Doubt using "set" command with registers

[Pedro Alves]

Hi João,

On 10/28/2014 04:01 PM, joaoandreferro@sapo.pt wrote:
> Hello all,
> 
> I've been using GDB (in fact, conjuged with KGDB) lately to do some  
> kernel debugging. I've been testing some GDB commands, and a doubt  
> arised while using the "set" command, trying to change the value of  
> some registers. I've been able to successfully change the value of all  
> the registers provided by the "info registers" command (i. e., in my  
> case $eax, $ecx, $edx, $ebx, $esp, $ebp, $esi, $edi, $eip, $eflags,  
> $cs, $ss, $ds, $es, $fs and $gs) *except* for $esp, $ss, $fs and $gs.  
> Why is it so? I've been making these tests after hitting a hardware  
> breakpoint, then I set the values with e. g. "set $es = 0xf1c2007c",  
> and verifiy the assignemt with "info reg $es". As I've pointed out, it  
> works with the majority of the registers, except for that four (in  
> this particular case, the first command doesn't output any error, but  
> the second command shows me that the registers remain with the initial  
> value). By the way, I've started GDB with the -write option (checked  
> it inside GDb with the "show write" command). My GDB version is 7.2.
> 
> If someone knows something about this situation and can share it with  
> me, it would be great.

I'd guess that it's kgdb itself that is blocking those writes.

Try "set debug remote 1" before the "set $foo = " command.

Thanks,
Pedro Alves