[PATCH V3 1/7] drm/amdgpu: correct tcp harvest setting

Lazar, Lijo lijo.lazar at amd.com
Tue Jun 22 10:40:29 UTC 2021

On 6/22/2021 2:49 PM, Michel Dänzer wrote:
> On 2021-06-22 8:08 a.m., Lazar, Lijo wrote:
>> [Public]
>> AFAIK, that expression is legal (some code analyzer may warn on value of 4*max_wgp_per_sh); similar kind is used in rotate shift operations.
> The default type for constants in C is int, so 0xffffffff is a 32-bit signed integer.

Probably not as per section 6.4.4.

"The type of an integer constant is the first of the corresponding list 
in which its value can be represented."

It is a hexadecimal constant and the first to fit this value is unsigned 
int. Regardless, adding u suffix will avoid any ambiguity.


> The C99 specification lists this under J.2 Undefined behavior:
> — An expression having signed promoted type is left-shifted and either the value of the
>   expression is negative or the result of shifting would be not be representable in the
>   promoted type (6.5.7).
> So it would be safer to make it unsigned: 0xffffffffu (or just ~0u).
>> -----Original Message-----
>> From: Quan, Evan <Evan.Quan at amd.com>
>> Sent: Tuesday, June 22, 2021 7:56 AM
>> To: Lazar, Lijo <Lijo.Lazar at amd.com>; amd-gfx at lists.freedesktop.org
>> Cc: Deucher, Alexander <Alexander.Deucher at amd.com>
>> Subject: RE: [PATCH V3 1/7] drm/amdgpu: correct tcp harvest setting
>> [AMD Official Use Only]
>> Thanks Lijo.
>> However, I'm not quite sure whether " 0xffffffff << (4 * max_wgp_per_sh);" is a valid expression since it kind of triggers some overflow.
>> Can that work for non-x86 platform or even work reliably for x86 platform?

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