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xray_init.cc revision 1.1 
      1 //===-- xray_init.cc --------------------------------------------*- 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 is a part of XRay, a dynamic runtime instrumentation system.
     11 //
     12 // XRay initialisation logic.
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include <fcntl.h>
     16 #include <strings.h>
     17 #include <unistd.h>
     18 
     19 #include "sanitizer_common/sanitizer_common.h"
     20 #include "xray_defs.h"
     21 #include "xray_flags.h"
     22 #include "xray_interface_internal.h"
     23 
     24 extern "C" {
     25 void __xray_init();
     26 extern const XRaySledEntry __start_xray_instr_map[] __attribute__((weak));
     27 extern const XRaySledEntry __stop_xray_instr_map[] __attribute__((weak));
     28 extern const XRayFunctionSledIndex __start_xray_fn_idx[] __attribute__((weak));
     29 extern const XRayFunctionSledIndex __stop_xray_fn_idx[] __attribute__((weak));
     30 
     31 #if SANITIZER_MAC
     32 // HACK: This is a temporary workaround to make XRay build on
     33 // Darwin, but it will probably not work at runtime.
     34 const XRaySledEntry __start_xray_instr_map[] = {};
     35 extern const XRaySledEntry __stop_xray_instr_map[] = {};
     36 extern const XRayFunctionSledIndex __start_xray_fn_idx[] = {};
     37 extern const XRayFunctionSledIndex __stop_xray_fn_idx[] = {};
     38 #endif
     39 }
     40 
     41 using namespace __xray;
     42 
     43 // When set to 'true' this means the XRay runtime has been initialised. We use
     44 // the weak symbols defined above (__start_xray_inst_map and
     45 // __stop_xray_instr_map) to initialise the instrumentation map that XRay uses
     46 // for runtime patching/unpatching of instrumentation points.
     47 //
     48 // FIXME: Support DSO instrumentation maps too. The current solution only works
     49 // for statically linked executables.
     50 atomic_uint8_t XRayInitialized{0};
     51 
     52 // This should always be updated before XRayInitialized is updated.
     53 SpinMutex XRayInstrMapMutex;
     54 XRaySledMap XRayInstrMap;
     55 
     56 // Global flag to determine whether the flags have been initialized.
     57 atomic_uint8_t XRayFlagsInitialized{0};
     58 
     59 // A mutex to allow only one thread to initialize the XRay data structures.
     60 SpinMutex XRayInitMutex;
     61 
     62 // __xray_init() will do the actual loading of the current process' memory map
     63 // and then proceed to look for the .xray_instr_map section/segment.
     64 void __xray_init() XRAY_NEVER_INSTRUMENT {
     65   SpinMutexLock Guard(&XRayInitMutex);
     66   // Short-circuit if we've already initialized XRay before.
     67   if (atomic_load(&XRayInitialized, memory_order_acquire))
     68     return;
     69 
     70   // XRAY is not compatible with PaX MPROTECT
     71   CheckMPROTECT();
     72 
     73   if (!atomic_load(&XRayFlagsInitialized, memory_order_acquire)) {
     74     initializeFlags();
     75     atomic_store(&XRayFlagsInitialized, true, memory_order_release);
     76   }
     77 
     78   if (__start_xray_instr_map == nullptr) {
     79     if (Verbosity())
     80       Report("XRay instrumentation map missing. Not initializing XRay.\n");
     81     return;
     82   }
     83 
     84   {
     85     SpinMutexLock Guard(&XRayInstrMapMutex);
     86     XRayInstrMap.Sleds = __start_xray_instr_map;
     87     XRayInstrMap.Entries = __stop_xray_instr_map - __start_xray_instr_map;
     88     XRayInstrMap.SledsIndex = __start_xray_fn_idx;
     89     XRayInstrMap.Functions = __stop_xray_fn_idx - __start_xray_fn_idx;
     90   }
     91   atomic_store(&XRayInitialized, true, memory_order_release);
     92 
     93 #ifndef XRAY_NO_PREINIT
     94   if (flags()->patch_premain)
     95     __xray_patch();
     96 #endif
     97 }
     98 
     99 // FIXME: Make check-xray tests work on FreeBSD without
    100 // SANITIZER_CAN_USE_PREINIT_ARRAY.
    101 // See sanitizer_internal_defs.h where the macro is defined.
    102 // Calling unresolved PLT functions in .preinit_array can lead to deadlock on
    103 // FreeBSD but here it seems benign.
    104 #if !defined(XRAY_NO_PREINIT) &&                                               \
    105     (SANITIZER_CAN_USE_PREINIT_ARRAY || SANITIZER_FREEBSD)
    106 // Only add the preinit array initialization if the sanitizers can.
    107 __attribute__((section(".preinit_array"),
    108                used)) void (*__local_xray_preinit)(void) = __xray_init;
    109 #else
    110 // If we cannot use the .preinit_array section, we should instead use dynamic
    111 // initialisation.
    112 __attribute__ ((constructor (0)))
    113 static void __local_xray_dyninit() {
    114   __xray_init();
    115 }
    116 #endif
    117