technical question on GDB for MacOS

technical question on GDB for MacOS

[Jeff Roberts]

I'm using GDB on MacOS and we do a lot of dynamically generated code in our
products.  This is all done safely on various platforms with valloc and
mprotect, and everything runs fine.  However, when I want to debug, I can't
convince GDB to display the disassembly for my generated code.  It silently
steps and nexts just fine, but it never shows me my asm.  I can't even use
the disass <addr> command, because it tells me that there is not any
functions at that address.

Is there a way to convince it to show this?

->Jeff
RAD Game Tools

Re: technical question on GDB for MacOS

[Daniel Jacobowitz]

On Sun, Jun 03, 2007 at 08:21:31PM -0700, Jeff Roberts wrote:
> I'm using GDB on MacOS

We can't help you much with this - GNU GDB releases don't support
MacOS X.  Apple has extensive changes.  Fortunately your question is
mostly platform independent.

> steps and nexts just fine, but it never shows me my asm.  I can't even use
> the disass <addr> command, because it tells me that there is not any
> functions at that address.

Right.  You can use "display/i $pc" and "x/i <addr>" to show the
assembly anyway.

-- 
Daniel Jacobowitz
CodeSourcery

Re: technical question on GDB for MacOS

[Jeff Roberts]

> Right.  You can use "display/i $pc" and "x/i <addr>" to show the
> assembly anyway.

Perfect, thank you!

->Jeff
RAD Game Tools

----- Original Message ----- 
From: "Daniel Jacobowitz" <drow@false.org>
To: "Jeff Roberts" <jeffr@radgametools.com>
Cc: <gdb@sourceware.org>
Sent: Monday, June 04, 2007 3:55 AM
Subject: Re: technical question on GDB for MacOS


> On Sun, Jun 03, 2007 at 08:21:31PM -0700, Jeff Roberts wrote:
>> I'm using GDB on MacOS
>
> We can't help you much with this - GNU GDB releases don't support
> MacOS X.  Apple has extensive changes.  Fortunately your question is
> mostly platform independent.
>
>> steps and nexts just fine, but it never shows me my asm.  I can't even 
>> use
>> the disass <addr> command, because it tells me that there is not any
>> functions at that address.
>
> Right.  You can use "display/i $pc" and "x/i <addr>" to show the
> assembly anyway.
>
> -- 
> Daniel Jacobowitz
> CodeSourcery
> 

Re: technical question on GDB for MacOS

[Michael Snyder]

On Mon, 2007-06-04 at 14:42 -0700, Jeff Roberts wrote:
> > Right.  You can use "display/i $pc" and "x/i <addr>" to show the
> > assembly anyway.
> 
> Perfect, thank you!

Yes, the problem is that "disassemble" wants to do a whole function --
so it has to find symbols for the beginning and end of the function.
Self generated code doesn't have any symbols.

The examine /i command can take a start address and a repeat count
(number of instructions), eg "x/100i 0x1000"

Re: technical question on GDB for MacOS

[Andreas Schwab]

Michael Snyder <Michael.Snyder@access-company.com> writes:

> On Mon, 2007-06-04 at 14:42 -0700, Jeff Roberts wrote:
>> > Right.  You can use "display/i $pc" and "x/i <addr>" to show the
>> > assembly anyway.
>> 
>> Perfect, thank you!
>
> Yes, the problem is that "disassemble" wants to do a whole function --
> so it has to find symbols for the beginning and end of the function.

disassemble also takes two arguments, using those as the bounds.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
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