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Date:      Wed, 16 Jan 2008 11:56:36 -0800
From:      Chuck Swiger <cswiger@mac.com>
To:        Arun Paneri <p26a@yahoo.com>
Cc:        FreeBSD User <freebsd@stigascorp.com>, freebsd-questions@freebsd.org
Subject:   Re: Pls help: regarding gdb internals
Message-ID:  <2C402693-DD71-4B3A-A3C1-3685F8A130E0@mac.com>
In-Reply-To: <771039.36759.qm@web90405.mail.mud.yahoo.com>
References:  <771039.36759.qm@web90405.mail.mud.yahoo.com>

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On Jan 16, 2008, at 10:58 AM, Arun Paneri wrote:
> Can anyone write few lines about how does gdb internally works. I  
> went to "Gdb internals guide" but couldn't find much information  
> specifically which i am looking for.

I'm not familiar with the document you mentioned, but the canonical  
documentation for GDB is available via "info gdb".

> I want information like when we give command "$gdb test.exe" then  
> how internaly it works. Does it start reading symbols and start  
> making symbol table with this command?

Binary objects such as executable programs, shared libraries, etc  
contain symbol tables; GDB does a quick load of this symbol data to  
identify all of the sources of symbols for the program, and then will  
look up the details when needed.

> Does it start creating stack frames as we give command "run" or  
> before even that?

The program being debugged does not exist as a process until you run  
it, so there isn't an address space or stack until then.  When the  
target program is run, it creates it's own stack frames according to  
the local architecture's machine calling conventions.

> I am basically interested to know about creation of frames and how  
> does gdb read them back when we give "backtrace" command?

Well, the calling conventions are different for every particular CPU  
architecture; but if you want to see the code that GDB uses, start with:

/usr/src/contrib/gdb/gdb/frame-base.c
/usr/src/contrib/gdb/gdb/frame-base.h
/usr/src/contrib/gdb/gdb/frame-unwind.c
/usr/src/contrib/gdb/gdb/frame-unwind.h
/usr/src/contrib/gdb/gdb/frame.c
/usr/src/contrib/gdb/gdb/frame.h

...but I suspect that something like these two articles are closer to  
what you are looking for:

http://en.wikipedia.org/wiki/Calling_convention
http://en.wikipedia.org/wiki/X86_calling_conventions

-- 
-Chuck




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