[NSWI004] getting stack pointer value

[Georgii Ekserdzhian]

Good evening,

I've also tried the "register" keyword route.

register int *foo asm ("sp");

this line produces error:
In file included from src/debug/code.c:4:
include/debug/code.h: In function 'debug_get_stack_pointer':
include/debug/code.h:11:23: error: expected '=', ',', ';', 'asm' or
'__attribute__' before 'asm'
   11 |     register int *foo asm ("sp");
      |                       ^~~
include/debug/code.h:11:23: error: implicit declaration of function 'asm'
[-Werror=implicit-function-declaration]
cc1: all warnings being treated as errors


Georgii Ekserdzhian


чт, 8 окт. 2020 г. в 20:06, Petr Tůma <petr.tuma at d3s.mff.cuni.cz>:

> Hi,
>
> inline assembly is one option, but you could also try the "register"
> keyword, as suggested by the README file. For exact syntax, see
> https://gcc.gnu.org/onlinedocs/gcc/Local-Register-Variables.html#Local-Register-Variables,
> this makes it possible to access specific register values directly from C
> (simply by defining a variable that resides in that particular register and
> then reading it).
>
> Many compiler optimizations make naive solutions for accessing stack
> location fail, so the above solution might really be better than trying
> without "register".
>
> Petr
>
>
> On 08/10/2020 19:11, Peter G wrote:
> > Hi,
> >
> > I have encountered similar behaviour. When solving the problem without
> inline assembly I got this output
> >
> > sp1 = 800003e0
> > sp2 = 800003e0
> >
> > tests/basic/stack_pointer/test.c:43: Kernel test assertion failed: sp1
> == sp2
> > tests/basic/stack_pointer/test.c:43: $sp unexpectedly changed
> (0x800003e0 => 0x800003e0)
> >
> > I could not figure out why this happen, but after I added these two
> lines the test passes:
> >
> > printk("&sp1 = %p\n", &sp1);
> > printk("&sp2 = %p\n", &sp2);
> > I think that after adding these two lines compiler saves sp1 and sp2 on
> the stack, otherwise they are kept in the registers. I tried to find where
> the problem lies in the disassembly but I have not figured it out.
> >
> > However, solution using inline assembly worked right away.
> >
> > Best regards,
> > Peter Grajcar
> >
> >> On 8 Oct 2020, at 17:13, Georgii Ekserdzhian <gxrjan at gmail.com> wrote:
> >>
> >> Good afternoon,
> >>
> >> I've been thinking on debug_get_stack_pointer function for quite a
> while now.
> >> I pushed my code into my repo.
> >> Also I attached my log.
> >> For some reason the test that asserts that sp1 == sp2 fails, but the
> log shows that they are the same.
> >>
> >> Also question. You said that we should try first without using inline
> assembly.
> >> I tried to use asm() function and the compiler doesn't recognize this
> function call.
> >> Is there another way to use assembly in C?
> >>
> >> Georgii Ekserdzhian
> >> <log>_______________________________________________
> >> NSWI004 mailing list
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