linux-kernel - Re: [PATCH 1/2] kselftests: mm: Fix wrong __NR

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Message-ID: <0b847784-a95f-4ed5-a0fb-1b7b4023df13@collabora.com>
Date: Wed, 18 Sep 2024 10:46:05 +0500
From: Muhammad Usama Anjum <Usama.Anjum@...labora.com>
To: Shuah Khan <skhan@...uxfoundation.org>,
 Andrew Morton <akpm@...ux-foundation.org>, Shuah Khan <shuah@...nel.org>,
 David Hildenbrand <david@...hat.com>, Peter Xu <peterx@...hat.com>
Cc: Usama.Anjum@...labora.com, kernel@...labora.com, linux-mm@...ck.org,
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
 John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH 1/2] kselftests: mm: Fix wrong __NR_userfaultfd value

On 9/17/24 6:56 AM, Shuah Khan wrote:
> On 9/16/24 00:32, Muhammad Usama Anjum wrote:
>> On 9/12/24 8:44 PM, Shuah Khan wrote:
>>> On 9/12/24 04:31, Muhammad Usama Anjum wrote:
>>>> The value of __NR_userfaultfd was changed to 282 when
>>>> asm-generic/unistd.h was included. It makes the test to fail every time
>>>> as the correct number of this syscall on x86_64 is 323. Fix the header
>>>> to asm/unistd.h.
>>>>
>>>
>>> "please elaborate every time" - I just built on my x86_64 and built
>>> just fine.
>> The build isn't broken.
>>
>>> I am not saying this isn't a problem, it is good to
>>> understand why and how it is failing before making the change.
>> I mean to say that the test is failing at run time because the correct
>> userfaultfd syscall isn't being found with __NR_userfaultfd = 282.
>> _NR_userfaultfd's value depends on the header. When asm-generic/unistd.h
>> is included, its value (282) is wrong. I've tested on x86_64.
>>
> 
> Okay - how do you know this is wrong? can you provide more details.
> 
> git grep _NR_userfaultfd
> include/uapi/asm-generic/unistd.h:#define __NR_userfaultfd 282
> include/uapi/asm-generic/unistd.h:__SYSCALL(__NR_userfaultfd,
> sys_userfaultfd)
> tools/include/uapi/asm-generic/unistd.h:#define __NR_userfaultfd 282
> 
>> The fix is simple. Add the correct header which has _NR_userfaultfd =
>> 323.

grep -rnIF "#define __NR_userfaultfd"
tools/include/uapi/asm-generic/unistd.h:681:#define __NR_userfaultfd 282
arch/x86/include/generated/uapi/asm/unistd_32.h:374:#define
__NR_userfaultfd 374
arch/x86/include/generated/uapi/asm/unistd_64.h:327:#define
__NR_userfaultfd 323
arch/x86/include/generated/uapi/asm/unistd_x32.h:282:#define
__NR_userfaultfd (__X32_SYSCALL_BIT + 323)
arch/arm/include/generated/uapi/asm/unistd-eabi.h:347:#define
__NR_userfaultfd (__NR_SYSCALL_BASE + 388)
arch/arm/include/generated/uapi/asm/unistd-oabi.h:359:#define
__NR_userfaultfd (__NR_SYSCALL_BASE + 388)
include/uapi/asm-generic/unistd.h:681:#define __NR_userfaultfd 282

The number is dependent on the architecture. The above data shows that:
x86	374
x86_64	323

I'm unable to find the history of why it is set to 282 in unistd.h and
when this problem happened.

> 
> I need more details on this number.
> 
> thanks,
> -- Shuah

-- 
BR,
Muhammad Usama Anjum