Initial Commit

absl/debugging/internal/stacktrace_libunwind-inl.inc

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+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_LIBUNWIND_INL_H_
+#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_LIBUNWIND_INL_H_
+
+// We only need local unwinder.
+#define UNW_LOCAL_ONLY
+
+extern "C" {
+#include "third_party/libunwind/include/libunwind.h"
+}
+#include "absl/debugging/stacktrace.h"
+
+#include "absl/base/dynamic_annotations.h"
+#include "absl/base/internal/raw_logging.h"
+
+// Sometimes, we can try to get a stack trace from within a stack
+// trace, because we don't block signals inside libunwind (which would be too
+// expensive: the two extra system calls per stack trace do matter here).
+// That can cause a self-deadlock (as in http://b/5722312).
+// Protect against such reentrant call by failing to get a stack trace.
+//
+// We use __thread here because the code here is extremely low level -- it is
+// called while collecting stack traces from within malloc and mmap, and thus
+// can not call anything which might call malloc or mmap itself.
+// In particular, using PerThread or STATIC_THREAD_LOCAL_POD
+// here will cause infinite recursion for at least dbg/piii builds with
+// crosstool-v12.
+static __thread int recursive;
+
+template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT>
+static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count,
+                      const void *, int *min_dropped_frames) {
+  if (recursive) {
+    return 0;
+  }
+  ++recursive;
+
+  int n = 0;
+  if (IS_STACK_FRAMES) {
+    void *ip;
+    unw_cursor_t cursor;
+    unw_context_t uc;
+    unw_word_t sp = 0, next_sp = 0;
+
+    unw_getcontext(&uc);
+    ABSL_RAW_CHECK(unw_init_local(&cursor, &uc) >= 0, "unw_init_local failed");
+    skip_count++;         // Do not include current frame
+
+    while (skip_count--) {
+      if (unw_step(&cursor) <= 0) {
+        goto out;
+      }
+      if (unw_get_reg(&cursor, UNW_REG_SP, &next_sp)) {
+        goto out;
+      }
+    }
+
+    while (n < max_depth) {
+      if (unw_get_reg(&cursor, UNW_REG_IP, (unw_word_t *) &ip) < 0) {
+        break;
+      }
+      sizes[n] = 0;
+      result[n++] = ip;
+      if (unw_step(&cursor) <= 0) {
+        break;
+      }
+      sp = next_sp;
+      if (unw_get_reg(&cursor, UNW_REG_SP, &next_sp) , 0) {
+        break;
+      }
+      sizes[n - 1] = next_sp - sp;
+    }
+    if (min_dropped_frames != nullptr) {
+      // Implementation detail: we clamp the max of frames we are willing to
+      // count, so as not to spend too much time in the loop below.
+      const int kMaxUnwind = 200;
+      int j = 0;
+      for (; j < kMaxUnwind; j++) {
+        if (unw_step(&cursor) < 0) {
+          break;
+        }
+      }
+      *min_dropped_frames = j;
+    }
+  } else {
+    skip_count++;  // Do not include current frame.
+    void **result_all = reinterpret_cast<void**>(
+        alloca(sizeof(void*) * (max_depth + skip_count)));
+    int rc = unw_backtrace(result_all, max_depth + skip_count);
+
+    if (rc > 0) {
+      // Tell MSan that result_all has been initialized. b/34965936.
+      ANNOTATE_MEMORY_IS_INITIALIZED(result_all, rc * sizeof(void*));
+    }
+
+    if (rc > skip_count) {
+      memcpy(result, &result_all[skip_count],
+             sizeof(void*) * (rc - skip_count));
+      n = rc - skip_count;
+    } else {
+      n = 0;
+    }
+
+    if (min_dropped_frames != nullptr) {
+      // Not implemented.
+      *min_dropped_frames = 0;
+    }
+  }
+
+ out:
+  --recursive;
+  return n;
+}
+
+#endif  // ABSL_DEBUGGING_INTERNAL_STACKTRACE_LIBUNWIND_INL_H_