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 // Copyright 2018 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.
 //
 // -----------------------------------------------------------------------------
 // File: stacktrace.h
 // -----------------------------------------------------------------------------
 //
 // This file contains routines to extract the current stack trace and associated
 // stack frames. These functions are thread-safe and async-signal-safe.
 //
 // Note that stack trace functionality is platform dependent and requires
 // additional support from the compiler/build system in most cases. (That is,
 // this functionality generally only works on platforms/builds that have been
 // specifically configured to support it.)
 //
 // Note: stack traces in Abseil that do not utilize a symbolizer will result in
 // frames consisting of function addresses rather than human-readable function
 // names. (See symbolize.h for information on symbolizing these values.)
 
 #ifndef ABSL_DEBUGGING_STACKTRACE_H_
 #define ABSL_DEBUGGING_STACKTRACE_H_
 
 #include "absl/base/config.h"
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 
 // GetStackFrames()
 //
 // Records program counter values for up to `max_depth` frames, skipping the
 // most recent `skip_count` stack frames, stores their corresponding values
 // and sizes in `results` and `sizes` buffers, and returns the number of frames
 // stored. (Note that the frame generated for the `absl::GetStackFrames()`
 // routine itself is also skipped.)
 //
 // Example:
 //
 //      main() { foo(); }
 //      foo() { bar(); }
 //      bar() {
 //        void* result[10];
 //        int sizes[10];
 //        int depth = absl::GetStackFrames(result, sizes, 10, 1);
 //      }
 //
 // The current stack frame would consist of three function calls: `bar()`,
 // `foo()`, and then `main()`; however, since the `GetStackFrames()` call sets
 // `skip_count` to `1`, it will skip the frame for `bar()`, the most recently
 // invoked function call. It will therefore return 2 and fill `result` with
 // program counters within the following functions:
 //
 //      result[0]       foo()
 //      result[1]       main()
 //
 // (Note: in practice, a few more entries after `main()` may be added to account
 // for startup processes.)
 //
 // Corresponding stack frame sizes will also be recorded:
 //
 //    sizes[0]       16
 //    sizes[1]       16
 //
 // (Stack frame sizes of `16` above are just for illustration purposes.)
 //
 // Stack frame sizes of 0 or less indicate that those frame sizes couldn't
 // be identified.
 //
 // This routine may return fewer stack frame entries than are
 // available. Also note that `result` and `sizes` must both be non-null.
 extern int GetStackFrames(void** result, int* sizes, int max_depth,
                           int skip_count);
 
 // GetStackFramesWithContext()
 //
 // Records program counter values obtained from a signal handler. Records
 // program counter values for up to `max_depth` frames, skipping the most recent
 // `skip_count` stack frames, stores their corresponding values and sizes in
 // `results` and `sizes` buffers, and returns the number of frames stored. (Note
 // that the frame generated for the `absl::GetStackFramesWithContext()` routine
 // itself is also skipped.)
 //
 // The `uc` parameter, if non-null, should be a pointer to a `ucontext_t` value
 // passed to a signal handler registered via the `sa_sigaction` field of a
 // `sigaction` struct. (See
 // http://man7.org/linux/man-pages/man2/sigaction.2.html.) The `uc` value may
 // help a stack unwinder to provide a better stack trace under certain
 // conditions. `uc` may safely be null.
 //
 // The `min_dropped_frames` output parameter, if non-null, points to the
 // location to note any dropped stack frames, if any, due to buffer limitations
 // or other reasons. (This value will be set to `0` if no frames were dropped.)
 // The number of total stack frames is guaranteed to be >= skip_count +
 // max_depth + *min_dropped_frames.
 extern int GetStackFramesWithContext(void** result, int* sizes, int max_depth,
                                      int skip_count, const void* uc,
                                      int* min_dropped_frames);
 
 // GetStackTrace()
 //
 // Records program counter values for up to `max_depth` frames, skipping the
 // most recent `skip_count` stack frames, stores their corresponding values
 // in `results`, and returns the number of frames
 // stored. Note that this function is similar to `absl::GetStackFrames()`
 // except that it returns the stack trace only, and not stack frame sizes.
 //
 // Example:
 //
 //      main() { foo(); }
 //      foo() { bar(); }
 //      bar() {
 //        void* result[10];
 //        int depth = absl::GetStackTrace(result, 10, 1);
 //      }
 //
 // This produces:
 //
 //      result[0]       foo
 //      result[1]       main
 //           ....       ...
 //
 // `result` must not be null.
 extern int GetStackTrace(void** result, int max_depth, int skip_count);
 
 // GetStackTraceWithContext()
 //
 // Records program counter values obtained from a signal handler. Records
 // program counter values for up to `max_depth` frames, skipping the most recent
 // `skip_count` stack frames, stores their corresponding values in `results`,
 // and returns the number of frames stored. (Note that the frame generated for
 // the `absl::GetStackFramesWithContext()` routine itself is also skipped.)
 //
 // The `uc` parameter, if non-null, should be a pointer to a `ucontext_t` value
 // passed to a signal handler registered via the `sa_sigaction` field of a
 // `sigaction` struct. (See
 // http://man7.org/linux/man-pages/man2/sigaction.2.html.) The `uc` value may
 // help a stack unwinder to provide a better stack trace under certain
 // conditions. `uc` may safely be null.
 //
 // The `min_dropped_frames` output parameter, if non-null, points to the
 // location to note any dropped stack frames, if any, due to buffer limitations
 // or other reasons. (This value will be set to `0` if no frames were dropped.)
 // The number of total stack frames is guaranteed to be >= skip_count +
 // max_depth + *min_dropped_frames.
 extern int GetStackTraceWithContext(void** result, int max_depth,
                                     int skip_count, const void* uc,
                                     int* min_dropped_frames);
 
 // SetStackUnwinder()
 //
 // Provides a custom function for unwinding stack frames that will be used in
 // place of the default stack unwinder when invoking the static
 // GetStack{Frames,Trace}{,WithContext}() functions above.
 //
 // The arguments passed to the unwinder function will match the
 // arguments passed to `absl::GetStackFramesWithContext()` except that sizes
 // will be non-null iff the caller is interested in frame sizes.
 //
 // If unwinder is set to null, we revert to the default stack-tracing behavior.
 //
 // *****************************************************************************
 // WARNING
 // *****************************************************************************
 //
 // absl::SetStackUnwinder is not suitable for general purpose use.  It is
 // provided for custom runtimes.
 // Some things to watch out for when calling `absl::SetStackUnwinder()`:
 //
 // (a) The unwinder may be called from within signal handlers and
 // therefore must be async-signal-safe.
 //
 // (b) Even after a custom stack unwinder has been unregistered, other
 // threads may still be in the process of using that unwinder.
 // Therefore do not clean up any state that may be needed by an old
 // unwinder.
 // *****************************************************************************
 extern void SetStackUnwinder(int (*unwinder)(void** pcs, int* sizes,
                                              int max_depth, int skip_count,
                                              const void* uc,
                                              int* min_dropped_frames));
 
 // DefaultStackUnwinder()
 //
 // Records program counter values of up to `max_depth` frames, skipping the most
 // recent `skip_count` stack frames, and stores their corresponding values in
 // `pcs`. (Note that the frame generated for this call itself is also skipped.)
 // This function acts as a generic stack-unwinder; prefer usage of the more
 // specific `GetStack{Trace,Frames}{,WithContext}()` functions above.
 //
 // If you have set your own stack unwinder (with the `SetStackUnwinder()`
 // function above, you can still get the default stack unwinder by calling
 // `DefaultStackUnwinder()`, which will ignore any previously set stack unwinder
 // and use the default one instead.
 //
 // Because this function is generic, only `pcs` is guaranteed to be non-null
 // upon return. It is legal for `sizes`, `uc`, and `min_dropped_frames` to all
 // be null when called.
 //
 // The semantics are the same as the corresponding `GetStack*()` function in the
 // case where `absl::SetStackUnwinder()` was never called. Equivalents are:
 //
 //                       null sizes         |        non-nullptr sizes
 //             |==========================================================|
 //     null uc | GetStackTrace()            | GetStackFrames()            |
 // non-null uc | GetStackTraceWithContext() | GetStackFramesWithContext() |
 //             |==========================================================|
 extern int DefaultStackUnwinder(void** pcs, int* sizes, int max_depth,
                                 int skip_count, const void* uc,
                                 int* min_dropped_frames);
 
 namespace debugging_internal {
 // Returns true for platforms which are expected to have functioning stack trace
 // implementations. Intended to be used for tests which want to exclude
 // verification of logic known to be broken because stack traces are not
 // working.
 extern bool StackTraceWorksForTest();
 }  // namespace debugging_internal
 ABSL_NAMESPACE_END
 }  // namespace absl
 
 #endif  // ABSL_DEBUGGING_STACKTRACE_H_

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