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_APPLE
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.
__xray_init()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 if (__start_xray_fn_idx != nullptr) {
88 XRayInstrMap.SledsIndex = __start_xray_fn_idx;
89 XRayInstrMap.Functions = __stop_xray_fn_idx - __start_xray_fn_idx;
90 } else {
91 size_t CountFunctions = 0;
92 uint64_t LastFnAddr = 0;
93
94 for (std::size_t I = 0; I < XRayInstrMap.Entries; I++) {
95 const auto &Sled = XRayInstrMap.Sleds[I];
96 const auto Function = Sled.function();
97 if (Function != LastFnAddr) {
98 CountFunctions++;
99 LastFnAddr = Function;
100 }
101 }
102
103 XRayInstrMap.Functions = CountFunctions;
104 }
105 }
106 atomic_store(&XRayInitialized, true, memory_order_release);
107
108 #ifndef XRAY_NO_PREINIT
109 if (flags()->patch_premain)
110 __xray_patch();
111 #endif
112 }
113
114 // FIXME: Make check-xray tests work on FreeBSD without
115 // SANITIZER_CAN_USE_PREINIT_ARRAY.
116 // See sanitizer_internal_defs.h where the macro is defined.
117 // Calling unresolved PLT functions in .preinit_array can lead to deadlock on
118 // FreeBSD but here it seems benign.
119 #if !defined(XRAY_NO_PREINIT) && \
120 (SANITIZER_CAN_USE_PREINIT_ARRAY || SANITIZER_FREEBSD)
121 // Only add the preinit array initialization if the sanitizers can.
122 __attribute__((section(".preinit_array"),
123 used)) void (*__local_xray_preinit)(void) = __xray_init;
124 #else
125 // If we cannot use the .preinit_array section, we should instead use dynamic
126 // initialisation.
127 __attribute__ ((constructor (0)))
__local_xray_dyninit()128 static void __local_xray_dyninit() {
129 __xray_init();
130 }
131 #endif
132