[Intel-gfx] [PATCH] drm/i915: Cast remain to unsigned long in eb_relocate_vma

[Intel-gfx] [PATCH] drm/i915: Cast remain to unsigned long in eb_relocate_vma

[Nathan Chancellor]

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>
---

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;
 
 	/*
-- 
2.25.0

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[Intel-gfx] ✓ Fi.CI.BAT: success for drm/i915: Cast remain to unsigned long in eb_relocate_vma

[Patchwork]

== Series Details ==

Series: drm/i915: Cast remain to unsigned long in eb_relocate_vma
URL   : https://patchwork.freedesktop.org/series/73440/
State : success

== Summary ==

CI Bug Log - changes from CI_DRM_7936 -> Patchwork_16565
====================================================

Summary
-------

  **SUCCESS**

  No regressions found.

  External URL: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/index.html

Known issues
------------

  Here are the changes found in Patchwork_16565 that come from known issues:

### IGT changes ###

#### Issues hit ####

  * igt@i915_selftest@live_gem_contexts:
    - fi-byt-n2820:       [PASS][1] -> [DMESG-FAIL][2] ([i915#1052])
   [1]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/fi-byt-n2820/igt@i915_selftest@live_gem_contexts.html
   [2]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/fi-byt-n2820/igt@i915_selftest@live_gem_contexts.html

  * igt@i915_selftest@live_gtt:
    - fi-glk-dsi:         [PASS][3] -> [TIMEOUT][4] ([fdo#112271] / [i915#690])
   [3]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/fi-glk-dsi/igt@i915_selftest@live_gtt.html
   [4]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/fi-glk-dsi/igt@i915_selftest@live_gtt.html

  
#### Possible fixes ####

  * igt@gem_exec_parallel@fds:
    - fi-byt-n2820:       [FAIL][5] ([i915#694]) -> [PASS][6]
   [5]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/fi-byt-n2820/igt@gem_exec_parallel@fds.html
   [6]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/fi-byt-n2820/igt@gem_exec_parallel@fds.html

  
#### Warnings ####

  * igt@gem_exec_parallel@contexts:
    - fi-byt-n2820:       [FAIL][7] ([i915#694]) -> [TIMEOUT][8] ([fdo#112271] / [i915#1084])
   [7]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/fi-byt-n2820/igt@gem_exec_parallel@contexts.html
   [8]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/fi-byt-n2820/igt@gem_exec_parallel@contexts.html

  
  [fdo#112271]: https://bugs.freedesktop.org/show_bug.cgi?id=112271
  [i915#1052]: https://gitlab.freedesktop.org/drm/intel/issues/1052
  [i915#1084]: https://gitlab.freedesktop.org/drm/intel/issues/1084
  [i915#690]: https://gitlab.freedesktop.org/drm/intel/issues/690
  [i915#694]: https://gitlab.freedesktop.org/drm/intel/issues/694


Participating hosts (48 -> 40)
------------------------------

  Additional (3): fi-byt-j1900 fi-hsw-peppy fi-bsw-n3050 
  Missing    (11): fi-ilk-m540 fi-hsw-4200u fi-skl-guc fi-byt-squawks fi-bsw-cyan fi-bwr-2160 fi-ctg-p8600 fi-ivb-3770 fi-bsw-kefka fi-byt-clapper fi-bdw-samus 


Build changes
-------------

  * CI: CI-20190529 -> None
  * Linux: CI_DRM_7936 -> Patchwork_16565

  CI-20190529: 20190529
  CI_DRM_7936: ca171ea6194e80454caeac3c7b1c0ee8eca8f32c @ git://anongit.freedesktop.org/gfx-ci/linux
  IGT_5441: 534ca091fe4ffed916752165bc5becd7ff56cd84 @ git://anongit.freedesktop.org/xorg/app/intel-gpu-tools
  Patchwork_16565: 46e16ae78b49d58bc349f24b4b01fc701a615023 @ git://anongit.freedesktop.org/gfx-ci/linux


== Linux commits ==

46e16ae78b49 drm/i915: Cast remain to unsigned long in eb_relocate_vma

== Logs ==

For more details see: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/index.html
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Re: [Intel-gfx] [PATCH] drm/i915: Cast remain to unsigned long in eb_relocate_vma

[Jani Nikula]

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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Re: [Intel-gfx] [PATCH] drm/i915: Cast remain to unsigned long in eb_relocate_vma

[Chris Wilson]

Quoting Jani Nikula (2020-02-14 06:36:15)
> 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,

But the whole point was that the compiler could see that it was
impossible and not emit the code. Doesn't this break that?
-Chris
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Re: [Intel-gfx] [PATCH] drm/i915: Cast remain to unsigned long in eb_relocate_vma

[Jani Nikula]

On Fri, 14 Feb 2020, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> Quoting Jani Nikula (2020-02-14 06:36:15)
>> 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,
>
> But the whole point was that the compiler could see that it was
> impossible and not emit the code. Doesn't this break that?

It seems that goal and the warning are fundamentally incompatible.

Back to the original patch?

BR,
Jani.


-- 
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Re: [Intel-gfx] [PATCH] drm/i915: Cast remain to unsigned long in eb_relocate_vma

[Nathan Chancellor]

On Fri, Feb 14, 2020 at 08:32:19AM +0000, Chris Wilson wrote:
> Quoting Jani Nikula (2020-02-14 06:36:15)
> > 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,
> 
> But the whole point was that the compiler could see that it was
> impossible and not emit the code. Doesn't this break that?
> -Chris

As noted in the commit message, I ran diff <(objdump -Dr) <(objdump -Dr)
on objects files compiled with and without the patch with clang and gcc
for x86_64 and gcc for i386 (i386 does not build with clang) and there
was zero difference aside from the file names.

At the end of the day, I do not really care how the warning get fixed,
just that it does since it is the only one on x86_64 defconfig.

Cheers,
Nathan
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Re: [Intel-gfx] [PATCH] drm/i915: Cast remain to unsigned long in eb_relocate_vma

[Michel Dänzer]

On 2020-02-14 12:49 p.m., Jani Nikula wrote:
> On Fri, 14 Feb 2020, Chris Wilson <chris@chris-wilson.co.uk> wrote:
>> Quoting Jani Nikula (2020-02-14 06:36:15)
>>> 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,
>>
>> But the whole point was that the compiler could see that it was
>> impossible and not emit the code. Doesn't this break that?
> 
> It seems that goal and the warning are fundamentally incompatible.

Not really:

    if (sizeof(remain) >= sizeof(unsigned long) &&
	unlikely(remain > N_RELOC(ULONG_MAX)))
             return -EINVAL;

In contrast to the cast, this doesn't generate any machine code on 64-bit:

https://godbolt.org/z/GmUE4S

but still generates the same code on 32-bit:

https://godbolt.org/z/hAoz8L


-- 
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Libre software enthusiast             |             Mesa and X developer
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[Intel-gfx] ✓ Fi.CI.IGT: success for drm/i915: Cast remain to unsigned long in eb_relocate_vma

[Patchwork]

== Series Details ==

Series: drm/i915: Cast remain to unsigned long in eb_relocate_vma
URL   : https://patchwork.freedesktop.org/series/73440/
State : success

== Summary ==

CI Bug Log - changes from CI_DRM_7936_full -> Patchwork_16565_full
====================================================

Summary
-------

  **SUCCESS**

  No regressions found.

  

Possible new issues
-------------------

  Here are the unknown changes that may have been introduced in Patchwork_16565_full:

### IGT changes ###

#### Suppressed ####

  The following results come from untrusted machines, tests, or statuses.
  They do not affect the overall result.

  * {igt@gem_ctx_persistence@close-replace-race}:
    - shard-apl:          [PASS][1] -> [FAIL][2]
   [1]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-apl8/igt@gem_ctx_persistence@close-replace-race.html
   [2]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-apl6/igt@gem_ctx_persistence@close-replace-race.html

  
Known issues
------------

  Here are the changes found in Patchwork_16565_full that come from known issues:

### IGT changes ###

#### Issues hit ####

  * igt@gem_busy@busy-vcs1:
    - shard-iclb:         [PASS][3] -> [SKIP][4] ([fdo#112080]) +10 similar issues
   [3]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-iclb4/igt@gem_busy@busy-vcs1.html
   [4]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-iclb8/igt@gem_busy@busy-vcs1.html

  * igt@gem_busy@close-race:
    - shard-tglb:         [PASS][5] -> [INCOMPLETE][6] ([i915#977])
   [5]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-tglb5/igt@gem_busy@close-race.html
   [6]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-tglb5/igt@gem_busy@close-race.html

  * igt@gem_eio@unwedge-stress:
    - shard-glk:          [PASS][7] -> [FAIL][8] ([i915#232])
   [7]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-glk2/igt@gem_eio@unwedge-stress.html
   [8]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-glk6/igt@gem_eio@unwedge-stress.html

  * igt@gem_exec_balancer@smoke:
    - shard-iclb:         [PASS][9] -> [SKIP][10] ([fdo#110854])
   [9]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-iclb1/igt@gem_exec_balancer@smoke.html
   [10]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-iclb7/igt@gem_exec_balancer@smoke.html

  * igt@gem_exec_schedule@pi-shared-iova-bsd:
    - shard-iclb:         [PASS][11] -> [SKIP][12] ([i915#677])
   [11]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-iclb5/igt@gem_exec_schedule@pi-shared-iova-bsd.html
   [12]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-iclb4/igt@gem_exec_schedule@pi-shared-iova-bsd.html

  * igt@gem_exec_schedule@preempt-other-chain-bsd:
    - shard-iclb:         [PASS][13] -> [SKIP][14] ([fdo#112146]) +9 similar issues
   [13]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-iclb5/igt@gem_exec_schedule@preempt-other-chain-bsd.html
   [14]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-iclb1/igt@gem_exec_schedule@preempt-other-chain-bsd.html

  * igt@gem_exec_schedule@preempt-queue-bsd1:
    - shard-iclb:         [PASS][15] -> [SKIP][16] ([fdo#109276]) +18 similar issues
   [15]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-iclb2/igt@gem_exec_schedule@preempt-queue-bsd1.html
   [16]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-iclb8/igt@gem_exec_schedule@preempt-queue-bsd1.html

  * igt@kms_frontbuffer_tracking@fbc-suspend:
    - shard-kbl:          [PASS][17] -> [DMESG-WARN][18] ([i915#180]) +4 similar issues
   [17]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-kbl7/igt@kms_frontbuffer_tracking@fbc-suspend.html
   [18]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-kbl2/igt@kms_frontbuffer_tracking@fbc-suspend.html

  * igt@kms_frontbuffer_tracking@fbcpsr-rgb101010-draw-render:
    - shard-tglb:         [PASS][19] -> [SKIP][20] ([i915#668]) +6 similar issues
   [19]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-tglb8/igt@kms_frontbuffer_tracking@fbcpsr-rgb101010-draw-render.html
   [20]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-tglb1/igt@kms_frontbuffer_tracking@fbcpsr-rgb101010-draw-render.html

  * igt@kms_plane_alpha_blend@pipe-a-constant-alpha-min:
    - shard-skl:          [PASS][21] -> [FAIL][22] ([fdo#108145])
   [21]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-skl9/igt@kms_plane_alpha_blend@pipe-a-constant-alpha-min.html
   [22]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-skl6/igt@kms_plane_alpha_blend@pipe-a-constant-alpha-min.html

  * igt@kms_plane_alpha_blend@pipe-c-coverage-7efc:
    - shard-skl:          [PASS][23] -> [FAIL][24] ([fdo#108145] / [i915#265]) +1 similar issue
   [23]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-skl7/igt@kms_plane_alpha_blend@pipe-c-coverage-7efc.html
   [24]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-skl1/igt@kms_plane_alpha_blend@pipe-c-coverage-7efc.html

  * igt@kms_psr@psr2_sprite_blt:
    - shard-iclb:         [PASS][25] -> [SKIP][26] ([fdo#109441]) +2 similar issues
   [25]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-iclb2/igt@kms_psr@psr2_sprite_blt.html
   [26]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-iclb8/igt@kms_psr@psr2_sprite_blt.html

  * igt@kms_setmode@basic:
    - shard-kbl:          [PASS][27] -> [FAIL][28] ([i915#31])
   [27]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-kbl2/igt@kms_setmode@basic.html
   [28]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-kbl6/igt@kms_setmode@basic.html

  * igt@kms_vblank@pipe-a-ts-continuation-suspend:
    - shard-apl:          [PASS][29] -> [DMESG-WARN][30] ([i915#180])
   [29]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-apl7/igt@kms_vblank@pipe-a-ts-continuation-suspend.html
   [30]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-apl6/igt@kms_vblank@pipe-a-ts-continuation-suspend.html

  * igt@perf@oa-exponents:
    - shard-tglb:         [PASS][31] -> [INCOMPLETE][32] ([i915#807])
   [31]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-tglb5/igt@perf@oa-exponents.html
   [32]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-tglb8/igt@perf@oa-exponents.html

  
#### Possible fixes ####

  * igt@gem_ctx_isolation@vcs1-none:
    - shard-iclb:         [SKIP][33] ([fdo#112080]) -> [PASS][34] +8 similar issues
   [33]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-iclb5/igt@gem_ctx_isolation@vcs1-none.html
   [34]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-iclb2/igt@gem_ctx_isolation@vcs1-none.html

  * igt@gem_exec_schedule@in-order-bsd:
    - shard-iclb:         [SKIP][35] ([fdo#112146]) -> [PASS][36] +3 similar issues
   [35]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-iclb4/igt@gem_exec_schedule@in-order-bsd.html
   [36]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-iclb3/igt@gem_exec_schedule@in-order-bsd.html

  * igt@gem_exec_schedule@pi-shared-iova-blt:
    - shard-skl:          [INCOMPLETE][37] ([i915#1193]) -> [PASS][38]
   [37]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-skl10/igt@gem_exec_schedule@pi-shared-iova-blt.html
   [38]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-skl5/igt@gem_exec_schedule@pi-shared-iova-blt.html

  * igt@gem_exec_schedule@pi-userfault-bsd:
    - shard-iclb:         [SKIP][39] ([i915#677]) -> [PASS][40]
   [39]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-iclb1/igt@gem_exec_schedule@pi-userfault-bsd.html
   [40]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-iclb7/igt@gem_exec_schedule@pi-userfault-bsd.html

  * igt@gem_exec_schedule@promotion-bsd1:
    - shard-iclb:         [SKIP][41] ([fdo#109276]) -> [PASS][42] +19 similar issues
   [41]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-iclb7/igt@gem_exec_schedule@promotion-bsd1.html
   [42]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-iclb1/igt@gem_exec_schedule@promotion-bsd1.html

  * igt@gem_ppgtt@flink-and-close-vma-leak:
    - shard-glk:          [FAIL][43] ([i915#644]) -> [PASS][44]
   [43]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-glk1/igt@gem_ppgtt@flink-and-close-vma-leak.html
   [44]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-glk3/igt@gem_ppgtt@flink-and-close-vma-leak.html

  * igt@kms_flip@flip-vs-expired-vblank-interruptible:
    - shard-skl:          [FAIL][45] ([i915#79]) -> [PASS][46]
   [45]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-skl1/igt@kms_flip@flip-vs-expired-vblank-interruptible.html
   [46]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-skl3/igt@kms_flip@flip-vs-expired-vblank-interruptible.html

  * igt@kms_flip@flip-vs-suspend-interruptible:
    - shard-apl:          [DMESG-WARN][47] ([i915#180]) -> [PASS][48] +2 similar issues
   [47]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-apl6/igt@kms_flip@flip-vs-suspend-interruptible.html
   [48]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-apl4/igt@kms_flip@flip-vs-suspend-interruptible.html

  * {igt@kms_hdr@bpc-switch}:
    - shard-skl:          [FAIL][49] ([i915#1188]) -> [PASS][50]
   [49]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-skl8/igt@kms_hdr@bpc-switch.html
   [50]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-skl1/igt@kms_hdr@bpc-switch.html

  * igt@kms_plane@plane-panning-bottom-right-suspend-pipe-b-planes:
    - shard-kbl:          [DMESG-WARN][51] ([i915#180]) -> [PASS][52] +5 similar issues
   [51]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-kbl2/igt@kms_plane@plane-panning-bottom-right-suspend-pipe-b-planes.html
   [52]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-kbl6/igt@kms_plane@plane-panning-bottom-right-suspend-pipe-b-planes.html

  * igt@kms_plane_alpha_blend@pipe-c-constant-alpha-min:
    - shard-skl:          [FAIL][53] ([fdo#108145]) -> [PASS][54]
   [53]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-skl5/igt@kms_plane_alpha_blend@pipe-c-constant-alpha-min.html
   [54]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-skl4/igt@kms_plane_alpha_blend@pipe-c-constant-alpha-min.html

  * igt@kms_plane_lowres@pipe-a-tiling-y:
    - shard-glk:          [FAIL][55] ([i915#899]) -> [PASS][56]
   [55]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-glk9/igt@kms_plane_lowres@pipe-a-tiling-y.html
   [56]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-glk9/igt@kms_plane_lowres@pipe-a-tiling-y.html

  * igt@kms_plane_multiple@atomic-pipe-c-tiling-yf:
    - shard-skl:          [DMESG-WARN][57] ([IGT#6]) -> [PASS][58]
   [57]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-skl5/igt@kms_plane_multiple@atomic-pipe-c-tiling-yf.html
   [58]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-skl4/igt@kms_plane_multiple@atomic-pipe-c-tiling-yf.html

  * igt@kms_psr2_su@frontbuffer:
    - shard-iclb:         [SKIP][59] ([fdo#109642] / [fdo#111068]) -> [PASS][60]
   [59]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-iclb7/igt@kms_psr2_su@frontbuffer.html
   [60]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-iclb2/igt@kms_psr2_su@frontbuffer.html

  * igt@kms_psr@psr2_sprite_mmap_cpu:
    - shard-iclb:         [SKIP][61] ([fdo#109441]) -> [PASS][62]
   [61]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-iclb5/igt@kms_psr@psr2_sprite_mmap_cpu.html
   [62]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-iclb2/igt@kms_psr@psr2_sprite_mmap_cpu.html

  * igt@kms_setmode@basic:
    - shard-apl:          [FAIL][63] ([i915#31]) -> [PASS][64]
   [63]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-apl7/igt@kms_setmode@basic.html
   [64]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-apl7/igt@kms_setmode@basic.html
    - shard-skl:          [FAIL][65] ([i915#31]) -> [PASS][66]
   [65]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-skl10/igt@kms_setmode@basic.html
   [66]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-skl7/igt@kms_setmode@basic.html

  
#### Warnings ####

  * igt@i915_pm_dc@dc6-dpms:
    - shard-tglb:         [SKIP][67] ([i915#468]) -> [FAIL][68] ([i915#454])
   [67]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-tglb2/igt@i915_pm_dc@dc6-dpms.html
   [68]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-tglb7/igt@i915_pm_dc@dc6-dpms.html

  * igt@kms_flip@flip-vs-suspend-interruptible:
    - shard-kbl:          [INCOMPLETE][69] ([fdo#103665] / [i915#600]) -> [DMESG-WARN][70] ([i915#180])
   [69]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_7936/shard-kbl7/igt@kms_flip@flip-vs-suspend-interruptible.html
   [70]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/shard-kbl2/igt@kms_flip@flip-vs-suspend-interruptible.html

  
  {name}: This element is suppressed. This means it is ignored when computing
          the status of the difference (SUCCESS, WARNING, or FAILURE).

  [IGT#6]: https://gitlab.freedesktop.org/drm/igt-gpu-tools/issues/6
  [fdo#103665]: https://bugs.freedesktop.org/show_bug.cgi?id=103665
  [fdo#108145]: https://bugs.freedesktop.org/show_bug.cgi?id=108145
  [fdo#109276]: https://bugs.freedesktop.org/show_bug.cgi?id=109276
  [fdo#109441]: https://bugs.freedesktop.org/show_bug.cgi?id=109441
  [fdo#109642]: https://bugs.freedesktop.org/show_bug.cgi?id=109642
  [fdo#110854]: https://bugs.freedesktop.org/show_bug.cgi?id=110854
  [fdo#111068]: https://bugs.freedesktop.org/show_bug.cgi?id=111068
  [fdo#112080]: https://bugs.freedesktop.org/show_bug.cgi?id=112080
  [fdo#112146]: https://bugs.freedesktop.org/show_bug.cgi?id=112146
  [i915#1188]: https://gitlab.freedesktop.org/drm/intel/issues/1188
  [i915#1193]: https://gitlab.freedesktop.org/drm/intel/issues/1193
  [i915#180]: https://gitlab.freedesktop.org/drm/intel/issues/180
  [i915#232]: https://gitlab.freedesktop.org/drm/intel/issues/232
  [i915#265]: https://gitlab.freedesktop.org/drm/intel/issues/265
  [i915#31]: https://gitlab.freedesktop.org/drm/intel/issues/31
  [i915#454]: https://gitlab.freedesktop.org/drm/intel/issues/454
  [i915#468]: https://gitlab.freedesktop.org/drm/intel/issues/468
  [i915#600]: https://gitlab.freedesktop.org/drm/intel/issues/600
  [i915#644]: https://gitlab.freedesktop.org/drm/intel/issues/644
  [i915#668]: https://gitlab.freedesktop.org/drm/intel/issues/668
  [i915#677]: https://gitlab.freedesktop.org/drm/intel/issues/677
  [i915#79]: https://gitlab.freedesktop.org/drm/intel/issues/79
  [i915#807]: https://gitlab.freedesktop.org/drm/intel/issues/807
  [i915#899]: https://gitlab.freedesktop.org/drm/intel/issues/899
  [i915#977]: https://gitlab.freedesktop.org/drm/intel/issues/977


Participating hosts (10 -> 10)
------------------------------

  No changes in participating hosts


Build changes
-------------

  * CI: CI-20190529 -> None
  * Linux: CI_DRM_7936 -> Patchwork_16565

  CI-20190529: 20190529
  CI_DRM_7936: ca171ea6194e80454caeac3c7b1c0ee8eca8f32c @ git://anongit.freedesktop.org/gfx-ci/linux
  IGT_5441: 534ca091fe4ffed916752165bc5becd7ff56cd84 @ git://anongit.freedesktop.org/xorg/app/intel-gpu-tools
  Patchwork_16565: 46e16ae78b49d58bc349f24b4b01fc701a615023 @ git://anongit.freedesktop.org/gfx-ci/linux
  piglit_4509: fdc5a4ca11124ab8413c7988896eec4c97336694 @ git://anongit.freedesktop.org/piglit

== Logs ==

For more details see: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_16565/index.html
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Re: [Intel-gfx] [PATCH] drm/i915: Cast remain to unsigned long in eb_relocate_vma

[Nick Desaulniers]

On Fri, Feb 14, 2020 at 7:36 AM Michel Dänzer <michel@daenzer.net> wrote:
>
> On 2020-02-14 12:49 p.m., Jani Nikula wrote:
> > On Fri, 14 Feb 2020, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> >> Quoting Jani Nikula (2020-02-14 06:36:15)
> >>> 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,
> >>
> >> But the whole point was that the compiler could see that it was
> >> impossible and not emit the code. Doesn't this break that?
> >
> > It seems that goal and the warning are fundamentally incompatible.
>
> Not really:
>
>     if (sizeof(remain) >= sizeof(unsigned long) &&
>         unlikely(remain > N_RELOC(ULONG_MAX)))
>              return -EINVAL;
>
> In contrast to the cast, this doesn't generate any machine code on 64-bit:
>
> https://godbolt.org/z/GmUE4S
>
> but still generates the same code on 32-bit:
>
> https://godbolt.org/z/hAoz8L

Exactly.

This check is only a tautology when `sizeof(long) == sizeof(int)` (ie.
ILP32 platforms, like 32b x86), notice how BOTH GCC AND Clang generate
exactly the same code: https://godbolt.org/z/6ShrDM

Both compilers eliminate the check when `-m32` is not set, and
generate the exact same check otherwise.  How about:
```
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index d3f4f28e9468..25b9d3f3ad57 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -1415,8 +1415,10 @@ static int eb_relocate_vma(struct
i915_execbuffer *eb, struct eb_vma *ev)

        urelocs = u64_to_user_ptr(entry->relocs_ptr);
        remain = entry->relocation_count;
+#ifndef CONFIG_64BIT
        if (unlikely(remain > N_RELOC(ULONG_MAX)))
                return -EINVAL;
+#endif

        /*
         * We must check that the entire relocation array is safe
```

We now have 4 proposed solutions:
1. https://lore.kernel.org/lkml/20191123195321.41305-1-natechancellor@gmail.com/
2. https://lore.kernel.org/lkml/20200211050808.29463-1-natechancellor@gmail.com/
3. https://lore.kernel.org/lkml/20200214054706.33870-1-natechancellor@gmail.com/
4. my diff above
Let's please come to a resolution on this.
-- 
Thanks,
~Nick Desaulniers
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[Intel-gfx] ✗ Fi.CI.BUILD: failure for drm/i915: Cast remain to unsigned long in eb_relocate_vma (rev2)

[Patchwork]

== Series Details ==

Series: drm/i915: Cast remain to unsigned long in eb_relocate_vma (rev2)
URL   : https://patchwork.freedesktop.org/series/73440/
State : failure

== Summary ==

Applying: drm/i915: Cast remain to unsigned long in eb_relocate_vma
error: git diff header lacks filename information when removing 1 leading pathname component (line 2)
error: could not build fake ancestor
hint: Use 'git am --show-current-patch' to see the failed patch
Patch failed at 0001 drm/i915: Cast remain to unsigned long in eb_relocate_vma
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

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Re: [Intel-gfx] [PATCH] drm/i915: Cast remain to unsigned long in eb_relocate_vma

[Nathan Chancellor]

On Mon, Mar 16, 2020 at 02:41:23PM -0700, Nick Desaulniers wrote:
> On Fri, Feb 14, 2020 at 7:36 AM Michel Dänzer <michel@daenzer.net> wrote:
> >
> > On 2020-02-14 12:49 p.m., Jani Nikula wrote:
> > > On Fri, 14 Feb 2020, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> > >> Quoting Jani Nikula (2020-02-14 06:36:15)
> > >>> 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,
> > >>
> > >> But the whole point was that the compiler could see that it was
> > >> impossible and not emit the code. Doesn't this break that?
> > >
> > > It seems that goal and the warning are fundamentally incompatible.
> >
> > Not really:
> >
> >     if (sizeof(remain) >= sizeof(unsigned long) &&
> >         unlikely(remain > N_RELOC(ULONG_MAX)))
> >              return -EINVAL;
> >
> > In contrast to the cast, this doesn't generate any machine code on 64-bit:
> >
> > https://godbolt.org/z/GmUE4S
> >
> > but still generates the same code on 32-bit:
> >
> > https://godbolt.org/z/hAoz8L
> 
> Exactly.
> 
> This check is only a tautology when `sizeof(long) == sizeof(int)` (ie.
> ILP32 platforms, like 32b x86), notice how BOTH GCC AND Clang generate
> exactly the same code: https://godbolt.org/z/6ShrDM
> 
> Both compilers eliminate the check when `-m32` is not set, and
> generate the exact same check otherwise.  How about:
> ```
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index d3f4f28e9468..25b9d3f3ad57 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -1415,8 +1415,10 @@ static int eb_relocate_vma(struct
> i915_execbuffer *eb, struct eb_vma *ev)
> 
>         urelocs = u64_to_user_ptr(entry->relocs_ptr);
>         remain = entry->relocation_count;
> +#ifndef CONFIG_64BIT
>         if (unlikely(remain > N_RELOC(ULONG_MAX)))
>                 return -EINVAL;
> +#endif
> 
>         /*
>          * We must check that the entire relocation array is safe
> ```
> 
> We now have 4 proposed solutions:
> 1. https://lore.kernel.org/lkml/20191123195321.41305-1-natechancellor@gmail.com/
> 2. https://lore.kernel.org/lkml/20200211050808.29463-1-natechancellor@gmail.com/
> 3. https://lore.kernel.org/lkml/20200214054706.33870-1-natechancellor@gmail.com/
> 4. my diff above
> Let's please come to a resolution on this.

This is the only warning on an x86_64 defconfig build. Apologies if we
are being too persistent or nagging but we need guidance from the i915
maintainers on which solution they would prefer so it can be picked up.
I understand you all are busy and I appreciate the work you all do but
I do not want this to fall between the cracks because it is annoying to
constantly see this warning.

Cheers,
Nathan
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Re: [Intel-gfx] [PATCH] drm/i915: Cast remain to unsigned long in eb_relocate_vma

[Jani Nikula]

On Thu, 26 Mar 2020, Nathan Chancellor <natechancellor@gmail.com> wrote:
> This is the only warning on an x86_64 defconfig build. Apologies if we
> are being too persistent or nagging but we need guidance from the i915
> maintainers on which solution they would prefer so it can be picked up.
> I understand you all are busy and I appreciate the work you all do but
> I do not want this to fall between the cracks because it is annoying to
> constantly see this warning.

Apologies for the delay. As I replied first thing in this thread, this
works for me. Thanks for the patch, pushed to drm-intel-next-queued.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center
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