Libc-1272.200.26.tar.gz

[apple/libc.git] / gen / backtrace.3

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.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
.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.
.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.
.Sh SEE ALSO
.Xr dladdr 3 ,
.Xr malloc 3