amd64/127276: ldd invokes linux yes

[Dominic Fandrey]

The following reply was made to PR amd64/127276; it has been noted by GNATS.

From: Dominic Fandrey <kamikaze at bsdforen.de>
To: Rui Paulo <rpaulo at FreeBSD.org>
Cc: John Baldwin <jhb at freebsd.org>, freebsd-gnats-submit at freebsd.org, 
 freebsd-amd64 at freebsd.org
Subject: Re: amd64/127276: ldd invokes linux yes
Date: Thu, 11 Sep 2008 18:37:23 +0200

 Rui Paulo wrote:
 > On Thu, Sep 11, 2008 at 07:01:09AM +0200, Dominic Fandrey wrote:
 >> I don't need it to work, I just need it not to invoke linux binaries. I'm
 >> using ldd in a script and by ldd not returning 0 the script should know that
 >> it hasn't encountered a valid binary. Instead ldd opens a linux binary like
 >> yes and the script spills out ys (yes) or waits for input from stdin
 >> (md5sum). I'm pretty certain ldd is in no way meant to invoke programs.
 > 
 > I chatted briefly with John about this. The way our ldd works is by
 > setting the environment variable TRACE_LOADED_OBJECTS and after some
 > dlopen() magic it exec()'s the binary. FreeBSD rtld detects the environmental
 > variable, prints the list of shared objects and quits.
 > 
 > Linux rtld doesn't work this way, so FreeBSD ldd on a Linux binary will
 > just run the Linux binary (Linux rtld will ignore the rest).
 > 
 > Also, ldd wil return 1 on static binaries. Your best bet is to use
 > file(1) to detect FreeBSD binaries. Something like `file $binary | grep
 > FreeBSD-style` does the trick.
 > 
 > Regards,
 
 Ok, thanks. I have already created a workaround with readelf, but I'd still
 consider this a bug in ldd. Shouldn't it check the elf brand if it only
 works for a single one?
 
 Regards