IABSD.fr/src/gnu/lib/libexecinfo/backtrace.3

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• Author : schwarze
  Date : 2025-06-07 20:54:35
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  Message : .Lb libexecinfo ; OK jca@

• gnu/lib/libexecinfo/backtrace.3

• .\"	$OpenBSD: backtrace.3,v 1.4 2025/06/07 20:54:35 schwarze Exp $
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  .Dd $Mdocdate: June 7 2025 $
  .Dt BACKTRACE 3
  .Os
  .Sh NAME
  .Nm backtrace ,
  .Nm backtrace_symbols ,
  .Nm backtrace_symbols_fd ,
  .Nm backtrace_symbols_fmt ,
  .Nm backtrace_symbols_fd_fmt
  .Nd fill in the backtrace of the currently executing thread
  .Sh SYNOPSIS
  .Lb libexecinfo
  .In execinfo.h
  .Ft size_t
  .Fn backtrace "void **addrlist" "size_t len"
  .Ft "char **"
  .Fn backtrace_symbols "void * const *addrlist" "size_t len"
  .Ft int
  .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"
  .Ft int
  .Fn backtrace_symbols_fd_fmt "void * const *addrlist" "size_t len" "int fd" "const char *fmt"
  .Sh DESCRIPTION
  The
  .Fn backtrace
  function places into the array pointed by
  .Fa addrlist
  the array of the values of the program counter for each frame called up to
  .Fa len
  frames.
  The number of frames found (which can be fewer than
  .Fa len )
  is returned.
  .Pp
  The
  .Fn backtrace_symbols_fmt
  function takes an array of previously filled addresses from
  .Fn backtrace
  in
  .Fa addrlist
  of
  .Fa len
  elements, and uses
  .Fa fmt
  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
  .It Dv d
  The difference of the symbol address and the address element printed
  using 0x%tx.
  .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 .
  .El
  .Pp
  The array of formatted strings is returned as a contiguous memory address which
  can be freed by a single
  .Xr free 3 .
  .Pp
  The
  .Fn backtrace_symbols
  function is equivalent of calling
  .Fn backtrace_symbols_fmt
  with a format argument of
  .Dq "%a <%n%D> at %f"
  .Pp
  The
  .Fn backtrace_symbols_fd
  and
  .Fn backtrace_symbols_fd_fmt
  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
  .Dv 0
  on success and
  .Dv \-1
  on failure.
  .Sh RETURN VALUES
  The
  .Fn backtrace
  function returns the number of elements that were filled in the backtrace.
  The
  .Fn backtrace_symbols
  and
  .Fn backtrace_symbols_fmt
  return a string array on success, and
  .Dv NULL
  on failure, setting
  .Va errno .
  .Sh SEE ALSO
  .Xr dladdr 3
  .Sh HISTORY
  The
  .Fn backtrace
  library of functions first appeared in
  .Nx 7.0
  and was imported into
  .Ox 7.0 .
  .Sh BUGS
  .Bl -enum
  .It
  Only unwinding with libunwind is supported.
  On architectures without libunwind the
  .Fn backtrace
  function simply returns 0.
  .It
  Since
  .Xr dladdr 3
  only deals with dynamic symbols, local symbols from the main
  portion of the program are not printed.
  .El