From: Jani Nikula <jani.nikula@linux.intel.com>
To: Nathan Chancellor <natechancellor@gmail.com>,
Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org,
dri-devel@lists.freedesktop.org,
clang-built-linux@googlegroups.com,
"Nathan Chancellor" <natechancellor@gmail.com>,
"Michel Dänzer" <michel@daenzer.net>
Subject: Re: [PATCH] drm/i915: Cast remain to unsigned long in eb_relocate_vma
Date: Fri, 14 Feb 2020 08:36:15 +0200 [thread overview]
Message-ID: <87v9o965gg.fsf@intel.com> (raw)
In-Reply-To: <20200214054706.33870-1-natechancellor@gmail.com>
On Thu, 13 Feb 2020, Nathan Chancellor <natechancellor@gmail.com> wrote:
> A recent commit in clang added -Wtautological-compare to -Wall, which is
> enabled for i915 after -Wtautological-compare is disabled for the rest
> of the kernel so we see the following warning on x86_64:
>
> ../drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c:1433:22: warning:
> result of comparison of constant 576460752303423487 with expression of
> type 'unsigned int' is always false
> [-Wtautological-constant-out-of-range-compare]
> if (unlikely(remain > N_RELOC(ULONG_MAX)))
> ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~
> ../include/linux/compiler.h:78:42: note: expanded from macro 'unlikely'
> # define unlikely(x) __builtin_expect(!!(x), 0)
> ^
> 1 warning generated.
>
> It is not wrong in the case where ULONG_MAX > UINT_MAX but it does not
> account for the case where this file is built for 32-bit x86, where
> ULONG_MAX == UINT_MAX and this check is still relevant.
>
> Cast remain to unsigned long, which keeps the generated code the same
> (verified with clang-11 on x86_64 and GCC 9.2.0 on x86 and x86_64) and
> the warning is silenced so we can catch more potential issues in the
> future.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/778
> Suggested-by: Michel Dänzer <michel@daenzer.net>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Works for me as a workaround,
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
> ---
>
> Round 3 :)
>
> Previous threads/patches:
>
> https://lore.kernel.org/lkml/20191123195321.41305-1-natechancellor@gmail.com/
> https://lore.kernel.org/lkml/20200211050808.29463-1-natechancellor@gmail.com/
>
> drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index 60c984e10c4a..47f4d8ab281e 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -1430,7 +1430,7 @@ static int eb_relocate_vma(struct i915_execbuffer *eb, struct i915_vma *vma)
>
> urelocs = u64_to_user_ptr(entry->relocs_ptr);
> remain = entry->relocation_count;
> - if (unlikely(remain > N_RELOC(ULONG_MAX)))
> + if (unlikely((unsigned long)remain > N_RELOC(ULONG_MAX)))
> return -EINVAL;
>
> /*
--
Jani Nikula, Intel Open Source Graphics Center
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next prev parent reply other threads:[~2020-02-14 6:35 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-14 5:47 [PATCH] drm/i915: Cast remain to unsigned long in eb_relocate_vma Nathan Chancellor
2020-02-14 6:36 ` Jani Nikula [this message]
2020-02-14 8:32 ` Chris Wilson
2020-02-14 11:49 ` Jani Nikula
2020-02-14 15:36 ` Michel Dänzer
2020-03-16 21:41 ` Nick Desaulniers
2020-03-26 20:11 ` Nathan Chancellor
2020-03-26 22:15 ` Jani Nikula
2020-02-14 13:46 ` Nathan Chancellor
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