Re: Accessing variables in .sdata

[Daniel Jacobowitz <drow@mvista.com>]

On Wed, Mar 12, 2003 at 12:53:17PM -0500, Bruce Ashfield wrote:
> Hi all,
> 
> I've been trying to characterize the types of variables I
> can't access when using a linker script during the construction
> of our bootable image. The linker script in question is a 
> slightly modified one from ppcboot and I can't see any 
> fundamental problems with the script.
> 
> I've been dumping the map file during the link and comparing
> the one that the linker internally generates to the one that
> results from our supplied linker map. I'm seeing a different
> location for the .text,.bss,.data segments and some other 
> ordering differences, but again nothing fundamentally wrong. 
> 
> But my problem persists. If I use a linker script and try to
> print the value of a variable in a .sdata I'm presented with
> the gdb error "Cannot access memory at address 0x...". Where
> address 0xABCD.. is no where near where the map file says 
> that section and variable should be found. It's like gdb is
> missing the offset of the sections.
> 
> I've also tried using add-symbol-file to force gdb to recognize
> the start address for the various sections, but at best I see
> the error address moving around. 
> 
> I've been told from people around the office that if they load
> the symbol file multiple times the error address changes and
> they can breakpoint functions, but not usually inside a 
> function.

This sounds like the sdata offset is uninitialized for some reason.  I
don't know why it would affect breakpoints, though.  Did you try
valgrind?  Do you have a smaller testcase working yet based on this new
insight?

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer