Comment 13 for bug 1432529

in comment #11, the reason it stopped where it did is simply that gdb intercepted a signal that occurs way before it ever gets to the same point of failure in your original comment. To make it proceed past this you'd have to enter 'handle sigusr1 nostop pass' in gdb.
Stas is suggesting that you simply let it crash in the build and then attach gdb though.

Do you have the build log with 'sb-show' but without attempting to run it under gdb? That should reveal something.
You just snip everything above LENGTH(TLFS) = ... and show from there onward.