linux-kernel - Re: rseq(2) man page

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Message-ID: <57e095f5-2cf8-3f9a-0765-86990b4c1873@efficios.com>
Date:   Tue, 10 Jan 2023 14:57:55 -0500
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Alejandro Colomar <alx.manpages@...il.com>,
        linux-man@...r.kernel.org, Alejandro Colomar <alx@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>, paulmck <paulmck@...nel.org>
Subject: Re: rseq(2) man page

On 2023-01-10 14:28, Alejandro Colomar wrote:
> 
> 
> On 1/10/23 17:54, Mathieu Desnoyers wrote:
> 

> 
> [...]
> 
>>>> .BI "int syscall(SYS_rseq, struct rseq *_Nullable " rseq ", uint32_t 
>>>> " rseq_len \
>>>
>>> What's the meaning for NULL?  Does it have a valid sentinel meaning, 
>>> or is it an invalid address?  If it's just interpreted as an invalid 
>>> address (for which from a user-space perspective a crash would be 
>>> legitimate), then I'd remove _Nullable.
>>
>> With the flags that are currently implemented (0 or 
>> RSEQ_FLAG_UNREGISTER),
>> the rseq argument is not expected to be legitimately NULL (it would 
>> return
>> -1, errno=EFAULT on registration, or -1, errno=EINVAL on unregister 
>> attempt).
>>
>> We may add new flags in the future which would not care about the rseq 
>> address
>> (it could very well be null then). Do you recommend that we only add the
>> _Nullable tag when this occurs ?
> 
> Yes; since it's what the user can pass, it makes sense to be as 
> constrained as possible.  If it were some return that the user would 
> have to inspect, it would make sense to be cautious on the NULL side of 
> things an use _Nullable preventively, but for an input, non-null is 
> preferred for now.

OK, updated.

> 
> 
> [...]
> 
>>
>> Updated version based on your comments pushed into my repo, thanks!
> 
> Cool! I'll have a look.

Thanks! Once you find it to your liking, I plan to sent it as a patch 
against the man-pages project.

Mathieu

> 
> Cheers,
> 
> Alex
> 
>>
>> Mathieu
>>
>>
> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com