|File: [cvs.NetBSD.org] / src / lib / libexecinfo / backtrace.3 (download)
Revision 1.10, Sun Oct 22 14:07:03 2017 UTC (2 years, 5 months ago) by abhinav
CVS Tags: phil-wifi-base, phil-wifi-20191119, phil-wifi-20190609, phil-wifi, pgoyette-compat-merge-20190127, pgoyette-compat-base, pgoyette-compat-20190127, pgoyette-compat-20190118, pgoyette-compat-1226, pgoyette-compat-1126, pgoyette-compat-1020, pgoyette-compat-0930, pgoyette-compat-0906, pgoyette-compat-0728, pgoyette-compat-0625, pgoyette-compat-0521, pgoyette-compat-0502, pgoyette-compat-0422, pgoyette-compat-0415, pgoyette-compat-0407, pgoyette-compat-0330, pgoyette-compat-0322, pgoyette-compat-0315, pgoyette-compat, netbsd-9-base, netbsd-9-0-RELEASE, netbsd-9-0-RC2, netbsd-9-0-RC1, netbsd-9, HEAD
Changes since 1.9: +6 -2
Add rest of the functions from the SYNOPSIS section to the NAME section
.\" $NetBSD: backtrace.3,v 1.10 2017/10/22 14:07:03 abhinav Exp $
.\" Copyright (c) 2012 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Christos Zoulas
.\" 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
.\" documentation and/or other materials provided with the distribution.
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" POSSIBILITY OF SUCH DAMAGE.
.Dd November 5, 2015
.Dt BACKTRACE 3
.Nm backtrace ,
.Nm backtrace_symbols ,
.Nm backtrace_symbols_fd ,
.Nm backtrace_symbols_fmt ,
.Nd fill in the backtrace of the currently executing thread
.Fn backtrace "void **addrlist" "size_t len"
.Ft "char **"
.Fn backtrace_symbols "void * const *addrlist" "size_t len"
.Fn backtrace_symbols_fd "void * const *addrlist" "size_t len" "int fd"
.Ft "char **"
.Fn backtrace_symbols_fmt "void * const *addrlist" "size_t len" "const char *fmt"
.Fn backtrace_symbols_fd_fmt "void * const *addrlist" "size_t len" "int fd" "const char *fmt"
function places into the array pointed by
the array of the values of the program counter for each frame called up to
The number of frames found (which can be fewer than
.Fa len )
function takes an array of previously filled addresses from
elements, and uses
to format them.
The formatting characters available are:
.Bl -tag -width a -offset indent
.It Dv a
The numeric address of each element as would be printed using %p.
.It Dv n
The name of the nearest function symbol (smaller than the address element)
as determined by
.Xr dladdr 3
if the symbol was dynamic, or looked up in the executable if static and
the /proc filesystem is available to determine the executable path.
.It Dv d
The difference of the symbol address and the address element printed
.It Dv D
The difference of the symbol address and the address element printed using
+0x%tx if non-zero, or nothing if zero.
.It Dv f
The filename of the symbol as determined by
.Xr dladdr 3 .
The array of formatted strings is returned as a contiguous memory address which
can be freed by a single
.Xr free 3 .
function is equivalent of calling
with a format argument of
.Dq "%a <%n%D> at %f"
are similar to the non _fd named functions, only instead of returning
an array of strings, they print a new-line separated array of strings in
fd, and return
on success and
.Sh RETURN VALUES
function returns the number of elements that were filled in the backtrace.
return a string array on success, and
on failure, setting
.Va errno .
Diagnostic output may also be produced by the ELF symbol lookup functions.
.Sh SEE ALSO
.Xr dladdr 3 ,
.Xr elf 3
library of functions first appeared in
.Nx 7.0 .
Errors should not be printed but communicated to the caller differently.
Because these functions use
.Xr elf 3
this is a separate library instead of being part of libc/libutil
so that no library dependencies are introduced.
The Linux versions of the functions (there are no _fmt variants) use
.Xr dladdr 3
only deals with dynamic symbols, we need to find the symbols from the main
portion of the program.
For that we need to locate the executable, and we use procfs for
finding it, which is not portable.