address remaining -Wtautological-constant-out-of-range-compare

[PATCH 7/9] infiniband: uverbs: avoid out-of-range warnings

Posted by Arnd Bergmann 1 year, 10 months ago

From: Arnd Bergmann <arnd@arndb.de>

clang warns for comparisons that are always true, which is the case
for these two page size checks on architectures with 64KB pages:

drivers/infiniband/core/uverbs_ioctl.c:90:39: error: result of comparison of constant 65536 with expression of type 'u16' (aka 'unsigned short') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
        WARN_ON_ONCE(method_elm->bundle_size > PAGE_SIZE);
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
include/asm-generic/bug.h:104:25: note: expanded from macro 'WARN_ON_ONCE'
        int __ret_warn_on = !!(condition);                      \
                               ^~~~~~~~~
drivers/infiniband/core/uverbs_ioctl.c:621:17: error: result of comparison of constant 65536 with expression of type '__u16' (aka 'unsigned short') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
        if (hdr.length > PAGE_SIZE ||
            ~~~~~~~~~~ ^ ~~~~~~~~~

Add a cast to u32 in both cases, so it never warns about this.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/infiniband/core/uverbs_ioctl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/core/uverbs_ioctl.c b/drivers/infiniband/core/uverbs_ioctl.c
index f80da6a67e24..e0cc3ddae71b 100644
--- a/drivers/infiniband/core/uverbs_ioctl.c
+++ b/drivers/infiniband/core/uverbs_ioctl.c
@@ -90,7 +90,7 @@ void uapi_compute_bundle_size(struct uverbs_api_ioctl_method *method_elm,
 		ALIGN(bundle_size + 256, sizeof(*pbundle->internal_buffer));
 
 	/* Do not want order-2 allocations for this. */
-	WARN_ON_ONCE(method_elm->bundle_size > PAGE_SIZE);
+	WARN_ON_ONCE((u32)method_elm->bundle_size > PAGE_SIZE);
 }
 
 /**
@@ -636,7 +636,7 @@ long ib_uverbs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	if (err)
 		return -EFAULT;
 
-	if (hdr.length > PAGE_SIZE ||
+	if ((u32)hdr.length > PAGE_SIZE ||
 	    hdr.length != struct_size(&hdr, attrs, hdr.num_attrs))
 		return -EINVAL;
 
-- 
2.39.2

Re: [PATCH 7/9] infiniband: uverbs: avoid out-of-range warnings

Posted by Jason Gunthorpe 1 year, 10 months ago

On Thu, Mar 28, 2024 at 03:30:45PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> clang warns for comparisons that are always true, which is the case
> for these two page size checks on architectures with 64KB pages:
> 
> drivers/infiniband/core/uverbs_ioctl.c:90:39: error: result of comparison of constant 65536 with expression of type 'u16' (aka 'unsigned short') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>         WARN_ON_ONCE(method_elm->bundle_size > PAGE_SIZE);
>         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
> include/asm-generic/bug.h:104:25: note: expanded from macro 'WARN_ON_ONCE'
>         int __ret_warn_on = !!(condition);                      \
>                                ^~~~~~~~~
> drivers/infiniband/core/uverbs_ioctl.c:621:17: error: result of comparison of constant 65536 with expression of type '__u16' (aka 'unsigned short') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>         if (hdr.length > PAGE_SIZE ||
>             ~~~~~~~~~~ ^ ~~~~~~~~~
> 
> Add a cast to u32 in both cases, so it never warns about this.

But doesn't that hurt the codegen?

Jason

Re: [PATCH 7/9] infiniband: uverbs: avoid out-of-range warnings

Posted by Arnd Bergmann 1 year, 10 months ago

On Wed, Apr 3, 2024, at 17:45, Jason Gunthorpe wrote:
> On Thu, Mar 28, 2024 at 03:30:45PM +0100, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@arndb.de>
>> 
>> clang warns for comparisons that are always true, which is the case
>> for these two page size checks on architectures with 64KB pages:
>> 
>> drivers/infiniband/core/uverbs_ioctl.c:90:39: error: result of comparison of constant 65536 with expression of type 'u16' (aka 'unsigned short') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>>         WARN_ON_ONCE(method_elm->bundle_size > PAGE_SIZE);
>>         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
>> include/asm-generic/bug.h:104:25: note: expanded from macro 'WARN_ON_ONCE'
>>         int __ret_warn_on = !!(condition);                      \
>>                                ^~~~~~~~~
>> drivers/infiniband/core/uverbs_ioctl.c:621:17: error: result of comparison of constant 65536 with expression of type '__u16' (aka 'unsigned short') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>>         if (hdr.length > PAGE_SIZE ||
>>             ~~~~~~~~~~ ^ ~~~~~~~~~
>> 
>> Add a cast to u32 in both cases, so it never warns about this.
>
> But doesn't that hurt the codegen?

I just double-checked in the compiler explorer to confirm that
this works as I expected: both gcc and clang are still able
to optimize out the comparison for 64K pages, but clang no
longer complains after my change that this is an obvious
case.

I also see that gcc still produces a -Wtype-limits warning, but that
likely has to stay disabled because it produces too much output
elsewhere and I don't see an easy way to shut it up.

     Arnd

Re: [PATCH 7/9] infiniband: uverbs: avoid out-of-range warnings

Posted by Justin Stitt 1 year, 10 months ago

On Thu, Mar 28, 2024 at 7:32 AM Arnd Bergmann <arnd@kernel.org> wrote:
> Add a cast to u32 in both cases, so it never warns about this.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Reviewed-by: Justin Stitt <justinstitt@google.com>

> ---
>  drivers/infiniband/core/uverbs_ioctl.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/infiniband/core/uverbs_ioctl.c b/drivers/infiniband/core/uverbs_ioctl.c
> index f80da6a67e24..e0cc3ddae71b 100644
> --- a/drivers/infiniband/core/uverbs_ioctl.c
> +++ b/drivers/infiniband/core/uverbs_ioctl.c
> @@ -90,7 +90,7 @@ void uapi_compute_bundle_size(struct uverbs_api_ioctl_method *method_elm,
>                 ALIGN(bundle_size + 256, sizeof(*pbundle->internal_buffer));
>
>         /* Do not want order-2 allocations for this. */
> -       WARN_ON_ONCE(method_elm->bundle_size > PAGE_SIZE);
> +       WARN_ON_ONCE((u32)method_elm->bundle_size > PAGE_SIZE);
>  }
>
>  /**
> @@ -636,7 +636,7 @@ long ib_uverbs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>         if (err)
>                 return -EFAULT;
>
> -       if (hdr.length > PAGE_SIZE ||
> +       if ((u32)hdr.length > PAGE_SIZE ||
>             hdr.length != struct_size(&hdr, attrs, hdr.num_attrs))
>                 return -EINVAL;
>
> --
> 2.39.2
>

[PATCH 1/9] dm integrity: fix out-of-range warning
[PATCH 2/9] libceph: avoid clang out-of-range warning
[PATCH 3/9] rbd: avoid out-of-range warning
[PATCH 4/9] kcov: avoid clang out-of-range warning
[PATCH 5/9] ipv4: tcp_output: avoid warning about NET_ADD_STATS
[PATCH 6/9] nilfs2: fix out-of-range warning
[PATCH 7/9] infiniband: uverbs: avoid out-of-range warnings
[PATCH 8/9] mlx5: stop warning for 64KB pages
[PATCH 9/9] kbuild: enable tautological-constant-out-of-range-compare