Re: the "load" command and the .bss section

[Michael Snyder <msnyder@specifix.com>]

On Wed, 2008-04-30 at 20:10 -0400, Mike Frysinger wrote:
> On Monday 28 April 2008, Michael Snyder wrote:
> > On Sun, 2008-04-27 at 05:09 -0400, Mike Frysinger wrote:
> > > i was doing a new board port using jtag and so was leveraging the "load"
> > > command to setup the initial ELF in the relevant memory regions.  things
> > > kept crashing on me and then i realized that the loading process wasnt
> > > actually zeroing out the bss.  is there a reason for this ?  i googled
> > > and flipped through the manual, but the details on what exactly the
> > > "load" command is supposed to do is a bit on sketchy side.  from what i
> > > can tell from the gdb source code and the actual output from running the
> > > command, it walks the section headers (rather than the program headers ?)
> > > and loads up everything that is in the file.  since the bss section
> > > doesnt actually exist in the file and is only allocated, that is why it
> > > gets skipped ?
> > >
> > > once i adapted my habits to first load the ELF and then manually zero the
> > > bss, life was so much saner :).
> >
> > In my understanding, it is not GDB's responsibility to zero the
> > .bss section.  That is the responsibility of the C Runtime.
> >
> > Otherwise, how could the program run without gdb in the picture?
> >
> > The gdb load command only addresses sections with the loadable
> > flag.  .bss is not loadable.
> 
> a fair point, but i think there is a valid use case for having an optional 
> flag to tell gdb to do this.  you may want to load a bare metal application 
> that itself would have normally been loaded by another application (say your 
> typical bootloader), so the assumption is that certain aspects of the C 
> runtime have been initialized before the bare metal application is executed.  
> Daniel also indicated that i wouldnt be the first (and probably not the last) 
> to experience this hiccup and ask for an optional (streamlined) method for 
> accounting for this.

That's why there are different implementations of "load".
A bare-metal target would presumably wind up using the 
appropriate "load" version.

However, I do not disagree.  In fact, I agree -- having an 
option to "load" that would tell it to clear certain sections
(such as .bss) automatically would be a handy thing.