lib/ExecutionEngine/JIT/Intercept.cpp

   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/Streams.h"
  20 #include "llvm/System/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 ///
  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
  55 /* stat functions are redirecting to __xstat with a version number.  On x86-64
  56  * linking with libc_nonshared.a and -Wl,--export-dynamic doesn't make 'stat'
  57  * available as an exported symbol, so we have to add it explicitly.
  58  */
  59 class StatSymbols {
  60 public:
  61   StatSymbols() {
  62     sys::DynamicLibrary::AddSymbol("stat", (void*)(intptr_t)stat);
  63     sys::DynamicLibrary::AddSymbol("fstat", (void*)(intptr_t)fstat);
  64     sys::DynamicLibrary::AddSymbol("lstat", (void*)(intptr_t)lstat);
  65     sys::DynamicLibrary::AddSymbol("stat64", (void*)(intptr_t)stat64);
  66     sys::DynamicLibrary::AddSymbol("fstat64", (void*)(intptr_t)fstat64);
  67     sys::DynamicLibrary::AddSymbol("lstat64", (void*)(intptr_t)lstat64);
  68     sys::DynamicLibrary::AddSymbol("atexit", (void*)(intptr_t)atexit);
  69     sys::DynamicLibrary::AddSymbol("mknod", (void*)(intptr_t)mknod);
  70   }
  71 };
  72 static StatSymbols initStatSymbols;
  73 #endif // __linux__
  74
  75 // jit_exit - Used to intercept the "exit" library call.
  76 static void jit_exit(int Status) {
  77   runAtExitHandlers();   // Run atexit handlers...
  78   exit(Status);
  79 }
  80
  81 // jit_atexit - Used to intercept the "atexit" library call.
  82 static int jit_atexit(void (*Fn)(void)) {
  83   AtExitHandlers.push_back(Fn);    // Take note of atexit handler...
  84   return 0;  // Always successful
  85 }
  86
  87 //===----------------------------------------------------------------------===//
  88 //
  89 /// getPointerToNamedFunction - This method returns the address of the specified
  90 /// function by using the dynamic loader interface.  As such it is only useful
  91 /// for resolving library symbols, not code generated symbols.
  92 ///
  93 void *JIT::getPointerToNamedFunction(const std::string &Name,
  94                                      bool AbortOnFailure) {
  95   if (!isSymbolSearchingDisabled()) {
  96     // Check to see if this is one of the functions we want to intercept.  Note,
  97     // we cast to intptr_t here to silence a -pedantic warning that complains
  98     // about casting a function pointer to a normal pointer.
  99     if (Name == "exit") return (void*)(intptr_t)&jit_exit;
 100     if (Name == "atexit") return (void*)(intptr_t)&jit_atexit;
 101
 102     const char *NameStr = Name.c_str();
 103     // If this is an asm specifier, skip the sentinal.
 104     if (NameStr[0] == 1) ++NameStr;
 105
 106     // If it's an external function, look it up in the process image...
 107     void *Ptr = sys::DynamicLibrary::SearchForAddressOfSymbol(NameStr);
 108     if (Ptr) return Ptr;
 109
 110     // If it wasn't found and if it starts with an underscore ('_') character,
 111     // and has an asm specifier, try again without the underscore.
 112     if (Name[0] == 1 && NameStr[0] == '_') {
 113       Ptr = sys::DynamicLibrary::SearchForAddressOfSymbol(NameStr+1);
 114       if (Ptr) return Ptr;
 115     }
 116
 117     // Darwin/PPC adds $LDBLStub suffixes to various symbols like printf.  These
 118     // are references to hidden visibility symbols that dlsym cannot resolve.
 119     // If we have one of these, strip off $LDBLStub and try again.
 120 #if defined(__APPLE__) && defined(__ppc__)
 121     if (Name.size() > 9 && Name[Name.size()-9] == '$' &&
 122         memcmp(&Name[Name.size()-8], "LDBLStub", 8) == 0) {
 123       // First try turning $LDBLStub into $LDBL128. If that fails, strip it off.
 124       // This mirrors logic in libSystemStubs.a.
 125       std::string Prefix = std::string(Name.begin(), Name.end()-9);
 126       if (void *Ptr = getPointerToNamedFunction(Prefix+"$LDBL128", false))
 127         return Ptr;
 128       if (void *Ptr = getPointerToNamedFunction(Prefix, false))
 129         return Ptr;
 130     }
 131 #endif
 132   }
 133
 134   /// If a LazyFunctionCreator is installed, use it to get/create the function.
 135   if (LazyFunctionCreator)
 136     if (void *RP = LazyFunctionCreator(Name))
 137       return RP;
 138
 139   if (AbortOnFailure) {
 140     cerr << "ERROR: Program used external function '" << Name
 141          << "' which could not be resolved!\n";
 142     abort();
 143   }
 144   return 0;
 145 }