GCC 4.6.1: ld cannot find shared libraries when in sysroot

[Zhengxiong Zhang <zzhan@xxxxxxxxx>]

I am trying to build some software in a 32-bit sysroot that shares the 
same directory organization as my 64-bit system. In my project, I build 
a dynamic library that links to other dynamic libraries as follows:

g++ -o libmylibrary.so -Wl,-Bdynamic -shared --sysroot=/sysroot {bunch 
of objects} -m32 -lsomeotherlibrary

I then attempt to build an application that links to my static library 
as follows:

g++ -o myprog --sysroot=/sysroot {bunch of objects} -m32 -lmylibrary

However, this time I get a bunch of errors like this:

/usr/bin/ld: warning: libsomeotherlibrary.so needed by libmylibrary.so, 
not found (try using -rpath or -rpath-link)
[bunch of errors about undefined references to someotherlibrary]

Adding -Wl,-rpath-link=/sysroot/usr/lib causes myprog to successfully 
link. This behavior confuses me because it seems to me that ld should be 
able to find libsomeotherlibrary.so in /sysroot/usr/lib/ just like it 
did when I built libmylibrary.so. Can someone explain this to me and 
describe how I can change my build process to avoid this?