Context switching for protected stacks

[Utkarsh Rai]

On Thu, Jun 18, 2020 at 6:34 PM Gedare Bloom <gedare at rtems.org> wrote:

> On Wed, Jun 17, 2020 at 11:17 PM Utkarsh Rai <utkarsh.rai60 at gmail.com>
> wrote:
> >
> > Hello,
> > For my GSoC project, I need to set/unset the memory attributes of the
> thread stacks on each context switch.
> > Right now I am making changes to the CPU-specific context switch
> assembly code. The arm/../cpu.h file has the Context_Control structure,
> which is used to store the relevant registers at each context switch.
> >  I have been trying to add the stack attributes to this structure from
> the 'rtems/score/stackmanagement.h' header (This header has been defined by
> me and has the stack attributes structure).
>
> When you change the context structure, there might be other places you
> need to update besides the context switch itself. One that comes to
> mind is _CPU_Context_validate. Maybe chase down where the context is
> referenced.
>
> >  After that, I would initialize the stack attributes in
> _CPU_Context_Initialize.
> >  For unsetting stack memories, I plan on making changes to
> _CPU_Context_Switch().
> > The problem is when I try to include the header in cpu.h it breaks the
> build with the following error -
> >
> > '.......
> > ........
> >
> /home/utkarsh/sandbox/rtems/5/arm-rtems5/include/machine/_default_types.h:
> Assembler messages:
> >
> /home/utkarsh/sandbox/rtems/cpukit/include/rtems/score/stackmanagement.h:42:
> Error: junk at end of line, first unrecognized character is `}'
> >
> /home/utkarsh/sandbox/rtems/cpukit/include/rtems/score/stackmanagement.h:44:
> Error: bad instruction `typedef struct stack_attr_prot'
> >
> /home/utkarsh/sandbox/rtems/cpukit/include/rtems/score/stackmanagement.h:45:
> Error: junk at end of line, first unrecognized character is `{'
> >
> /home/utkarsh/sandbox/rtems/cpukit/include/rtems/score/stackmanagement.h:46:
> Error: bad instruction `stack_attr_shared *shared_stacks'
> >
> /home/utkarsh/sandbox/rtems/cpukit/include/rtems/score/stackmanagement.h:47:
> Error: bad instruction `stack_attr Base'
> >
> /home/utkarsh/sandbox/rtems/cpukit/include/rtems/score/stackmanagement.h:48:
> Error: bad instruction `_bool current_stack'
> > {standard input}: Error: invalid operands (*UND* and *ABS* sections) for
> `*' when setting `iter'
> > Makefile:11563: recipe for target 'score/cpu/arm/arm-context-validate.o'
> failed
> > make[4]: *** [score/cpu/arm/arm-context-validate.o] Error 1
> > '
> > I have defined the stackmanagement.h header in the cpukit/headers.am
> and this is obviously an assembler error.  Can someone point out what is it
> that I am doing wrong?
> >
>
> When a .h file can be included in both C and ASM, you need to separate
> some of it, and disable some of it in ASM scope that doesn't
> understand C data types. See, for example,
> cpukit/include/rtems/score/percpu.h
>
> > I also would like to verify if the above way of handling context
> switching is the appropriate way to proceed.
>
> Seems like the right general idea. We probably need a CPP switch to
> enable/disable this stuff though.
>

Can you please elaborate on CPP switch? I am not sure if I am clear about
this.
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