linux-kernel - Re: [Patch 3/3] elf: use a macro instead of a raw number

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Message-Id: <20090702095554.4913B404FD@magilla.sf.frob.com>
Date:	Thu,  2 Jul 2009 02:55:54 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Amerigo Wang <amwang@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Serge Hallyn <serue@...ibm.com>,
	David Howells <dhowells@...hat.com>,
	James Morris <jmorris@...ei.org>,
	linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Patch 3/3] elf: use a macro instead of a raw number

> But in the kernel code, pr_fname is copied from ->comm, they should
> be equal, shouldn't they?

The point is that we are not at liberty to change the size of pr_fname.
Its size and layout are known to userland and thus set in stone.  To
have a larger size, we would have to invent a new NT_* type code with a
new layout that would also be known to userland.  It's not worth the
bother.  

Nowadays a debugger can see AT_EXECFN in auxv (NT_AUXV in core files,
/proc/pid/auxv live), and look at that address in the user memory (core
file or process).  That's clobberable on the user-mode stack, but it can
be of unbounded size.

Thanks,
Roland
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