FW: RE: gdb 6.4 not allowing me to change the value of registers like $SP,$RBP and $RIP.

["Kalpana Ramamurthy" <kal_pana at hotmail dot com>]

> On further debugging I noticed that when I comment out 
> observer_notify_target_changed () in
> the function value_assign(), my registers stay intact. Basically until this 
> point, if I try to set a
> register say $sp to some other value, the new value is reflected correctly 
> in the regcache. But
> as soon as observer_notify_target_changed() is invoked, the new value of 
> $sp is replaced back
> to its old value. This is because in register_raw_read(), the 
> target_fetch_registers() gets called which replaces all the registers from 
> my target. And my target fetches the registers from the
> panic thread.
>
> Please help.
>
> Kalpana
> ===
>
>
> > From: "Kalpana Ramamurthy" <kal_pana@hotmail.com>
> > To: kal_pana@hotmail.com, gdb@sourceware.org
> > Subject: gdb 6.4 not allowing me to change the value of registers like 
> > $SP,$RBP and $RIP.
> > Date: Wed, 02 May 2007 14:10:04 +0000
> >
> > I have a core dump whose registers look like this when I say "info reg" 
> > when I give this command in gdb 6.4.
> >
> > (gdb) info reg
> > rax            0x0      0
> > rbx            0x9c960a98       2627078808
> > rcx            0x2      2
> > rdx            0x0      0
> > rsi            0x4e1    1249
> > rdi            0xfee00300       4276093696
> > rbp            0x9c960a88       0x9c960a88
> > rsp            0x9c960a50       0x9c960a50
> > r8             0x1      1
> > r9             0x3      3
> > r10            0x0      0
> > r11            0x216    534
> > r12            0x9c960be8       2627079144
> > r13            0x3      3
> > r14            0x1      1
> > r15            0x0      0
> > rip            0x16489d 0x16489d <PANIC+51>
> > eflags         0x46     70
> > cs             0x8      8
> > ss             0x0      0
> > ds             0x0      0
> > es             0x0      0
> > fs             0x0      0
> > ---Type <return> to continue, or q <return> to quit---
> > gs             0x0      0
> >
> > I want to change the value of $rsp from 0x9c960a50  to 0x6d04ee0. But gdb 
> > is not allowing me
> > to do that. When I say
> > (gdb) set $sp=0x6d04ee0
> > or if I say
> > (gdb) set $rsp=0x6d04ee0
> > gdb just refuses to change the values and $sp ($rsp) stays on as 
> > 0x9c960a50.
> >
> > I am using gdb 6.4. When I do the same thing as above using gdb 6.0, it 
> > works great. I am able
> > to change the values of the registers. Why does this happen only in gdb 
> > 6.4 ? I am not able to write macros because of this problem. Please help - 
> > where am I going wrong ? I have been debugging gdb 6.4 source code for 3 
> > whole days now and its driving me nuts. I could see the registers in the 
> > regcache - and SP shows the new value. From the regcache onwards
> > I have no idea how gdb translates the contents of the register cache to 
> > permanent values
> > where the globals like$rsp etc get set permanently unless we change it 
> > back again.
> >
> > Any help will be really appreciated.
> >
> > Kalpana
> > ====
> >
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