On Fri, 5 May 2000 j_clifton@aerosimulation.com wrote:
> When I use gdb to examine mmapped memory all I see are zeros. Is this a bug or
> is there a workaround?
>
> I tried 4.17.0.4 on 2.0.36 to an area of memory reserved by lilo with an
> append=31m, and
> with 4.17.gnat.3.13w-18 on 2.2.5-12 to PCI memory (VMIC Reflective memory). I
> used the Reflective Memory diagnostic to confirm that the data is getting
> written to the memory.
>
> Please e-mail response as I had to drop off the mailing list.
If you mean ioremap'd memory and by gdb you mean using gdb on /proc/kcore
then won't access it. Some time ago, I added two vm_flags flags VM_IOREMAP
and VM_ALLOC so that /proc/kcore (see fs/proc/kcore.c) can skip the area
if VM_IOREMAP is set. Why? Because when I did not do so, my SCSI HBA was
generating parity errors while dumping off /proc/kcore. The reason is -
some registers may be mapped in and reading them in such an arbitrary
manner is a no-no because of side-effects.
(hmmm, you mention 2.0.36 - but ELF /proc/kcore support was only added in
2.3.x - how do you access vmalloc/ioremap'd areas in 2.0.x - it is
impossible (you'd probably get all zeroes)).
Regards,
Tigran.
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