Re: [PATCH v5] Add negative repeat count to 'x' command

[Pedro Alves <palves at redhat dot com>]

On 08/11/2016 03:08 PM, Thomas Preudhomme wrote:
>>
> 
> While trying this I noticed that the following 2 tests fail when running
> with qemu-user (it works with qemu-system):

So this is emulating a no-MMU configuration, right?  Since gdb managed to
read from address 0.  Otherwise, the problem is in is_address_zero_readable.

> 
> gdb.base/examine-backward.exp: address zero boundary: examine 6 bytes backward
> 
> gdb.base/examine-backward.exp: address zero boundary: examine 3 bytes
> backward from 0x0
> 
> They fail with:
> 
> 0xfffffffd:     Cannot access memory at address 0xfffffffd
> 
> I suppose these two tests should also be guarded or maybe have several
> expected results.

If you try reading from that address directly, does it work?
E.g. "x 0xfffffffd".

Wondering whether gdb is actually trying to read from 0xfffffffffffffffd,
and that failing somewhere.  The address print routine (paddress) trims
the upper 32-bits of CORE_ADDR when debugging a 32-bit target.

But probably this just means that that physical address really
does not exist on the emulated system, and so qemu's stub returns
error when gdb tries to read off of it?

Thanks,
Pedro Alves