compiler-rt/lib/xray/xray_init.cpp

   1 //===-- xray_init.cpp -------------------------------------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file is a part of XRay, a dynamic runtime instrumentation system.
  10 //
  11 // XRay initialisation logic.
  12 //===----------------------------------------------------------------------===//
  13
  14 #include <fcntl.h>
  15 #include <strings.h>
  16 #include <unistd.h>
  17
  18 #include "sanitizer_common/sanitizer_common.h"
  19 #include "xray_defs.h"
  20 #include "xray_flags.h"
  21 #include "xray_interface_internal.h"
  22
  23 extern "C" {
  24 void __xray_init();
  25 extern const XRaySledEntry __start_xray_instr_map[] __attribute__((weak));
  26 extern const XRaySledEntry __stop_xray_instr_map[] __attribute__((weak));
  27 extern const XRayFunctionSledIndex __start_xray_fn_idx[] __attribute__((weak));
  28 extern const XRayFunctionSledIndex __stop_xray_fn_idx[] __attribute__((weak));
  29
  30 #if SANITIZER_MAC
  31 // HACK: This is a temporary workaround to make XRay build on
  32 // Darwin, but it will probably not work at runtime.
  33 const XRaySledEntry __start_xray_instr_map[] = {};
  34 extern const XRaySledEntry __stop_xray_instr_map[] = {};
  35 extern const XRayFunctionSledIndex __start_xray_fn_idx[] = {};
  36 extern const XRayFunctionSledIndex __stop_xray_fn_idx[] = {};
  37 #endif
  38 }
  39
  40 using namespace __xray;
  41
  42 // When set to 'true' this means the XRay runtime has been initialised. We use
  43 // the weak symbols defined above (__start_xray_inst_map and
  44 // __stop_xray_instr_map) to initialise the instrumentation map that XRay uses
  45 // for runtime patching/unpatching of instrumentation points.
  46 //
  47 // FIXME: Support DSO instrumentation maps too. The current solution only works
  48 // for statically linked executables.
  49 atomic_uint8_t XRayInitialized{0};
  50
  51 // This should always be updated before XRayInitialized is updated.
  52 SpinMutex XRayInstrMapMutex;
  53 XRaySledMap XRayInstrMap;
  54
  55 // Global flag to determine whether the flags have been initialized.
  56 atomic_uint8_t XRayFlagsInitialized{0};
  57
  58 // A mutex to allow only one thread to initialize the XRay data structures.
  59 SpinMutex XRayInitMutex;
  60
  61 // __xray_init() will do the actual loading of the current process' memory map
  62 // and then proceed to look for the .xray_instr_map section/segment.
  63 void __xray_init() XRAY_NEVER_INSTRUMENT {
  64   SpinMutexLock Guard(&XRayInitMutex);
  65   // Short-circuit if we've already initialized XRay before.
  66   if (atomic_load(&XRayInitialized, memory_order_acquire))
  67     return;
  68
  69   // XRAY is not compatible with PaX MPROTECT
  70   CheckMPROTECT();
  71
  72   if (!atomic_load(&XRayFlagsInitialized, memory_order_acquire)) {
  73     initializeFlags();
  74     atomic_store(&XRayFlagsInitialized, true, memory_order_release);
  75   }
  76
  77   if (__start_xray_instr_map == nullptr) {
  78     if (Verbosity())
  79       Report("XRay instrumentation map missing. Not initializing XRay.\n");
  80     return;
  81   }
  82
  83   {
  84     SpinMutexLock Guard(&XRayInstrMapMutex);
  85     XRayInstrMap.Sleds = __start_xray_instr_map;
  86     XRayInstrMap.Entries = __stop_xray_instr_map - __start_xray_instr_map;
  87     XRayInstrMap.SledsIndex = __start_xray_fn_idx;
  88     XRayInstrMap.Functions = __stop_xray_fn_idx - __start_xray_fn_idx;
  89   }
  90   atomic_store(&XRayInitialized, true, memory_order_release);
  91
  92 #ifndef XRAY_NO_PREINIT
  93   if (flags()->patch_premain)
  94     __xray_patch();
  95 #endif
  96 }
  97
  98 // FIXME: Make check-xray tests work on FreeBSD without
  99 // SANITIZER_CAN_USE_PREINIT_ARRAY.
 100 // See sanitizer_internal_defs.h where the macro is defined.
 101 // Calling unresolved PLT functions in .preinit_array can lead to deadlock on
 102 // FreeBSD but here it seems benign.
 103 #if !defined(XRAY_NO_PREINIT) &&                                               \
 104     (SANITIZER_CAN_USE_PREINIT_ARRAY || SANITIZER_FREEBSD)
 105 // Only add the preinit array initialization if the sanitizers can.
 106 __attribute__((section(".preinit_array"),
 107                used)) void (*__local_xray_preinit)(void) = __xray_init;
 108 #else
 109 // If we cannot use the .preinit_array section, we should instead use dynamic
 110 // initialisation.
 111 __attribute__ ((constructor (0)))
 112 static void __local_xray_dyninit() {
 113   __xray_init();
 114 }
 115 #endif