Need help in figuring out why gdb gives different value of a variable in callee vs caller context

[Gedare Bloom]

On Sat, Aug 15, 2020 at 3:15 AM Richi Dubey <richidubey at gmail.com> wrote:
>
> Hi,
>
> With reference to the code (github link), it aims to check if the Affinty of a node is set to 0 by calling the function _Processor_mask_Is_zero.
>
> While debugging with gdb, I can see using 'p' command that the variable is indeed 0 but after the variable gets passed to the function, the value of the variable isn't 0 anymore. Why is this happening?
>
> Gdb trace:
> ----------------------------------------------------------------------
> (gdb)
> 0x00118af4 187         _Processor_mask_Is_set(&node->Affinity, _Per_CPU_Get_index(curr_CPU) ||
> (gdb)
> 0x00118af6 187         _Processor_mask_Is_set(&node->Affinity, _Per_CPU_Get_index(curr_CPU) ||
> (gdb) p &node->Affinity
> $8 = (Processor_mask *) 0x200efc <_Thread_Objects+2172>
address 0x200efc

> (gdb) p node->Affinity
> $9 = {
>   __bits = {0}
> }
> (gdb) si
> 0x00118af8 187         _Processor_mask_Is_set(&node->Affinity, _Per_CPU_Get_index(curr_CPU) ||
> (gdb)
> 190         _Processor_mask_Is_zero( &node->Affinity ) )
> (gdb)
> 0x00118afc 190         _Processor_mask_Is_zero( &node->Affinity ) )
> (gdb)
> 0x00118afe 190         _Processor_mask_Is_zero( &node->Affinity ) )
> (gdb)
> 0x00118b00 190         _Processor_mask_Is_zero( &node->Affinity ) )
> (gdb)
> _Processor_mask_Is_zero (mask=0x203580 <_Per_CPU_Information>) at /home/richi/quick-start/src/rtems/cpukit/include/rtems/score/processormask.h:75
> 75 {
> (gdb)
> 0x0011726a 75 {
> (gdb)
> 0x0011726c 75 {
> (gdb) p mask
> $10 = (const Processor_mask *) 0x203580 <_Per_CPU_Information>
address 0x203580

You're not looking at the same memory location

> (gdb) p *mask
> $11 = {
>   __bits = {2126656}
> }
> ------------------------------------------------------------
>
> Please provide your views on this.
> Thanks,
> Richi,
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