(raw_ostream &OS, AsmPrinter &AP,
34                         const TargetAsmInfo &TAI);
35   };
36 
37 }
38 
39 static GCMetadataPrinterRegistry::Add<OcamlGCMetadataPrinter>
40 Y("ocaml", "ocaml 3.10-compatible collector");
41 
42 void llvm::linkOcamlGCPrinter() { }
43 
44 static void EmitCamlGlobal(const Module &M, raw_ostream &OS, AsmPrinter &AP,
45                            const TargetAsmInfo &TAI, const char *Id) {
46   const std::string &MId = M.getModuleIdentifier();
47 
48   std::string Mangled;
49   Mangled += TAI.getGlobalPrefix();
50   Mangled += "caml";
51   size_t Letter = Mangled.size();
52   Mangled.append(MId.begin(), std::find(MId.begin(), MId.end(), '.'));
53   Mangled += "__";
54   Mangled += Id;
55 
56   // Capitalize the first letter of the module name.
57   Mangled[Letter] = toupper(Mangled[Letter]);
58 
59   if (const char *GlobalDirective = TAI.getGlobalDirective())
60     OS << GlobalDirective << Mangled << "\n";
61   OS << Mangled << ":\n";
62 }
63 
64 void OcamlGCMetadataPrinter::beginAssembly(raw_ostream &OS, AsmPrinter &AP,
65                                            const TargetAsmInfo &TAI) {
66   AP.SwitchToSection(TAI.getTextSection());
67   EmitCamlGlobal(getModule(), OS, AP, TAI, "code_begin");
68 
69   AP.SwitchToSection(TAI.getDataSection());
70   EmitCamlGlobal(getModule(), OS, AP, TAI, "data_begin");
71 }
72 
73 /// emitAssembly - Print the frametable. The ocaml frametable format is thus:
74 ///
75 ///   extern "C" struct align(sizeof(intptr_t)) {
76 ///     uint16_t NumDescriptors;
77 ///     struct align(sizeof(intptr_t)) {
78 ///       void *ReturnAddress;
79 ///       uint16_t FrameSize;
80 ///       uint16_t NumLiveOffsets;
81 ///       uint16_t LiveOffsets[NumLiveOffsets];
82 ///     } Descriptors[NumDescriptors];
83 ///   } caml${module}__frametable;
84 ///
85 /// Note that this precludes programs from stack frames larger than 64K
86 /// (FrameSize and LiveOffsets would overflow). FrameTablePrinter will abort if
87 /// either condition is detected in a function which uses the GC.
88 ///
89 void OcamlGCMetadataPrinter::finishAssembly(raw_ostream &OS, AsmPrinter &AP,
90                                             const TargetAsmInfo &TAI) {
91   const char *AddressDirective;
92   int AddressAlignLog;
93   if (AP.TM.getTargetData()->getPointerSize() == sizeof(int32_t)) {
94     AddressDirective = TAI.getData32bitsDirective();
95     AddressAlignLog = 2;
96   } else {
97     AddressDirective = TAI.getData64bitsDirective();
98     AddressAlignLog = 3;
99   }
100 
101   AP.SwitchToSection(TAI.getTextSection());
102   EmitCamlGlobal(getModule(), OS, AP, TAI, "code_end");
103 
104   AP.SwitchToSection(TAI.getDataSection());
105   EmitCamlGlobal(getModule(), OS, AP, TAI, "data_end");
106 
107   OS << AddressDirective << 0; // FIXME: Why does ocaml emit this??
108   AP.EOL();
109 
110   AP.SwitchToSection(TAI.getDataSection());
111   EmitCamlGlobal(getModule(), OS, AP, TAI, "frametable");
112 
113   for (iterator I = begin(), IE = end(); I != IE; ++I) {
114     GCFunctionInfo &FI = **I;
115 
116     uint64_t FrameSize = FI.getFrameSize();
117     if (FrameSize >= 1<<16) {
118       cerr << "Function '" << FI.getFunction().getNameStart()
119            << "' is too large for the ocaml GC! "
120            << "Frame size " << FrameSize << " >= 65536.\n";
121       cerr << "(" << uintptr_t(&FI) << ")\n";
122       abort(); // Very rude!
123     }
124 
125     OS << "\t" << TAI.getCommentString() << " live roots for "
126        << FI.getFunction().getNameStart() << "\n";
127 
128     for (GCFunctionInfo::iterator J = FI.begin(), JE = FI.end(); J != JE; ++J) {
129       size_t LiveCount = FI.live_size(J);
130       if (LiveCount >= 1<<16) {
131         cerr << "Function '" << FI.getFunction().getNameStart()
132              << "' is too large for the ocaml GC! "
133              << "Live root count " << LiveCount << " >= 65536.\n";
134         abort(); // Very rude!
135       }
136 
137       OS << AddressDirective
138          << TAI.getPrivateGlobalPrefix() << "label" << J->Num;
139       AP.EOL("call return address");
140 
141       AP.EmitInt16(FrameSize);
142       AP.EOL("stack frame size");
143 
144       AP.EmitInt16(LiveCount);
145       AP.EOL("live root count");
146 
147       for (GCFunctionInfo::live_iterator K = FI.live_begin(J),
148                                          KE = FI.live_end(J); K != KE; ++K) {
149         assert(K->StackOffset < 1<<16 &&
150                "GC root stack offset is outside of fixed stack frame and out "
151                "of range for ocaml GC!");
152 
153         OS << "\t.word\t" << K->StackOffset;
154         AP.EOL("stack offset");
155       }
156 
157       AP.EmitAlignment(AddressAlignLog);
158     }
159   }
160 }
161