Re: new option --readnever & script gstack?

[Andrew Cagney <ac131313@redhat.com>]

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Eli Zaretskii wrote:
>>Date: Mon, 22 Nov 2004 15:34:22 -0500
>>From: Andrew Cagney <ac131313@redhat.com>
>>
>>As the oposite to --readnow, I'd like to propose a new option 
>>--readnever (i.e., don't read in the symbolic debug inf).  That and a 
>>few lines of script should let GDB implemement a direct equivalent to 
>>pstack (called gstack say).
> 
> 
> An alternative to this would be to have a --read=WHEN switch, which
> could accept 3 arguments: `now', `asneeded' (the default), and
> `never'.
> 
> However, I must admit that, like Mark, I don't see the situation where
> this would be useful.  Could you perhaps describe such a situation,
> and explain how the existance of the new option would help, including
> the auxiliary script and the relation to `pstack'?

Lets focus on "pstack", or a potential GDB alternative, "gstack".

The pstack program attaches to a running process, dumps out a minimal 
backtrace (i.e., no symbolic information such as parameter names) of all 
threads, and then detaches. It's useful when tying to quickly capture 
information from a live system.

The top three google hits for "pstack" are:

http://packages.debian.org/unstable/devel/pstack
The existing pstack port.  Last time I checked it didn't work with 
threads, didn't work when there was no unwind information, and didn't 
work on most architectures (i386 specific)?

http://oss.oracle.com/projects/pstack-gdb/
An existing wrapper to GDB.  It works as well as GDB (i.e., threads, 
when there's no unwind information, and across architectures).

http://docs.sun.com/doc/816-0210/6m6nb7mih?a=view
For reference, doco on the entire p* family of commands.

Now to get a more functional pstack, I can think of two strategies:

- throw new code at pstack (or similar) until it supports threads, 
non-debug-info frames and multiple architectures, ...

- modify the existing GDB, which already handles threads and 
non-debug-info frames, and multiple architectures, so that it can 
implement pstack.

I've attached a prototype GDB wrapper that implements the second 
alternative.  The only missing piece is the suppression of symbolic info 
in the backtrace - pstack, which is trying to be quick, doesn't include 
that more detailed information.

So, to my questions:

- what of an option to suppress symbolic debug info (--readnever, 
--read=never, --symtab-read=never, ...)?
- what of a new script called gstack, bundled with GDB?

Andrew

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