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1 //===-- sanitizer_unwind_linux_libcdep.cc ---------------------------------===//
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 contains the unwind.h-based (aka "slow") stack unwinding routines
11 // available to the tools on Linux, Android, and FreeBSD.
12 //===----------------------------------------------------------------------===//
13 
14 #include "sanitizer_platform.h"
15 #if SANITIZER_FREEBSD || SANITIZER_LINUX
16 #include "sanitizer_common.h"
17 #include "sanitizer_stacktrace.h"
18 
19 #if SANITIZER_ANDROID
20 #include <dlfcn.h>  // for dlopen()
21 #endif
22 
23 #if SANITIZER_FREEBSD
24 #define _GNU_SOURCE  // to declare _Unwind_Backtrace() from <unwind.h>
25 #endif
26 #include <unwind.h>
27 
28 namespace __sanitizer {
29 
30 //------------------------- SlowUnwindStack -----------------------------------
31 
32 typedef struct {
33   uptr absolute_pc;
34   uptr stack_top;
35   uptr stack_size;
36 } backtrace_frame_t;
37 
38 extern "C" {
39 typedef void *(*acquire_my_map_info_list_func)();
40 typedef void (*release_my_map_info_list_func)(void *map);
41 typedef sptr (*unwind_backtrace_signal_arch_func)(
42     void *siginfo, void *sigcontext, void *map_info_list,
43     backtrace_frame_t *backtrace, uptr ignore_depth, uptr max_depth);
44 acquire_my_map_info_list_func acquire_my_map_info_list;
45 release_my_map_info_list_func release_my_map_info_list;
46 unwind_backtrace_signal_arch_func unwind_backtrace_signal_arch;
47 } // extern "C"
48 
49 #if SANITIZER_ANDROID
SanitizerInitializeUnwinder()50 void SanitizerInitializeUnwinder() {
51   if (AndroidGetApiLevel() >= ANDROID_LOLLIPOP_MR1) return;
52 
53   // Pre-lollipop Android can not unwind through signal handler frames with
54   // libgcc unwinder, but it has a libcorkscrew.so library with the necessary
55   // workarounds.
56   void *p = dlopen("libcorkscrew.so", RTLD_LAZY);
57   if (!p) {
58     VReport(1,
59             "Failed to open libcorkscrew.so. You may see broken stack traces "
60             "in SEGV reports.");
61     return;
62   }
63   acquire_my_map_info_list =
64       (acquire_my_map_info_list_func)(uptr)dlsym(p, "acquire_my_map_info_list");
65   release_my_map_info_list =
66       (release_my_map_info_list_func)(uptr)dlsym(p, "release_my_map_info_list");
67   unwind_backtrace_signal_arch = (unwind_backtrace_signal_arch_func)(uptr)dlsym(
68       p, "unwind_backtrace_signal_arch");
69   if (!acquire_my_map_info_list || !release_my_map_info_list ||
70       !unwind_backtrace_signal_arch) {
71     VReport(1,
72             "Failed to find one of the required symbols in libcorkscrew.so. "
73             "You may see broken stack traces in SEGV reports.");
74     acquire_my_map_info_list = 0;
75     unwind_backtrace_signal_arch = 0;
76     release_my_map_info_list = 0;
77   }
78 }
79 #endif
80 
81 #ifdef __arm__
82 #define UNWIND_STOP _URC_END_OF_STACK
83 #define UNWIND_CONTINUE _URC_NO_REASON
84 #else
85 #define UNWIND_STOP _URC_NORMAL_STOP
86 #define UNWIND_CONTINUE _URC_NO_REASON
87 #endif
88 
Unwind_GetIP(struct _Unwind_Context * ctx)89 uptr Unwind_GetIP(struct _Unwind_Context *ctx) {
90 #if defined(__arm__) && !SANITIZER_MAC
91   uptr val;
92   _Unwind_VRS_Result res = _Unwind_VRS_Get(ctx, _UVRSC_CORE,
93       15 /* r15 = PC */, _UVRSD_UINT32, &val);
94   CHECK(res == _UVRSR_OK && "_Unwind_VRS_Get failed");
95   // Clear the Thumb bit.
96   return val & ~(uptr)1;
97 #else
98   return _Unwind_GetIP(ctx);
99 #endif
100 }
101 
102 struct UnwindTraceArg {
103   BufferedStackTrace *stack;
104   u32 max_depth;
105 };
106 
Unwind_Trace(struct _Unwind_Context * ctx,void * param)107 _Unwind_Reason_Code Unwind_Trace(struct _Unwind_Context *ctx, void *param) {
108   UnwindTraceArg *arg = (UnwindTraceArg*)param;
109   CHECK_LT(arg->stack->size, arg->max_depth);
110   uptr pc = Unwind_GetIP(ctx);
111   const uptr kPageSize = GetPageSizeCached();
112   // Let's assume that any pointer in the 0th page (i.e. <0x1000 on i386 and
113   // x86_64) is invalid and stop unwinding here.  If we're adding support for
114   // a platform where this isn't true, we need to reconsider this check.
115   if (pc < kPageSize) return UNWIND_STOP;
116   arg->stack->trace_buffer[arg->stack->size++] = pc;
117   if (arg->stack->size == arg->max_depth) return UNWIND_STOP;
118   return UNWIND_CONTINUE;
119 }
120 
SlowUnwindStack(uptr pc,u32 max_depth)121 void BufferedStackTrace::SlowUnwindStack(uptr pc, u32 max_depth) {
122   CHECK_GE(max_depth, 2);
123   size = 0;
124   UnwindTraceArg arg = {this, Min(max_depth + 1, kStackTraceMax)};
125   _Unwind_Backtrace(Unwind_Trace, &arg);
126   // We need to pop a few frames so that pc is on top.
127   uptr to_pop = LocatePcInTrace(pc);
128   // trace_buffer[0] belongs to the current function so we always pop it,
129   // unless there is only 1 frame in the stack trace (1 frame is always better
130   // than 0!).
131   // 1-frame stacks don't normally happen, but this depends on the actual
132   // unwinder implementation (libgcc, libunwind, etc) which is outside of our
133   // control.
134   if (to_pop == 0 && size > 1)
135     to_pop = 1;
136   PopStackFrames(to_pop);
137   trace_buffer[0] = pc;
138 }
139 
SlowUnwindStackWithContext(uptr pc,void * context,u32 max_depth)140 void BufferedStackTrace::SlowUnwindStackWithContext(uptr pc, void *context,
141                                                     u32 max_depth) {
142   CHECK_GE(max_depth, 2);
143   if (!unwind_backtrace_signal_arch) {
144     SlowUnwindStack(pc, max_depth);
145     return;
146   }
147 
148   void *map = acquire_my_map_info_list();
149   CHECK(map);
150   InternalScopedBuffer<backtrace_frame_t> frames(kStackTraceMax);
151   // siginfo argument appears to be unused.
152   sptr res = unwind_backtrace_signal_arch(/* siginfo */ 0, context, map,
153                                           frames.data(),
154                                           /* ignore_depth */ 0, max_depth);
155   release_my_map_info_list(map);
156   if (res < 0) return;
157   CHECK_LE((uptr)res, kStackTraceMax);
158 
159   size = 0;
160   // +2 compensate for libcorkscrew unwinder returning addresses of call
161   // instructions instead of raw return addresses.
162   for (sptr i = 0; i < res; ++i)
163     trace_buffer[size++] = frames[i].absolute_pc + 2;
164 }
165 
166 }  // namespace __sanitizer
167 
168 #endif  // SANITIZER_FREEBSD || SANITIZER_LINUX
169