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From:   Arusekk <arek_koz@o2.pl>
To:     Christoph Hellwig <hch@lst.de>,
        Linus Torvalds <torvalds@linux-foundation.org>
Cc:     linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] proc: Use seq_read_iter where possible
Date:   Wed, 28 Apr 2021 15:02:13 +0200
Message-ID: <9905352.nUPlyArG6x@swift.dev.arusekk.pl>
In-Reply-To: <20210428061259.GA5084@lst.de>
References: <20210427183414.12499-1-arek_koz@o2.pl> <20210428061259.GA5084@lst.de>
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On Wed, Apr 28, 2021 at 08:12:59 CEST, Christoph Hellwig wrote:
> Patching what entry point?

The instructions at the entry point of the executable being inspected.
The flow of the tool:
- parse ELF headers of the binary to be inspected,
- locate its entry point position in the file,
- write short code at the location (this short code has used sendfile so far),
- execute the patched binary,
- parse the output and extract information about the relevant mappings.
This can be seen as equivalent to setting LD_TRACE_LOADED_OBJECTS,
but also works for static binaries, and is a bit safer.

The problem was reported at:
https://github.com/Gallopsled/pwntools/issues/1871

> Linus did object to blindly switching over all instances.

I know, I read that, but I thought that pointing a real use case, combined 
with the new interface being used all throughout the other code, might be 
convincing.
I would be happy with only changing the f_ops of /proc/.../maps, even if only 
on MMU-enabled systems, but I thought that consistence would be better.
This is my first time contributing to Linux, so I am very sorry for any wrong 
assumptions, and glad to learn more.

-- 
Arusekk