Using /etc/ld.so.preload in a multi arch setup

Question

Is there some way to use ld.so.preload and cover both 32bit and 64bit binaries?

If I list both the 32bit and 64bit versions of the fault handler in ld.so.preload then the loader always complains that one of them fails to preload for whatever command I run. Not exactly earth shaking since the error is more a warning but I could certainly do without the printout.

Instead of specifying an absolute path I tried specifying simply "segv_handler.so" in the hopes that the loader would choose the lib in the arch appropriate path (a 32bit version is in /lib and a 64bit version is in /lib64).

Not likely apparently.

Is there a way to setup ld.so.preload to be architecturally aware? Or if not is there some way to turn off the error message?

Answer 1

This works:

1. put library under /path/lib for 32bit one, and put the 64bit one under /path/lib64 and they should have the same name
2. put the following line in /etc/ld.so.preload: /path/$LIB/libname.so

$LIB will get the value "lib" (for 32bit) or "lib64" (for 64bit) automatically.

Answer 2

There's no reason to try to use ld.so.preload like this. By default ld is smart enough to know that if you're running a 64bit app to only lookup 64bit libs, and same with 32bit.

Case in point, if you have

/lib64/libawesome.so /lib/libawesome.so

And you try

gcc -lawesome -o funtime funtime.c

It'll choose whatever the default that gcc wants to build, ld will skip libraries of incorrect bit size for that build.

gcc -m64 -lawesome -o funtime funtime.c will pick the 64bit one

gcc -m32 -lawesome -o funtime funetime.c will pick the 32bit one.

This presumes that /etc/ld.so.conf lists /lib and /lib64 by default..