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absl/debugging/stacktrace.h
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absl/debugging/stacktrace.h
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//
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// Copyright 2017 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// Routines to extract the current stack trace. These functions are
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// thread-safe and async-signal-safe.
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// Note that stack trace functionality is platform dependent and requires
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// additional support from the compiler/build system in many cases. (That is,
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// this generally only works on platforms/builds that have been specifically
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// configured to support it.)
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#ifndef ABSL_DEBUGGING_STACKTRACE_H_
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#define ABSL_DEBUGGING_STACKTRACE_H_
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namespace absl {
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// Skips the most recent "skip_count" stack frames (also skips the
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// frame generated for the "absl::GetStackFrames" routine itself), and then
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// records the pc values for up to the next "max_depth" frames in
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// "result", and the corresponding stack frame sizes in "sizes".
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// Returns the number of values recorded in "result"/"sizes".
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//
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// Example:
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// main() { foo(); }
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// foo() { bar(); }
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// bar() {
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// void* result[10];
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// int sizes[10];
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// int depth = absl::GetStackFrames(result, sizes, 10, 1);
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// }
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//
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// The absl::GetStackFrames call will skip the frame for "bar". It will
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// return 2 and will produce pc values that map to the following
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// procedures:
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// result[0] foo
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// result[1] main
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// (Actually, there may be a few more entries after "main" to account for
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// startup procedures.)
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// And corresponding stack frame sizes will also be recorded:
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// sizes[0] 16
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// sizes[1] 16
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// (Stack frame sizes of 16 above are just for illustration purposes.)
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// Stack frame sizes of 0 or less indicate that those frame sizes couldn't
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// be identified.
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//
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// This routine may return fewer stack frame entries than are
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// available. Also note that "result" and "sizes" must both be non-null.
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extern int GetStackFrames(void** result, int* sizes, int max_depth,
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int skip_count);
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// Same as above, but to be used from a signal handler. The "uc" parameter
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// should be the pointer to ucontext_t which was passed as the 3rd parameter
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// to sa_sigaction signal handler. It may help the unwinder to get a
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// better stack trace under certain conditions. The "uc" may safely be null.
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//
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// If min_dropped_frames is not null, stores in *min_dropped_frames a
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// lower bound on the number of dropped stack frames. The stored value is
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// guaranteed to be >= 0. The number of real stack frames is guaranteed to
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// be >= skip_count + max_depth + *min_dropped_frames.
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extern int GetStackFramesWithContext(void** result, int* sizes, int max_depth,
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int skip_count, const void* uc,
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int* min_dropped_frames);
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// This is similar to the absl::GetStackFrames routine, except that it returns
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// the stack trace only, and not the stack frame sizes as well.
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// Example:
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// main() { foo(); }
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// foo() { bar(); }
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// bar() {
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// void* result[10];
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// int depth = absl::GetStackTrace(result, 10, 1);
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// }
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//
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// This produces:
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// result[0] foo
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// result[1] main
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// .... ...
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//
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// "result" must not be null.
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extern int GetStackTrace(void** result, int max_depth, int skip_count);
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// Same as above, but to be used from a signal handler. The "uc" parameter
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// should be the pointer to ucontext_t which was passed as the 3rd parameter
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// to sa_sigaction signal handler. It may help the unwinder to get a
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// better stack trace under certain conditions. The "uc" may safely be null.
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//
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// If min_dropped_frames is not null, stores in *min_dropped_frames a
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// lower bound on the number of dropped stack frames. The stored value is
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// guaranteed to be >= 0. The number of real stack frames is guaranteed to
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// be >= skip_count + max_depth + *min_dropped_frames.
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extern int GetStackTraceWithContext(void** result, int max_depth,
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int skip_count, const void* uc,
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int* min_dropped_frames);
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// Call this to provide a custom function for unwinding stack frames
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// that will be used every time someone invokes one of the static
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// GetStack{Frames,Trace}{,WithContext}() functions above.
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//
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// The arguments passed to the unwinder function will match the
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// arguments passed to absl::GetStackFramesWithContext() except that sizes
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// will be non-null iff the caller is interested in frame sizes.
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//
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// If unwinder is null, we revert to the default stack-tracing behavior.
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//
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// ****************************************************************
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// WARNINGS
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//
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// absl::SetStackUnwinder is not suitable for general purpose use. It is
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// provided for custom runtimes.
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// Some things to watch out for when calling absl::SetStackUnwinder:
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//
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// (a) The unwinder may be called from within signal handlers and
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// therefore must be async-signal-safe.
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//
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// (b) Even after a custom stack unwinder has been unregistered, other
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// threads may still be in the process of using that unwinder.
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// Therefore do not clean up any state that may be needed by an old
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// unwinder.
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// ****************************************************************
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extern void SetStackUnwinder(int (*unwinder)(void** pcs, int* sizes,
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int max_depth, int skip_count,
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const void* uc,
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int* min_dropped_frames));
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// Function that exposes built-in stack-unwinding behavior, ignoring
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// any calls to absl::SetStackUnwinder().
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//
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// pcs must NOT be null.
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//
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// sizes may be null.
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// uc may be null.
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// min_dropped_frames may be null.
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//
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// The semantics are the same as the corresponding GetStack*() function in the
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// case where absl::SetStackUnwinder() was never called. Equivalents are:
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//
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// null sizes | non-nullptr sizes
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// |==========================================================|
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// null uc | GetStackTrace() | GetStackFrames() |
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// non-null uc | GetStackTraceWithContext() | GetStackFramesWithContext() |
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// |==========================================================|
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extern int DefaultStackUnwinder(void** pcs, int* sizes, int max_depth,
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int skip_count, const void* uc,
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int* min_dropped_frames);
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} // namespace absl
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#endif // ABSL_DEBUGGING_STACKTRACE_H_
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