1//===-- llvm/Support/DynamicLibrary.h - Portable Dynamic Library -*- 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 declares the sys::DynamicLibrary class.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_SYSTEM_DYNAMICLIBRARY_H
15#define LLVM_SYSTEM_DYNAMICLIBRARY_H
16
17#include <string>
18
19namespace llvm {
20
21class StringRef;
22
23namespace sys {
24
25  /// This class provides a portable interface to dynamic libraries which also
26  /// might be known as shared libraries, shared objects, dynamic shared
27  /// objects, or dynamic link libraries. Regardless of the terminology or the
28  /// operating system interface, this class provides a portable interface that
29  /// allows dynamic libraries to be loaded and searched for externally
30  /// defined symbols. This is typically used to provide "plug-in" support.
31  /// It also allows for symbols to be defined which don't live in any library,
32  /// but rather the main program itself, useful on Windows where the main
33  /// executable cannot be searched.
34  ///
35  /// Note: there is currently no interface for temporarily loading a library,
36  /// or for unloading libraries when the LLVM library is unloaded.
37  class DynamicLibrary {
38    // Placeholder whose address represents an invalid library.
39    // We use this instead of NULL or a pointer-int pair because the OS library
40    // might define 0 or 1 to be "special" handles, such as "search all".
41    static char Invalid;
42
43    // Opaque data used to interface with OS-specific dynamic library handling.
44    void *Data;
45
46    explicit DynamicLibrary(void *data = &Invalid) : Data(data) {}
47  public:
48    /// Returns true if the object refers to a valid library.
49    bool isValid() { return Data != &Invalid; }
50
51    /// Searches through the library for the symbol \p symbolName. If it is
52    /// found, the address of that symbol is returned. If not, NULL is returned.
53    /// Note that NULL will also be returned if the library failed to load.
54    /// Use isValid() to distinguish these cases if it is important.
55    /// Note that this will \e not search symbols explicitly registered by
56    /// AddSymbol().
57    void *getAddressOfSymbol(const char *symbolName);
58
59    /// This function permanently loads the dynamic library at the given path.
60    /// The library will only be unloaded when the program terminates.
61    /// This returns a valid DynamicLibrary instance on success and an invalid
62    /// instance on failure (see isValid()). \p *errMsg will only be modified
63    /// if the library fails to load.
64    ///
65    /// It is safe to call this function multiple times for the same library.
66    /// @brief Open a dynamic library permanently.
67    static DynamicLibrary getPermanentLibrary(const char *filename,
68                                              std::string *errMsg = nullptr);
69
70    /// This function permanently loads the dynamic library at the given path.
71    /// Use this instead of getPermanentLibrary() when you won't need to get
72    /// symbols from the library itself.
73    ///
74    /// It is safe to call this function multiple times for the same library.
75    static bool LoadLibraryPermanently(const char *Filename,
76                                       std::string *ErrMsg = nullptr) {
77      return !getPermanentLibrary(Filename, ErrMsg).isValid();
78    }
79
80    /// This function will search through all previously loaded dynamic
81    /// libraries for the symbol \p symbolName. If it is found, the address of
82    /// that symbol is returned. If not, null is returned. Note that this will
83    /// search permanently loaded libraries (getPermanentLibrary()) as well
84    /// as explicitly registered symbols (AddSymbol()).
85    /// @throws std::string on error.
86    /// @brief Search through libraries for address of a symbol
87    static void *SearchForAddressOfSymbol(const char *symbolName);
88
89    /// @brief Convenience function for C++ophiles.
90    static void *SearchForAddressOfSymbol(const std::string &symbolName) {
91      return SearchForAddressOfSymbol(symbolName.c_str());
92    }
93
94    /// This functions permanently adds the symbol \p symbolName with the
95    /// value \p symbolValue.  These symbols are searched before any
96    /// libraries.
97    /// @brief Add searchable symbol/value pair.
98    static void AddSymbol(StringRef symbolName, void *symbolValue);
99  };
100
101} // End sys namespace
102} // End llvm namespace
103
104#endif // LLVM_SYSTEM_DYNAMIC_LIBRARY_H
105