linux-kernel - Re: Re: [PATCH 2/3] gpu: drm: dead code elimination

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Message-ID: <1576726711-14394-1-git-send-email-zhangpan26@huawei.com>
Date:   Thu, 19 Dec 2019 11:38:31 +0800
From:   Pan Zhang <zhangpan26@...wei.com>
To:     <christian.koenig@....com>, <michel@...nzer.net>,
        <alexander.deucher@....com>, <David1.Zhou@....com>,
        <airlied@...ux.ie>, <daniel@...ll.ch>, <ray.huang@....com>,
        <irmoy.das@....com>, <sam@...nborg.org>, <zhangpan26@...wei.com>,
        <hushiyuan@...wei.com>
CC:     <amd-gfx@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: Re: [PATCH 2/3] gpu: drm: dead code elimination

On 2019-12-18 5:52 p.m., Michel Dänzer <michel@...nzer.net> wrote:

>> this set adds support for removal of gpu drm dead code.
>> 
>> patch2:
>> `num_entries` is a data of unsigned type(compilers always treat as 
>> unsigned int) and SIZE_MAX == ~0,
>> 
>> so there is a impossible condition:
>> '(num_entries > ((~0) - 56) / 72) => (max(0-u32) > 256204778801521549)'.

>While this looks correct for 64-bit, where size_t is unsigned long, on 32-bit it's unsigned int, in which case this isn't dead code.

and

On 2019-12-18 5:52 p.m., Christian König <christian.koenig@...xxxx> wrote:

>NAK, that calculation is not correct on 32-bit systems.

>Christian.

Yes, you are right. I just figured this out (because our Server usually uses 64 bits).

thanks.


>>Signed-off-by: Pan Zhang <zhangpan26@...xxxxxxx>
>>---
>>  drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c | 4 ----
>>  1 file changed, 4 deletions(-)
>>diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
>>index 85b0515..10a7f30 100644
>>--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
>>+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
>>@@ -71,10 +71,6 @@ int amdgpu_bo_list_create(struct amdgpu_device *adev, struct drm_file *filp,
>> 	unsigned i;
>> 	int r;
>> 
>>-	if (num_entries > (SIZE_MAX - sizeof(struct amdgpu_bo_list))
>>-				/ sizeof(struct amdgpu_bo_list_entry))
>>-		return -EINVAL;
>>-
>> 	size = sizeof(struct amdgpu_bo_list);
>> 	size += num_entries * sizeof(struct amdgpu_bo_list_entry);
>> 	list = kvmalloc(size, GFP_KERNEL);
>>