RE: Can gdb handle aliased memory regions ?

[Marc TITINGER <Marc dot TITINGER at st dot com>]

Hi Mike,

> -----Original Message-----
> From: Kevin Pouget [mailto:kevin.pouget@gmail.com]
> Sent: Thursday, October 13, 2011 6:16 PM
> To: gdb@sources.redhat.com
> Cc: MikeW; Marc TITINGER
> Subject: Re: Can gdb handle aliased memory regions ?
> 
> On Wed, Oct 12, 2011 at 5:35 PM, MikeW <mw_phil@yahoo.co.uk> wrote:
> > Target platform: STLinux / ST Micro Connect
> >
> > On the target CPU, there is one region of physical memory that is
> accessible by
> > two different mapped memory address regions: one as cached memory and
> one as
> > uncached, eg.
> > ?0x8000000 (virt cached) ? -> 0x40000000 (phys)
> > ?0xDF00000 (virt uncached) -> 0x40000000 (phys)

Is it 0xDF00000 or 0xDF00_0000 like below in this text ? I'm asking because in the first case it looks like a VM (usermode) to Phy translation issue (I'm assuming it is a Linux kernel), while below, it looks like a kernel to physical memory mapping question ? 


> >
> > During the kernel init, there is a code sequence which switches
> between cached
> > and uncached (to update cache registers etc) and expects the
> execution to
> > proceed from eg. 0x80001234 to 0xDF001236.
So IIUC, you are running kernel code and at that point you which to tell the debugger to use a different offset and resume. Maybe the kernel has a meminfo.bank dedicated to the uncached mapping that we could use.

> >
> > Stepping with gdb is fine until the switchover point is reached,
> > whereupon gdb thinks it's lost control ('step[i]', 'next' or 'finish'
> > do not return to the (gdb) prompt), but of course the ms bits of
> > the PC just refer to the other region.
> >
> > I note gbd has support for the older technique of overlays; is there
> any way to
> > tell gdb that the 0x8000... and 0xDF00... regions are actually the
> same physical
> > memory ?
AFAIK the linux-awareness target does not support this currently unfortunately, but it would be easy to add a command to switch the memory bank from the tty at that point. 

May I ask you to send me the type of SoC, stlinux and gdb versions you are using ?

Many thanks,
Marc. 
 

> >
> > Thanks.
> 
> stlinux kernel debugger maintainer cc'd