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_SUPPORT_DYNAMICLIBRARY_H
15#define LLVM_SUPPORT_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  public:
47    explicit DynamicLibrary(void *data = &Invalid) : Data(data) {}
48
49    /// Returns true if the object refers to a valid library.
50    bool isValid() const { return Data != &Invalid; }
51
52    /// Searches through the library for the symbol \p symbolName. If it is
53    /// found, the address of that symbol is returned. If not, NULL is returned.
54    /// Note that NULL will also be returned if the library failed to load.
55    /// Use isValid() to distinguish these cases if it is important.
56    /// Note that this will \e not search symbols explicitly registered by
57    /// AddSymbol().
58    void *getAddressOfSymbol(const char *symbolName);
59
60    /// This function permanently loads the dynamic library at the given path.
61    /// The library will only be unloaded when the program terminates.
62    /// This returns a valid DynamicLibrary instance on success and an invalid
63    /// instance on failure (see isValid()). \p *errMsg will only be modified
64    /// if the library fails to load.
65    ///
66    /// It is safe to call this function multiple times for the same library.
67    /// @brief Open a dynamic library permanently.
68    static DynamicLibrary getPermanentLibrary(const char *filename,
69                                              std::string *errMsg = nullptr);
70
71    /// This function permanently loads the dynamic library at the given path.
72    /// Use this instead of getPermanentLibrary() when you won't need to get
73    /// symbols from the library itself.
74    ///
75    /// It is safe to call this function multiple times for the same library.
76    static bool LoadLibraryPermanently(const char *Filename,
77                                       std::string *ErrMsg = nullptr) {
78      return !getPermanentLibrary(Filename, ErrMsg).isValid();
79    }
80
81    /// This function will search through all previously loaded dynamic
82    /// libraries for the symbol \p symbolName. If it is found, the address of
83    /// that symbol is returned. If not, null is returned. Note that this will
84    /// search permanently loaded libraries (getPermanentLibrary()) as well
85    /// as explicitly registered symbols (AddSymbol()).
86    /// @throws std::string on error.
87    /// @brief Search through libraries for address of a symbol
88    static void *SearchForAddressOfSymbol(const char *symbolName);
89
90    /// @brief Convenience function for C++ophiles.
91    static void *SearchForAddressOfSymbol(const std::string &symbolName) {
92      return SearchForAddressOfSymbol(symbolName.c_str());
93    }
94
95    /// This functions permanently adds the symbol \p symbolName with the
96    /// value \p symbolValue.  These symbols are searched before any
97    /// libraries.
98    /// @brief Add searchable symbol/value pair.
99    static void AddSymbol(StringRef symbolName, void *symbolValue);
100  };
101
102} // End sys namespace
103} // End llvm namespace
104
105#endif
106