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+.\" Copyright (c) 2007 Apple Inc.
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
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+.\" 3. Neither the name of Apple Inc. ("Apple") nor the names of its
+.\"    contributors may be used to endorse or promote products derived from
+.\"    this software without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY APPLE AND CONTRIBUTORS ``AS IS'' AND
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+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"
+.Dd March 1, 2018
+.Dt backtrace 3
+.Os "Darwin"
+.Sh NAME
+.Nm backtrace ,
+.Nm backtrace_symbols ,
+.Nm backtrace_symbols_fd ,
+.Nm backtrace_image_offsets ,
+.Nm backtrace_from_fp
+.Nd call stack backtrace and display functions
+.Sh SYNOPSIS
+.In execinfo.h
+.Ft int
+.Fo backtrace
+.Fa "void** array"
+.Fa "int size"
+.Fc
+.Ft char**
+.Fo backtrace_symbols
+.Fa "void* const* array"
+.Fa "int size"
+.Fc
+.Ft void
+.Fo backtrace_symbols_fd
+.Fa "void* const* array"
+.Fa "int size"
+.Fa "int fd"
+.Fc
+.Ft void
+.Fo backtrace_image_offsets
+.Fa "void* const* array"
+.Fa "struct image_offset *image_offsets"
+.Fa "int size"
+.Fc
+.Ft int
+.Fo backtrace_from_fp
+.Fa "void* startfp"
+.Fa "void** array"
+.Fa "int size"
+.Fc
+.Ft size_t
+.Fo backtrace_async
+.Fa "void** array"
+.Fa "size_t size"
+.Fa "uint32_t* task_id"
+.Fc
+.Sh DESCRIPTION
+These routines provide a mechanism to examine the current thread's call stack.
+.Pp
+.Fn backtrace
+writes the function return addresses of the current call stack to the array of
+pointers referenced by
+.Fa array .
+At most,
+.Fa size
+pointers are written.  The number of pointers actually written to
+.Fa array
+is returned.
+.Pp
+.Fn backtrace_symbols
+attempts to transform a call stack obtained by
+.Fn backtrace
+into an array of human-readable strings using
+.Fn dladdr .
+The array of strings returned has
+.Fa size
+elements.  It is allocated using
+.Fn malloc
+and should be released using
+.Fn free .
+There is no need to free the individual strings in the array.
+.Pp
+.Fn backtrace_symbols_fd
+performs the same operation as
+.Fn backtrace_symbols ,
+but the resulting strings are immediately written to the file descriptor
+.Fa fd ,
+and are not returned.
+.Pp
+.Fn backtrace_image_offsets
+attempts to transform a call stack obtained by
+.Fn backtrace
+into an array of image offsets, for deferred symbolication.  Each entry in the
+array has an offset relative to the
+.Li __TEXT
+section of the image with the given UUID.  The results are written to
+.Fa image_offsets
+which should be an array of
+.Fa size
+length.
+.Pp
+.Fn backtrace_from_fp
+takes a backtrace of frames starting from the given frame pointer.
+.Pp
+.Fn backtrace_async
+behaves exactly like
+.Fn backtrace
+unless it is invoked from a Swift async context.  In that case, instead of
+writing the return addresses of the OS call stack, the continuation addresses
+of the async invocations that led to the current state are provided.  If
+unwinding an async stack rather than an OS stack, the value pointed to by
+.Fa task_id
+will be set to a non-zero identifier that for the current process uniquely
+identifies the async task currently running.  Otherwise, 0 is stored.
+.Pp
+Note that the continuation addresses provided by
+.Fn backtrace_async
+have an offset of 1 added to them.  Most symbolication engines will substract
+1 from the call stack return addresses in order to symbolicate the call site
+rather than the return location.  With a Swift async continuation, substracting
+1 from its address would result in an address in a different function.  This
+offset allows the returned addresses to be handled correctly by most existing
+symbolication engines.
+.Pp
+.Sh EXAMPLE
+.Pp
+    #include <execinfo.h>
+    #include <stdio.h>
+    ...
+    void* callstack[128];
+    int i, frames = backtrace(callstack, 128);
+    char** strs = backtrace_symbols(callstack, frames);
+    for (i = 0; i < frames; ++i) {
+        printf("%s\\n", strs[i]);
+    }
+    free(strs);
+    ...
+.Pp
+.Sh HISTORY
+.Fn backtrace ,
+.Fn backtrace_symbols ,
+and
+.Fn backtrace_symbols_fd
+first appeared in Mac OS X 10.5.
+.Fn backtrace_image_offsets
+and
+.Fn backtrace_from_fp
+first appeared macOS 10.14 and iOS 12.
+.Fn backtrace_async
+first appeared in macOS 12.
+.Sh SEE ALSO
+.Xr dladdr 3 ,
+.Xr malloc 3