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Date: Fri, 16 Oct 2015 11:00:11 +0700
From: Рысь <lynx@...xlynx.tk>
To: musl@...ts.openwall.com
Subject: Re: handling dlopen("/.../libc.so", ...) etc.
On Thu, 15 Oct 2015 23:46:42 -0400
Rich Felker <dalias@...c.org> wrote:
> Presently, attempting to load "libc.so" (without pathname) or a number
> of other standard library names via dlopen suppresses the actual
> loading and returns a reference to the existing libc dso object.
> However, loading it via a pathname or alternate name/symlink will
> actually cause another copy to be loaded into memory (since we can't
> check the dev/ino against the existing one, because the kernel didn't
> give those to us) and bad things will happen. I've been thinking some
> about ways to prevent that.
>
> The most obvious way is to link libc.so with -Wl,-z,nodlopen and make
> the dynamic linker enforce DF_1_NOOPEN, but this would cause the load
> to fail when we probably want it to succeed but return a reference to
> the existing libc.
>
> Another option would be to somehow encode musl's identity in libc.so
> so that the loader code can check "is the dso we've just loaded
> actually musl?" In that case it can abort the load and use the
> existing libc instead. Options for how to do this might include a
> special reserved-namespace symbol. If an approach like this is taken,
> it would be ideal to be able to detect existing/previous versions of
> libc.so (to avoid loading them too), and the approach should be
> future-proof so that the current libc.so can avoid loading future
> versions of itself, and so that future versions can avoid loading the
> current version.
>
> I'd like to hear any further ideas on how to achieve this.
>
> Rich
Who would even want to load "libc.so"? I mean, does not it already
being loaded in every libc implementations with dynamic linking support
already today?
And what are use cases? Who does this today? I am confused.
--
http://lynxlynx.tk/
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Unix and simple KISS C code
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