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__("$sp");
^
= 0
Rework to make an explicit inline move.
Signed-off-by: Anders Roxell <[email protected]>
---
arch/mips/lib/uncached.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/mips/lib/uncached.c b/arch/mips/lib/uncached.c
index 09d5deea747f..21a4b94a0558 100644
--- a/arch/mips/lib/uncached.c
+++ b/arch/mips/lib/uncached.c
@@ -37,10 +37,11 @@
*/
unsigned long run_uncached(void *func)
{
- register long sp __asm__("$sp");
register long ret __asm__("$2");
long lfunc = (long)func, ufunc;
long usp;
+ long sp;
+ asm ("move %0, $sp" : "=r" (sp));
if (sp >= (long)CKSEG0 && sp < (long)CKSEG2)
usp = CKSEG1ADDR(sp);
--
2.29.2
On Fri, Nov 27, 2020 at 12:39 AM Anders Roxell <[email protected]> wrote:
>
> When building mips tinyconfig with clang the following warning show up:
>
> /tmp/arch/mips/lib/uncached.c:40:18: note: initialize the variable 'sp' to silence this warning
> register long sp __asm__("$sp");
> ^
> = 0
Hi Anders, thank you for sending the patch. Do you have the full text
of the warning; it looks like only the note was included?
>
> Rework to make an explicit inline move.
>
> Signed-off-by: Anders Roxell <[email protected]>
> ---
> 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, $sp" : "=r" (sp));
>
> if (sp >= (long)CKSEG0 && sp < (long)CKSEG2)
> usp = CKSEG1ADDR(sp);
> --
> 2.29.2
>
--
Thanks,
~Nick Desaulniers
On Mon, 30 Nov 2020 at 21:22, Nick Desaulniers <[email protected]> wrote:
>
> On Fri, Nov 27, 2020 at 12:39 AM Anders Roxell <[email protected]> wrote:
> >
> > When building mips tinyconfig with clang the following warning show up:
> >
> > /tmp/arch/mips/lib/uncached.c:40:18: note: initialize the variable 'sp' to silence this warning
> > register long sp __asm__("$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__("$sp");
^
= 0
1 warning generated.
Cheers,
Anders
>
> >
> > Rework to make an explicit inline move.
> >
> > Signed-off-by: Anders Roxell <[email protected]>
> > ---
> > arch/mips/lib/uncached.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/mips/lib/uncached.c b/arch/mips/lib/uncached.c
> > index 09d5deea747f..21a4b94a0558 100644
> > --- a/arch/mips/lib/uncached.c
> > +++ b/arch/mips/lib/uncached.c
> > @@ -37,10 +37,11 @@
> > */
> > unsigned long run_uncached(void *func)
> > {
> > - register long sp __asm__("$sp");
> > register long ret __asm__("$2");
> > long lfunc = (long)func, ufunc;
> > long usp;
> > + long sp;
> > + asm ("move %0, $sp" : "=r" (sp));
> >
> > if (sp >= (long)CKSEG0 && sp < (long)CKSEG2)
> > usp = CKSEG1ADDR(sp);
> > --
> > 2.29.2
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers
On Fri, 27 Nov 2020, Anders Roxell wrote:
> When building mips tinyconfig with clang the following warning show up:
>
> /tmp/arch/mips/lib/uncached.c:40:18: note: initialize the variable 'sp' to silence this warning
> register long sp __asm__("$sp");
> ^
> = 0
>
> Rework to make an explicit inline move.
It's not uninitialised, because by definition $sp has been initialised.
This code wouldn't have worked for the last 15 years otherwise.
It is however non-standard usage (which may not have been clarified at
the time this piece was made; I recall extensive discussions around this
feature over the years):
"6.47.5.2 Specifying Registers for Local Variables
.................................................
[...]
"The only supported use for this feature is to specify registers for
input and output operands when calling Extended 'asm' (*note Extended
Asm::). [...]"
so the change description should refer to that as the rationale rather
than an implementation-specific misleading warning (although that can be
quoted for a reference of course).
> diff --git a/arch/mips/lib/uncached.c b/arch/mips/lib/uncached.c
> index 09d5deea747f..21a4b94a0558 100644
> --- a/arch/mips/lib/uncached.c
> +++ b/arch/mips/lib/uncached.c
> @@ -37,10 +37,11 @@
> */
> unsigned long run_uncached(void *func)
> {
> - register long sp __asm__("$sp");
> register long ret __asm__("$2");
> long lfunc = (long)func, ufunc;
> long usp;
> + long sp;
> + asm ("move %0, $sp" : "=r" (sp));
Missing newline between the variable block and code here; you may well
swap it with the empty line below you have left. Also use `__asm__' for
consistency, and remove the extraneous space ahead of the parenthesis as
we don't use them in Linux. Using a tab to separate the mnemonic from
operands is also preferable, i.e. "move\t%0, $sp" in this case (using
actual tabs works better with multi-line assembly, but this is not one).
I think this should be OK once the issues I mentioned here have been
addressed.
Maciej
On Sun, 6 Dec 2020, Maciej W. Rozycki wrote:
> I think this should be OK once the issues I mentioned here have been
> addressed.
Or alternatively making the variable global would possibly be a better
fix as it would let the compiler decide if to waste another register to
keep a copy of $sp.
Maciej