1 //===-- Intercept.cpp - System function interception routines -------------===//
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 // If a function call occurs to an external function, the JIT is designed to use
11 // the dynamic loader interface to find a function to call.  This is useful for
12 // calling system calls and library functions that are not available in LLVM.
13 // Some system calls, however, need to be handled specially.  For this reason,
14 // we intercept some of them here and use our own stubs to handle them.
15 //
16 //===----------------------------------------------------------------------===//
17 
18 #include "JIT.h"
19 #include "llvm/Support/ErrorHandling.h"
20 #include "llvm/Support/DynamicLibrary.h"
21 #include "llvm/Config/config.h"
22 using namespace llvm;
23 
24 // AtExitHandlers - List of functions to call when the program exits,
25 // registered with the atexit() library function.
26 static std::vector<void (*)()> AtExitHandlers;
27 
28 /// runAtExitHandlers - Run any functions registered by the program's
29 /// calls to atexit(3), which we intercept and store in
30 /// AtExitHandlers.
31 ///
runAtExitHandlers()32 static void runAtExitHandlers() {
33   while (!AtExitHandlers.empty()) {
34     void (*Fn)() = AtExitHandlers.back();
35     AtExitHandlers.pop_back();
36     Fn();
37   }
38 }
39 
40 //===----------------------------------------------------------------------===//
41 // Function stubs that are invoked instead of certain library calls
42 //===----------------------------------------------------------------------===//
43 
44 // Force the following functions to be linked in to anything that uses the
45 // JIT. This is a hack designed to work around the all-too-clever Glibc
46 // strategy of making these functions work differently when inlined vs. when
47 // not inlined, and hiding their real definitions in a separate archive file
48 // that the dynamic linker can't see. For more info, search for
49 // 'libc_nonshared.a' on Google, or read http://llvm.org/PR274.
50 #if defined(__linux__)
51 #if defined(HAVE_SYS_STAT_H)
52 #include <sys/stat.h>
53 #endif
54 #include <fcntl.h>
55 #include <unistd.h>
56 /* stat functions are redirecting to __xstat with a version number.  On x86-64
57  * linking with libc_nonshared.a and -Wl,--export-dynamic doesn't make 'stat'
58  * available as an exported symbol, so we have to add it explicitly.
59  */
60 namespace {
61 class StatSymbols {
62 public:
StatSymbols()63   StatSymbols() {
64     sys::DynamicLibrary::AddSymbol("stat", (void*)(intptr_t)stat);
65     sys::DynamicLibrary::AddSymbol("fstat", (void*)(intptr_t)fstat);
66     sys::DynamicLibrary::AddSymbol("lstat", (void*)(intptr_t)lstat);
67     sys::DynamicLibrary::AddSymbol("stat64", (void*)(intptr_t)stat64);
68     sys::DynamicLibrary::AddSymbol("fstat64", (void*)(intptr_t)fstat64);
69     sys::DynamicLibrary::AddSymbol("lstat64", (void*)(intptr_t)lstat64);
70     sys::DynamicLibrary::AddSymbol("atexit", (void*)(intptr_t)atexit);
71     sys::DynamicLibrary::AddSymbol("mknod", (void*)(intptr_t)mknod);
72   }
73 };
74 }
75 static StatSymbols initStatSymbols;
76 #endif // __linux__
77 
78 // jit_exit - Used to intercept the "exit" library call.
jit_exit(int Status)79 static void jit_exit(int Status) {
80   runAtExitHandlers();   // Run atexit handlers...
81   exit(Status);
82 }
83 
84 // jit_atexit - Used to intercept the "atexit" library call.
jit_atexit(void (* Fn)())85 static int jit_atexit(void (*Fn)()) {
86   AtExitHandlers.push_back(Fn);    // Take note of atexit handler...
87   return 0;  // Always successful
88 }
89 
jit_noop()90 static int jit_noop() {
91   return 0;
92 }
93 
94 //===----------------------------------------------------------------------===//
95 //
96 /// getPointerToNamedFunction - This method returns the address of the specified
97 /// function by using the dynamic loader interface.  As such it is only useful
98 /// for resolving library symbols, not code generated symbols.
99 ///
getPointerToNamedFunction(const std::string & Name,bool AbortOnFailure)100 void *JIT::getPointerToNamedFunction(const std::string &Name,
101                                      bool AbortOnFailure) {
102   if (!isSymbolSearchingDisabled()) {
103     // Check to see if this is one of the functions we want to intercept.  Note,
104     // we cast to intptr_t here to silence a -pedantic warning that complains
105     // about casting a function pointer to a normal pointer.
106     if (Name == "exit") return (void*)(intptr_t)&jit_exit;
107     if (Name == "atexit") return (void*)(intptr_t)&jit_atexit;
108 
109     // We should not invoke parent's ctors/dtors from generated main()!
110     // On Mingw and Cygwin, the symbol __main is resolved to
111     // callee's(eg. tools/lli) one, to invoke wrong duplicated ctors
112     // (and register wrong callee's dtors with atexit(3)).
113     // We expect ExecutionEngine::runStaticConstructorsDestructors()
114     // is called before ExecutionEngine::runFunctionAsMain() is called.
115     if (Name == "__main") return (void*)(intptr_t)&jit_noop;
116 
117     const char *NameStr = Name.c_str();
118     // If this is an asm specifier, skip the sentinal.
119     if (NameStr[0] == 1) ++NameStr;
120 
121     // If it's an external function, look it up in the process image...
122     void *Ptr = sys::DynamicLibrary::SearchForAddressOfSymbol(NameStr);
123     if (Ptr) return Ptr;
124 
125     // If it wasn't found and if it starts with an underscore ('_') character,
126     // and has an asm specifier, try again without the underscore.
127     if (Name[0] == 1 && NameStr[0] == '_') {
128       Ptr = sys::DynamicLibrary::SearchForAddressOfSymbol(NameStr+1);
129       if (Ptr) return Ptr;
130     }
131 
132     // Darwin/PPC adds $LDBLStub suffixes to various symbols like printf.  These
133     // are references to hidden visibility symbols that dlsym cannot resolve.
134     // If we have one of these, strip off $LDBLStub and try again.
135 #if defined(__APPLE__) && defined(__ppc__)
136     if (Name.size() > 9 && Name[Name.size()-9] == '$' &&
137         memcmp(&Name[Name.size()-8], "LDBLStub", 8) == 0) {
138       // First try turning $LDBLStub into $LDBL128. If that fails, strip it off.
139       // This mirrors logic in libSystemStubs.a.
140       std::string Prefix = std::string(Name.begin(), Name.end()-9);
141       if (void *Ptr = getPointerToNamedFunction(Prefix+"$LDBL128", false))
142         return Ptr;
143       if (void *Ptr = getPointerToNamedFunction(Prefix, false))
144         return Ptr;
145     }
146 #endif
147   }
148 
149   /// If a LazyFunctionCreator is installed, use it to get/create the function.
150   if (LazyFunctionCreator)
151     if (void *RP = LazyFunctionCreator(Name))
152       return RP;
153 
154   if (AbortOnFailure) {
155     report_fatal_error("Program used external function '"+Name+
156                       "' which could not be resolved!");
157   }
158   return 0;
159 }
160