Re: Thread backtrace termination

[Daniel Jacobowitz <drow@false.org>]

On Mon, Jul 11, 2005 at 06:52:13PM +0100, Jonathan Larmour wrote:
> Daniel Jacobowitz wrote:
> >On Mon, Jul 11, 2005 at 05:20:55PM +0100, Jonathan Larmour wrote:
> >
> >>The two "global constructors keyed to cyg_scheduler_start" lines are 
> >>bogus frame entries, although those also happened with GDB 6.1. The 
> >>"corrupt stack" whinge is new, and is treated as an error, including 
> >>terminating gdbinit scripts etc.
> >
> >
> >This is already changed in CVS.
> 
> Okay. I haven't seen that. It still looks like an error to me in frame.c.

The error is caught in the top level code for the backtrace command;
that effectively downgrades it to a warning and backtrace termination.

> BTW, my other web searches seem to indicate that a fair few (naive) people 
> are thinking they are having stack corruption because GDB thinks there 
> might be. That's unfortunate.

What else would you suggest?  GDB is confused.  From its point of view,
the stack _is_ corrupt.

> I've had a search for this and not found anything. I'm probably just not 
> using the right terms. Do you have a pointer, time frame or some search 
> terms I can use to pin this down? Thanks.

Well, the patch was:

2005-04-08  Daniel Jacobowitz  <dan@codesourcery.com>

        * dwarf2-frame.c (struct dwarf2_frame_cache): New field
        undefined_retaddr.
        (dwarf2_frame_cache): Initialize undefined_retaddr.
        (dwarf2_frame_this_id): Return an invalid frame ID if
        undefined_retaddr.

You can find the discussion and sample use on gdb@ a month or two
earlier.

> >For compiler-generated code there's really no useful way to do this.
> 
> I guess atleast now I know that, which saves me spending more time.
> 
> Wouldn't it make sense to make such a convention though, such as having a 
> return address of 0?

This is basically a convention.  You could, I suppose, patch a compiler
to generate it.  I'm not sure that would be wise.

> Alternatively, how about adding a new command that allows you to define a 
> set of entry point symbol names? People can then put an appropriate list 
> for themselves or their OS in ~/.gdbinit. Or it can be pre-initialised by 
> the OS support within GDB if there is one. e.g. nm-linux.h. Here's what 
> I'm thinking of:
> 
> set entry-point-name-list main _start _entry
> 
> Although handling mangled symbols and multiple languages might be fun. I'm 
> not an expert on such things.

*shrug* maybe.

-- 
Daniel Jacobowitz
CodeSourcery, LLC