[v1] linux-user: Fix clang warning for nios2-linux-user code

[PATCH] linux-user: Fix clang warning for nios2-linux-user code

Posted by Peter Maydell 2 years, 3 months ago

The clang in Ubuntu 18.04 (10.0.0-4ubuntu1) produces a warning
on the code added in commit f5ef0e518d03 where we use a
shifted expression in a boolean context:

../../linux-user/elfload.c:2423:16: error: converting the result of '<<' to a boolean always evaluates to true [-Werror,-Wtautological-constant-compare]
    } else if (LO_COMMPAGE) {
               ^
../../linux-user/elfload.c:1102:22: note: expanded from macro 'LO_COMMPAGE'
#define LO_COMMPAGE  TARGET_PAGE_SIZE
                     ^
/mnt/nvmedisk/linaro/qemu-from-laptop/qemu/include/exec/cpu-all.h:231:31: note: expanded from macro 'TARGET_PAGE_SIZE'
#define TARGET_PAGE_SIZE   (1 << TARGET_PAGE_BITS)
                              ^
1 error generated.

The warning is bogus because whether LO_COMMPAGE is zero or not
depends on compile-time ifdefs; shut the compiler up by adding
an explicit comparison to zero.

Fixes: f5ef0e518d0331 ("linux-user/nios2: Map a real kuser page")
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
I'm probably going to apply this directly once it's reviewed, because
it fixes a build-break on one of my machines.

 linux-user/elfload.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 329b2375ef1..2993b01e60c 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -2420,7 +2420,7 @@ static void pgb_static(const char *image_name, abi_ulong orig_loaddr,
         } else {
             offset = -(HI_COMMPAGE & -align);
         }
-    } else if (LO_COMMPAGE) {
+    } else if (LO_COMMPAGE == 0) {
         loaddr = MIN(loaddr, LO_COMMPAGE & -align);
     }
 
-- 
2.25.1

Re: [PATCH] linux-user: Fix clang warning for nios2-linux-user code

Posted by Warner Losh 2 years, 3 months ago


> On Jan 10, 2022, at 12:17 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
> 
> The clang in Ubuntu 18.04 (10.0.0-4ubuntu1) produces a warning
> on the code added in commit f5ef0e518d03 where we use a
> shifted expression in a boolean context:
> 
> ../../linux-user/elfload.c:2423:16: error: converting the result of '<<' to a boolean always evaluates to true [-Werror,-Wtautological-constant-compare]
>    } else if (LO_COMMPAGE) {
>               ^
> ../../linux-user/elfload.c:1102:22: note: expanded from macro 'LO_COMMPAGE'
> #define LO_COMMPAGE  TARGET_PAGE_SIZE
>                     ^
> /mnt/nvmedisk/linaro/qemu-from-laptop/qemu/include/exec/cpu-all.h:231:31: note: expanded from macro 'TARGET_PAGE_SIZE'
> #define TARGET_PAGE_SIZE   (1 << TARGET_PAGE_BITS)
>                              ^
> 1 error generated.
> 
> The warning is bogus because whether LO_COMMPAGE is zero or not
> depends on compile-time ifdefs; shut the compiler up by adding
> an explicit comparison to zero.
> 
> Fixes: f5ef0e518d0331 ("linux-user/nios2: Map a real kuser page")
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> I'm probably going to apply this directly once it's reviewed, because
> it fixes a build-break on one of my machines.
> 
> linux-user/elfload.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Warner Losh <imp@bsdimp.com>


> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> index 329b2375ef1..2993b01e60c 100644
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -2420,7 +2420,7 @@ static void pgb_static(const char *image_name, abi_ulong orig_loaddr,
>         } else {
>             offset = -(HI_COMMPAGE & -align);
>         }
> -    } else if (LO_COMMPAGE) {
> +    } else if (LO_COMMPAGE == 0) {
>         loaddr = MIN(loaddr, LO_COMMPAGE & -align);
>     }
> 
> -- 
> 2.25.1
> 
>

Re: [PATCH] linux-user: Fix clang warning for nios2-linux-user code

Posted by Laurent Vivier 2 years, 3 months ago

Le 10/01/2022 à 20:17, Peter Maydell a écrit :
> The clang in Ubuntu 18.04 (10.0.0-4ubuntu1) produces a warning
> on the code added in commit f5ef0e518d03 where we use a
> shifted expression in a boolean context:
> 
> ../../linux-user/elfload.c:2423:16: error: converting the result of '<<' to a boolean always evaluates to true [-Werror,-Wtautological-constant-compare]
>      } else if (LO_COMMPAGE) {
>                 ^
> ../../linux-user/elfload.c:1102:22: note: expanded from macro 'LO_COMMPAGE'
> #define LO_COMMPAGE  TARGET_PAGE_SIZE
>                       ^
> /mnt/nvmedisk/linaro/qemu-from-laptop/qemu/include/exec/cpu-all.h:231:31: note: expanded from macro 'TARGET_PAGE_SIZE'
> #define TARGET_PAGE_SIZE   (1 << TARGET_PAGE_BITS)
>                                ^
> 1 error generated.
> 
> The warning is bogus because whether LO_COMMPAGE is zero or not
> depends on compile-time ifdefs; shut the compiler up by adding
> an explicit comparison to zero.
> 
> Fixes: f5ef0e518d0331 ("linux-user/nios2: Map a real kuser page")
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> I'm probably going to apply this directly once it's reviewed, because
> it fixes a build-break on one of my machines.
> 
>   linux-user/elfload.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> index 329b2375ef1..2993b01e60c 100644
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -2420,7 +2420,7 @@ static void pgb_static(const char *image_name, abi_ulong orig_loaddr,
>           } else {
>               offset = -(HI_COMMPAGE & -align);
>           }
> -    } else if (LO_COMMPAGE) {
> +    } else if (LO_COMMPAGE == 0) {

It seems to revert the logic should it be "(LO_COMMPAGE != 0)"?

Thanks,
Laurent
>           loaddr = MIN(loaddr, LO_COMMPAGE & -align);
>       }
>

Re: [PATCH] linux-user: Fix clang warning for nios2-linux-user code

Posted by Peter Maydell 2 years, 3 months ago

On Tue, 11 Jan 2022 at 07:01, Laurent Vivier <laurent@vivier.eu> wrote:
>
> Le 10/01/2022 à 20:17, Peter Maydell a écrit :
> > The clang in Ubuntu 18.04 (10.0.0-4ubuntu1) produces a warning
> > on the code added in commit f5ef0e518d03 where we use a
> > shifted expression in a boolean context:
> >
> > ../../linux-user/elfload.c:2423:16: error: converting the result of '<<' to a boolean always evaluates to true [-Werror,-Wtautological-constant-compare]
> >      } else if (LO_COMMPAGE) {
> >                 ^
> > ../../linux-user/elfload.c:1102:22: note: expanded from macro 'LO_COMMPAGE'
> > #define LO_COMMPAGE  TARGET_PAGE_SIZE
> >                       ^
> > /mnt/nvmedisk/linaro/qemu-from-laptop/qemu/include/exec/cpu-all.h:231:31: note: expanded from macro 'TARGET_PAGE_SIZE'
> > #define TARGET_PAGE_SIZE   (1 << TARGET_PAGE_BITS)
> >                                ^
> > 1 error generated.
> >
> > The warning is bogus because whether LO_COMMPAGE is zero or not
> > depends on compile-time ifdefs; shut the compiler up by adding
> > an explicit comparison to zero.
> >
> > Fixes: f5ef0e518d0331 ("linux-user/nios2: Map a real kuser page")
> > Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> > ---
> > I'm probably going to apply this directly once it's reviewed, because
> > it fixes a build-break on one of my machines.
> >
> >   linux-user/elfload.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> > index 329b2375ef1..2993b01e60c 100644
> > --- a/linux-user/elfload.c
> > +++ b/linux-user/elfload.c
> > @@ -2420,7 +2420,7 @@ static void pgb_static(const char *image_name, abi_ulong orig_loaddr,
> >           } else {
> >               offset = -(HI_COMMPAGE & -align);
> >           }
> > -    } else if (LO_COMMPAGE) {
> > +    } else if (LO_COMMPAGE == 0) {
>
> It seems to revert the logic should it be "(LO_COMMPAGE != 0)"?

You're right, it should -- I was too hasty in writing this fix, clearly...

-- PMM