amd64/127276: ldd invokes linux yes

[John Baldwin]

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

From: John Baldwin <jhb at freebsd.org>
To: Dominic Fandrey <kamikaze at bsdforen.de>
Cc: freebsd-amd64 at freebsd.org, freebsd-gnats-submit at freebsd.org
Subject: Re: amd64/127276: ldd invokes linux yes
Date: Thu, 11 Sep 2008 10:38:32 -0400

 On Thursday 11 September 2008 01:01:09 am Dominic Fandrey wrote:
 > John Baldwin wrote:
 > > On Wednesday 10 September 2008 01:44:36 pm Dominic Fandrey wrote:
 > >>> Number:         127276
 > >>> Category:       amd64
 > >>> Synopsis:       ldd invokes linux yes
 > >>> Confidential:   no
 > >>> Severity:       serious
 > >>> Priority:       medium
 > >>> Responsible:    freebsd-amd64
 > >>> State:          open
 > >>> Quarter:        
 > >>> Keywords:       
 > >>> Date-Required:
 > >>> Class:          sw-bug
 > >>> Submitter-Id:   current-users
 > >>> Arrival-Date:   Wed Sep 10 17:50:01 UTC 2008
 > >>> Closed-Date:
 > >>> Last-Modified:
 > >>> Originator:     Dominic Fandrey
 > >>> Release:        RELENG_7
 > >>> Organization:
 > >> private
 > >>> Environment:
 > >> FreeBSD mobileKamikaze.norad 7.1-PRERELEASE FreeBSD 7.1-PRERELEASE #0: 
 Fri 
 > > Aug 29 23:22:22 CEST 2008     
 > > root at mobileKamikaze.norad:/usr/obj/HP6510b/amd64/usr/src/sys/HP6510b  
 amd64
 > >>> Description:
 > >> When ldd is used on linux yes it invokes it instead of producing the 
 usual 
 > > output.
 > >> # pkg_info -W /compat/linux/usr/bin/yes
 > >> /compat/linux/usr/bin/yes was installed by package linux_base-f8-8_4
 > >> # sysctl compat.linux.osrelease
 > >> compat.linux.osrelease: 2.6.16
 > >>
 > >> This behaviour breaks pkg_libchk from the sysutils/bsdadminscripts port.
 > >>> How-To-Repeat:
 > >> # ldd /compat/linux/usr/bin/yes
 > > 
 > > ldd is not going to work for Linux binaries.  The Linux ldd should be used 
 for 
 > > Linux binaries.
 > > 
 > 
 > 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.
 
 As Rui indicated, ldd always execs binaries.  It just sets environment 
 variables that the FreeBSD runtime linker checks for.  If the runtime linker 
 sees them, it will modify it's behavior.  You can achieve the same thing 
 using env:
 
 % ldd /bin/ls
 /bin/ls:
         libutil.so.7 => /lib/libutil.so.7 (0x2808b000)
         libncurses.so.7 => /lib/libncurses.so.7 (0x28099000)
         libc.so.7 => /lib/libc.so.7 (0x280d8000)
 % env LD_TRACE_LOADED_OBJECTS=yes /bin/ls
         libutil.so.7 => /lib/libutil.so.7 (0x2808b000)
         libncurses.so.7 => /lib/libncurses.so.7 (0x28099000)
         libc.so.7 => /lib/libc.so.7 (0x280d8000)
  
 All the "ldd" printfs, etc. are actually from the runtime linker, not ldd 
 itself.  The Linux runtime linker doesn't modify it's behavior for 
 LD_TRACE_LOADED_OBJECTS, so Linux apps just run normally when invoked by ldd.
 
 -- 
 John Baldwin