I accidently tried to install an i586 toolchain on my x86_64 machine and it showed:

$ ./poky-eglibc-x86_64-i586-toolchain-1.3+snapshot-20130326.sh
Enter target directory for SDK (default: /opt/poky/1.3+snapshot): /tmp/rp456
You are about to install the SDK to "/tmp/rp456". Proceed[Y/n]?y
Extracting SDK...done
Setting it up...Traceback (most recent call last):
  File "/tmp/rp456/relocate_sdk.py", line 208, in <module>
    arch = get_arch()
  File "/tmp/rp456/relocate_sdk.py", line 39, in get_arch
    ei_mag0,ei_mag1_3,ei_class = struct.unpack("<B3sB11x", e_ident)
struct.error: unpack requires a string argument of length 16
SDK could not be set up. Relocate script failed. Abort!

which isn't a nice failure mode. Being self contained, it should even install and work correctly in this case as it would likely work!