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From:   YunQiang Su <syq@debian.org>
Date:   Fri, 6 Mar 2020 19:48:35 +0800
Message-ID: <CAKcpw6VF1N2gTVXeWLU4aVOuARf5oN6yPg9O=RCzgkMrjXmxYQ@mail.gmail.com>
Subject: Re: [PATCH] binfmt_misc: pass binfmt_misc P flag to the interpreter
To:     Florian Weimer <fw@deneb.enyo.de>
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
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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.