Hi,

the current version of showing the backtrace is not async-signal-safe
as it uses backtrace_symbols() which, in turn, uses malloc(). The
attached patch changes the backtrace printing functionality to instead
use backtrace_symbols_fd() and pipes.

Also, it does some other work on backtrace printing:

- Nowadays the main program has the same debug symbol name as whatever
the name of the main program is, rather than MAIN__. Therefore remove
special case logic related to that.

- Don't filter out stack frames from inside libgfortran, as this might
lose information in case the reason for the crash is in the library.

- Reformat the output slightly, so the each stack frame fits on one
line, and begins with #NUM, similar to GDB.

For instance, the small program

subroutine c
  call abort ()
end subroutine c

subroutine b
  call c
end subroutine b

subroutine a
  call b
end subroutine a

program bt
  call a
end program bt


compiled with -g -fno-whole-file now generates


Backtrace for this error:
  #0  /home/janne/src/gfortran/trunk/install/lib64/libgfortran.so.3(+0x182b7)[0x7f9c8a2c42b7]
  #1  /home/janne/src/gfortran/trunk/install/lib64/libgfortran.so.3(+0x19d07)[0x7f9c8a2c5d07]
  #2  /home/janne/src/gfortran/trunk/install/lib64/libgfortran.so.3(+0xe1e49)[0x7f9c8a38de49]
  #3  in b_ at bt.f90:5 (0x400612)
  #4  in b_ at bt.f90:7 (0x400620)
  #5  in a_ at bt.f90:11 (0x400630)
  #6  in bt at bt.f90:15 (0x400640)
Aborted

In this case the 3 first frames are the output from
backtrace_symbols_fd() since addr2line can't get the symbols from
libgfortran. With static linking addr2line can see it:


Backtrace for this error:
  #0  in _gfortrani_show_backtrace at backtrace.c:85 (0x405427)
  #1  in _gfortrani_sys_abort at error.c:176 (0x4007B7)
  #2  in _gfortran_abort (0x404469)
  #3  in b_ at bt.f90:5 (0x400402)
  #4  in b_ at bt.f90:7 (0x400410)
  #5  in a_ at bt.f90:11 (0x400420)
  #6  in bt at bt.f90:15 (0x400430)
Aborted

Regtested on x86_64-unknown-linux-gnu, Ok for trunk?

2011-05-14  Janne Blomqvist  <jb@gcc.gnu.org>

	PR libfortran/48931
	* configure.ac: Check for backtrace_symbols_fd instead of
	backtrace_symbols.
	* config.h.in: Regenerated.
	* configure: Regenerated.
	* runtime/backtrace.c (local_strcasestr): Remove.
	(bt_header): New function.
	(dump_glibc_backtrace): Remove.
	(show_backtrace): Rework to use backtrace_symbols_fd and pipes,
	reformat output.


-- 
Janne Blomqvist