Re: Thread backtrace termination

[Jonathan Larmour <jifl@eCosCentric.com>]

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.

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.

>>I'd be interested if someone could clarify to me what 
>>the termination conditions for a backtrace actually _are_. i.e. as an OS 
>>author, how do I initialise a thread context to persuade GDB to stop when 
>>it reaches the innermost frame. 
> 
> In general there's no defined way to do this.  If the start routine is
> written in assembly, take a look at the example I posted earlier this
> year of using dwarf2 unwind information to terminate a backtrace by
> marking the return address column as undefined.  There's a matching GDB
> patch, which was committed to HEAD after 6.3.

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.

> 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?

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.

Thanks,

Jifl
-- 
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