I finally had a bit of time to look into this again. I concluded
that the DOF data is invalid, or follows a format that's different
from the one that GDB expected, and so added some code to detect
and ignore... Attached is the patch with full explanation. Does it
make sense to you?

gdb/ChangeLog:

        * dtrace-probe.c (dtrace_process_dof): Ignore the objfile's DOF
        data if a DTRACE_DOF_SECT_TYPE_PROVIDER section is found to be
        smaller than expected.

Tested on x86_64-linux (official GDB testsuite) + x86-solaris
(AdaCore's testsuite).

Thanks,
-- 
Joel