6.11 ARM and Thumb
instruction portability diagnostics
The assembler can issue warnings about instructions that cannot assemble to both ARM and Thumb code.
There are a few UAL instructions that can assemble as either
ARM code or Thumb code, but not both. You can identify these instructions
in the source code using the following command-line option when
invoking the assembler:
armasm --diag_warning 1812
It warns for any instruction that cannot be assembled in the
other instruction set. This is only a hint, and other factors, like
relocation availability or target distance might affect the accuracy
of the message.