LD_PRELOAD and mixed architectures

[Dave Vitek <dvitek%grammatech.com@localhost>]

Hi all,

I'm on an amd64 machine that has a mixture of i386 and amd64 binaries 
present.  I want to build a shared object file and use LD_PRELOAD to 
inject it into every process in some process tree. The executables in 
the tree could be a mixture of amd64 and i386 executables.  Many other 
operating systems have a way of using LD_PRELOAD in a mixed architecture 
environment, but I'm not seeing a path to victory on netbsd.

I had a look at the source code for ld.so (the elf one anyway).  It 
doesn't search search LD_LIBRARY_PATH -- it just tries to open() the 
filename in LD_PRELOAD relative to CWD and blows up if the architecture 
doesn't match the process.  Other operating systems facilitate this sort 
of thing in various ways:

Solaris: LD_PRELOAD_32 and LD_PRELOAD_64
Linux: Search LD_LIBRARY_PATH, only fail if every attempt fails. Also, 
"$LIB" is magical.
Mac OS X: Universal binaries

One (ugly) thought I had is to have the shared object file hook every 
function in the "exec" family and fix LD_PRELOAD so it points at the 
architecture of the binary about to be exec'd before delegating to the 
real exec.  Anyone have a less ugly alternative that doesn't require 
modifying system files (e.g., adjusting ld.so)?

- Dave