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/ErrorHandling.h"
  20 #include "llvm/Support/Streams.h"
  21 #include "llvm/System/DynamicLibrary.h"
  22 #include "llvm/Config/config.h"
  23 using namespace llvm;
  24
  25 // AtExitHandlers - List of functions to call when the program exits,
  26 // registered with the atexit() library function.
  27 static std::vector<void (*)()> AtExitHandlers;
  28
  29 /// runAtExitHandlers - Run any functions registered by the program's
  30 /// calls to atexit(3), which we intercept and store in
  31 /// AtExitHandlers.
  32 ///
  33 static void runAtExitHandlers() {
  34   while (!AtExitHandlers.empty()) {
  35     void (*Fn)() = AtExitHandlers.back();
  36     AtExitHandlers.pop_back();
  37     Fn();
  38   }
  39 }
  40
  41 //===----------------------------------------------------------------------===//
  42 // Function stubs that are invoked instead of certain library calls
  43 //===----------------------------------------------------------------------===//
  44
  45 // Force the following functions to be linked in to anything that uses the
  46 // JIT. This is a hack designed to work around the all-too-clever Glibc
  47 // strategy of making these functions work differently when inlined vs. when
  48 // not inlined, and hiding their real definitions in a separate archive file
  49 // that the dynamic linker can't see. For more info, search for
  50 // 'libc_nonshared.a' on Google, or read http://llvm.org/PR274.
  51 #if defined(__linux__)
  52 #if defined(HAVE_SYS_STAT_H)
  53 #include <sys/stat.h>
  54 #endif
  55 #include <fcntl.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:
  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("\x1stat64", (void*)(intptr_t)stat64);
  69     sys::DynamicLibrary::AddSymbol("\x1open64", (void*)(intptr_t)open64);
  70     sys::DynamicLibrary::AddSymbol("\x1lseek64", (void*)(intptr_t)lseek64);
  71     sys::DynamicLibrary::AddSymbol("fstat64", (void*)(intptr_t)fstat64);
  72     sys::DynamicLibrary::AddSymbol("lstat64", (void*)(intptr_t)lstat64);
  73     sys::DynamicLibrary::AddSymbol("atexit", (void*)(intptr_t)atexit);
  74     sys::DynamicLibrary::AddSymbol("mknod", (void*)(intptr_t)mknod);
  75   }
  76 };
  77 }
  78 static StatSymbols initStatSymbols;
  79 #endif // __linux__
  80
  81 // jit_exit - Used to intercept the "exit" library call.
  82 static void jit_exit(int Status) {
  83   runAtExitHandlers();   // Run atexit handlers...
  84   exit(Status);
  85 }
  86
  87 // jit_atexit - Used to intercept the "atexit" library call.
  88 static int jit_atexit(void (*Fn)()) {
  89   AtExitHandlers.push_back(Fn);    // Take note of atexit handler...
  90   return 0;  // Always successful
  91 }
  92
  93 //===----------------------------------------------------------------------===//
  94 //
  95 /// getPointerToNamedFunction - This method returns the address of the specified
  96 /// function by using the dynamic loader interface.  As such it is only useful
  97 /// for resolving library symbols, not code generated symbols.
  98 ///
  99 void *JIT::getPointerToNamedFunction(const std::string &Name,
 100                                      bool AbortOnFailure) {
 101   if (!isSymbolSearchingDisabled()) {
 102     // Check to see if this is one of the functions we want to intercept.  Note,
 103     // we cast to intptr_t here to silence a -pedantic warning that complains
 104     // about casting a function pointer to a normal pointer.
 105     if (Name == "exit") return (void*)(intptr_t)&jit_exit;
 106     if (Name == "atexit") return (void*)(intptr_t)&jit_atexit;
 107
 108     const char *NameStr = Name.c_str();
 109     // If this is an asm specifier, skip the sentinal.
 110     if (NameStr[0] == 1) ++NameStr;
 111
 112     // If it's an external function, look it up in the process image...
 113     void *Ptr = sys::DynamicLibrary::SearchForAddressOfSymbol(NameStr);
 114     if (Ptr) return Ptr;
 115
 116     // If it wasn't found and if it starts with an underscore ('_') character,
 117     // and has an asm specifier, try again without the underscore.
 118     if (Name[0] == 1 && NameStr[0] == '_') {
 119       Ptr = sys::DynamicLibrary::SearchForAddressOfSymbol(NameStr+1);
 120       if (Ptr) return Ptr;
 121     }
 122
 123     // Darwin/PPC adds $LDBLStub suffixes to various symbols like printf.  These
 124     // are references to hidden visibility symbols that dlsym cannot resolve.
 125     // If we have one of these, strip off $LDBLStub and try again.
 126 #if defined(__APPLE__) && defined(__ppc__)
 127     if (Name.size() > 9 && Name[Name.size()-9] == '$' &&
 128         memcmp(&Name[Name.size()-8], "LDBLStub", 8) == 0) {
 129       // First try turning $LDBLStub into $LDBL128. If that fails, strip it off.
 130       // This mirrors logic in libSystemStubs.a.
 131       std::string Prefix = std::string(Name.begin(), Name.end()-9);
 132       if (void *Ptr = getPointerToNamedFunction(Prefix+"$LDBL128", false))
 133         return Ptr;
 134       if (void *Ptr = getPointerToNamedFunction(Prefix, false))
 135         return Ptr;
 136     }
 137 #endif
 138   }
 139
 140   /// If a LazyFunctionCreator is installed, use it to get/create the function.
 141   if (LazyFunctionCreator)
 142     if (void *RP = LazyFunctionCreator(Name))
 143       return RP;
 144
 145   if (AbortOnFailure) {
 146     llvm_report_error("Program used external function '"+Name+
 147                       "' which could not be resolved!");
 148   }
 149   return 0;
 150 }