Add 'third_party/abseil_cpp/' from commit '768eb2ca28'

git-subtree-dir: third_party/abseil_cpp
git-subtree-mainline: ffb2ae54be
git-subtree-split: 768eb2ca28

third_party/abseil_cpp/absl/debugging/internal/stacktrace_arm-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
+//
+//      https://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.
+//
+// This is inspired by Craig Silverstein's PowerPC stacktrace code.
+
+#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_ARM_INL_H_
+#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_ARM_INL_H_
+
+#include <cstdint>
+
+#include "absl/debugging/stacktrace.h"
+
+// WARNING:
+// This only works if all your code is in either ARM or THUMB mode.  With
+// interworking, the frame pointer of the caller can either be in r11 (ARM
+// mode) or r7 (THUMB mode).  A callee only saves the frame pointer of its
+// mode in a fixed location on its stack frame.  If the caller is a different
+// mode, there is no easy way to find the frame pointer.  It can either be
+// still in the designated register or saved on stack along with other callee
+// saved registers.
+
+// Given a pointer to a stack frame, locate and return the calling
+// stackframe, or return nullptr if no stackframe can be found. Perform sanity
+// checks (the strictness of which is controlled by the boolean parameter
+// "STRICT_UNWINDING") to reduce the chance that a bad pointer is returned.
+template<bool STRICT_UNWINDING>
+static void **NextStackFrame(void **old_sp) {
+  void **new_sp = (void**) old_sp[-1];
+
+  // Check that the transition from frame pointer old_sp to frame
+  // pointer new_sp isn't clearly bogus
+  if (STRICT_UNWINDING) {
+    // With the stack growing downwards, older stack frame must be
+    // at a greater address that the current one.
+    if (new_sp <= old_sp) return nullptr;
+    // Assume stack frames larger than 100,000 bytes are bogus.
+    if ((uintptr_t)new_sp - (uintptr_t)old_sp > 100000) return nullptr;
+  } else {
+    // In the non-strict mode, allow discontiguous stack frames.
+    // (alternate-signal-stacks for example).
+    if (new_sp == old_sp) return nullptr;
+    // And allow frames upto about 1MB.
+    if ((new_sp > old_sp)
+        && ((uintptr_t)new_sp - (uintptr_t)old_sp > 1000000)) return nullptr;
+  }
+  if ((uintptr_t)new_sp & (sizeof(void *) - 1)) return nullptr;
+  return new_sp;
+}
+
+// This ensures that absl::GetStackTrace sets up the Link Register properly.
+#ifdef __GNUC__
+void StacktraceArmDummyFunction() __attribute__((noinline));
+void StacktraceArmDummyFunction() { __asm__ volatile(""); }
+#else
+# error StacktraceArmDummyFunction() needs to be ported to this platform.
+#endif
+
+template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT>
+static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count,
+                      const void * /* ucp */, int *min_dropped_frames) {
+#ifdef __GNUC__
+  void **sp = reinterpret_cast<void**>(__builtin_frame_address(0));
+#else
+# error reading stack point not yet supported on this platform.
+#endif
+
+  // On ARM, the return address is stored in the link register (r14).
+  // This is not saved on the stack frame of a leaf function.  To
+  // simplify code that reads return addresses, we call a dummy
+  // function so that the return address of this function is also
+  // stored in the stack frame.  This works at least for gcc.
+  StacktraceArmDummyFunction();
+
+  int n = 0;
+  while (sp && n < max_depth) {
+    // The absl::GetStackFrames routine is called when we are in some
+    // informational context (the failure signal handler for example).
+    // Use the non-strict unwinding rules to produce a stack trace
+    // that is as complete as possible (even if it contains a few bogus
+    // entries in some rare cases).
+    void **next_sp = NextStackFrame<!IS_STACK_FRAMES>(sp);
+
+    if (skip_count > 0) {
+      skip_count--;
+    } else {
+      result[n] = *sp;
+
+      if (IS_STACK_FRAMES) {
+        if (next_sp > sp) {
+          sizes[n] = (uintptr_t)next_sp - (uintptr_t)sp;
+        } else {
+          // A frame-size of 0 is used to indicate unknown frame size.
+          sizes[n] = 0;
+        }
+      }
+      n++;
+    }
+    sp = next_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 (; sp != nullptr && j < kMaxUnwind; j++) {
+      sp = NextStackFrame<!IS_STACK_FRAMES>(sp);
+    }
+    *min_dropped_frames = j;
+  }
+  return n;
+}
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+bool StackTraceWorksForTest() {
+  return false;
+}
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_INTERNAL_STACKTRACE_ARM_INL_H_