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/MC/MCStreamer.h"
19 #include "llvm/MC/MCAsmInfo.h"
20 #include "llvm/Target/TargetData.h"
21 #include "llvm/Target/TargetLoweringObjectFile.h"
22 #include "llvm/Target/TargetMachine.h"
23 #include "llvm/Support/Compiler.h"
24 #include "llvm/Support/ErrorHandling.h"
25 #include "llvm/Support/raw_ostream.h"
26 using namespace llvm;
27 
28 namespace {
29 
30   class VISIBILITY_HIDDEN OcamlGCMetadataPrinter : public GCMetadataPrinter {
31   public:
32     void beginAssembly(raw_ostream &OS, AsmPrinter &AP,
33                        const MCAsmInfo &MAI);
34 
35     void finishAssembly(raw_ostream &OS, AsmPrinter &AP,
36                         const MCAsmInfo &MAI);
37   };
38 
39 }
40 
41 static GCMetadataPrinterRegistry::Add<OcamlGCMetadataPrinter>
42 Y("ocaml", "ocaml 3.10-compatible collector");
43 
44 void llvm::linkOcamlGCPrinter() { }
45 
46 static void EmitCamlGlobal(const Module &M, raw_ostream &OS, AsmPrinter &AP,
47                            const MCAsmInfo &MAI, const char *Id) {
48   const std::string &MId = M.getModuleIdentifier();
49 
50   std::string Mangled;
51   Mangled += MAI.getGlobalPrefix();
52   Mangled += "caml";
53   size_t Letter = Mangled.size();
54   Mangled.append(MId.begin(), std::find(MId.begin(), MId.end(), '.'));
55   Mangled += "__";
56   Mangled += Id;
57 
58   // Capitalize the first letter of the module name.
59   Mangled[Letter] = toupper(Mangled[Letter]);
60 
61   if (const char *GlobalDirective = MAI.getGlobalDirective())
62     OS << GlobalDirective << Mangled << "\n";
63   OS << Mangled << ":\n";
64 }
65 
66 void OcamlGCMetadataPrinter::beginAssembly(raw_ostream &OS, AsmPrinter &AP,
67                                            const MCAsmInfo &MAI) {
68   AP.OutStreamer.SwitchSection(AP.getObjFileLowering().getTextSection());
69   EmitCamlGlobal(getModule(), OS, AP, MAI, "code_begin");
70 
71   AP.OutStreamer.SwitchSection(AP.getObjFileLowering().getDataSection());
72   EmitCamlGlobal(getModule(), OS, AP, MAI, "data_begin");
73 }
74 
75 /// emitAssembly - Print the frametable. The ocaml frametable format is thus:
76 ///
77 ///   extern "C" struct align(sizeof(intptr_t)) {
78 ///     uint16_t NumDescriptors;
79 ///     struct align(sizeof(intptr_t)) {
80 ///       void *ReturnAddress;
81 ///       uint16_t FrameSize;
82 ///       uint16_t NumLiveOffsets;
83 ///       uint16_t LiveOffsets[NumLiveOffsets];
84 ///     } Descriptors[NumDescriptors];
85 ///   } caml${module}__frametable;
86 ///
87 /// Note that this precludes programs from stack frames larger than 64K
88 /// (FrameSize and LiveOffsets would overflow). FrameTablePrinter will abort if
89 /// either condition is detected in a function which uses the GC.
90 ///
91 void OcamlGCMetadataPrinter::finishAssembly(raw_ostream &OS, AsmPrinter &AP,
92                                             const MCAsmInfo &MAI) {
93   const char *AddressDirective;
94   int AddressAlignLog;
95   if (AP.TM.getTargetData()->getPointerSize() == sizeof(int32_t)) {
96     AddressDirective = MAI.getData32bitsDirective();
97     AddressAlignLog = 2;
98   } else {
99     AddressDirective = MAI.getData64bitsDirective();
100     AddressAlignLog = 3;
101   }
102 
103   AP.OutStreamer.SwitchSection(AP.getObjFileLowering().getTextSection());
104   EmitCamlGlobal(getModule(), OS, AP, MAI, "code_end");
105 
106   AP.OutStreamer.SwitchSection(AP.getObjFileLowering().getDataSection());
107   EmitCamlGlobal(getModule(), OS, AP, MAI, "data_end");
108 
109   OS << AddressDirective << 0; // FIXME: Why does ocaml emit this??
110   AP.EOL();
111 
112   AP.OutStreamer.SwitchSection(AP.getObjFileLowering().getDataSection());
113   EmitCamlGlobal(getModule(), OS, AP, MAI, "frametable");
114 
115   for (iterator I = begin(), IE = end(); I != IE; ++I) {
116     GCFunctionInfo &FI = **I;
117 
118     uint64_t FrameSize = FI.getFrameSize();
119     if (FrameSize >= 1<<16) {
120       std::string msg;
121       raw_string_ostream Msg(msg);
122       Msg << "Function '" << FI.getFunction().getName()
123            << "' is too large for the ocaml GC! "
124            << "Frame size " << FrameSize << " >= 65536.\n";
125       Msg << "(" << uintptr_t(&FI) << ")";
126       llvm_report_error(Msg.str()); // Very rude!
127     }
128 
129     OS << "\t" << MAI.getCommentString() << " live roots for "
130        << FI.getFunction().getName() << "\n";
131 
132     for (GCFunctionInfo::iterator J = FI.begin(), JE = FI.end(); J != JE; ++J) {
133       size_t LiveCount = FI.live_size(J);
134       if (LiveCount >= 1<<16) {
135         std::string msg;
136         raw_string_ostream Msg(msg);
137         Msg << "Function '" << FI.getFunction().getName()
138              << "' is too large for the ocaml GC! "
139              << "Live root count " << LiveCount << " >= 65536.";
140         llvm_report_error(Msg.str()); // Very rude!
141       }
142 
143       OS << AddressDirective
144          << MAI.getPrivateGlobalPrefix() << "label" << J->Num;
145       AP.EOL("call return address");
146 
147       AP.EmitInt16(FrameSize);
148       AP.EOL("stack frame size");
149 
150       AP.EmitInt16(LiveCount);
151       AP.EOL("live root count");
152 
153       for (GCFunctionInfo::live_iterator K = FI.live_begin(J),
154                                          KE = FI.live_end(J); K != KE; ++K) {
155         assert(K->StackOffset < 1<<16 &&
156                "GC root stack offset is outside of fixed stack frame and out "
157                "of range for ocaml GC!");
158 
159         OS << "\t.word\t" << K->StackOffset;
160         AP.EOL("stack offset");
161       }
162 
163       AP.EmitAlignment(AddressAlignLog);
164     }
165   }
166 }
167