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From: Alexander Monakov <amonakov@ispras.ru>
To: musl@lists.openwall.com
Subject: Re: Making a shared library that intercepts call to main work with musl compiled binary
Date: Mon, 6 Jul 2015 23:34:49 +0300 (MSK)	[thread overview]
Message-ID: <alpine.LNX.2.11.1507062323490.2485@monopod.intra.ispras.ru> (raw)
In-Reply-To: <20150706190651.GY1173@brightrain.aerifal.cx>

> > Furthermore, even with dynamic linking you cannot interpose 'main' in the
> > executable via LD_PRELOAD.  Even more baffling is that the linked code
> > interposes __libc_start_main; I'm lost for words that it happens to work with
> > glibc.
> 
> Presumably it interposes __libc_start_main because it can't interpose
> main. As far as I can tell the only reason it does this is to inject
> fake argv. I'm skeptical as to whether it works correctly.

I was wrong about interposition on __libc_start_main being somehow surprising
-- I missed that it's called from the main executable's startup routine, not
from the dynamic linker (thanks to Rich for explaining that on IRC!).  So as a
result I expect that original code should usually work in practice.

Alexander


      reply	other threads:[~2015-07-06 20:34 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-07-06 17:00 Riyad Parvez
2015-07-06 17:32 ` Rich Felker
2015-07-06 19:00   ` Alexander Monakov
2015-07-06 19:06     ` Rich Felker
2015-07-06 20:34       ` Alexander Monakov [this message]

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