// 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 <stddef.h>

#include <stdint.h>

#include "absl/base/attributes.h"

#include "absl/base/config.h"

namespace absl {

ABSL_NAMESPACE_BEGIN

namespace internal_stacktrace {

// Same as `absl::GetStackFrames`, but with an optional `frames` parameter to

// allow callers to receive the raw stack frame addresses.

// This is internal for now; use `absl::GetStackFrames()` instead.

extern int GetStackFrames(void** result, uintptr_t* frames, int* sizes,

                          int max_depth, int skip_count);

// Same as `absl::GetStackFramesWithContext`, but with an optional `frames`

// parameter to allow callers to receive a start address for each stack frame.

// The address may be zero in cases where it cannot be computed.

//

// DO NOT use this function without consulting the owners of absl/debuggging.

// There is NO GUARANTEE on the precise frame addresses returned on any given

// platform. It is only intended to provide sufficient non-overlapping bounds on

// the local variables of a stack frame when used in conjunction with the

// returned frame sizes. The actual pointers may be ABI-dependent, may vary at

// run time, and are subject to breakage without notice.

//

// Implementation note:

// Currently, we *attempt* to return the Canonical Frame Address (CFA) in DWARF

// on most platforms. This is the value of the stack pointer just before the

// 'call' instruction is executed in the caller.

// Not all platforms and toolchains support this exact address, so this should

// not be relied on for correctness.

extern int GetStackFramesWithContext(void** result, uintptr_t* frames,

                                     int* sizes, int max_depth, int skip_count,

                                     const void* uc, int* min_dropped_frames);

// As above, but skips fix-ups for efficiency.

extern int GetStackTraceNoFixup(void** result, int max_depth, int skip_count);

// Same as `absl::DefaultStackUnwinder`, but with an optional `frames` parameter

// to allow callers to receive the raw stack frame addresses.

// This is internal for now; do not depend on this externally.

extern int DefaultStackUnwinder(void** pcs, uintptr_t* frames, int* sizes,

                                int max_depth, int skip_count, const void* uc,

                                int* min_dropped_frames);

}  // namespace internal_stacktrace

// 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.

ABSL_ATTRIBUTE_ALWAYS_INLINE inline int GetStackFrames(void** result,

                                                       int* sizes,

                                                       int max_depth,

                                                       int skip_count) {

  return internal_stacktrace::GetStackFrames(result, nullptr, sizes, max_depth,

                                             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.

ABSL_ATTRIBUTE_ALWAYS_INLINE inline int GetStackFramesWithContext(

    void** result, int* sizes, int max_depth, int skip_count, const void* uc,

    int* min_dropped_frames) {

  return internal_stacktrace::GetStackFramesWithContext(

      result, nullptr, sizes, max_depth, skip_count, uc, 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

namespace internal_stacktrace {

extern bool ShouldFixUpStack();

// Fixes up the stack trace of the current thread, in the first `depth` frames

// of each buffer. The buffers need to be larger than `depth`, to accommodate

// any newly inserted elements. `depth` is updated to reflect the new number of

// elements valid across all the buffers. (It is therefore recommended that all

// buffer sizes be equal.)

//

// The `frames` and `sizes` parameters denote the bounds of the stack frame

// corresponding to each instruction pointer in the `pcs`.

// Any elements inside these buffers may be zero or null, in which case that

// information is assumed to be absent/unavailable.

extern void FixUpStack(void** pcs, uintptr_t* frames, int* sizes,

                       size_t capacity, size_t& depth);

}  // namespace internal_stacktrace

ABSL_NAMESPACE_END

}  // namespace absl

#endif  // ABSL_DEBUGGING_STACKTRACE_H_