1//===-- sanitizer_coverage_fuchsia.cpp ------------------------------------===//
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// Sanitizer Coverage Controller for Trace PC Guard, Fuchsia-specific version.
10//
11// This Fuchsia-specific implementation uses the same basic scheme and the
12// same simple '.sancov' file format as the generic implementation.  The
13// difference is that we just produce a single blob of output for the whole
14// program, not a separate one per DSO.  We do not sort the PC table and do
15// not prune the zeros, so the resulting file is always as large as it
16// would be to report 100% coverage.  Implicit tracing information about
17// the address ranges of DSOs allows offline tools to split the one big
18// blob into separate files that the 'sancov' tool can understand.
19//
20// Unlike the traditional implementation that uses an atexit hook to write
21// out data files at the end, the results on Fuchsia do not go into a file
22// per se.  The 'coverage_dir' option is ignored.  Instead, they are stored
23// directly into a shared memory object (a Zircon VMO).  At exit, that VMO
24// is handed over to a system service that's responsible for getting the
25// data out to somewhere that it can be fed into the sancov tool (where and
26// how is not our problem).
27
28#include "sanitizer_platform.h"
29#if SANITIZER_FUCHSIA
30#include <zircon/process.h>
31#include <zircon/sanitizer.h>
32#include <zircon/syscalls.h>
33
34#include "sanitizer_atomic.h"
35#include "sanitizer_common.h"
36#include "sanitizer_internal_defs.h"
37#include "sanitizer_symbolizer_fuchsia.h"
38
39using namespace __sanitizer;
40
41namespace __sancov {
42namespace {
43
44// TODO(mcgrathr): Move the constant into a header shared with other impls.
45constexpr u64 Magic64 = 0xC0BFFFFFFFFFFF64ULL;
46static_assert(SANITIZER_WORDSIZE == 64, "Fuchsia is always LP64");
47
48constexpr const char kSancovSinkName[] = "sancov";
49
50// Collects trace-pc guard coverage.
51// This class relies on zero-initialization.
52class TracePcGuardController final {
53 public:
54  // For each PC location being tracked, there is a u32 reserved in global
55  // data called the "guard".  At startup, we assign each guard slot a
56  // unique index into the big results array.  Later during runtime, the
57  // first call to TracePcGuard (below) will store the corresponding PC at
58  // that index in the array.  (Each later call with the same guard slot is
59  // presumed to be from the same PC.)  Then it clears the guard slot back
60  // to zero, which tells the compiler not to bother calling in again.  At
61  // the end of the run, we have a big array where each element is either
62  // zero or is a tracked PC location that was hit in the trace.
63
64  // This is called from global constructors.  Each translation unit has a
65  // contiguous array of guard slots, and a constructor that calls here
66  // with the bounds of its array.  Those constructors are allowed to call
67  // here more than once for the same array.  Usually all of these
68  // constructors run in the initial thread, but it's possible that a
69  // dlopen call on a secondary thread will run constructors that get here.
70  void InitTracePcGuard(u32 *start, u32 *end) {
71    if (end > start && *start == 0 && common_flags()->coverage) {
72      // Complete the setup before filling in any guards with indices.
73      // This avoids the possibility of code called from Setup reentering
74      // TracePcGuard.
75      u32 idx = Setup(end - start);
76      for (u32 *p = start; p < end; ++p) {
77        *p = idx++;
78      }
79    }
80  }
81
82  void TracePcGuard(u32 *guard, uptr pc) {
83    atomic_uint32_t *guard_ptr = reinterpret_cast<atomic_uint32_t *>(guard);
84    u32 idx = atomic_exchange(guard_ptr, 0, memory_order_relaxed);
85    if (idx > 0)
86      array_[idx] = pc;
87  }
88
89  void Dump() {
90    BlockingMutexLock locked(&setup_lock_);
91    if (array_) {
92      CHECK_NE(vmo_, ZX_HANDLE_INVALID);
93
94      // Publish the VMO to the system, where it can be collected and
95      // analyzed after this process exits.  This always consumes the VMO
96      // handle.  Any failure is just logged and not indicated to us.
97      __sanitizer_publish_data(kSancovSinkName, vmo_);
98      vmo_ = ZX_HANDLE_INVALID;
99
100      // This will route to __sanitizer_log_write, which will ensure that
101      // information about shared libraries is written out.  This message
102      // uses the `dumpfile` symbolizer markup element to highlight the
103      // dump.  See the explanation for this in:
104      // https://fuchsia.googlesource.com/zircon/+/master/docs/symbolizer_markup.md
105      Printf("SanitizerCoverage: " FORMAT_DUMPFILE " with up to %u PCs\n",
106             kSancovSinkName, vmo_name_, next_index_ - 1);
107    }
108  }
109
110 private:
111  // We map in the largest possible view into the VMO: one word
112  // for every possible 32-bit index value.  This avoids the need
113  // to change the mapping when increasing the size of the VMO.
114  // We can always spare the 32G of address space.
115  static constexpr size_t MappingSize = sizeof(uptr) << 32;
116
117  BlockingMutex setup_lock_ = BlockingMutex(LINKER_INITIALIZED);
118  uptr *array_ = nullptr;
119  u32 next_index_ = 0;
120  zx_handle_t vmo_ = {};
121  char vmo_name_[ZX_MAX_NAME_LEN] = {};
122
123  size_t DataSize() const { return next_index_ * sizeof(uintptr_t); }
124
125  u32 Setup(u32 num_guards) {
126    BlockingMutexLock locked(&setup_lock_);
127    DCHECK(common_flags()->coverage);
128
129    if (next_index_ == 0) {
130      CHECK_EQ(vmo_, ZX_HANDLE_INVALID);
131      CHECK_EQ(array_, nullptr);
132
133      // The first sample goes at [1] to reserve [0] for the magic number.
134      next_index_ = 1 + num_guards;
135
136      zx_status_t status = _zx_vmo_create(DataSize(), ZX_VMO_RESIZABLE, &vmo_);
137      CHECK_EQ(status, ZX_OK);
138
139      // Give the VMO a name including our process KOID so it's easy to spot.
140      internal_snprintf(vmo_name_, sizeof(vmo_name_), "%s.%zu", kSancovSinkName,
141                        internal_getpid());
142      _zx_object_set_property(vmo_, ZX_PROP_NAME, vmo_name_,
143                              internal_strlen(vmo_name_));
144      uint64_t size = DataSize();
145      status = _zx_object_set_property(vmo_, ZX_PROP_VMO_CONTENT_SIZE, &size,
146                                       sizeof(size));
147      CHECK_EQ(status, ZX_OK);
148
149      // Map the largest possible view we might need into the VMO.  Later
150      // we might need to increase the VMO's size before we can use larger
151      // indices, but we'll never move the mapping address so we don't have
152      // any multi-thread synchronization issues with that.
153      uintptr_t mapping;
154      status =
155          _zx_vmar_map(_zx_vmar_root_self(), ZX_VM_PERM_READ | ZX_VM_PERM_WRITE,
156                       0, vmo_, 0, MappingSize, &mapping);
157      CHECK_EQ(status, ZX_OK);
158
159      // Hereafter other threads are free to start storing into
160      // elements [1, next_index_) of the big array.
161      array_ = reinterpret_cast<uptr *>(mapping);
162
163      // Store the magic number.
164      // Hereafter, the VMO serves as the contents of the '.sancov' file.
165      array_[0] = Magic64;
166
167      return 1;
168    } else {
169      // The VMO is already mapped in, but it's not big enough to use the
170      // new indices.  So increase the size to cover the new maximum index.
171
172      CHECK_NE(vmo_, ZX_HANDLE_INVALID);
173      CHECK_NE(array_, nullptr);
174
175      uint32_t first_index = next_index_;
176      next_index_ += num_guards;
177
178      zx_status_t status = _zx_vmo_set_size(vmo_, DataSize());
179      CHECK_EQ(status, ZX_OK);
180      uint64_t size = DataSize();
181      status = _zx_object_set_property(vmo_, ZX_PROP_VMO_CONTENT_SIZE, &size,
182                                       sizeof(size));
183      CHECK_EQ(status, ZX_OK);
184
185      return first_index;
186    }
187  }
188};
189
190static TracePcGuardController pc_guard_controller;
191
192}  // namespace
193}  // namespace __sancov
194
195namespace __sanitizer {
196void InitializeCoverage(bool enabled, const char *dir) {
197  CHECK_EQ(enabled, common_flags()->coverage);
198  CHECK_EQ(dir, common_flags()->coverage_dir);
199
200  static bool coverage_enabled = false;
201  if (!coverage_enabled) {
202    coverage_enabled = enabled;
203    Atexit(__sanitizer_cov_dump);
204    AddDieCallback(__sanitizer_cov_dump);
205  }
206}
207}  // namespace __sanitizer
208
209extern "C" {
210SANITIZER_INTERFACE_ATTRIBUTE void __sanitizer_dump_coverage(const uptr *pcs,
211                                                             uptr len) {
212  UNIMPLEMENTED();
213}
214
215SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_pc_guard, u32 *guard) {
216  if (!*guard)
217    return;
218  __sancov::pc_guard_controller.TracePcGuard(guard, GET_CALLER_PC() - 1);
219}
220
221SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_pc_guard_init,
222                             u32 *start, u32 *end) {
223  if (start == end || *start)
224    return;
225  __sancov::pc_guard_controller.InitTracePcGuard(start, end);
226}
227
228SANITIZER_INTERFACE_ATTRIBUTE void __sanitizer_dump_trace_pc_guard_coverage() {
229  __sancov::pc_guard_controller.Dump();
230}
231SANITIZER_INTERFACE_ATTRIBUTE void __sanitizer_cov_dump() {
232  __sanitizer_dump_trace_pc_guard_coverage();
233}
234// Default empty implementations (weak). Users should redefine them.
235SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_cmp, void) {}
236SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_cmp1, void) {}
237SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_cmp2, void) {}
238SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_cmp4, void) {}
239SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_cmp8, void) {}
240SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_const_cmp1, void) {}
241SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_const_cmp2, void) {}
242SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_const_cmp4, void) {}
243SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_const_cmp8, void) {}
244SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_switch, void) {}
245SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_div4, void) {}
246SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_div8, void) {}
247SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_gep, void) {}
248SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_pc_indir, void) {}
249}  // extern "C"
250
251#endif  // !SANITIZER_FUCHSIA
252