linux-kernel - Re: [PATCH] binfmt_misc: pass binfmt

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Message-ID: <fded1845-98db-f0fb-9320-842c9fdc30dc@vivier.eu>
Date:   Fri, 6 Mar 2020 13:07:35 +0100
From:   Laurent Vivier <laurent@...ier.eu>
To:     YunQiang Su <syq@...ian.org>, Florian Weimer <fw@...eb.enyo.de>
Cc:     torvalds@...ux-foundation.org,
        Greg KH <gregkh@...uxfoundation.org>,
        akpm@...ux-foundation.org, Al Viro <viro@...iv.linux.org.uk>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        libc-alpha@...rceware.org
Subject: Re: [PATCH] binfmt_misc: pass binfmt_misc P flag to the interpreter

Le 06/03/2020 à 12:48, YunQiang Su a écrit :
> Florian Weimer <fw@...eb.enyo.de> 于2020年3月6日周五 下午7:42写道：
>>
>> * YunQiang Su:
>>
>>> AT_* only has 32 slot and now. I was afraid that maybe we shouldn't take one.
>>>    /* AT_* values 18 through 22 are reserved */
>>>    27,28,29,30 are not used now.
>>> Which should we use?
>>
>> Where does this limit of 32 tags come from?  I don't see it from a
>> userspace perspective.
> 
> Sorry it is my mistake: In linux/auxvec.h, I saw
> 
> #define AT_RANDOM 25    /* address of 16 random bytes */
> #define AT_HWCAP2 26    /* extension of AT_HWCAP */
> 
> #define AT_EXECFN  31   /* filename of program */
> 
> The number jump to 31 from 26.
> 
> It is my fault: in x86_64-linux-gnu/bits/auxv.h, the max number is 47 now.
> 

Numbers starting from 32 are arch specific.
18 to 22 are also reserved (and used by some archs).
(linux/arch/*/include/uapi/asm/auxvec.h)

So there is only 4 entries available (27 to 30)
(linux/include/uapi/linux/auxvec.h)
Do we want to waste one more entry whereas we can use an unused one?

Thanks,
Laurent