9.3.6 Mapping Symbols

The ARM ELF specification requires that special symbols be inserted into object files to mark certain features:

$a

At the start of a region of code containing ARM instructions.

$t

At the start of a region of code containing THUMB instructions.

$d

At the start of a region of data.

The assembler will automatically insert these symbols for you - there is no need to code them yourself. Support for tagging symbols ($b, $f, $p and $m) which is also mentioned in the current ARM ELF specification is not implemented. This is because they have been dropped from the new EABI and so tools cannot rely upon their presence.