1 //===- OcamlGCPrinter.cpp - Ocaml 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 printing the assembly code for an Ocaml frametable.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/ADT/STLExtras.h"
14 #include "llvm/ADT/SmallString.h"
15 #include "llvm/ADT/Twine.h"
16 #include "llvm/CodeGen/AsmPrinter.h"
17 #include "llvm/CodeGen/GCMetadata.h"
18 #include "llvm/CodeGen/GCMetadataPrinter.h"
19 #include "llvm/IR/BuiltinGCs.h"
20 #include "llvm/IR/DataLayout.h"
21 #include "llvm/IR/Function.h"
22 #include "llvm/IR/Mangler.h"
23 #include "llvm/IR/Module.h"
24 #include "llvm/MC/MCContext.h"
25 #include "llvm/MC/MCDirectives.h"
26 #include "llvm/MC/MCStreamer.h"
27 #include "llvm/Support/ErrorHandling.h"
28 #include "llvm/Target/TargetLoweringObjectFile.h"
29 #include <cctype>
30 #include <cstddef>
31 #include <cstdint>
32 #include <string>
33 
34 using namespace llvm;
35 
36 namespace {
37 
38 class OcamlGCMetadataPrinter : public GCMetadataPrinter {
39 public:
40   void beginAssembly(Module &M, GCModuleInfo &Info, AsmPrinter &AP) override;
41   void finishAssembly(Module &M, GCModuleInfo &Info, AsmPrinter &AP) override;
42 };
43 
44 } // end anonymous namespace
45 
46 static GCMetadataPrinterRegistry::Add<OcamlGCMetadataPrinter>
47     Y("ocaml", "ocaml 3.10-compatible collector");
48 
49 void llvm::linkOcamlGCPrinter() {}
50 
51 static void EmitCamlGlobal(const Module &M, AsmPrinter &AP, const char *Id) {
52   const std::string &MId = M.getModuleIdentifier();
53 
54   std::string SymName;
55   SymName += "caml";
56   size_t Letter = SymName.size();
57   SymName.append(MId.begin(), llvm::find(MId, '.'));
58   SymName += "__";
59   SymName += Id;
60 
61   // Capitalize the first letter of the module name.
62   SymName[Letter] = toupper(SymName[Letter]);
63 
64   SmallString<128> TmpStr;
65   Mangler::getNameWithPrefix(TmpStr, SymName, M.getDataLayout());
66 
67   MCSymbol *Sym = AP.OutContext.getOrCreateSymbol(TmpStr);
68 
69   AP.OutStreamer->emitSymbolAttribute(Sym, MCSA_Global);
70   AP.OutStreamer->emitLabel(Sym);
71 }
72 
73 void OcamlGCMetadataPrinter::beginAssembly(Module &M, GCModuleInfo &Info,
74                                            AsmPrinter &AP) {
75   AP.OutStreamer->switchSection(AP.getObjFileLowering().getTextSection());
76   EmitCamlGlobal(M, AP, "code_begin");
77 
78   AP.OutStreamer->switchSection(AP.getObjFileLowering().getDataSection());
79   EmitCamlGlobal(M, AP, "data_begin");
80 }
81 
82 /// emitAssembly - Print the frametable. The ocaml frametable format is thus:
83 ///
84 ///   extern "C" struct align(sizeof(intptr_t)) {
85 ///     uint16_t NumDescriptors;
86 ///     struct align(sizeof(intptr_t)) {
87 ///       void *ReturnAddress;
88 ///       uint16_t FrameSize;
89 ///       uint16_t NumLiveOffsets;
90 ///       uint16_t LiveOffsets[NumLiveOffsets];
91 ///     } Descriptors[NumDescriptors];
92 ///   } caml${module}__frametable;
93 ///
94 /// Note that this precludes programs from stack frames larger than 64K
95 /// (FrameSize and LiveOffsets would overflow). FrameTablePrinter will abort if
96 /// either condition is detected in a function which uses the GC.
97 ///
98 void OcamlGCMetadataPrinter::finishAssembly(Module &M, GCModuleInfo &Info,
99                                             AsmPrinter &AP) {
100   unsigned IntPtrSize = M.getDataLayout().getPointerSize();
101 
102   AP.OutStreamer->switchSection(AP.getObjFileLowering().getTextSection());
103   EmitCamlGlobal(M, AP, "code_end");
104 
105   AP.OutStreamer->switchSection(AP.getObjFileLowering().getDataSection());
106   EmitCamlGlobal(M, AP, "data_end");
107 
108   // FIXME: Why does ocaml emit this??
109   AP.OutStreamer->emitIntValue(0, IntPtrSize);
110 
111   AP.OutStreamer->switchSection(AP.getObjFileLowering().getDataSection());
112   EmitCamlGlobal(M, AP, "frametable");
113 
114   int NumDescriptors = 0;
115   for (std::unique_ptr<GCFunctionInfo> &FI :
116        llvm::make_range(Info.funcinfo_begin(), Info.funcinfo_end())) {
117     if (FI->getStrategy().getName() != getStrategy().getName())
118       // this function is managed by some other GC
119       continue;
120     NumDescriptors += FI->size();
121   }
122 
123   if (NumDescriptors >= 1 << 16) {
124     // Very rude!
125     report_fatal_error(" Too much descriptor for ocaml GC");
126   }
127   AP.emitInt16(NumDescriptors);
128   AP.emitAlignment(IntPtrSize == 4 ? Align(4) : Align(8));
129 
130   for (std::unique_ptr<GCFunctionInfo> &FI :
131        llvm::make_range(Info.funcinfo_begin(), Info.funcinfo_end())) {
132     if (FI->getStrategy().getName() != getStrategy().getName())
133       // this function is managed by some other GC
134       continue;
135 
136     uint64_t FrameSize = FI->getFrameSize();
137     if (FrameSize >= 1 << 16) {
138       // Very rude!
139       report_fatal_error("Function '" + FI->getFunction().getName() +
140                          "' is too large for the ocaml GC! "
141                          "Frame size " +
142                          Twine(FrameSize) +
143                          ">= 65536.\n"
144                          "(" +
145                          Twine(reinterpret_cast<uintptr_t>(FI.get())) + ")");
146     }
147 
148     AP.OutStreamer->AddComment("live roots for " +
149                                Twine(FI->getFunction().getName()));
150     AP.OutStreamer->addBlankLine();
151 
152     for (GCFunctionInfo::iterator J = FI->begin(), JE = FI->end(); J != JE;
153          ++J) {
154       size_t LiveCount = FI->live_size(J);
155       if (LiveCount >= 1 << 16) {
156         // Very rude!
157         report_fatal_error("Function '" + FI->getFunction().getName() +
158                            "' is too large for the ocaml GC! "
159                            "Live root count " +
160                            Twine(LiveCount) + " >= 65536.");
161       }
162 
163       AP.OutStreamer->emitSymbolValue(J->Label, IntPtrSize);
164       AP.emitInt16(FrameSize);
165       AP.emitInt16(LiveCount);
166 
167       for (GCFunctionInfo::live_iterator K = FI->live_begin(J),
168                                          KE = FI->live_end(J);
169            K != KE; ++K) {
170         if (K->StackOffset >= 1 << 16) {
171           // Very rude!
172           report_fatal_error(
173               "GC root stack offset is outside of fixed stack frame and out "
174               "of range for ocaml GC!");
175         }
176         AP.emitInt16(K->StackOffset);
177       }
178 
179       AP.emitAlignment(IntPtrSize == 4 ? Align(4) : Align(8));
180     }
181   }
182 }
183