mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-12 16:20:06 +00:00
2244ddf2bf
2001-01-17 Ulrich Drepper <drepper@redhat.com> * manual/Makefile (chapters): Add debug. * manual/debug.texi: New file. * manual/examples/execinfo.c: New file. Patch by suckfish@ihug.co.nz.
111 lines
4.8 KiB
Plaintext
111 lines
4.8 KiB
Plaintext
@node Debugging Support
|
|
@c @node Debugging Support, , Cryptographic Functions, Top
|
|
@c %MENU% Functions to help debugging applications.
|
|
@chapter Debugging support
|
|
|
|
Applications often get debugged using dedicated debugger programs. But
|
|
sometimes this is not possible and it is in any case useful to provide
|
|
the developer at the time the problems are experienced with as much
|
|
information as possible. For this reason there exist a few functions
|
|
which a program can use to help the developer more easily locate the
|
|
problem.
|
|
|
|
|
|
@menu
|
|
* Backtraces:: Obtaining and printing a back trace of the
|
|
current stack.
|
|
@end menu
|
|
|
|
|
|
@node Backtraces, , , Debugging Support
|
|
@section Backtraces
|
|
|
|
@cindex backtrace
|
|
@cindex backtrace_symbols
|
|
@cindex backtrace_fd
|
|
A @dfn{backtrace} is a list of the function calls that are currently
|
|
active in a thread. The usual way to inspect a backtrace of a program
|
|
is to use an external debugger such as gdb. However, sometimes it is
|
|
useful to obtain a backtrace programatically from within a program,
|
|
e.g., for the purposes of logging or diagnostics.
|
|
|
|
The header file @file{execinfo.h} declares three functions that obtain
|
|
and manipulate backtraces of the current thread.
|
|
@pindex execinfo.h
|
|
|
|
@comment execinfo.h
|
|
@comment GNU
|
|
@deftypefun int backtrace (void **@var{buffer}, int @var{size})
|
|
The @code{backtrace} function obtains a backtrace for the current
|
|
thread, as a list of pointers, and places the information into
|
|
@var{buffer}. The argument @var{size} should be the number of
|
|
@w{@code{void *}} elements fitting into @var{buffer}. The return value
|
|
is the actual number of entries of @var{buffer} that are obtained, and
|
|
is at most @var{size}.
|
|
|
|
The pointers placed in @var{buffer} are actually return addresses
|
|
obtained by inspecting the stack, one return address per stack frame.
|
|
|
|
Note that certain compiler optimisations may interfere with obtaining a
|
|
valid backtrace. Function inlining causes the inlined function to not
|
|
have a stack frame; tail call optimisation replaces one stack frame with
|
|
another; frame pointer elimination will stop @code{backtrace} from
|
|
interpreting the stack contents correctly.
|
|
@end deftypefun
|
|
|
|
@comment execinfo.h
|
|
@comment GNU
|
|
@deftypefun {char **} backtrace_symbols (void *const *@var{buffer}, int @var{size})
|
|
The @code{backtrace_symbols} function translates the information
|
|
obtained from the @code{backtrace} function into an array of strings.
|
|
The argument @var{buffer} should be a pointer to an array of addresses
|
|
obtained via the @code{backtrace} function, and @var{size} is the number
|
|
of entries in that array (the return value of @code{backtrace}).
|
|
|
|
The return value is a pointer to an array of strings, which has
|
|
@var{size} entries just like the array @var{buffer}. Each string
|
|
contains a printable representation of the corresponding element of
|
|
@var{buffer}. It includes the function name (if this can be
|
|
determined), an offset into the function, and the actual return address
|
|
(in hexidecimal).
|
|
|
|
Currently, the function name and offset can currently only be obtained
|
|
on systems that use the ELF binary format for programs and libraries.
|
|
On other systems, only the hexidecimal return address will be present.
|
|
Also, you may need to pass additional flags to the linker
|
|
(@code{-rdynamic} on systems using GNU ld) to make the function names
|
|
available to the program.
|
|
|
|
The return value of @code{backtrace_symbols} is a pointer obtained via
|
|
the @code{malloc} function, and it is the responsibility of the caller
|
|
to @code{free} that pointer. Note that only the return value need be
|
|
freed, but not the individual strings.
|
|
|
|
The return value is @code{NULL} if sufficient memory for the strings
|
|
cannot be obtained.
|
|
@end deftypefun
|
|
|
|
@comment execinfo.h
|
|
@comment GNU
|
|
@deftypefun void backtrace_symbols_fd (void *const *@var{buffer}, int @var{size}, int @var{fd})
|
|
The @code{backtrace_symbols_fd} function performs the same translation
|
|
as the function @code{backtrace_symbols} function. Instead of returning
|
|
the strings to the caller, it writes the strings to the file descriptor
|
|
@var{fd}, one per line. It does not use the @code{malloc} function, and
|
|
can therefore be used in situations where that function might fail.
|
|
@end deftypefun
|
|
|
|
The following program illustrates the use of these functions. Note that
|
|
the array to contain the return addresses returned by @code{backtrace}
|
|
is allocated on the stack. Therefore code like this can be used in
|
|
situations where the memory handling via @code{malloc} does not work
|
|
anymore (in which case the @code{backtrace_symbols} has to be replaced
|
|
by a @code{backtrace_symbols_fd} call as well). The number of return
|
|
addresses is normally not very large. Even complicated programs rather
|
|
seldom have a nesting level of more than, say, 50 and with 200 possible
|
|
entries probably all programs should be covered.
|
|
|
|
@smallexample
|
|
@include execinfo.c.texi
|
|
@end smallexample
|