linux-kernel - Re: [PATCH] mips: lib: uncached: fix uninitialized variable 'sp'

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Date:   Tue, 1 Dec 2020 01:50:43 +0100
From:   Anders Roxell <anders.roxell@...aro.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Nathan Chancellor <natechancellor@...il.com>,
        linux-mips@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] mips: lib: uncached: fix uninitialized variable 'sp'

On Mon, 30 Nov 2020 at 21:22, Nick Desaulniers <ndesaulniers@...gle.com> wrote:
>
> On Fri, Nov 27, 2020 at 12:39 AM Anders Roxell <anders.roxell@...aro.org> wrote:
> >
> > When building mips tinyconfig with clang the following warning show up:
> >
> > /tmp/arch/mips/lib/uncached.c:40:18: note: initialize the variable 'sp' to silence this warning
> >         register long sp __asm__("$sp");
> >                         ^
> >                          = 0
>
> Hi Anders

Hi Nick,

>, thank you for sending the patch. Do you have the full text
> of the warning; it looks like only the note was included?

oops, looks like I missed this:

/srv/src/kernel/next/arch/mips/lib/uncached.c:45:6: warning: variable
'sp' is uninitialized when used here [-Wuninitialized]
        if (sp >= (long)CKSEG0 && sp < (long)CKSEG2)
            ^~
/srv/src/kernel/next/arch/mips/lib/uncached.c:40:18: note: initialize
the variable 'sp' to silence this warning
        register long sp __asm__("$sp");
                        ^
                         = 0
1 warning generated.

Cheers,
Anders

>
> >
> > Rework to make an explicit inline move.
> >
> > Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
> > ---
> >  arch/mips/lib/uncached.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/mips/lib/uncached.c b/arch/mips/lib/uncached.c
> > index 09d5deea747f..21a4b94a0558 100644
> > --- a/arch/mips/lib/uncached.c
> > +++ b/arch/mips/lib/uncached.c
> > @@ -37,10 +37,11 @@
> >   */
> >  unsigned long run_uncached(void *func)
> >  {
> > -       register long sp __asm__("$sp");
> >         register long ret __asm__("$2");
> >         long lfunc = (long)func, ufunc;
> >         long usp;
> > +       long sp;
> > +       asm ("move %0, $sp" : "=r" (sp));
> >
> >         if (sp >= (long)CKSEG0 && sp < (long)CKSEG2)
> >                 usp = CKSEG1ADDR(sp);
> > --
> > 2.29.2
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers