ld's support for interworking between ARM and Thumb code
For the ARM,
ld will generate code stubs to allow functions calls
betweem ARM and Thumb code. These stubs only work with code that has
been compiled and assembled with the `-mthumb-interwork' command
line option. If it is necessary to link with old ARM object files or
libraries, which have not been compiled with the -mthumb-interwork
option then the `--support-old-code' command line switch should be
given to the linker. This will make it generate larger stub functions
which will work with non-interworking aware ARM code. Note, however,
the linker does not support generating stubs for function calls to
non-interworking aware Thumb code.
The `--thumb-entry' switch is a duplicate of the generic
`--entry' switch, in that it sets the program's starting address.
But it also sets the bottom bit of the address, so that it can be
branched to using a BX instruction, and the program will start
executing in Thumb mode straight away.