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From:   Florian Weimer <fw@deneb.enyo.de>
To:     YunQiang Su <syq@debian.org>
Cc:     Laurent Vivier <laurent@vivier.eu>, torvalds@linux-foundation.org,
        Greg KH <gregkh@linuxfoundation.org>,
        akpm@linux-foundation.org, Al Viro <viro@zeniv.linux.org.uk>,
        James Bottomley <James.Bottomley@hansenpartnership.com>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
        libc-alpha@sourceware.org
Subject: Re: [PATCH] binfmt_misc: pass binfmt_misc P flag to the interpreter
References: <20200306080905.173466-1-syq@debian.org>
        <87r1y53npd.fsf@mid.deneb.enyo.de>
        <8441f497-61eb-5c14-bf1e-c90a464105a7@vivier.eu>
        <87mu8t3mlw.fsf@mid.deneb.enyo.de>
        <40da389d-4e74-2644-2e7c-04d988fcc26f@vivier.eu>
        <CAKcpw6WEO5Rmsv+WFkOMrkH+0jwtFKKy7b2n3U9xgv-xGC0UUQ@mail.gmail.com>
        <87v9nhzp6w.fsf@mid.deneb.enyo.de>
        <CAKcpw6VF1N2gTVXeWLU4aVOuARf5oN6yPg9O=RCzgkMrjXmxYQ@mail.gmail.com>
Date:   Fri, 06 Mar 2020 13:07:33 +0100
In-Reply-To: <CAKcpw6VF1N2gTVXeWLU4aVOuARf5oN6yPg9O=RCzgkMrjXmxYQ@mail.gmail.com>
        (YunQiang Su's message of "Fri, 6 Mar 2020 19:48:35 +0800")
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* YunQiang Su:

> Florian Weimer <fw@deneb.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.

So AT_* tags aren't a scarce resource after all?